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Last Updated :2024/10/18

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Master

Affiliation (Master)

  • Faculty of Information Science and Technology　Media and Network Technologies　Information Communication Systems

Affiliation (Master)

  • Faculty of Information Science and Technology　Media and Network Technologies　Information Communication Systems

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Profile and Settings

Degree

  • M. S.（1994 Hokkaido University）
  • Ph. D.（1997 Hokkaido University）
  • B.S.（1992 Hokkaido University）

Profile and Settings

  • Name (Japanese)

    Nishimura

  • Name (Kana)

    Toshihiko

  • Name

    200901055001921255

Alternate Names

Achievement

Research Interests

  • OAM mULTIPLEXING   ESDM   MIMOチャネル   UWB   位置検出   トライポールアンテナ   SDM   伝搬環境   第4世代移動通信   通信方式(無線、有線、衛星、光、移動)   到来方向推定   ヌル形成   下り回線   ビーム形成   SDMA   大容量移動通信   w-BLAST   チャネル容量   ITS   偏波   歩車間通信   ルーティング   OFDM   移動通信   ビット配分   固有ビーム空間分割多重   MIMOシステム   チャネル推定   干渉   アダプティブアンテナ   MIMO   MIMO   

Research Areas

  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Communication and network engineering
  • Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electronic devices and equipment

Research Experience

  • 2021/09 - Today Hokkaido University Faculty of Information Science and Technology Proffesor
  • 2017/04 - 2021/08 Hokkaido University Graduate School of Information Science and Technology
  • 2007 - 2017/03 Hokkaido University Graduate School of Information Science and Technology
  • 1998 - 2007 Hokkaido University Graduate School of Engineering

Awards

  • 2018 電子情報通信学会通信ソサイエティ チュートリアル（和文）論文賞
  • 2011 電子情報通信学会通信ソサイエティ マガジン論文賞
  • 2008 電気通信普及財団 テレコムシステム技術賞
     
    受賞者: 西村 寿彦
  • 2007 電子情報通信学会 論文賞
     
    受賞者: 西村 寿彦
  • 2000 電子情報通信学会 学術奨励賞
     
    受賞者: 西村 寿彦

Published Papers

  • Daniel Akira Ando, Toshihiko Nishimura, Takanori Sato, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    IEICE Transactions on Communications 1 - 17 0916-8516 2024
  • Daniel Akira ANDO, Yuya KASE, Toshihiko NISHIMURA, Takanori SATO, Takeo OHGANE, Yasutaka OGAWA, Junichiro HAGIWARA
    IEICE Transactions on Communications E106.B (12) 1350 - 1362 0916-8516 2023/12/01 [Refereed]
  • Daniel Akira Ando, Toshihiko Nishimura, Takanori Sato, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    2023 22nd International Symposium on Communications and Information Technologies (ISCIT) 2023/10/16
  • Yasutaka OGAWA, Shuto TADOKORO, Satoshi SUYAMA, Masashi IWABUCHI, Toshihiko NISHIMURA, Takanori SATO, Junichiro HAGIWARA, Takeo OHGANE
    IEICE Transactions on Communications E106.B (9) 735 - 747 0916-8516 2023/09/01 [Refereed][Invited]
  • 望月大瑚, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄
    電子情報通信学会論文誌 B(Web) 電子情報通信学会 J106-B (6) 361 - 372 1881-0209 2023/06/01 [Refereed][Not invited]
     
    A sub-Terahertz band above 100 GHz will be used in 6G for extremely high-speed communication. In such a high frequency band, channels change rapidly in time-varying environments. The channel information obtained using pilot symbols may deviate from the actual channel information over time, resulting in degradation of channel characteristics. Thus, it is expected to be effective to predict channels at a future time. Since the number of multipaths in sub-THz bands is extremely small, we can resolve them and predict the channel. In this paper, we assume a MIMO system with a hybrid beamforming architecture, and resolve multipaths incident on a subarray in the delay domain with FISTA, one of the compressed sensing algorithms. Using the resolved multipaths, we predict the future channels. It is shown that the prediction technique works well, and that we can achieve the normalized mean square error from -30 dB to -20 dB.
  • Junichiro Hagiwara, Kazushi Matsumura, Hiroki Asumi, Yukiko Kasuga, Toshihiko Nishimura, Takanori Sato, Yasutaka Ogawa, Takeo Ohgane
    CoRR abs/2301.03196 2023
  • OGAWA Yasutaka, UTSUNO Taichi, NISHIMURA Toshihiko, OHGANE Takeo, SATO Takanori
    IEICE Transactions on Communications E105.B (10) 1130 - 1138 0916-8516 2022/10/01 [Refereed][Invited]
     
    A sub-Terahertz band is envisioned to play a great role in 6G to achieve extreme high data-rate communication. In addition to very wide band transmission, we need spatial multiplexing using a hybrid MIMO system. A recently presented paper, however, reveals that the number of observed multipath components in a sub-Terahertz band is very few in indoor environments. A channel with few multipath components is called sparse. The number of layers (streams), i.e. multiplexing gain in a MIMO system does not exceed the number of multipaths. The sparsity may restrict the spatial multiplexing gain of sub-Terahertz systems, and the poor multiplexing gain may limit the data rate of communication systems. This paper describes fundamental considerations on sub-Terahertz MIMO spatial multiplexing in indoor environments. We examined how we should steer analog beams to multipath components to achieve higher channel capacity. Furthermore, for different beam allocation schemes, we investigated eigenvalue distributions of a channel Gram matrix, power allocation to each layer, and correlations between analog beams. Through simulation results, we have revealed that the analog beams should be steered to all the multipath components to lower correlations and to achieve higher channel capacity.
  • Mari Miyoshi, Wakaba Tsujimoto, Toshihiko Nishimura, Takanori Sato, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    2022 IEEE VTS Asia Pacific Wireless Communications Symposium (APWCS) 2022/08/24
  • KASE Yuya, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, SATO Takanori, KISHIYAMA Yoshihisa
    IEICE Transactions on Communications E105.B (5) 588 - 599 0916-8516 2022/05/01 [Refereed][Not invited]
     
    Direction of arrival (DOA) estimation of wireless signals is demanded in many applications. In addition to classical methods such as MUSIC and ESPRIT, non-linear algorithms such as compressed sensing have become common subjects of study recently. Deep learning or machine learning is also known as a non-linear algorithm and has been applied in various fields. Generally, DOA estimation using deep learning is classified as on-grid estimation. A major problem of on-grid estimation is that the accuracy may be degraded when the DOA is near the boundary. To reduce such estimation errors, we propose a method of combining two DNNs whose grids are offset by one half of the grid size. Simulation results show that our proposal outperforms MUSIC which is a typical off-grid estimation method. Furthermore, it is shown that the DNN specially trained for a close DOA case achieves very high accuracy for that case compared with MUSIC.
  • Daniel Akira Ando, Toshihiko Nishimura, Takanori Sato, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    International Symposium on Wireless Personal Multimedia Communications, WPMC 2022-October 98 - 103 1347-6890 2022 
    Direction of arrival (DoA) estimation is a technique used in, for instance, radar systems, source localization, and wireless channel estimation, and improving its accuracy is becoming more important as its applications expand. In previous works, we verified that deep neural networks (DNN) trained offline are a viable tool for achieving great on-grid DoA estimation performance, even compared to the traditional root multiple signal classification (root-MUSIC) algorithm. Moreover, we separately proposed the signal-to-noise ratio (SNR)-based DNN selection method in order to fully leverage the DNN learning potential at specific SNRs; and the superposition of two DNNs (staggered DNNs) in order to overcome the estimation failure caused by incident radio waves at the grid border. In this paper, we propose an end-to-end DoA estimation system, which consists of three modules: DoA, SNR and source number estimators. Here, we expand the performance of the DoA estimator module by presenting a new algorithm more efficient in detecting DoA from the DNN output, and by using the combination of the two previously mentioned methods: SNR-based DNN selection and staggered DNNs. Also, an SNR estimation scheme with better precision is presented.
  • 丸田一輝, 井田悠太, 實松豊, 牟田修, 岡田啓, 西村寿彦, 岡本英二, 眞田幸俊, 村田英一, 田野哲
    電子情報通信学会誌 105 (6) 0913-5693 2022 [Not refereed][Not invited]
  • Kazushi Matsumura, Junichiro Hagiwara, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Takanori Sato
    2021 24th International Symposium on Wireless Personal Multimedia Communications (WPMC) 2021/12/14
  • 西村寿彦, 佐藤孝憲, 小川恭孝, 大鐘武雄
    電子情報通信学会誌 電子情報通信学会 104 (5) 485 - 489 0913-5693 2021/05 [Not refereed][Invited]
  • Yuya KASE, Toshihiko NISHIMURA, Takeo OHGANE, Yasutaka OGAWA, Daisuke KITAYAMA, Yoshihisa KISHIYAMA
    IEICE Transactions on Communications E103.B (10) 1127 - 1135 0916-8516 2020/10/01 [Refereed]
  • Jumpei Yamamoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Daiki Takeda, Yoshihisa Kishiyama
    IEICE TRANSACTIONS ON COMMUNICATIONS E103B (6) 703 - 711 0916-8516 2020/06/01 [Refereed]
     
    Massive MIMO is known as a promising technology for multiuser multiplexing in the fifth generation mobile communication system to accommodate the rapidly-increasing traffic. It has a large number of antenna elements and thus provides very sharp beams. As seen in hybrid beamforming, there have already been many papers on the concatenation of two precoders (beamformers). The inner precoder, i.e., a multi-beam former, performs a linear transformation between the element space and the beam space. The outer precoder forms nulls in the limited beam space spanned by selected beams to suppress the inter-user interference. In this two-step precoder, the beam shape is expected to determine the system performance. In this paper, we evaluate the achievable throughput performance for different beam-shaping schemes: a discrete Fourier transform (DFT) beam, Chebyshev weighted beams, and Taylor weighted beam. Simulations show that the DFT beam provides the best performance except the case of imperfect precoding and cell edge SNR of 30 dB.
  • Ayano Yamamoto, Toshihiko Nishimura, Takeo Ohgane, Tomoya Tandai, Daisuke Uchida
    2020 14TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION (EUCAP 2020) 2164-3342 2020/03 [Refereed]
     
    In recent years, a new spatial multiplexing transmission scheme using the orthogonality of orbital angular momentum (OAM) modes has attracted attention with growth of the millimeter wave technology and demands for further high-speed large capacity transmission. A uniform circular array (UCA) is one of the candidates for generating multiple OAM modes. However, each mode's quality changes with distance when a single UCA of fixed diameter is used due to a property of Laguerre-Gaussian beam. In this paper, we propose maximum ratio transmission method by using multiple UCAs at the transmitter side for improving the quality and stability of each mode. Adjusting the amplitude and phase for each mode of all UCA, we can increase the received power and reduce the fluctuation depending on the transmission distance. The simulation results assuming free-space propagation show that high throughput is maintained over a wide transmission range even if radii of UCAs at transmitting and receiving sides are fixed.
  • Yuta Takano, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane, Junichiro Hagiwara
    2020 International Workshop on Antenna Technology (iWAT) 2020/02 [Refereed][Not invited]
  • TOSHIHIKO NISHIMURA
    電子情報通信学会論文誌 B J103-B (2) 100 - 109 2020/02/01 [Refereed]
  • Toshihiko NISHIMURA, Yasutaka OGAWA, Takeo OHGANE, Junichiro HAGIWARA
    IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences 0916-8508 2020 [Refereed][Invited]
  • Kentaro Fukuda, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    2019 22nd International Symposium on Wireless Personal Multimedia Communications (WPMC) 2019/11 [Refereed]
  • Wataru Kawabata, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2019 22nd International Symposium on Wireless Personal Multimedia Communications (WPMC) 2019/11 [Refereed][Not invited]
  • Yuya Kase, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Daisuke Kitayama, Yoshihisa Kishiyama
    2019 22nd International Symposium on Wireless Personal Multimedia Communications (WPMC) 2019/11 [Refereed][Not invited]
  • Renjie Li, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    2019 22nd International Symposium on Wireless Personal Multimedia Communications (WPMC) 2019/11 [Refereed][Not invited]
  • Kanako Yamaguchi, Masatsugu Higashinaka, Hiroyasu Sano, Atsushi Okamura, Takeo Ohgane, Toshihiko Nishimura
    2019 IEEE 90th Vehicular Technology Conference (VTC2019-Fall) 2019/09 [Refereed][Not invited]
  • Kensei Saito, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane, Junichiro Hagiwara
    2019 International Conference on Computing, Networking and Communications (ICNC) 2019/02
  • Yuya Suzuki, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    International Conference on Computing, Networking and Communications(ICNC) 29 - 33 2019
  • Uehashi, Shunsuke, Ogawa, Yasutaka, Nishimura, Toshihiko, Ohgane, Takeo
    IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 68 (1) 565 - 577 0018-9545 2019/01 [Refereed][Not invited]
     
    In multi-user multiple-input multiple-output (MIMO) systems, a base station requires downlink channel state information for each user to suppress interferences. In time-varying environments, however, channels at the actual transmission time differ from the estimated ones because we have delay. This causes interference and deteriorates the packet error rate performance. To overcome this problem, we previously proposed a channel prediction method based on direction of arrival (DOA) estimation of multipath components obtained with a compressed sensing technique. This method can predict channels with high accuracy when we can assume that user equipment alone moves and the surrounding scatterers are stationary. In real environments, however, this assumption does not hold, and this method cannot be applied. In this paper, we propose a prediction method using two-step compressed sensing without the above assumption. In the first step, we estimate the DOAs of multipath signals. In the second step, we estimate the Doppler frequencies and their complex amplitudes using the estimated DOA information. From these values, we predict the MIMO channels at the actual transmission time. We discuss the performance of this method in this paper.
  • Yamamoto, Ayano, Nishimura, Toshihiko, Ohgane, Takeo, Tandai, Tomoya, Uchida, Daisuke
    2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS) 2164-7038 2019 [Refereed][Not invited]
     
    Orbital angular momentum (OAM) is a physical quantity of an electromagnetic wave which is independent of polarization, and the electromagnetic wave having the OAM becomes a helical wave. A mode of the OAM can be defined according to the number of turns of helix per wavelength distance, and the different modes are mutually orthogonal. In recent years, with growth of the millimeter wave technology and demands for further high-speed large capacity transmission, a new spatial multiplexing transmission scheme using the orthogonality of OAM has attracted attention. In this paper, the impact of the ground reflected wave were evaluated by comparing the characteristics of OAM mode multiplexing and eigenbeam-space division multiplexing. As a result, it is found that the inter-mode interference due to the ground reflected wave is not so large and can be reduced with a small amount of degradation.
  • Toyoki Hoshikawa, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Junichiro Hagiwara
    2018 15th Workshop on Positioning, Navigation and Communications (WPNC) 2018/10 [Refereed]
  • Yuya Kase, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Daisuke Kitayama, Yoshihisa Kishiyama
    2018 15th Workshop on Positioning, Navigation and Communications (WPNC) 2018/10 [Refereed][Not invited]
  • TOSHIHIKO NISHIMURA
    電子情報通信学会論文誌B J101.B (7) 2018/07/01 [Refereed][Not invited]
  • Koichi Inoue, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2018 IEEE INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY (IWAT) 2018/03 [Refereed][Not invited]
  • 大鐘武雄, 西村寿彦, 小川恭孝
    電子情報通信学会誌 101 (11) 0913-5693 2018 [Refereed][Invited]
  • Jumpei Yamamoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Daiki Takeda, Yoshihisa Kishiyama
    2018 IEEE INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY (IWAT) 2018 [Refereed][Not invited]
     
    The massive MIMO technology which generates many sharp beams is known as a promising technology to accommodate rapidly-increasing traffic in mobile radio. In massive MIMO systems, there have already been a number of papers on 2-step beamforming where precoding matrix is calculated in a limited beam space after beam selection. In such a case, it is very important to select proper beams. Then, the beam shape affects the system performance. In the paper, we evaluate the achievable throughput performance for different beam-shaping schemes: a discrete Fourier transform (DFT) beam and Chebyshev weighted beams. The simulation results show that the DFT beam is a good choice although the optimum beam depends on the channel situation.
  • Watabe, Taisei, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka, Hagiwara, Junichiro
    2018 ASIA-PACIFIC SIGNAL AND INFORMATION PROCESSING ASSOCIATION ANNUAL SUMMIT AND CONFERENCE (APSIPA ASC) 1416 - 1420 2309-9402 2018 [Refereed][Not invited]
     
    Gaussian belief propagation ( GaBP) has been proposed to detect a large number of signals. It is based on message passing of the second-order complexity. In general, the GaBP uses bit-wise reliability. Thus, it is not straightforward to apply the GaBP to the multi-level-modulated signals. In this paper, we propose to compose a 16-QAM symbol from two QPSK symbols using superposition modulation and evaluate the detection performance of the GaBP for superposed 16-QAM signals in a massive MIMO system. In the uncoded case, the uniform and Gray-mapped 16-QAM provides the best performance. However, in the coded case, the performance of superposed 16-QAM becomes much better and outperforms the uniform and Gray-mapped 16-QAM. Thus, the potential capability of superposition modulation in the GaBP detection has been confirmed.
  • K. Kihara, T. Nishimura, T. Ohgane, Y. Ogawa
    2017 ASIA-PACIFIC SIGNAL AND INFORMATION PROCESSING ASSOCIATION ANNUAL SUMMIT AND CONFERENCE (APSIPA ASC 2017) 1790 - 1794 2309-9402 2017/12 [Refereed][Not invited]
  • TOSHIHIKO NISHIMURA
    電子情報通信学会論文誌B J100.B (9) 658 - 672 2017/09/01 [Refereed][Not invited]
  • Mitsuyoshi Hagiwara, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E100B (8) 1285 - 1292 0916-8516 2017/08 [Refereed][Not invited]
     
    Recently, much progress has been made in the study of belief propagation (BP) based signal detection with large-scale factor graphs. When we apply the BP algorithm to equalization in a SISO multipath channel, the corresponding factor graph has many short loops and patterns in an edge connection/strength. Thus, proper convergence may not be achieved. In general, the log-likelihood ratio (LLR) oscillates in ill-converged cases. Therefore, LLR oscillation avoidance is important for BP-based equalization. In this paper, we propose applying node selection (NS) to prevent the LLR from oscillating. The NS extends the loop length virtually by a serial LLR update. Thus, some performance improvement is expected. Simulation results show that the error floor is significantly reduced by NS in the uncoded case and that the NS works very well in the coded case.
  • Shuhei Tanno, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E100B (8) 1277 - 1284 0916-8516 2017/08 [Refereed][Not invited]
     
    Detecting signals in a very large multiple-input multiple output (MIMO) system requires high complexy of implementation. Thus, belief propagation based detection has been studied recently because of its low complexity. When the transmitted signal sequence is encoded using a channel code decodable by a factor-graph-based algorithm, MIMO signal detection and channel decoding can be combined in a single factor graph. In this paper, a low density parity check (LDPC) coded MIMO system is considered, and two types of factor graphs: bipartite and tripartite graphs are compared. The former updates the log-likelihood-ratio (LLR) values at MIMO detection and parity checking simultaneously. On the other hand, the latter performs the updates alternatively. Simulation results show that the tripartite graph achieves faster convergence and slightly better bit error rate performance. In addition, it is confirmed that the LLR damping in LDPC decoding is important for a stable convergence.
  • Shun Nishizaki, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2017 INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY: SMALL ANTENNAS, INNOVATIVE STRUCTURES, AND APPLICATIONS (IWAT) 335 - 338 2017 [Refereed][Not invited]
     
    Studies on a massive Multiple-Input MultipleOutput (MIMO) system have been studied in recent years. In a massive MIMO system, antenna elements are arranged not in one dimension but in two dimensions because very large number of antenna elements are used, and the system is called a fulldimension MIMO. In this paper, we generate channel matrices between a transmitter at a base station and user equipments by using a ray tracing technique and evaluate the channel capacity with different places of a transmit antenna array in an indoor environment. In addition, we introduce block SNR maximization and compare the performance with that of block diagonalization. Sum capacity in the case when the BS is placed at the ceiling is larger than one in the case of placing at the wall.
  • Daisuke Abe, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    2017 INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY: SMALL ANTENNAS, INNOVATIVE STRUCTURES, AND APPLICATIONS (IWAT) 74 - 77 2017 [Refereed][Not invited]
     
    A compressed sensing technique has been studied for accurate scatterer detection. It has many kinds of algorithms, and the features are different. In this paper, we evaluate the performance of compressed sensing algorithms for scatterer detection. We examine three algorithms, OMP, OIHT, and FISTA. We investigate the performance of the algorithms for a single-target and two-target scenarios. It is concluded that FISTA reveals the best performance among the three algorithms.
  • Daisuke Abe, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    2016 INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (ISAP) 1008 - 1009 2016 [Refereed][Not invited]
     
    A compressed sensing technique can be used for scatterer detection with less antenna elements. The detection accuracy, however, degrades when scatterers exist also in the outside of a search area. In this paper, we propose a preprocessing scheme for compressed sensing based scatterer detection. The scheme uses a gating technique in a cross range, and suppresses scattering waves from the outside of a search area. Also, we introduce a wide area detection scheme dealing with scatterers located very close to the search area that the gating technique cannot suppress. We show the performance of scatterer detection with the proposed method.
  • Usami, Tomoya, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka
    2016 INTERNATIONAL CONFERENCE ON COMPUTING, NETWORKING AND COMMUNICATIONS (ICNC) 2016 [Refereed][Not invited]
     
    A massive multiple-input multiple-output (MIMO) system using a couple of hundred antenna elements has been arising as an important technology to keep the communication range in higher frequency bands. A further enhancement to increase the number of both transmit and receive antennas will be the next step. It requires the complexity proportional to at least the third power of the number of antenna elements to detect spatially-multiplexed signals in general. However, the belief propagation (BP)-based detector is implementable with lower complexity, i. e., the order of square of the number of elements, and achieves very good BER performance in a QPSK modulated massive MIMO system. In this paper, we apply the BP algorithm to a 16-QAM modulated massive MIMO system and propose a sequential reliability update to exploit a difference in error tolerance. The BER evaluation results have shown that the BP works well for a 16-QAM signal detection and that the sequential update is effective to the M-QAM modulated systems.
  • Shuhei Tanno, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    PROCEEDINGS OF 2016 INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY AND ITS APPLICATIONS (ISITA 2016) 473 - 477 2016 [Refereed][Not invited]
     
    Recently, very large multiple-input multiple-output (MIMO) systems have been actively studied for 5G mobile radios. Belief propagation based detection is known as a technique reducing the computational complexity for uplink signal detection. When we consider an LDPC coded MIMO system, it is possible to combine both factor graphs of MIMO detection and LDPC decoding. In the paper, two types: bipartite and tripartite graphs are compared. The former one updates the LLR values on MIMO detection and parity checking simultaneously. On the other hand, the latter one updates alternatively. The simulation results show that the tripartite graph provides faster convergence with the same BER performance.
  • Toshihiko Nishimura, Taiki Endo, Takeo Ohgane, Yasutaka Ogawa
    2016 ASIA-PACIFIC SIGNAL AND INFORMATION PROCESSING ASSOCIATION ANNUAL SUMMIT AND CONFERENCE (APSIPA) 2016 [Refereed][Not invited]
     
    Much attention has been paid to precise direction of arrival (DOA) estimation techniques using compressed sensing. We have been investigating DOA estimation of multi-band signals using the half-quadratic regularization method, one of the compressed sensing techniques. Use of multi-band signals provides more precise estimation than that of single-band signals even if the multi-band signals have frequency characteristics. There are three parameters that must be determined appropriately in our proposed method. It is very important to determine the parameters adequately but it is difficult to do that analytically. In this paper, we evaluate impacts of parameter settings on the DOA estimation performance and find quasi optimum values for the parameters.
  • Mitsuyoshi Hagiwara, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    PROCEEDINGS OF 2016 INTERNATIONAL SYMPOSIUM ON INFORMATION THEORY AND ITS APPLICATIONS (ISITA 2016) 483 - 487 2016 [Refereed][Not invited]
     
    In recent years, several progresses have been made in belief propagation (BP) based signal detection with large scale factor graphs. When we apply the BP algorithm to equalization in a SIMO multipath channel, the factor graph has many short loops where the edge strengths have a fixed pattern. Thus, the proper convergence is not always expected. In general, the LLR oscillates in ill-converged cases. Therefore, preventing the LLR oscillation becomes important for the BP-based equalization. In the paper, we propose applications of node selection (NS) and LLR damping to prevent the LLR from oscillating. The NS extends the loop length virtually by a serial LLR update whereas the LLR damping suppresses the oscillation directly. The simulation results show that the error floor is significantly reduced with the LLR damping and NS in the uncoded case and that the NS works very well in the coded case.
  • Taiki Endo, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    2016 IEEE INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY (IWAT) 192 - 195 2016 [Refereed][Not invited]
     
    In recent years, much attention has been paid to direction of arrival (DOA) estimation using a compressed sensing technique. In our previous study, we have proposed a method to estimate DOAs of multi -band signals with frequency characteristics. However, we have assumed that all the arrival waves have the same amplitude. In this paper, we propose DOA estimation of signals with frequency characteristics and different powers among the arrived signals. Furthermore, we evaluate the method regardless of whether we know the frequency characteristics in advance.
  • Kosuke Suzuki, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2016 INTERNATIONAL CONFERENCE ON COMPUTING, NETWORKING AND COMMUNICATIONS (ICNC) 2016 [Refereed][Not invited]
     
    In a wireless mesh network (WMN), the interference from active links in the vicinity of the node of interest is frequently not negligible and thus degrades the area spectral efficiency. An adaptive array is capable to control not only beams but also nulls. Thus, it is expected to help new link establishment. Moreover, the alternative routing boosts such spatial link multiplexing by decreasing the nodes in the stand-by state. In the paper, we evaluate the system throughput performance of the alternative routing in a WMN with an adaptive array of three elements. The evaluation results show that the alternative routing is very effective in the case of a gateway access model or when the average hop counts in the network is not so small.
  • Uehashi, Shunsuke, Ogawa, Yasutaka, Nishimura, Toshihiko, Ohgane, Takeo
    2016 INTERNATIONAL CONFERENCE ON COMPUTING, NETWORKING AND COMMUNICATIONS (ICNC) 2016 [Refereed][Not invited]
     
    In downlink multi-user multiple-input multiple-output (MIMO) systems, a base station needs downlink channel state information (CSI) for each user to eliminate inter-user interference and inter-stream interference. In wireless communication, however, signal propagation environments change over time, and CSI obtained at the base station is different from the channel at the actual transmission time because we have delay. This deteriorates communication quality, and the effect of outdated CSI is a critical issue. To overcome this problem, some channel prediction schemes have been developed. Among them, a sum-of-sinusoids (SOS) method can predict time-varying channels over a long range. The SOS method, however, needs to resolve an incident signal into individual multipath components. In this paper, we propose a compressed sensing technique for the resolution, and formulate the channel prediction scheme for multi-user MIMO systems. Also, we evaluate the performance of the proposed scheme using computer simulations.
  • Yuki Nakanishi, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yusuke Ohwatari, Yoshihisa Kishiyama
    IEICE TRANSACTIONS ON COMMUNICATIONS E98B (8) 1465 - 1473 0916-8516 2015/08 [Refereed][Not invited]
     
    A distributed antenna system, where the antennas of a base station are spatially distributed throughout the cell, can achieve better throughput at the cell edge than a centralized antenna system. On the other hand, the peak throughput degrades in general because each remote antenna unit has only a few antennas. To achieve both high peak and cell-edge throughputs, we need to increase the total number of antennas. However, this is not easy due to the pilot resource limitation when we use frequency division duplexing. In this paper, we propose using more antennas than pilot resources. The number mismatch between antennas and signals is solved by using a connection matrix. Here, we test two types of connection matrix: signal-distributing and signal-switching. Simulation results show that the sum throughput is improved by increasing the number of antenna elements per remote antenna unit under a constraint on the same number of pilot resources.
  • Heedong Choi, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    SIGNAL PROCESSING 111 39 - 49 0165-1684 2015/06 [Refereed][Not invited]
     
    This study develops the preprocessing theory for time-reversal multiple signal classification (TR-MUSIC) imaging from the one-dimensional (time-domain) gating proposed in earlier papers to a two-dimensional one. Although the one-dimensional gating technique for TR-MUSIC mitigates the effect of noise as well as reduces the required number of antenna elements, the resulting image is subject to focusing errors when there are many targets in the gated region. In this paper, we propose a two-dimensional (angle-and-time-domain) gating technique based on the fast Fourier transform (FFT) and spatial FFT processing. By using these transforms and gating iteratively, we can reduce the number of targets to be detected at one time. The TR-MUSIC technique for the gated data provides more reliable images and precisely estimated coordinates compared with the previous work. (C) 2014 Elsevier B.V. All rights reserved.
  • Hayato Fukuda, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    2015 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE (WCNC) 159 - 164 1525-3511 2015 [Refereed][Not invited]
     
    A massive multiple-input multiple-output (MIMO) system, which has a very large number of antenna elements at the base station (BS), is a promising technology for future high-speed, high-capacity communication systems. However, it faces a serious issue of limited installation space. To cope with this limitation, a full-dimension MIMO (FD-MIMO) system has been proposed. This system can save installation space as well as control the azimuth and elevation beamforming because the antenna elements are arranged in a two-dimensional (2D) array. In this paper, we evaluate the performance of FD-MIMO in indoor line-of-sight environments by comparing it with a linearly arranged array, that is, a one-dimensional (1D) array. The channel matrices for the evaluations are obtained by using a ray-tracing technique. The results reveal that the FD-MIMO system with a small rectangular 2D array outperforms a 1D array when users are located near the BS.
  • Junichiro Hagiwara, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2015 21ST ASIA-PACIFIC CONFERENCE ON COMMUNICATIONS (APCC) 454 - 459 2163-0771 2015 [Refereed][Not invited]
     
    Regarding linear estimation theory, the equivalence of the Wiener and Kalman filters is a well-known topic; however, the difference in a practical environment has not been thoroughly discussed. This paper compares the Kalman smoother to the Wiener smoother in terms of practical orthogonal frequency division multiplexing channel estimation on the receiver side. First, conditions for fair comparison are discussed. Under these conditions, the performance and complexity for both methods are numerically investigated. Comparison results show that the Wiener smoother slightly outperforms the Kalman smoother because it avoids cumulative error in sequential processing, while the complexity of the Kalman smoother is always lower than that for the Wiener smoother because there is no large matrix operation.
  • Yamaguchi, Kanako, Huu Phu Bui, Ogawa, Yasutaka, Nishimura, Toshihiko, Ohgane, Takeo
    IEICE TRANSACTIONS ON COMMUNICATIONS E97B (12) 2747 - 2755 0916-8516 2014/12 [Refereed][Not invited]
     
    Although multi-user multiple-input multiple-output (MIMO) systems provide high data rate transmission, they may suffer from interference. Block diagonalization and eigenbeam-space division multi-plexing (E-SDM) can suppress interference. The transmitter needs to determine beamforming weights from channel state information (CSI) to use these techniques. However, MIMO channels change in time-varying environments during the time intervals between when transmission parameters are determined and actual MIMO transmission occurs. The outdated CSI causes interference and seriously degrades the quality of transmission. Channel prediction schemes have been developed to mitigate the effects of outdated CSI. We evaluated the accuracy of prediction of autoregressive (AR)-model-based prediction and Lagrange extrapolation in the presence of channel estimation error. We found that Lagrange extrapolation was easy to implement and that it provided performance comparable to that obtained with the AR-model-based technique.
  • Kanako Yamaguchi, Huu Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEICE Transactions on Communications E97B (12) 2747 - 2755 1745-1345 2014/12/01 [Refereed][Not invited]
     
    Although multi-user multiple-input multiple-output (MIMO) systems provide high data rate transmission, they may suffer from interference. Block diagonalization and eigenbeam-space division multiplexing (E-SDM) can suppress interference. The transmitter needs to determine beamforming weights from channel state information (CSI) to use these techniques. However, MIMO channels change in time-varying environments during the time intervals between when transmission parameters are determined and actual MIMO transmission occurs. The outdated CSI causes interference and seriously degrades the quality of transmission. Channel prediction schemes have been developed to mitigate the effects of outdated CSI. We evaluated the accuracy of prediction of autoregressive (AR)-model-based prediction and Lagrange extrapolation in the presence of channel estimation error. We found that Lagrange extrapolation was easy to implement and that it provided performance comparable to that obtained with the AR-model-based technique.
  • Terada, Tsubasa, Nishimura, Toshihiko, Ogawa, Yasutaka, Ohgane, Takeo, Yamada, Hiroyoshi
    IEICE TRANSACTIONS ON COMMUNICATIONS E97B (10) 2110 - 2117 1745-1345 2014/10 [Refereed][Not invited]
     
    Much attention has recently been paid to direction of arrival (DOA) estimation using compressed sensing (CS) techniques, which are sparse signal reconstruction methods. In our previous study, we developed a method for estimating the DOAs of multi-band signals that uses CS processing and that is based on the assumption that incident signals have the same complex amplitudes in all the bands. That method has a higher probability of correct estimation than a single-band DOA estimation method using CS. In this paper, we propose novel DOA estimation methods for multi-band signals with frequency characteristics using the Khatri-Rao product. First, we formulate a method that can estimate DOAs of multiband signals whose phases alone have frequency dependence. Second, we extend the scheme in such a way that we can estimate DOAs of multi-band signals whose amplitudes and phases both depend on frequency. Finally, we evaluate the performance of the proposed methods through computer simulations and reveal the improvement in estimation performance.
  • 小川恭孝, 西村寿彦, 大鐘武雄
    電子情報通信学会誌 97 (4) 285 - 289 0913-5693 2014/04/01 [Not refereed][Not invited]
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka
    2014 16TH INTERNATIONAL CONFERENCE ON ADVANCED COMMUNICATION TECHNOLOGY (ICACT) 206 - + 1738-9445 2014 [Refereed][Not invited]
     
    The near Shannon capacity approaching low-density parity-check (LDPC) linear block codes are now in widespread use in modern systems including the long term evolution advanced (LTE-A) cellular, 802.11n Wi-Fi and DVB-S2 satellite communications standards. The decoders based on the iterative belief propagation algorithm provide near optimum performance but also have very high computational complexity. Therefore significant research has recently focused on reduced complexity architectures based on the group of so-called bit-flipping algorithms. In the basic bit-flipping algorithm the number of failed parity checks for each bit is computed and the bit with the maximum failed parity checks is inverted. Inverting bits above a certain threshold removes the complexity involved with a maximum-search and, adaptive thresholds on each bit can further reduce the computation overhead. The criterion for the threshold update affects the error and convergence performances. Here, we describe a low-complexity architecture that has two (or more) decoder branches each with a different threshold scaling factor and select the threshold and bits at each iteration from the branch with the lowest syndrome sum. We then investigate the effect of adding a random Uniform or Gaussian noise perturbation to the threshold in order to reduce the average iteration count further in order to provide the opportunity to escape from stuck decoding states.
  • Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    2014 IEEE INTERNATIONAL WORKSHOP ON ELECTROMAGNETICS (IEEE IWEM): APPLICATIONS AND STUDENT INNOVATION COMPETITION 121 - 122 2014 [Refereed][Not invited]
     
    A novel estimation method for direction of arrival angle is introduced. A compressed sensing technique is applied to this application. The resolution of the proposed method is superior to conventional methods such as the MUSIC. Furthermore, we show that the performance can be enhanced when the source signal is multi-band.
  • Yuki Nakanishi, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yusuke Ohwatari, Yoshihisa Kishiyama
    2014 IEEE 25TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATION (PIMRC) 193 - 197 2166-9570 2014 [Refereed][Not invited]
     
    A distributed antenna system, where antennas at a base station are spatially distributed over the cell, can improve throughput at the cell edge compared to a centralized antenna system. However, the peak capacity degrades when a remote antenna unit has a few antenna elements due to rank deficiency. In general, the number of antennas at the base station is limited by the number of pilot sequences. Thus, it is difficult to increase the number of antennas. In this paper, we use antenna splitting to increase the number of antennas without increasing the number of pilot sequences and evaluate the impact of antenna splitting on the sum capacity in a multiuser MIMO system. From computer simulations, it is shown that we can obtain higher sum capacity by increasing the number of antennas even though the number of pilot sequences is limited.
  • Terada, Tsubasa, Nishimura, Toshihiko, Ogawa, Yasutaka, Ohgane, Takeo, Yamada, Hiroyoshi
    2014 INTERNATIONAL WORKSHOP ON ANTENNA TECHNOLOGY: "SMALL ANTENNAS, NOVEL EM STRUCTURES AND MATERIALS, AND APPLICATIONS" (IWAT) 359 - 362 2014 [Refereed][Not invited]
     
    Much attention has been paid to direction of arrival (DOA) estimation using a compressed sensing technique. In our previous study, we have proposed a method to estimate DOAs of multi-band signals using an array antenna at a receiver. As a result, we have produced an improvement of the probability of correct estimation. Moreover, the method can deal with waves exceeding the degrees of freedom of the array. However, we have assumed that incident waves have multi-bands where complex amplitudes are the same. First, in this paper, we propose a method that allows the estimation of DOAs when only the phases at the bands are different using not the complex amplitudes but powers of the signals. Second, we extend the technique in such a way that it can estimate DOAs of the signals having different amplitudes among bands.
  • Yamada, Hiroyoshi, Shirai, Satoshi, Nishimura, Toshihiko, Ogawa, Yasutaka, Ohgane, Takeo, Yamaguchi, Yoshio
    2014 USNC-URSI RADIO SCIENCE MEETING (JOINT WITH AP-S SYMPOSIUM) 205 - 205 2572-3804 2014 [Refereed][Not invited]
  • Yasutaka Ogawa, Kanako Yamaguchi, Huu Phu Bui, Toshihiko Nishimura, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E96B (10) 2364 - 2371 1745-1345 2013/10 [Refereed][Not invited]
     
    We evaluated the behavior of a multi-user multiple-input multiple-output (MIMO) system in time-varying channels using measured data. A base station for downlink or broadcast transmission requires downlink channel state information (CSI), which is outdated in time-varying environments and we encounter degraded performance due to interference. One of the countermeasures against time-variant environments is predicting channels with an autoregressive (AR) model-based method. We modified the AR prediction for a time division duplex system. We conducted measurement campaigns in indoor environments to verify the performance of the scheme of channel prediction in an actual environment and measured channel data. We obtained the bit-error rate (BER) using these data. The AR-model-based technique of prediction assuming the Jakes' model was found to reduce BER. Also, the optimum AR-model order was investigated by using the channel data we measured.
  • Huu Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 61 (1) 371 - 379 0018-926X 2013/01 [Refereed][Not invited]
     
    In this paper, the performance of a multi-user multiple-input multiple-output (MIMO) system in time-varying channels is evaluated using measurement data. We consider the multi-user MIMO system using a block diagonalization (BD) scheme and an eigenbeam-space division multiplexing (E-SDM) technique. In an ideal case, the BD scheme eliminates inter-user interference, and the E-SDM technique suppresses inter-stream interference. In actual radio environments, however, channels change over time. This causes interference in the multi-user MIMO system even though the BD scheme and the E-SDM technique are used. To overcome this problem, the authors have developed a simple channel prediction scheme on the basis of a linear extrapolation and have demonstrated its effectiveness by computer simulations assuming the Jakes' model. To verify the performance of the channel prediction scheme in actual environments, we conducted a measurement campaign in indoor environments and measured a large amount of channel data. Using these data, we examined the channel transition and channel tracking with the prediction method. Then we obtained the bit-error rate (BER) performance. The prediction technique was shown to track the channel and improve the BER performance almost to that in the ideal time invariant case.
  • Wataru Fukuda, Takashi Abiko, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yusuke Ohwatari, Yoshihisa Kishiyama
    2013 INTERNATIONAL SYMPOSIUM ON INTELLIGENT SIGNAL PROCESSING AND COMMUNICATIONS SYSTEMS (ISPACS) 245 - 250 2013 [Refereed][Not invited]
     
    The easiest way to improve the throughput performance of multiple-input multiple-output (MIMO) systems is to increase the number of both transmit and receive antennas. Thus, a massive MIMO concept has been proposed recently. In general, however, algorithms detecting spatially-multiplexed signals require the complexity to be proportional to the cubed power of the number of antenna elements at least. Several studies have shown that a detection based on belief propagation with a parallel interference canceller is implementable in the order of the second power of the number of elements and achieves very good BER performance. For further reduction of complexity, we apply layered belief propagation, forced convergence, and node selection methods to the belief propagation based detection. The results show that the layered belief propagation can halve the complexity without performance degradation.
  • Keita Harada, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    2013 INTERNATIONAL SYMPOSIUM ON INTELLIGENT SIGNAL PROCESSING AND COMMUNICATIONS SYSTEMS (ISPACS) 240 - 244 2013 [Refereed][Not invited]
     
    Multi-user multiple-input multiple-output (MU-MIMO) systems in which signals are simultaneously transmitted from a base station to multiple users are well known as a method to improve the throughput performance. In MU-MIMO systems, the block diagonalization scheme is used to eliminate inter-user interference and the eigenbeam-space division multiplexing (E-SDM) technique is used for channel capacity maximization. In this paper, a multi-user single-carrier E-SDM scheme in wideband transmissions is formulated. The transmit and receive weights are obtained in the frequency domain. The receive weights are based on the zero-forcing method, which simultaneously operates on the spatial domain processing and frequency domain equalization. Then, the bit error rate performance is evaluated using computer simulations.
  • Terada, Tsubasa, Nishimura, Toshihiko, Ogawa, Yasutaka, Ohgane, Takeo
    2013 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI) 866 - 867 1522-3965 2013 [Refereed][Not invited]
     
    A method to estimate direction of arrival (DOA) of multi-band signals is proposed in this paper. The authors apply the compressed sensing theory which can reconstruct sparse data in a few measurements, to multi-band signals. Compared to various DOA estimation methods, this approach has produced a considerable improvement of DOA estimation accuracy. Moreover, this proposal can estimate more waves than the degrees of freedom of the array.
  • Yamaguchi, Kanako, Huu Phu Bui, Ogawa, Yasutaka, Nishimura, Toshihiko, Ohgane, Takeo
    2013 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI) 550 - + 1522-3965 2013 [Refereed][Not invited]
     
    We consider a multi-user multiple-input multiple-output (MIMO) system using block diagonalization and eigenbeam-space division multiplexing to suppress inter-user interference and inter-stream interference. In time-varying environments, the performance seriously degrades due to mistracking of beamforming. A channel prediction scheme can eliminate the effect of the time-varying environments. In this paper, using indoor measurement data, we evaluate the bit error rate (BER) performance of a multi-user MIMO system with channel prediction based on an autoregressive model. It is shown that the proposed channel prediction technique can improve the BER performance significantly.
  • Yousuke Sano, Yusuke Ohwatari, Nobuhiko Miki, Yuta Sagae, Yukihiko Okumura, Yasutaka Ogawa, Takeo Ohgane, Toshihiko Nishimura
    IEICE TRANSACTIONS ON COMMUNICATIONS E95B (12) 3728 - 3738 0916-8516 2012/12 [Refereed][Not invited]
     
    This paper investigates the dominant impact on the interference rejection combining (IRC) receiver due to the downlink reference signal (RS) based covariance matrix estimation scheme. When the transmission modes using the cell-specific RS (CRS) in LTE/LTE-Advanced are assumed, the property of the non-precoded GRS is different from that of the data signals. This difference poses two problems to the IRC receiver. First, it results in different levels of accuracy for the RS based covariance matrix estimation. Second, assuming the case where the CRS from the interfering cell collides with the desired data signals of the serving cell, the IRC receiver cannot perfectly suppress this CRS interference. The results of simulations assuming two transmitter and receiver antenna branches show that the impact of the CRS-to-CRS collision among cells is greater than that for the CRS interference on the desired data signals especially in closed-loop multiple-input multiple-output (MIMO) systems, from the viewpoint of the output signal-to-interference-plus-noise power ratio (SINR). However, the IRC receiver improves the user throughput by more than 20% compared to the conventional maximal ratio combining (MRC) receiver under the simulation assumptions made in this paper even when the CRS-to-CRS collision is assumed. Furthermore, the results verify the observations made in regard to the impact of inter-cell interference of the CRS for various average received signal-to-noise power ratio (SNR) and signal-to-interference power ratio (SIR) environments.
  • Heedong Choi, Yasutaka Ogawa, Toshihiko Nishmura, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E95B (7) 2377 - 2385 0916-8516 2012/07 [Not refereed][Not invited]
     
    A time-reversal (TR) approach with multiple signal classification (MUSIC) provides super-resolution for detection and localization using multistatic data collected from an array antenna system. The theory of TR-MUSIC assumes that the number of antenna elements is greater than that of scatterers (targets). Furthermore, it requires many sets of frequency-domain data (snapshots) in seriously noisy environments. Unfortunately, these conditions are not practical for real environments due to the restriction of a reasonable antenna structure as well as limited measurement time. We propose an approach that treats both noise reduction and relaxation of the transceiver restriction by using a time-domain gating technique accompanied with the Fourier transform before applying the TR-MUSIC imaging algorithm. Instead of utilizing the conventional multistatic data matrix (MDM), we employ a modified MDM obtained from the gating technique. The resulting imaging functions yield more reliable images with only a few snapshots regardless of the limitation of the antenna arrays.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka
    INTERNATIONAL JOURNAL OF ELECTRICAL ENGINEERING EDUCATION 49 (3) 232 - 242 0020-7209 2012/07 [Refereed][Not invited]
     
    This paper describes the teaching and research of signal processing and communications systems that took place during the development of a real-time transceiver and radio channel testbed at Hokkaido University, Japan. Digital signal processing (DSP) concepts were taught and learnt during both the testbed system development and also the results gathering and analysis stages. The performance of a modern multiple antenna communications system is dependent on a number of key parameters, and the student interaction with such a real-time system can assist in the understanding of key but often abstract theoretical concepts. The communications algorithm and architecture overview on a signal processing board containing a Xilinx field programmable gate array (FPGA) and Analog Devices TigerSharc DSP is detailed. The lessons learned and potential uses of the testbed in both teaching and research are also described.
  • Considerations on a Frequency Correlation for Distributed Antenna Systems
    Kanako Yamaguchi, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 1128 - 1131 1522-3965 2012 
    Radio technology has been developed extensively for mobile communications and wireless LANs. In a wireless communication channel, we have multipath propagation due to reflections and scatterings. When the delay difference between multipath waves is large, we have frequency selective fading. Thus far, a frequency correlation defined for a single antenna has been used for evaluating the frequency selectivity [1], [2]. Multiple antennas have been introduced to realize space diversity and/or spatial multiplexing. The conventional frequency correlation cannot be used for multiple-antenna systems. © 2012 IEICE.
  • Angle-and-time-domain Gating Technique for Time-reversal MUSIC Imaging
    Heedong Choi, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 86 - 89 1522-3965 2012 
    Time-reversal multiple signal classification (TR-MUSIC) [1] has been a topic of recent interest in a variety of disciplines, including acoustics, communication and industrial applications [2]. Among the developed TR-MUSIC methodology, the TR-MUSIC imaging with the time-domain gating technique not only provides noise reduction by filtering in the time domain, but also relaxes the transceiver restriction by reducing the number of targets (scatterers) to be detected at one time [3]. Because the developed TR-MUSIC algorithm based on the time-domain gating technique extracts target response(s) in the time domain, it has a one-dimensional (time-domain) filtering effect in the scattering scenario. Unfortunately, this image is subject to focusing errors which are caused by many targets in the gated region. It also requires non-trivial conditions, that is, target response(s) or sidelobes (skirts) of the responses must be separated with one another to extract desired response(s) [3]. However, it may be difficult for this condition to be satisfied because targets are irregularly and/or randomly spread out over the scattering scenario. In this study, we propose a two-dimensional (angle-and-time-domain) gating technique accompanied with the fast Fourier transform (FFT) and spatial FFT processing. The concept of the spatial FFT has been proposed and considered as a beamforming technique [4]. By utilizing the weight adaptation, the beamforming technique can estimate coarse directions of arrival. Therefore, if we suppress unwanted signal(s) in the angle domain, we can overcome the above obstacle in the same scattering configuration. That is, since the proposed gating technique extracts targets in the two-dimensional region, we can expect the improvement of imaging function. © 2012 IEICE.
  • Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    International Conference on Advanced Communication Technology, ICACT 497 - 501 1738-9445 2012 
    Low-density parity-check (LDPC) codes are capacity approaching codes that have rapidly been adopted in modern systems such as the IEEE 802.11n and long term evolution advanced (LTE-A) communications standards. The decoders based on the iterative belief propagation offer exceedingly high performance but unfortunately have high computational complexity. Therefore significant research has focused on lower complexity architectures based on the family of so-called bit-flipping algorithms. In the basic bit-flipping algorithm the number of failed parity checks for each bit is calculated and the sign of the bit with the maximum failed checks is inverted. Inverting bits above a certain threshold removes the complexity of calculating a maximum function and adaptive thresholds on each bit further simplifies the design. The choice of threshold updates directly affects the error and convergence performances. Here we describe a simple architecture that has two decoders with different scaling factors and select the branch with the lowest syndrome sum. It is shown that the addition of a random uniform perturbation to the threshold can reduce the average iteration count further by providing an escape from stuck decoding states. © 2012 GIRI.
  • Naohito Kiyomi, Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2012 IEEE 75TH VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING) 1550-2252 2012 [Refereed][Not invited]
     
    A cooperative relay has been studied as a method to improve transmission quality in wireless mesh networks and cellular systems. Multiple antenna elements at a source node enable adaptive beamforming and thus improve total performance of relay transmission. In this paper, we propose simple transmit beamforming at a source node when the source node has two or more antenna elements and knows all channel information in MISO-SISO/MIMO-MIMO amplify-and-forward relays with direct link and evaluate the packet error rate. The simulation results show that the proposed method achieves both low complexity and high performance.
  • Cristian Davidescu, Yasutaka Ogawa, Julian Webber, Toshihiko Nishimura, Takeo Ohgane
    2012 IEEE 75TH VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING) 1550-2252 2012 [Refereed][Not invited]
     
    In the case of broadband wireless access systems operating over non-line-of-sight (NLOS) links, the multipath can be severe. This leads to frequency-selective fading channel which causes distortions of the received signal. The single-carrier (SC) modulation method combined with frequency-domain equalization (FDE) at the receiver has been proposed as an alternative to the orthogonal frequency division multiplexing (OFDM) system due to its relative small peak-to-average power ratio (PAPR) achieved at a similar complexity. Furthermore, an eigenbeam-space division multiplexing (E-SDM) technique can be applied to the single-carrier system to improve the spectrum efficiency. This scheme makes use of both spatial and frequency diversity while maintaining a low PAPR. The computation load still remains a challenge for the uplink transmission where the power resources are limited, therefore, in this paper we propose some reduced-complexity techniques. The transmission performance of these techniques and the trade-off between complexity and bit error rate (BER) are evaluated in a frequency-selective Rayleigh channel by computer simulations.
  • Heedong Choi, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    2012 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM (APSURSI) 1522-3965 2012 [Refereed][Not invited]
     
    An ultrawideband (UWB) imaging technique with time-reversal (TR) MUSIC has been studied for a remote sensing system because of the super-resolution characteristics. Particularly, TR-MUSIC imaging with the time-domain gating technique offers dramatical noise reduction as well as relaxation of the transceiver restriction. In this paper, we introduce selective UWB-TR-MUSIC imaging with the time-domain gating technique by utilizing partial frequencies. Instead of utilizing a single-frequency or all the available frequencies, we combine images from partial frequencies. The resulting pseudo-spectra yield distinctive features such as super resolution and statistical stability.
  • TOSHIHIKO NISHIMURA
    IEICE Proceeding Series 2011/10/25
  • TOSHIHIKO NISHIMURA
    IEICE Proceeding Series 2011/10/25
  • TOSHIHIKO NISHIMURA
    IEICE Proceeding Series 2011/10/25
  • Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    APSIPA ASC 2011 - Asia-Pacific Signal and Information Processing Association Annual Summit and Conference 2011 492 - 495 2011 
    This paper describes the hardware design of a wideband radio channel emulator for evaluating the bit error rate (BER) performances of two modern communications systems. The main system application described here is a multiple input multiple output - orthogonal frequency division multiplexing (MIMO-OFDM) system with beamforming. The performance of MIMO systems are dependent on the spatial correlation between channels and this is emulated using Cholesky factorization to compute real-time channels with a desired correlation. The emulator implements various contemporary radio channel models (e.g. Gaussian, Jakes, and Zheng). Up to sixteen independent channels are programmable for a 4 × 4 MIMO system. The second application is single-carrier frequency domain equalization. Single carrier frequency division multiple access (SC-FDMA) is deployed in the uplink of 3GPP long term evolution (LTE) systems and uses a single-input single-output (SISO) channel. The system development on a field programmable gate array (FPGA) is described.
  • Heedong Choi, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    iWEM2011 - IEEE International Workshop on Electromagnetics: Applications and Student Innovation Competition 140 - 144 2011 [Refereed][Not invited]
     
    This paper introduces a time-reversal MUSIC (TR-MUSIC) approach based on the gating technique for detection and localization. TR-MUSIC has been proposed to surpass the classical diffraction limit. The general TR-MUSIC imaging algorithm uses a single snapshot to obtain a data matrix, however many snapshots are needed in a heavy noise environment. It is not preferable to require many snapshots because it takes a long measurement time. In this paper, we propose to reduce the noise component by using the gating technique accompanied with the Fourier transform. The proposed technique needs fewer snapshots and also provides a better performance. © 2011 IEEE.
  • Kyouhei Maeda, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    2011 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (APSURSI) 835 - 838 1522-3965 2011 [Refereed][Not invited]
     
    The method to estimate direction of arrival (DOA) with multi-band signals is proposed in this paper. The MUSIC method, which is one of the conventional super-resolution DOA estimation methods, is applied to sets of snapshots filtered from the multi-band signal. In the beginning, a set of snapshots is extracted by the narrow-band filter (NBF) for the lowest frequency where the half wavelength of center frequency equals the array antenna spacing for a uniform linear array, and processed by the MUSIC method in order to avoid grating lobes. Next, using another set of snapshots in higher frequency, more precise DOA estimation is done in a narrower range with finer step angle. Therefore, this method can realize more accurate DOA estimation than the conventional method using a single set of snapshots. By examining RMSE and success probability of DOA detection, this method is compared with a conventional method.
  • Huu Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    2011 IEEE INTERNATIONAL SYMPOSIUM ON ANTENNAS AND PROPAGATION (APSURSI) 59 - 62 1522-3965 2011 [Refereed][Not invited]
     
    The performance of a downlink multi-user MIMO system seriously degrades in time-varying environments because MIMO channels change during the time interval between transmission parameter determination and actual MIMO transmission. Channel prediction techniques have been proposed to improve the performance in dynamic environments. In this paper, based on indoor measurement data, we show the effect of the linear channel extrapolation, and evaluate the bit error rate performance of the multi-user MIMO system with the channel prediction technique.
  • Huu Phu Bui, Hiroshi Nishimoto, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    EURASIP JOURNAL ON WIRELESS COMMUNICATIONS AND NETWORKING 1687-1499 2010 [Refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems employ advanced signal processing techniques. However, the performance is affected by propagation environments and antenna characteristics. The main contributions of the paper are to investigate Doppler spectrum based on measured data in a typical meeting room and to evaluate the performance of MIMO systems based on an eigenbeam-space division multiplexing (E-SDM) technique in an indoor time-varying fading environment, which has various distributions of scatterers, line-of-sight wave existence, and mutual coupling effect among antennas. We confirm that due to the mutual coupling among antennas, patterns of antenna elements are changed and different from an omnidirectional one of a single antenna. Results based on the measured channel data in our measurement campaigns show that received power, channel autocorrelation, and Doppler spectrum are dependent not only on the direction of terminal motion but also on the antenna configuration. Even in the obstructed-line-of-sight environment, observed Doppler spectrum is quite different from the theoretical U-shaped Jakes one. In addition, it has been also shown that a channel change during the time interval between the transmit weight matrix determination and the actual data transmission can degrade the performance of MIMO E-SDM systems.
  • Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    APSIPA ASC 2010 - Asia-Pacific Signal and Information Processing Association Annual Summit and Conference 757 - 760 2010 
    In multiple-input multiple-output (MIMO) systems, eigenbeam-space division multiplexing (E-SDM) can achieve high performance using channel state information that is fedback to the transmitter. Orthogonal frequency division multiplexing (OFDM) systems can efficiently operate in wideband fading channels using a simple 1-tap equalizer on each sub-carrier. Here, MIMO channels are generated with increasing correlation through Cholesky factorization of the channel covariance matrix. To maintain a given BER and hence compensate for the effects of correlation, an increase in the transmit power is required (e.g. 0.4 dB for ρ=0.25 at 10 BER for a reduced complexity pseudo E-SDM system), but this increases significantly as ρ increases. In this paper, a description of the E-SDM system implementation on an FPGA-DSP platform is also detailed. -5
  • Masaki Takanashi, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E92B (8) 2698 - 2707 0916-8516 2009/08 [Refereed][Not invited]
     
    Ultrawide-band impulse radio (UWB-IR) technology and multiple-input multiple-output (MIMO) systems have attracted interest regarding their use in next-generation high-speed radio communication. We have studied the use of MIMO ultrawide-band (MIMO-UWB) systems to enable higher-speed radio communication. We used frequency-domain equalization based on the minimum mean square error criterion (MMSE-FDE) to reduce intersymbol interference (ISI) and co-channel interference (CCI) in MIMO-UWB systems. Because UWB systems are expected to be used for short-range wireless communication, MIMO-UWB systems will usually operate in line-of-sight (LOS) environments and direct waves will be received at the receiver side. Direct waves have high power and cause high correlations between antennas in such environments. Thus, it is thought that direct waves will adversely affect the performance of spatial filtering and equalization techniques used to enhance signal detection. To examine the feasibility of MIMO-UWB systems, we conducted MIMO-UWB system propagation measurements in LOS environments. From the measurements, we found that the arrival time of direct waves from different transmitting antennas depends on the MIMO configuration. Because we can obtain high power from the direct waves, direct wave reception is critical for maximizing transmission performance. In this paper, we present our measurement results, and propose a way to improve performance using a method of transmit (Tx) and receive (Rx) timing control. We evaluate the bit error rate (BER) performance for this form of timing control using measured channel data.
  • Hun Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E92B (7) 2374 - 2388 0916-8516 2009/07 [Refereed][Not invited]
     
    In this paper, the performance of multiuser MIMO E-SDM systems in downlink transmission is evaluated in both uncorrelated and correlated time-varying fading environments. In the ideal case, using the block diagonalization scheme, inter-user interference can be completely eliminated at each user; and using the E-SDM technique for each user, optimal resource allocation can be achieved, and spatially orthogonal substreams can be obtained. Therefore, a combination of the block diagonalization scheme and the E-SDM technique applied to multiuser MIMO systems gives very good results. In realistic environments, however, due to the dynamic nature of the channel and processing delay at both the transmitter and the receiver, the channel change during the delay may cause inter-user interference even if the BD scheme is used. In addition, the change may also result in large inter-substream interference and prevent optimal resource allocation from being achieved. As a result, system performance may be degraded seriously. To overcome the problem. we propose a method of channel extrapolation to compensate for the channel change. Applying our proposed method, simulation results show that much better system performance can be obtained than the conventional case. Moreover, it also shows that the system performance in the correlated fading environments is much dependent on the antenna configuration and the angle spread from the base station to scatterers.
  • Ohgane Takeo, Ogawa Yasutaka, Nishimura Toshihiko
    Journal of the Japan Society for Simulation Technology 日本シミュレーション学会 28 (2) 86 - 90 0285-9947 2009/06/15 [Not refereed][Not invited]
  • Keiichi Kambara, Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E92B (5) 1466 - 1474 0916-8516 2009/05 [Refereed][Not invited]
     
    Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within an FIDE block cannot be ignored. The ISI reduction performance of FDE degrade, since the cyclicity of the channel matrix is lost. To solve this problem, a method of dividing the received data block into multiple subblocks has been proposed, where pseudo cyclic prefix (CP) processing is introduced to realize periodicity in each subblock. In this method, the performance is degraded by the inherently-inaccurate pseudo CP. In this paper, we study the application of frequency-domain turbo equalization (FDTE) to subblock processing for improving the accuracy of pseudo CP. The simulation results show that FDTE with subblock processing yields remarkable performance improvements.
  • Ogawa Yasutaka, Ohgane Takeo, Nishimura Toshihiko
    B-Plus The Institute of Electronics, Information and Communication Engineers 2009 (11) 11_32 - 11_38 2186-0661 2009 [Not refereed][Not invited]
     
    数十Gbit/s以上の超高速通信が必要になった場合，MIMO伝送が必須技術となることは容易に想像できる．しかし，実際に超高速伝送を実現できるかどうかは，アンテナ本数のみならず，周波数帯，伝搬環境，実装技術に大きく依存する．特に超高速伝送が使用されると考えられる見通しのある解放空間では，空間相関が高くなるため，MIMO伝送の効果が減少する．したがって，アンテナ配置や伝搬構造の能動的最適化など，改善手法について述べる．
  • KIM Sang-Woo, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka
    The IEICE transactions on communications B 一般社団法人電子情報通信学会 92 (1) 185 - 195 1344-4697 2009/01/01 [Not refereed][Not invited]
     
    周波数有効利用やマルチパス対策においてOFDMは有効な伝送方式である.しかし,高速移動によるマルチパスフェージング環境下では,プリアンブルで推定したチャネルが時間とともに変動するため,それに続くデータ区間においてその変動を補償する必要がある.本論文では,その補償法として判定帰還を用いたチャネル更新法を検討し,帰還系列の精度を向上させる手法を新たに提案した.また,追従特性をより改善するため線形予測を導入し,予測係数を少ないデータから決定する二つの手法について検討した.シミュレーションによる特性評価から,これらの提案手法が有効であることが確認できた.
  • Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    APSIPA ASC 2009 - Asia-Pacific Signal and Information Processing Association 2009 Annual Summit and Conference 684 - 687 2009 
    When channel state information is fed-back to the transmitter, multiple-input multiple-output (MIMO) systems can realize eigenbeam-space division multiplexing (E-SDM) and system performance can be improved. Pseudo E-SDM offers both reduced computational complexity (the mean number of multiplications for 4×4 is reduced to about 1/10) and a reduction in the effective channel delay spread compared to E-SDM. This work describes the design of such a MIMO orthogonal frequency division multiplexing (OFDM) system based on the IEEE802.11n standard. The paper describes the real-time processing on field programmable gate arrays (FPGA) capable of sustaining a maximum 260 Mbps service within a 20 MHz bandwidth and the MIMO signal processing computed on digital signal processors (DSP). The modified Jakes model permits the Rayleigh fading channel to be emulated in real-time with limited hardware complexity.
  • Keisuke Saito, Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    GLOBECOM 2009 - 2009 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, VOLS 1-8 2688 - 2692 1930-529X 2009 [Refereed][Not invited]
     
    Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within an FFT block cannot be ignored. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. To solve this problem, we extend the conventional diagonal matrix in FDE to a tri-diagonal matrix. In addition, a simple procedure without strict calculation in tri-diagonalization is proposed. The proposed technique is applied to FDE and frequency-domain turbo equalization (FDTE). The results of numerical analysis show a remarkable improvement by the tri-diagonalization. When the normalized Doppler frequency is 0.0015, the bit error rate (BER) floor is decreased to less than 0.01 in the FDE case; and about 2.8 dB gain at the BER of 0.001 is obtained in the FDTE case.
  • Toshihiko Nishimura, Ysutaka Ogawa, Takeo Ohgane
    2009 INTERNATIONAL SYMPOSIUM ON INTELLIGENT SIGNAL PROCESSING AND COMMUNICATION SYSTEMS (ISPACS 2009) 240 - 243 2009 [Refereed][Not invited]
     
    The method of separating two or more wideband signals that arrive from close angles is proposed. Its high-resolution capability of direction of arrival estimation is based on extracting narrowband components from the wideband signals in the frequency domain. Then, the resolution is stepwise improved by changing the target frequency band upward. By this process, we can avoid the effect of grating lobes. It was shown to be able to separate the signals that arrive from close angles by repeating the above routine even though the electric power spectrum density is low.
  • Masaki Takanashi, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E91B (11) 3784 - 3787 0916-8516 2008/11 [Refereed][Not invited]
     
    A uniform circular array (UCA) is a well-known array configuration which can accomplish estimation of 360 degrees field of view with identical accuracy. However, a UCA cannot estimate coherent signals because we cannot apply the SSP owing to the structure of UCA. Although a variety of studies on UCA in coherent multipath environments have been done, it is impossible to estimate the DOA of coherent signals with different incident polar angles. Then, we have proposed Root-MUSIC algorithm with a cylindrical array. However, the estimation performance is degraded when incident signals arrive with close polar angles. To solve this problem. in the letter, we propose to use SAGE algorithm with a cylindrical array. Here, we adopt a CLA Root-MUSIC for the initial estimation and decompose two-dimensional search to double one-dimensional search to reduce the calculation load. The results show that the proposal achieves high resolution with low complexity.
  • Masatsugu Higashinaka, Hiroshi Kubo, Akihiro Okazaki, Yasutaka Ogawa, Takeo Ohgane, Toshihiko Nishimura
    IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES E91A (10) 2787 - 2797 0916-8508 2008/10 [Refereed][Not invited]
     
    This paper proposes a novel channel estimation method for iterative equalization in MIMO systems. The proposed method incorporates co-channel interference (CCI) cancellation in the channel estimator and the channel estimation is successively performed with respect to each stream. Accuracy of Channel estimation holds the key to be successfully converged the iterative equalization and decoding process. Although the channel estimates can be re-estimated by means of LS (Least Square) channel estimation using tentative decisions obtained in the iterative process, its performance is severely limited in a MIMO system because of erroneous decisions and ill-conditioned channel estimation matrix. The proposed method can Suppress the above effects by means of CCI cancellation and successive channel estimation. Computer simulation confirms that the proposed channel estimation method can accurately estimate the channel, and the receiver with iterative equalization and the proposed method achieves excellent decoding performance in a MIMO-SM system.
  • SAITO Yuta, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko
    The IEICE transactions on communications B 一般社団法人電子情報通信学会 91 (9) 940 - 947 1344-4697 2008/09/01 [Not refereed][Not invited]
     
    将来の高速移動通信は現在よりも高い周波数帯を使用することが考えられる.この場合,端末の電源がバッテリーであるため,上り回線の送信電力が制限され,通信品質は劣化する.そこで,近傍の複数端末が送信データを共有して互いに協力し合う協調無線が注目されている.しかし,仮想的なアレーアンテナを形成してビームフォーミングを行う場合,各端末は異なる発振器で動作しているため,キャリヤ周波数のずれによる端末周波数オフセットの存在が通信特性に大きな影響を与えてしまう.そこで,本論文では過去のチャネル情報を用いた端末周波数オフセット推定法とそれを用いた送信側での補償法,及び,RLSアルゴリズムを用いた受信ウェイト制御との組合せについて検討し,計算機シミュレーションによりその特性について評価する.その結果,これらの制御を組み合わせることで,特性を大きく改善できることが確認された.
  • Huu Phu Bui, Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E91B (6) 1713 - 1723 0916-8516 2008/06 [Refereed][Not invited]
     
    In time-varying fading environments, the performance of multiple-input multiple-output (MIMO) systems applying an eigenbeam-space division multiplexing (E-SDM) technique may be degraded due to a channel change during the time interval between the transmit weight matrix determination and the actual data transmission. To compensate for the channel change, we have proposed some channel prediction methods. Simulation results based on computer-generated channel data showed that better performance can be obtained when using the prediction methods in Rayleigh fading environments assuming the Jakes model with rich scatterers. However, actual MIMO systems may be used in line-of-sight (LOS) environments, and even in a non-LOS case, scatterers may not be uniformly distributed around a receiver and/or a transmitter. In addition, mutual coupling between antennas at both the transmitter and the receiver cannot be ignored as it affects the system performance in actual implementation. We conducted MIMO channel measurement campaigns at a 5.2 GHz frequency band to evaluate the channel prediction techniques. In this paper, we present the experiment and simulation results using the measured channel data. The results show that robust bit-error rate performance is obtained when using the channel prediction methods and that the methods can be used in both Rayleigh and Rician fading environments, and do not need to know the maximum Doppler frequency.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E91B (5) 1648 - 1652 0916-8516 2008/05 [Refereed][Not invited]
     
    The MIMO system can meet the growing demand for higher capacity in wireless communication fields. So far, the authors have reported that, based on channel measurements, uncoded performance of narrowband MIMO spatial multiplexing in indoor line-of-sight (LOS) environments generally outperforms that in non-LOS (NLOS) ones under the same transmit power condition. In space-frequency coded MIMO-OFDM spatial multiplexing, however, we cannot expect high space-frequency diversity gain in LOS environments because of high fading correlations and low frequency selectivity of channels so that the performance may degrade unlike uncoded cases. In this letter, we present the practical performance of coded MIMO-OFDM spatial multiplexing based on indoor channel measurements. The results show that an LOS environment tends to provide lower space-frequency diversity effect whereas the MIMO-OFDM spatial multiplexing performance is still better in the environment compared with an NLOS environment.
  • Masaki Takanashi, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E91B (4) 1084 - 1094 0916-8516 2008/04 [Refereed][Not invited]
     
    MIMO ((M) under bar ultiple-(I) under bar nput (M) under bar ultiple-(O) under bar utput) technologies have attracted much interest for high-rate and high-capacity wireless communications. MIMO technologies under frequency-selective fading environments (wideband MIMO technologies) have also been studied. A wideband MIMO system is affected by ISI ((I) under bar nter (S) under bar ymbol (I) under bar nterference) and CCI ((C) under baro-(C) under bar hannel (I) under bar nterference). Hence, we need a MIMO signal detection technique that simultaneously suppresses ISI and CCL The OFDM system and SC-FDE ((S) under bar ingle (C) under bar arrier-(F) under bar requency (D) under bar omain (E) under bar qualization) techniques are often used for suppressing ISL By employing these techniques with the ZF ((Z) under bar ero (F) under bar orcing) or the MMSE ((M) under bar inimum (M) under bar ean (S) under bar quare (E) under bar rror) spatial filtering technique, we can cancel both ISI and CCL To use ZF or MMSE, we need channel state information for calculating the receive weights. Although an LS ((L) under bar east (S) under bar quare) channel estimation technique has been proposed for MIMO-OFDM systems, it needs a large estimation matrix at the receiver side to obtain sufficient estimation performance in heavy multipath environments. However, the use of a large matrix increases computational complexity and the circuit size. We use frequency domain channel estimation to solve these problems and propose an iterative method for achieving better estimation performance. In this paper, we assume the use of a MIMO-UWB system that employs a UWB-IR ((U) under bar ltra-(W) under bar ideband (I) under bar mpulse Radio) scheme with the FDE technique as the wideband wireless transmission scheme for heavy multipath environments, and we evaluate the iterative frequency domain channel estimation through computer simulations and computational complexity calculations.
  • Keiichi Kambara, Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 26 (2) 359 - 365 0733-8716 2008/02 [Refereed][Not invited]
     
    Frequency domain equalization (FDE) has been studied for reducing inter-symbol interference (ISI) caused by frequency selective fading in single carrier systems. When a high-mobility terminal exists in the system, the channel state may change within a DFT block. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. We propose to divide a received data block into multiple subblocks to decrease the channel transition within the DFT block in fast fading environments. Also, to satisfy periodicity of the received signal in each subblock, we introduce a pseudo cyclic prefix technique. The results of numerical analysis show that the proposed method can effectively decrease the error floor in fast fading environments.
  • K. Kambara, H. Nishimoto, T. Nishimura, T. Ohgane, Y. Ogawa
    IEEE Vehicular Technology Conference 1550-2252 2008 [Refereed][Not invited]
     
    Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within an FFT block cannot be ignored. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. To solve this problem, a method of dividing the received data block into multiple subblocks has been proposed. In the paper, the subblock processing is applied to frequency-domain turbo equalization (FDTE). The results of numerical analysis show a remarkable improvement by the proposed method. Specifically, the FDTE with two-subblock processing can decrease the block error rate floor to less than 0.001 when the maximum Doppler frequency normalized by the block length is 0.4. ©2008 IEEE.
  • K. Kambara, H. Nishimoto, T. Nishimura, T. Ohgane, Y. Ogawa
    68TH IEEE VEHICULAR TECHNOLOGY CONFERENCE, FALL 2008 839 - 843 1090-3038 2008 [Refereed][Not invited]
     
    Frequency-domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within an FFT block cannot be ignored. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. To solve this problem, a method of dividing the received data block into multiple subblocks has been proposed. In the paper, the subblock processing is applied to frequency-domain turbo equalization (FDTE). The results of numerical analysis show a remarkable improvement by the proposed method. Specifically, the FDTE with two-subblock processing can decrease the block error rate floor to less than 0.001 when the maximum Doppler frequency normalized by the block length is 0.4.
  • Bui Huu Phu, Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    2008 SECOND INTERNATIONAL CONFERENCE ON COMMUNICATIONS AND ELECTRONICS 356 - 361 2008 [Refereed][Not invited]
     
    In this paper, we examine some channel characteristics of SISO and MIMO systems based on the measured channel data in our measurement campaigns. We confirm that due to the mutual coupling between antennas, patterns of antenna elements are changed and different from an omnidirectional one of a single antenna. Results also show that received power, channel auto-correlation, and Doppler spectrum are much dependent not only on the direction of the RX motion, but also on the array orientation. In the NLOS environment, observed Doppler spectrum is quite different from the theoretical U-shaped Jakes' one.
  • Hiroshi Nishimoto, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 55 (12) 3677 - 3689 0018-926X 2007/12 [Refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) spatial multiplexing that needs to separate and detect transmitted signal streams by using processing at the receiver end can increase the data rates of transmissions on independent and identically distributed (i.i.d.) channels. Such channels have been considered to exist in nonline-of-sight (NLOS) environments. However, actual communications may also be conducted in line-of-sight (LOS) environments. While an LOS component can increase the received power level, it may also cause correlated channels that make it difficult to detect the transmitted streams. In this paper, we describe the performance of 4 x 4 MIMO spatial multiplexing based on LOS and NLOS channel measurements in an indoor environment. For eight configurations of uniform linear arrays (four antenna spacings and two array orientations), we evaluated the cumulative distribution function (CDF) of the channel capacity and bit error rate performance versus transmit power, and we analyzed them in terms of antenna pattern, fading correlation, CDFs of MIMO channel elements, and CDFs of eigenvalues. Results show that, despite higher fading correlations and non i.i.d. channel characteristics, the performance of MIMO spatial multiplexing in the LOS environment is better than that in the NLOS one. However, the performance in the measured LOS environment largely depends on the MIMO configuration.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E90B (11) 3311 - 3314 0916-8516 2007/11 [Refereed][Not invited]
     
    For simulating i.i.d. time-varying MIMO channels using multiple Jakes' rings, it is desirable to generate channels having stable statistics with fewer scatterers. The statistical property of the conventional Jakes' model may depend on the initial phase set assigned to scattering points. In this letter, we present simple and effective conditions on arrangement of scattering points to achieve stable fading properties. The results show that the proposed arrangement provides higher statistical stability in generating time-varying channels.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEICE TRANSACTIONS ON COMMUNICATIONS E90B (11) 3197 - 3207 0916-8516 2007/11 [Refereed][Not invited]
     
    In a frequency-selective multiple-input multiple-output (MIMO) channel, the optimum transmission is achieved by beamforming with eigenvectors obtained at each discrete frequency point, i.e., an extension of eigenbeam-space division multiplexing (E-SDM). However, the calculation load of eigenvalue decomposition at the transmitter increases in proportion to the number of frequency points. In addition, frequency-independent eigenvectors increase the delay spread of the effective channel observed at the receiver. In this paper, we propose a pseudo eigenvector scheme for the purpose of mitigating the calculation load and maintaining frequency continuity (or decreasing the delay spread). First, we demonstrate that pseudo eigenvectors reduce the delay spread of the effective channels with low computational complexity. Next, the practical performance of the pseudo E-SDM (PE-SDM) transmission is evaluated. The simulation results show that PE-SDM provides almost the same or better performance compared with E-SDM when the receiver employs a time-windowing-based channel estimation available in the low delay spread cases.
  • OHWATARI Yusuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo
    The IEICE transactions on communications B 一般社団法人電子情報通信学会 90 (9) 885 - 895 1344-4697 2007/09/01 [Not refereed][Not invited]
     
    MIMO-OFDM空間分割多重において,送信側でチャネル情報(CSI)が既知,若しくは,受信側から用いるべき送信ウェートが報知される場合,固有ビーム空間分割多重(E-SDM)方式を用いることができ,MIMOチャネル最大の容量が得られる.筆者らはこれまで時間領域で最小二乗法を適用し,推定したCSIのうち,主要な成分のみをフィードバックすることにより,情報量が削減できることを報告してきた.本論文では,筆者らが提案しているCSIフィードバック手法及びコードブックを用いた送信ウェートフィードバック手法について比較検討を行った.その結果,各手法におけるフィードバック情報量をほぼ等しくした場合,情報量が少ない4×2MIMOにおいては送信ウェート行列をフィードバックする手法の特性が,情報量が多い4×2MIMO,及び4×4MIMOにおいてはCSIフィードバック手法の特性が良好であることが確認された.
  • Hiroshi Nishimoto, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E90B (6) 1474 - 1486 0916-8516 2007/06 [Refereed][Not invited]
     
    MIMO systems using a space division multiplexing (SDM) technique in which each transmit antenna sends an independent signal substrearn have been studied as one of the successful applications to increase data rates in wireless communications. The throughput of a MIMO channel can be maximized by using an eigenbeam-SDM (E-SDM) technique, and this paper investigates the practical performance of 2x2 and 4 x 4 MIMO E-SDM based on indoor measurements. The channel capacity and bit error rate obtained in various uniform linear array configurations are evaluated and are compared with the corresponding values for conventional SDM. Analysis results show that the bit error rate performance of E-SDM is better than that of SDM and that E-SDM gives better performance in line-of-sight (LOS) conditions than in non-LOS ones. They also show that the performance of E-SDM in LOS conditions depends very much on the array configuration.
  • Y. Ogawa, H. P. Bui, H. Nishimoto, T. Nishimura, T. Ohgane
    IET Seminar Digest 2007 (11961) 2007 [Refereed][Not invited]
     
    MIMO channel characteristics and spatial multiplexing are investigated from the viewpoint of antennas and propagation in this paper. We conducted 4x4 MIMO channel measurement campaigns in an indoor propagation environment. Using the measured data, we examined the detail of the MIMO channels. The MIMO channels and eigenvalues are largely different for MIMO array orientations in an LOS environment. This is due to the effect of mutual coupling between antenna elements. Then, the bit error rate (BER) of eigenbeam space division multiplexing (E-SDM) in a quasi-static environment is examined using the measured MIMO channel data. It is shown that the BER performance in an LOS environment is affected by the mutual coupling. Furthermore, we obtained time-varying MIMO channel data, and calculated the channel auto-correlation and Doppler spectrum. The BER performance is evaluated for different maximum Doppler frequencies and different (LOS/NLOS) environments.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 3876 - 3879 1522-3965 2007 [Refereed][Not invited]
  • Bui Huu Phu, Toshihiko Nishimura, Hiroshi Nishimoto, Takeo Ohgane, Yasutaka Ogawa
    IEEE Vehicular Technology Conference 1322 - 1326 1550-2252 2007 [Refereed][Not invited]
     
    The performance of MIMO-OFDM E-SDM systems may be seriously degraded in time-varying fading environments due to a channel transition. In the paper, we propose two methods of channel extrapolation to compensate for the channel change. Futhermore, we also consider a method to reduce the amount of header signal and the computational complexity for the systems. We conducted MIMO measurement campaigns at a 5.2 GHz frequency band to evaluate the system performance. Simulation results based on the measured channel data show that robust bit-error rate performance can be obtained by using our channel prediction methods in both line-of-sight (LOS) and non-LOS environments. It is also shown that the method of reducing the amount of header signal and the computational complexity may be used in the practical implementation point of view. © 2007 IEEE.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa
    IEEE Vehicular Technology Conference 541 - 545 1550-2252 2007 [Refereed][Not invited]
     
    In a frequency-selective MIMO channel, the optimum beamforming is achieved by using eigenvectors, i.e., eigenbeam-space division multiplexing (E-SDM), in the frequency domain. However, the calculation load of eigenvalue decomposition increases in proportion to the number of FFT points. In addition, eigenvectors without consideration of frequency continuity increase the delay spread of the effective channel observed at the receiver. To solve these issues, a pseudo eigenvector technique has been proposed. It has also been reported that a pseudo E-SDM (PE-SDM) technique can provide almost the same or better performance compared with the E-SDM when the receiver employs a simple channel estimator with time windowing. In this paper, focusing on the calculating process of pseudo eigenvectors, we propose a spatial windowing scheme improving the accuracy of the effective channel estimates. The simulation results show that the accuracy in the PE-SDM can be improved by combining the proposed scheme with the conventional time windowing scheme. © 2007 IEEE.
  • Huu Phu Bui, Toshihiko Nishimura, Hiroshi Nishimoto, Yasutaka Ogawa, Takeo Ohgane
    2007 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM, VOLS 1-12 209 - 212 1522-3965 2007 [Refereed][Not invited]
  • Huu Phu Bui, Hiroshi Nishimoto, Toshihiko Nishimura, Yasutaka Ogmata, Takeo Ohgane
    2007 IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM, VOLS 1-12 1245 - 1248 1522-3965 2007 [Refereed][Not invited]
  • Hun Phu Bui, Yasutaka Ogawa, Takeo Ohgane, Toshihiko Nishimura
    IEICE TRANSACTIONS ON COMMUNICATIONS E89B (11) 3083 - 3092 0916-8516 2006/11 [Refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems using eigenbeam space division multiplexing (E-SDM) perform well and have increased capacities compared with those using conventional space division multiplexing (SDM). However, channel state information (CSI) is required at a transmitter, and the performance of E-SDM systems depends much on the accuracy of the CSI at a transmitter and a receiver. In time-varying fading environments, the channel change between the transmit weight determination time and the actual data transmission time causes the system performance to degrade. To compensate for the channel error, a linear extrapolation method has been proposed for a time division duplexing system. Unfortunately, the system performance still deteriorates as the maximum Doppler frequency increases. Here, two new techniques of channel extrapolation are proposed. One is second order extrapolation, and the other is exponential extrapolation. Also, we propose maximum Doppler frequency estimation methods for exponential extrapolation. Simulation results for 4tx 4rx MIMO systems showed that using the proposed techniques, E-SDM system performs better in a higher Doppler frequency region.
  • OHWATARI Yusuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo
    The IEICE transactions on communications B 一般社団法人電子情報通信学会 89 (9) 1765 - 1775 1344-4697 2006/09/01 [Not refereed][Not invited]
     
    送受信側に複数のアンテナを設置し,各送信アンテナごとに独立したOFDM信号を送信するMIMO-OFDM空間分割多重では,マルチパス環境においても符号問干渉なしに伝送速度の向上が期待できる.更に,送信側でチャネル情報(CSI)が既知の場合,MIMOチャネルにおける最大スループットを得る固有ビーム空間分割多重(E-SDM)方式を用いることができる.しかしながら,OFDMでは各サブキャリヤごとにCSIをフィードバックする必要があり,通信容量を圧迫してしまう.本論文では,筆者らが以前より提案している時間領域で最小二乗法を適用し,推定したCSIをフィードバックすることで情報量を削減でき,更に良好な特性が得られることを示している.
  • TANAKA Toyohisa, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka
    The IEICE transactions on communications B 一般社団法人電子情報通信学会 89 (2) 264 - 277 1344-4697 2006/02/01 [Not refereed][Not invited]
     
    第3世代の移動通信方式として既にサービスが提供されているW-CDMAは,3rd Generation Partnership Project (3GPP)で引き続き性能向上のため仕様策定が行われている.下り回線に関しては最高データレート14.0Mbit/sのHigh Speed Downlink Packet Access (HSDPA)が規定され,更にMIMOの適用が検討されている.本論文では,W-CDMA方式の上り回線にMIMO伝送を適用した場合について,シングルユーザでの通信を対象として計算機シミュレーションにより検討した.3GPPのRelease99規格で仕様化されているチャネルコーディング,拡散方法を用いて,12.2kbit/s,384kbit/s,更に2,048kbit/sのデータレートについて評価した.特に遅延波の存在する周波数選択性フェージング環境下で,チャネルの状態に応じて送信電力を制御できるE-SDM (Eigen Space Division Multiplexing)アルゴリズムが有効であることが分かった.
  • Transmit and Receive Timing Control in LOS MIMO-UWB Environments
    Masaki Takanashi, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane
    Progress in Electromagnetics Research Symposium 605 - 609 1559-9450 2006 
    The UWB-IR(Ultra Wideband-Impulse Radio) technology and MIMO system have attracted interest for next generation high speed radio communications. We have researched multiple-input multiple-output ultra wideband(MIMO-UWB) systems for higher speed radio communications. The UWB system will be used in a range of less than 10 meters. Then, we usually have line-of-signt(LOS) environments in the MIMO-UWB systems. We can consider that the direct waves have high power and cause high correlations between antennas in this environment. Thus, it is conjectured that the direct waves affect the performance of signal detection by spatial filtering and equalization techniques. In order to examine the feasibility of MIMO-UWB systems, we conducted propagation measurement of MIMO-UWB systems in LOS environments, and evaluated bit error rate(BER) performance using the measured data. Considering the measurement results, we noticed that the arrival time of direct waves from different tranmit antennas differs for MIMO configurations, and affects the BER performance. In this paper, we show the measurement results, and propose performance improvement with the transmit (Tx) and receive (Rx) timing control.
  • Yusuke Ohwatari, Bui Huu Phu, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane
    IEEE Vehicular Technology Conference 401 - 405 1550-2252 2006 [Refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system (MIMO-OFDM) can achive high-data-rate transmission without additional frequency spectra. Furthermore, eigenbeam-space division multiplexing (E-SDM) which is also called the singular value decomposition (SVD) algorithm can provide maximum throughput in the MIMO channel when channel state information (CSI) is available at the transmitter. When the uplink and downlink channels are not reciprocal as in a FDD system, we need to feed back the CSI from the receiver to the transmitter. However, capacity is limited because CSI feedback is needed for each subcarrier in an OFDM system. This paper proposes the feedback of the time-domain channel estimated using the minimum mean square error method. The proposed method can reduce the amount of feedback information, and reveals better bit error rate performance than the other schemes. © 2006 IEEE.
  • NAKAMURA Yuichiro, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo
    The IEICE transactions on communications B 一般社団法人電子情報通信学会 88 (9) 1813 - 1820 1344-4697 2005/09/01 [Not refereed][Not invited]
     
    マルチパス環境下で, 周波数選択性フェージングを受けにくいOFDM方式は, 無線LANに利用されている.また, 送受信側の双方に複数のアンテナを設置し, 各送信アンテナから独立なOFDM信号を送ることによって, 100Mbit/sを超える高速伝送を実現するMIMO-OFDM空間分割多重方式の研究が行われている.本論文では, MIMO-OFDM空間分割多重について, 筆者らが以前より提案している時間領域で最小二乗法を適用しチャネル推定を行う方法を, チャネルと送受信機間の周波数オフセット推定法に拡張し, IEEE802.11aと同じプリアンブルの長さで両者の推定が可能であることを示している.
  • M Takanashi, T Nishimura, Y Ogawa, T Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E88B (6) 2588 - 2596 0916-8516 2005/06 [Refereed][Not invited]
     
    Mainly, a uniform linear array (ULA) has been used for DOA estimation of coherent signals because we can apply the spatial smoothing preprocessing (SSP) technique. However, estimation by a ULA has ambiguity due to the symmetry, and the estimation accuracy depends on the DOA. Although these problems can be solved by using a uniform circular array (UCA), we cannot estimate the DOA of coherent signals because the SSP technique cannot be applied directly to the UCA. In this paper, we propose to estimate 2-dimensional DOA (polar angles and azimuth angles) estimation of coherent signals using a cylindrical array which is composed of stacked UCAs.
  • Takeo Ohgane, Toshihiko Nishimura, Yasutaka Ogawa
    IEICE Transactions on Communications E88-B (5) 1843 - 1851 0916-8516 2005 [Refereed][Not invited]
     
    Currently, space division multiplexing (SDM), where individual data streams are transmitted from different antennas simultaneously, is expected to be a promising technology for achieving a high data rate within a limited frequency band in a multiple-input multiple-output channel. In this paper, transmitter and receiver architectures of SDM applications are described, and performance improvement with the increase of data streams is shown referring to results of computer simulations. In addition, channel coded systems are also evaluated. Copyright © 2005 The Institute of Electronics, Information and Communication Engineers.
  • Y Ogawa, K Nishio, T Nishimura, T Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E88B (1) 10 - 18 0916-8516 2005/01 [Refereed][Not invited]
     
    We consider space division multiplexing in a MIMO-OFDM system for high data rate transmission. Channel estimation is very important for suppressing interference and demultiplexing signals. In a wireless LAN system such as IEEE 802.11a, only a few training symbols are inserted in each subcarrier. First, we propose a channel estimation method for a MIMO-OFDM system with two training symbols per subcarrier. The basic idea is to estimate the time-domain channel responses between the transmit and receive antennas. The array response vectors for each subcarrier are calculated by applying a fast Fourier transform to them. We then can obtain the adaptive weights to cancel the interference. We show that employing training symbols having a lower condition number of the matrix used for the channel estimation improves the estimation accuracy. Furthermore, we show the bit error rate for several signal detection schemes using the above estimated channel, it is shown that an ordered successive detection based on an MMSE criterion has excellent performance, that is, it can achieve higher-speed transmissions with a lower transmit power.
  • Yasutaka Ogawa, Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane
    IEEE Vehicular Technology Conference 4 2398 - 2402 1550-2252 2005 [Refereed][Not invited]
     
    Spatial multiplexing in a MIMO system can achieve high speed transmission in i.i.d. Rayleigh channels. However, actual communications can be conducted in LOS environments where we have higher received signal power, whereas channels may be correlated. Although many MIMO measurement campaigns have been conducted so far, conventional investigations are not considered to be sufficient from wireless engineering viewpoint. In this paper, we examine bit error rate (BER) of spatial multiplexing as a function of total transmit power in indoor LOS environments. This consideration is done using 4 × 4 MIMO channel measurements. We compare the BER performance with the one in NLOS environments. Then, we investigate also the BER performance for a case where the channel state information is available also at a transmitter. It has been shown that the BER performance is generally better in the LOS environments than in the NLOS ones despite higher fading correlations, and that the performance in the LOS environments tends to change largely depending on a MIMO system configuration. We have also considered the effect of mutual coupling in antennas to the performance, and relations between eigenvalue distributions and the performance.
  • T Nishimura, T Tsutsumi, T Ohgane, Y Ogawa
    2005 IEEE/ACES INTERNATIONAL CONFERENCE ON WIRELESS COMMUNICATIONS AND APPLIED COMPUTATIONAL ELECTROMAGNETICS 44 - 47 2005 [Refereed][Not invited]
  • Y Ogawa, H Nishimoto, T Nishimura, T Ohgane
    2005 IEEE/ACES International Conference on Wireless Communications and Applied Computational Electromagnetics 486 - 489 2005 [Refereed][Not invited]
  • Y Ogawa, H Nishimoto, T Nishimura, T Ohgane
    VTC2005-FALL: 2005 IEEE 62ND VEHICULAR TECHNOLOGY CONFERENCE, 1-4, PROCEEDINGS 2398 - 2402 1090-3038 2005 [Refereed][Not invited]
     
    Spatial multiplexing in a MIMO system can achieve high speed transmission in i.i.d. Rayleigh channels. However, actual communications can be conducted in LOS environments where we have higher received signal power, whereas channels may be correlated. Although many MIMO measurement campaigns have been conducted so far, conventional investigations are not considered to be sufficient from wireless engineering viewpoint. In this paper, we examine bit error rate (BER) of spatial multiplexing as a function of total transmit power in indoor LOS environments. This: consideration is done using 4 x 4 MIMO channel measurements. We compare the BER performance with the one in NLOS environments. Then, we investigate also the BER performance for a case where the channel state information is available also at a transmitter. It has been shown that the BER performance is generally better in the LOS environments than in the NLOS ones despite higher fading correlations, and that the performance in the LOS environments tends to change largely depending on a MIMO system configuration. We have also considered the effect of mutual coupling in antennas to the performance, and relations between eigenvalue distributions and the performance.
  • K Sumii, T Nishimura, T Ohgane, Y Ogawa
    VTC2005-SPRING: 2005 IEEE 61ST VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5, PROCEEDINGS 882 - 886 1090-3038 2005 [Refereed][Not invited]
     
    When we consider a large number of substreams and constellations in channel-coded space division multiplexing (SDM) in a MIMO channel, computational complexity of a soft MIMO decoder based on the maximum likelihood (ML) detection becomes enormous. Even in complexity-reduced processing such as sphere decoding, the MIMO detector must search several non-ML points to calculate a log-likelihood ratio (LLR) of each bit for a soft-input channel decoder. In the paper, we propose a simplified iterative processing method for the soft MIMO detector and soft-input/soft-output (SISO) channel decoder to decrease the number of Euclidean distance calculations of non-NIL points. To update the non-ML points to be searched, we monitor the LLR value of each bit returned from the SISO channel decoder. The computer simulation assuming 4tx-4rx turbo-coded SDM of 16-QAM shows that the proposed method provides the gain of 0.7 dB at FER of 0.01 against the non-iterative method using 65536 points, where the number of searched points per iteration at average E(b)/N(0) = 1 dB was 17.8 in average and 62.4 at most in the proposed method.
  • OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka
    The Transactions of the Institute of Electronics, Information and Communication Engineers B 一般社団法人電子情報通信学会 87 (9) 1162 - 1173 1344-4697 2004/09/01 [Not refereed][Not invited]
     
    MIMO(Multiple-Input Multiple-Output)チャネル伝送において,複数のアンテナから同時に異なる信号系列を伝送する空間分割多重方式は,限られた周波数帯域で高速伝送を可能とする手法として注目されている.本論文では,各種空間分割多重方式の送受信方式について解説するとともに,送受信アンテナ本数の増加による特性改善効果について計算機シミュレーションにより明らかにする.また,誤り訂正符号化時における特性評価も併せて行う.
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo
    The Transactions of the Institute of Electronics, Information and Communication Engineers B 電子情報通信学会 87 (9) 1442 - 1453 1344-4697 2004/09/01 [Not refereed][Not invited]
     
    従来,MIMOシステムに空間分割多重方式を適用させるMIMO-SDMの研究では,送受信アンテナ間のチャネルは独立なレイリーフェージング環境と仮定されることが多く,この仮定のもとでは,受信側での処理により信号ストリームの分離検出が可能となる.本論文では,チャネル間の独立性が崩れる可能性のある,見通し内伝搬路で行った5.2GHz帯での伝搬実験結果から,そのような環境における2×2MIMO-SDMの有効性を検証し,見通しとならない環境における特性との比較を行っている.また,同様の実験を電波暗室でも行い,極めてマルチパス波の少ない環境でのMIMO-SDMの挙動を紹介する.これらの実験の結果,見通し内伝搬環境においても散乱波が存在する場合にはSDM方式が有効であること,見通し外伝搬環境に比べてアンテナ素子の配置等により,特性が大きく変動する傾向にあることが分かった.
  • TSUTSUMI Takahiko, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka
    The Transactions of the Institute of Electronics, Information and Communication Engineers B 一般社団法人電子情報通信学会 87 (9) 1496 - 1504 1344-4697 2004/09/01 [Not refereed][Not invited]
     
    各種空間分割多重方式について,チャネル情報に誤差がある場合の誤り率特性を比較検討した.また,固有ビーム空間分割多重(E-SDM)方式と重み付きSDM (W-SDM)においては,一次外挿法を用いることにより,特性の改善を図った.その結果,チャネルの時間変動が大きい場合には,送信側で処理を行わない結合推定を用いたSDM (JD)の特性より劣化することが明らかとなった.しかし,送信側で一次外挿法を用いることで,大きな改善効果が得られることが確認できた.
  • Hiroyuki Saito, Toshihiko Nishimura, Manabu Yamamoto, Kiyohiko Itoh
    Electronics and Communications in Japan, Part I: Communications (English translation of Denshi Tsushin Gakkai Ronbunshi) 87 (4) 45 - 53 8756-6621 2004/04 [Refereed][Not invited]
     
    The quasi-optical antenna-mixer is a receiving system that spatially receives RF signals and local oscillator (LO) signals and at the same time converts the RF signals to intermediate (IF) frequency signals. The line transmission loss, which causes a problem at millimeter wave frequencies, can be suppressed. In this paper, test fabrication and measurement of a quasi-optical antenna-mixer array receiving RF and LO signals with a magnetic loop antenna are carried out at 10 GHz and quasi-optical mixing is shown to be possible. A two-dimensional array antenna using this element is proposed. Its receiving characteristics are theoretically predicted. By changing the illumination angle or frequency of the LO, it is found that the receiving direction of the RF can be scanned. In addition, the suppression of RF and LO signals appearing at the output end is demonstrated. An experiment with a two-dimensional array consisting of eight elements of quasi-optical antenna-mixers is carried out and the validity of the proposal is confirmed. © 2003 Wiley Periodicals, Inc.
  • M Hoshino, M Uesugi, T Ohgane, Y Ogawa, T Nishimura
    IEICE TRANSACTIONS ON COMMUNICATIONS E86B (12) 3476 - 3482 0916-8516 2003/12 [Refereed][Not invited]
     
    Space-Time Turbo code is an effective method for the enhancement of link capacity and maximizing the link-budget by balancing the coding gain obtained via Turbo codes and the diversity gain obtained through multiple antenna transmission. A study on an antenna selection scheme for Space-Time Turbo code for OFDM systems is presented in this paper. In the proposed method, the systematic bits and the punctured parity bits are sent from the selected antenna for each sub-carrier, while data transmission is suspended from the antenna experiencing poor channel conditions at the receiver. Simulation results show that the proposed method yields a 2.2dB gain in the required TxE(b)/N-0 relative to the conventional method, and makes the channel estimation accuracy more robust. Moreover, the proposed method reduces transmission power by about 4dB compared to the conventional method.
  • Yasutaka Ogawa, Keisuke Nishio, Toshihiko Nishimura, Takeo Ohgane
    IEEE Vehicular Technology Conference 58 (1) 493 - 497 0740-0551 2003 
    We propose new signal detection for space division multiplexing in a MIMO-OFDM system for high data rate transmission. Channel estimation is very important for suppressing the interference and demultiplexing the signals. In a wireless LAN system such as IEEE 802.11a, only a few training symbols are inserted in each subcarrier. We propose a channel estimation method for the MIMO-OFDM system with two training symbols per subcarrier. The basic idea is to estimate the time-domain channel responses between the transmit and receive antennas. Applying the fast Fourier transform to them, the array response vectors for each subcarrier are calculated. Then, we can obtain the adaptive weights to cancel the interference. We show that employing training symbols having a lower condition number of a matrix used for the channel estimation improves the estimation accuracy.
  • Y Ogawa, K Nishio, T Nishimura, T Ohgane
    2003 IEEE 58TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS1-5, PROCEEDINGS 493 - 497 1090-3038 2003 [Refereed][Not invited]
     
    We propose new signal detection for space division multiplexing in a MIMO-OFDM system for high data rate transmission. Channel estimation is very important for suppressing the interference and demultiplexing the signals. In a wireless LAN system such as IEEE 802.11a, only a few training symbols are inserted in each subcarrier. We propose a channel estimation method for the MIMO-OFDM system with two training symbols per subcarrier. The basic idea is to estimate the time-domain channel responses between the transmit and receive antennas. Applying the fast Fourier transform to them, the array response vectors for each subcarrier are calculated. Then, we can obtain the adaptive weights to cancel the interference. We show that employing training symbols having a lower condition number of a matrix used for the channel estimation improves the estimation accuracy.
  • Y Kishiyama, T Nishimura, T Ohgane, Y Ogawa, Y Doi
    ELECTRONICS AND COMMUNICATIONS IN JAPAN PART I-COMMUNICATIONS 86 (5) 81 - 91 8756-6621 2003 [Refereed][Not invited]
     
    Recently, the Space Division Multiple Access (SDMA) scheme has been proposed to improve channel utilization efficiency. SDMA requires separation and detection schemes in the base station because serious interference develops among all of the users accommodated by the same channel. In this paper, we propose the Channel Response Assisted Adaptive Array (CRA-AA) that estimates the channel response in the uplink and uses this result to indirectly control the directivity, and compare its performance to those of MMSE adaptive array and joint detection. We also study a scheme to compensate for the carrier frequency offsets generated at each user. We found that CRA-AA had superior performance in the presence of both fast fading and carrier frequency offsets. (C) 2003 Wiley Periodicals, Inc.
  • SAITO Hiroyuki, NISHIMURA Toshihiko, YAMAMOTO Manabu, ITOH Kiyohiko
    The Transactions of the Institute of Electronics,Information and Communication Engineers B 一般社団法人電子情報通信学会 85 (9) 1493 - 1500 1344-4697 2002/09/01 [Not refereed][Not invited]
     
    準光学アンテナ・ミキサは,高周波信号(RF)と局部発振周波(LO)の信号を空間的に受信すると同時に中間周波数(IF)信号へ変換する受信システムであり,ミリ波帯で問題となる線路の伝送損失をおさえることができる.本論文では,RFとLOを磁流ループアンテナで受信する準光学アンテナ・ミキサアレーの10GHz帯における試作測定を行い,準光学的ミキシングが可能であることを示す.また,この素子を用いた2次元アレーアンテナを提案し,理論的にその受信特性を明らかにする.LOの照射角または周波数を変えることでRFの受信方向が走査できることに加えて,出力端にろうえいするRF・LO信号の抑制が可能であることを示す.8素子の準光学アンテナ・ミキサで構成される2次元アレーの実験を行い,提案の妥当性を確認する.
  • High Data-rate Transmission with Eigenbeam-space Division Multiplexing (E-SDM) in a MIMO Channel
    Kazumi Miyashita, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yasushi Takatori, Keizo Cho
    IEEE Vehicular Technology Conference 56 (3) 1302 - 1306 0740-0551 2002 
    When channel state information is known at a transmitter in multiple-input multiple-output systems, the optimum capacity is given by eigenmode channel division with water-pouring power control. In this eigenbeam-space division multiplexing (E-SDM), bit assignments to substreams based on the capacity is not optimum due to the fact that the number of assigned bits is expressed by discrete quantity. In the paper, a method to assign both bit and transmit power to each substream based on the criterion minimizing total bit error rate (BER) is developed, and the BER performance is numerically analyzed in comparison to spatial division multiplexing (SDM). The simulation results assuming 5-transmit and 2-receive antennas show that the E-SDM provides about 10 dB gain compared to the conventional SDM at average BER of 10-3.
  • T Nishimura, Y Takatori, T Ohgane, Y Ogawa, KZ Cho
    IEEE 56TH VEHICULAR TECHNOLOGY CONFERENCE, VTC FALL 2002, VOLS 1-4, PROCEEDINGS 190 - 194 1090-3038 2002 [Refereed][Not invited]
     
    In this paper, we propose a novel downlink null-forming technique for space division multiple access (SDMA) in a multiple-input multiple-output (MIMO) channel where a base station and all terminal stations have multiple antennas. In the SDMA system, simple beamforming is not efficient to achieve good performance due to cochannel interference. Proposed method is based on nullforming and characterized by antenna element selection at each terminal where the selected antenna pair satisfies the lowest spatial correlation condition in all combinations. The results obtained by computer simulations show selective diversity gain of the proposed method and performance improvement due to joint detection at each terminal.
  • K Miyashita, T Nishimura, T Ohgane, Y Ogawa, Y Takatori, K Cho
    IEEE 56TH VEHICULAR TECHNOLOGY CONFERENCE, VTC FALL 2002, VOLS 1-4, PROCEEDINGS 1302 - 1306 1090-3038 2002 [Refereed][Not invited]
     
    When channel state information is known at a transmitter in multiple-input multiple-output systems, the optimum capacity is given by eigenmode channel division with water-pouring power control. In this eigenbeam-space division multiplexing (ESDM), bit assignments to substreams based on the capacity is not optimum due to the fact that the-number of assigned bits is expressed by discrete quantity. In the paper, a method to assign both bit and transmit power to each substream based on the criterion minimizing total bit error rate (BER) is developed, and the BER performance is numerically analyzed in comparison to spatial division multiplexing (SDM). The simulation results assuming 5-transmit and 2-receive antennas show that the E-SDM provides about 10 dB gain compared to the conventional SDM at average BER of 10(-3).
  • T Nishimura, Y Tanabe, T Ohgane, Y Ogawa, Y Doi, J Kitakado
    IEICE TRANSACTIONS ON COMMUNICATIONS E84B (7) 1735 - 1742 0916-8516 2001/07 [Refereed][Not invited]
     
    In SDMA, a spatial domain interference canceller applying a multistage processing concept to the MMSE multibeam adaptive array has an attractive feature. Weak power signals strongly interfered can be detected in the succeeded stages after removing other strong power signals which are already detected. This idea can be enhanced to the reference timing estimation required in the MMSE algorithm. In this paper, the spatial domain interference canceller introducing multistage timing estimation is proposed and its performance is evaluated by computer simulations. The results show that the timing estimation performance highly improved.
  • T Nishimura, T Ohgane, Y Ogawa, Y Doi, J Kitakado
    IEICE TRANSACTIONS ON COMMUNICATIONS E84B (3) 377 - 382 0916-8516 2001/03 [Refereed][Not invited]
     
    It is difficult for an adaptive array to reduce interference signals efficiently from received signals when the interference signals and desired signal are closely located. This is a problem for a spatial division multiple access (SDMA) system using the multibeam adaptive array as a multiuser detector. In this paper, we propose a space domain multistage interference canceller (SD-MIC) for the SDMA system. Its performance is evaluated by computer simulations, assuming Japanese personal handy phone system (PHS) uplink environments. The results show remarkable improvement in high spatial correlation situations.
  • KISHIYAMA Yoshihisa, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, DOI Yoshiharu
    The Transactions of the Institute of Electronics,Information and Communication Engineers B 一般社団法人電子情報通信学会 84 (2) 178 - 187 1344-4697 2001/02/01 [Not refereed][Not invited]
     
    近年, チャネルの利用効率を向上させるためSDMA(Space Division Multiple Access)方式が提案されている.SDMA方式では, 同一チャネルに収容されたすべてのユーザ間で深刻な干渉が生じるため, 基地局でこれらを分離・検出する手法が必要となる.そこで, 本論文では, 上り回線においてチャネル応答推定を行い, その結果を用いて間接的に指向性制御を行うCRA-AA(Channel Response Assisted Adaptive Array)を提案し, MMSE基準のアダプティブアレー, 及び結合推定との特性比較を行った.また, 各ユーザにおいてそれぞれ発生するキャリヤ周波数オフセットを補償する手法についても検討を行った.その結果, CRA-AAが高速フェージングに対する特性, 及びキャリヤ周波数オフセットに対する特性がともに優れていることがわかった.
  • Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yoshiharu Doi, Jun Kitakado
    IEEE Vehicular Technology Conference 3 (54) 1538 - 1542 0740-0551 2001 [Refereed][Not invited]
     
    In this paper, we discuss downlink beamforming methods in consideration of a terminal having a joint detector function for space division multiple access (SDMA) in both a multi-input single-output (MISO) channel and a multi-input multi-output (MIMO) channel. We investigate two methods a general beamformer, which maximizes the desired signal's power at the receiver (at transmit MRC1 diversity) and a null steering concept, which avoids the interference signal reaching the receiver. The computer simulation results show that the null steering concept yields better performance compared to the beam steering even considering the joint detection at the receiver.
  • Tsuyoshi Kaichida, Nozomu Ishii, Manabu Yamamoto, Toshihiko Nishimura, Kiyohiko Itoh
    Electronics and Communications in Japan, Part I: Communications (English translation of Denshi Tsushin Gakkai Ronbunshi) 84 (3) 21 - 28 8756-6621 2001 [Refereed][Not invited]
     
    At millimeter wave frequencies, the loss in the transmission line is significant. To alleviate this problem, a quasi-optical mixer will reduce the transmission loss by combining the antenna and the mixer. The RF and the local signals at two different frequencies are received spatially, and the intermediate frequency is generated immediately. To realize this function, there is a microstrip antenna fed by a coplanar waveguide to operate at two frequencies. In this paper, the spectral domain method is used to analyze the input characteristics of the 1/20 scale model of this antenna at microwave frequencies. It is shown that the antenna can be operated at two frequencies independently. Further, the radiation characteristics of this antenna are evaluated in terms of the absolute gain.
  • Y Ogawa, Y Tanabe, T Nishimura, T Ohgane
    2001 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, VOLS 1-10, CONFERENCE RECORD 2558 - 2562 2001 [Refereed][Not invited]
     
    Multipath propagation causes serious performance degradation in a high-speed mobile TDMA system. We have proposed the adaptive antenna which copes with the multipath signals. These considerations have been limited to an uplink channel. In this paper, we propose the basestation adaptive antennas both for the uplink and downlink channels. We assume the FDD/TDMA system where the frequencies are different between the uplink and downlink channels. The weight vectors proposed in this paper are determined using DOA estimation. The problem of the frequency difference in FDD is removed by this scheme. For the uplink channel, we can realize the path-diversity using the adaptive antenna with several weight vectors. For the downlink channel, we propose a singlebeam adaptive antenna and two-beam one. It will be shown that the combination of the two-beam basestation adaptive antenna and the mobile terminal with two-input (two-antenna) MLSE equalizer shows better performance.
  • T Nishimura, T Ohgane, Y Ogawa, Y Doi, J Kitakado
    IEEE 54TH VEHICULAR TECHNOLOGY CONFERENCE, VTC FALL 2001, VOLS 1-4, PROCEEDINGS 1538 - 1542 1090-3038 2001 [Refereed][Not invited]
     
    In this paper, we discuss downlink beam-forming methods in consideration of a terminal having a joint detector function for space division multiple access (SDMA) in both a multi-input single-output (MISO) channel and a multi-input multi-output (MIMO) channel. We investigate two methods; a general beamformer, which maximizes the desired signal's power at the receiver (a transmit MRC(1) diversity) and a null steering concept, which avoids the interference signal reaching the receiver. The computer simulation results show that the null steering concept yields better performance compared to the beam steering even considering the joint detection at the receiver.
  • K Fujishima, Y Tanabe, T Nishimura, Y Ogawa, T Ohgane
    IEICE TRANSACTIONS ON COMMUNICATIONS E83B (12) 2593 - 2599 0916-8516 2000/12 [Refereed][Not invited]
     
    Frequency-selective fading duc to multipath propagation is serious hindrance in high-speed TDMA mobile communications. An adaptive antenna has been proposed to reduce the frequency-selective fading and realize path-diversity. This paper presents a criterion which selects multipath signals and weighting factors for combining them. First, we describe a selection criterion which chooses the multipath signals for the path-diversity, We propose a ratio of signal power to error power for the criterion. Furthermore, we propose weighting factors which realize approximately the maximal ratio combining. Computer simulation results show that the proposed selection criterion and weighting factors reveal excellent performance.
  • Takeo Ohgane, Yasutaka Ogawa, Yoshihisa Kishiyama, Toshihiko Nishimura
    IEICE Proceeding Series 9 4A3-2  2000/08/22
  • Spatial Domain Interference Canceler Using Multistage Adaptive Array with Precise Timing Estimation
    T. Nishimura, Y. Tanabe, T. Ohgane, Y. Ogawa, Y. Doi, J. Kitakado
    IEEE Vehicular Technology Conference 2 (52) 719 - 724 0740-0551 2000 
    In SDMA, a spatial domain interference canceler applying a multistage processing concept to the MMSE multibeam adaptive array has an attractive feature that weak power signals strongly interfered can be detected in the succeeded stages after removing other strong power signals which are already detected. This idea can be enhanced to the reference timing estimation required in the MMSE algorithm. In this paper, the spatial domain interference canceler introducing multistage timing estimation is proposed and its performance is evaluated by computer simulations. The results show that the timing estimation performance highly improved.
  • T Nishimura, Y Tanabe, T Ohgane, Y Ogawa, Y Doi, J Kitakado
    IEEE VEHICULAR TECHNOLOGY CONFERENCE, FALL 2000, VOLS 1-6, PROCEEDINGS 719 - 724 1090-3038 2000 [Refereed][Not invited]
     
    In SDMA, a spatial domain interference cancels applying a multistage processing concept to the MMSE multi-beam adaptive array has an attractive feature that weak power signals strongly interfered can be detected in the succeeded stages after removing other strong power signals which are already detected This idea can be enhanced to the reference timing estimation required in the MMSE algorithm. In this paper the spatial domain interference canceler introducing multistage timing estimation is proposed and its performance is evaluated by computer simulations. The results show that the timing estimation performance highly improved.
  • T Nishimura, T Ohgane, Y Ogawa, Y Doi, J Kitakado
    2000 IEEE 51ST VEHICULAR TECHNOLOGY CONFERENCE, PROCEEDINGS, VOLS 1-3 655 - 659 2000 [Refereed][Not invited]
     
    It is difficult for the adaptive array to reduce interference signals efficiently from the received signals when the interference signals and desired signal are closely located. This is a serious problem for a spatial division multiple access (SDMA) system using the multibeam adaptive array as a multiuser detector. In this paper, we propose a space domain multistage interference canceler (SD-MIC) for the SDMA. Its performance is evaluated in frame error rate (FER) by computer simulations, considering uplink environment in the Japanese personal handy-phone system (PHS). The results show the remarkable improvement in high spatial correlation situations.
  • Y Kishiyama, T Nishimura, T Ohgane, Y Ogawa, Y Doi
    2000 IEEE 51ST VEHICULAR TECHNOLOGY CONFERENCE, PROCEEDINGS, VOLS 1-3 346 - 350 2000 [Refereed][Not invited]
     
    In employing an adaptive array for TDD/SDMA at a base station, generally, the array pattern for downlink is calculated from that for uplink. Considering the angle spread in a Rayleigh fading channel, time difference between uplink and downlink causes null position change on the optimum array pattern. In this paper, we propose the weight estimation method for the downlink null steering. It is based on the indirect weight estimation using the channel response prediction. The computer simulations show that the proposed method improves the BER performance in the downlink, effectively.
  • Y Tanabe, K Fujishima, T Nishimura, Y Ogawa, T Ohgane
    2000 IEEE 51ST VEHICULAR TECHNOLOGY CONFERENCE, PROCEEDINGS, VOLS 1-3 1 - 5 2000 [Refereed][Not invited]
     
    In high-speed TDMA mobile communications, frequency-selective fading is a serious problem because a delay time difference between multipath signals is large in comparison with symbol duration. We have proposed a spatial-domain path-diversity system using a multibeam adaptive antenna to reduce frequency-selective fading and to realize path-diversity. The multibeam adaptive antenna resolves multipath signals in the spatial domain, and combines array outputs. In this paper, we propose the application of MUSIC algorithm to estimation of the time delays of multipath signals to make the incident signals coincide with a common reference signal. Because the MUSIC algorithm can estimate the time delays accurately, the BER performance of the proposed scheme is improved.
  • Nishimura Toshihiko, Ishii Nozomu, Itoh Kiyohiko
    IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION IEEE 47 (7) 1160 - 1166 0001-4966 1999/07 [Refereed][Not invited]
     
    The quasi-optical antenna mixer system transformsan RF signal into an intermediate frequency signal just after itspatially receives the RF signal and the local oscillator's (LO)signal. In this paper, we present a novel beam-scanning systemusing the quasi-optical antenna mixer array and describe its principleof operation and the experimental results in the microwaveband. The arrival direction of RF signals can be controlled byadjusting the LO incident angle and/or the LO frequency withoutimplementing RF circuits such as phase shifters. Therefore, thenovel beam-scanning system has no loss due to RF circuits andcan be easily designed because of its simple composition.
  • Toshihiko Nishimura, Katsumi Tsuchida, Nozomu Ishii, Kiyohiko Itoh
    Electronics and Communications in Japan, Part I: Communications (English translation of Denshi Tsushin Gakkai Ronbunshi) 82 (1) 22 - 30 8756-6621 1999 [Refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms a radio frequency (RF) signal into the intermediate frequency (IF) signal as soon as the system receives the RF and the local oscillator (LO) signals spatially. This system can be expected to reduce transmission line loss, especially in higher frequency bands, such as the millimeter-wave band, because the RF transmission line is removed. In this paper, we propose a dual frequency operating microstrip antenna fed by coplanar waveguide, with a mixer diode to realize the quasi-optical antenna mixer system. It is a problem of the receiving part in conventional quasi-optical antenna mixer systems that LO incidence obstructs RF incidence because both RF and LO signals are received from one side of the system. Therefore, we construct a quasi-optical antenna mixer system that can receive the RF and LO signals separately on both sides of the substrate. To begin with, the receiving part is designed and its characteristics are evaluated with an electromagnetic simulator. Next, the system is fabricated and tested on the dual frequency operation of the receiving part and the mixing operation in the microwave band. As a result, we confirm that our proposed system functions as a quasi-optical antenna mixer. © 1998 Scripta Technica.
  • Toshihiko Nishimura, Nozomu Ishii, Kiyohiko Itoh
    IEEE Transactions on Antennas and Propagation 47 (7) 1160 - 1166 0018-926X 1999 [Refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms an RF signal into an intermediate frequency signal just after it spatially receives the RF signal and the local oscillator's (LO) signal. In this paper, we present a novel beam-scanning system using the quasi-optical antenna mixer array and describe its principle of operation and the experimental results in the microwave band. The arrival direction of RF signals can be controlled by adjusting the LO incident angle and/or the LO frequency without implementing RF circuits such as phase shifters. Therefore, the novel beam-scanning system has no loss due to RF circuits and can be easily designed because of its simple composition.
  • Toshihiko Nishimura, Katsumi Tsuchida, Nozomu Ishii, Kiyohiko Itoh
    Electronics and Communications in Japan, Part I: Communications (English translation of Denshi Tsushin Gakkai Ronbunshi) 81 (12) 1 - 8 8756-6621 1998/12 
    The quasi-optical antenna-mixer system transforms a radio frequency (RF) signal into an intermediate-frequency signal as soon as the system receives the RF and local oscillator's (LO) signals spatially. We propose a novel beam scanning system with a quasi-optical antenna-mixer array. The traditional phased array needs RF circuits such as phase shifters for beam scanning, but our system can steer the beam without them. RF arrival direction is steered by changing the LO incidence angle and/or frequency. Therefore, not only are losses reduced in RF circuits, but the system is easily designed because of its simple structure. First, we describe the principle of beam scanning with concrete model. Next, a fabricated model working in the microwave band is tested to verify beam-scanning performance. The experimental results agree with the theory very well and our proposal is confirmed.
  • Toshihiko Nishimura, Katsumi Tsuchida, Nozomu Ishii, Kiyohiko Itoh, Yasutaka Ogawa
    1998 28th European Microwave Conference, EuMC 1998 1 415 - 420 1998 [Refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms radio frequency (RF) signal into intermediate frequency (IF) signal just after the system receives the RF and local oscillator's (LO) signal spatially [1]. We present a novel beam scanning system with the quasi-optical antenna-mixer array. In this paper, we describe the principle and the experimental results in the microwave band. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters. Therefore, not only losses in RF circuits are reduced but also the system is easily designed because of its simple structure. This feature is an advantage in applying to the millimeter wave band. © 1998 IEEE.

MISC

  • 阿隅大輝, 角田俊介, 萩原淳一郎, 西村寿彦, 佐藤孝憲, 小川恭孝, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (355(IT2022 29-67))  2023
  • 田所柊人, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (355(IT2022 29-67))  2023
  • 望月大瑚, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (355(IT2022 29-67))  2023
  • 國本周大, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (355(IT2022 29-67))  2023
  • 西村健斗, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (355(IT2022 29-67))  2023
  • 林優太, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会大会講演論文集(CD-ROM)  2023-  2023
  • 濱田直輝, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会大会講演論文集(CD-ROM)  2023-  2023
  • 釜谷俊輝, 西村寿彦, 大鐘武雄, 旦代智哉, 内田大輔  電子情報通信学会大会講演論文集(CD-ROM)  2023-  2023
  • 角田俊介, 萩原淳一郎, 西村寿彦, 佐藤孝憲, 小川恭孝, 大鐘武雄  電子情報通信学会技術研究報告(Web)  123-  (76(RCS2023 28-78))  2023
  • 林優太, 西村寿彦, 佐藤孝憲, 小川恭孝, 大鐘武雄  電子情報通信学会技術研究報告(Web)  123-  (76(RCS2023 28-78))  2023
  • 濱田直輝, 西村寿彦, 佐藤孝憲, 小川恭孝, 大鐘武雄  電子情報通信学会技術研究報告(Web)  123-  (76(RCS2023 28-78))  2023
  • 釡谷俊輝, 西村寿彦, 大鐘武雄, 旦代智哉, 内田大輔  電子情報通信学会大会講演論文集(CD-ROM)  2022-  2022
  • 小川恭孝, 西村寿彦, 佐藤孝憲, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (235(RCS2022 128-154))  2022
  • 望月大瑚, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (235(RCS2022 128-154))  2022
  • 西村寿彦  電子情報通信学会技術研究報告(Web)  122-  (251(AP2022 147-172))  2022
  • 林優太, 西村寿彦, 佐藤孝憲, 萩原淳一郎, 小川恭孝, 大鐘武雄  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2022-  2022
  • 望月大瑚, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2022-  2022
  • 村田英一, 井田悠太, 丸田一輝, 實松豊, 牟田修, 岡田啓, 岡本英二, 眞田幸俊, 西村寿彦, 田野哲  電子情報通信学会技術研究報告(Web)  122-  (235(RCS2022 128-154))  2022
  • 春日由紀子, 萩原淳一郎, 西村寿彦, 佐藤孝憲, 大鐘武雄, 小川恭孝  電子情報通信学会大会講演論文集(CD-ROM)  2022-  2022
  • 大塚達樹, 西村寿彦, 大鐘武雄, 佐藤孝憲, 萩原淳一郎, 小川恭孝  電子情報通信学会大会講演論文集(CD-ROM)  2022-  2022
  • 望月大瑚, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (73(RCS2022 24-67))  2022
  • 阿隅大輝, 春日由紀子, 松村和士, 萩原淳一郎, 西村寿彦, 佐藤孝憲, 小川恭孝, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (73(RCS2022 24-67))  2022
  • 國本周大, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (73(RCS2022 24-67))  2022
  • 田所柊人, 西村寿彦, 佐藤孝憲, 小川恭孝, 萩原淳一郎, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (73(RCS2022 24-67))  2022
  • 三好茉莉, 西村寿彦, 佐藤孝憲, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告(Web)  122-  (73(RCS2022 24-67))  2022
  • 小川恭孝, 西村寿彦, 大鐘武雄  電子情報通信学会技術研究報告(Web)  122-  (117(EMT2022 7-43))  2022
  • 望月大瑚, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  121-  (327(IT2021 28-82))  2022
  • 宇津野太一, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  121-  (327(IT2021 28-82))  2022
  • 櫻谷信彦, 西村寿彦, 大鐘武雄, 旦代智哉, 内田大輔  電子情報通信学会技術研究報告(Web)  121-  (327(IT2021 28-82))  2022
  • 西村健斗, 大鐘武雄, 西村寿彦, 萩原淳一郎, 佐藤孝憲, 小川恭孝  電子情報通信学会大会講演論文集(CD-ROM)  2021-  2021
  • 大塚達樹, 西村寿彦, 大鐘武雄, 佐藤孝憲, 萩原淳一郎, 小川恭孝  電子情報通信学会技術研究報告(Web)  120-  (320(IT2020 63-111))  2021
  • 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会大会講演論文集(CD-ROM)  2021-  2021
  • 登坂紫織, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (404(RCS2020 203-261))  2021
  • 宇津野太一, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会大会講演論文集(CD-ROM)  2021-  2021
  • 櫻谷信彦, 西村寿彦, 大鐘武雄, 旦代智哉, 内田大輔  電子情報通信学会技術研究報告(Web)  120-  (404(RCS2020 203-261))  2021
  • 加瀬裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 佐藤孝憲, 岸山祥久  電子情報通信学会技術研究報告(Web)  121-  (101(RCC2021 22-40))  2021
  • 望月大瑚, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  121-  (72(RCS2021 29-76))  2021
  • 阿隅大輝, 萩原淳一郎, 西村寿彦, 大鐘武雄, 小川恭孝, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  121-  (72(RCS2021 29-76))  2021
  • 三好茉莉, 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  121-  (72(RCS2021 29-76))  2021
  • 安藤ダニエル明, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  121-  (72(RCS2021 29-76))  2021
  • Daniel Akira ANDO, Toshihiko NISHIMURA, Takeo OHGANE, Yasutaka OGAWA, Junichiro HAGIWARA, Takanori SATO  IEICE Proceeding Series  63-  K1-2  2020/12/02  [Refereed]
     
    Gaussian belief propagation (GaBP) is one of the light-weight signal detectors. Basically, it is expected that reliability information exchanged in the network gradually converges to the correct one. However, it has been confirmed that error-free detection can be achieved even if incorrect beliefs still exist in the network.
  • Takano Yuta, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Hagiwara Junichiro  IEICE Communications Express  9-  (12)  561  -566  2020/12/01  [Not refereed]
     
    Multi-user MIMO systems enable high capacity transmission. A base station, however, needs accurate channel state information (CSI). In time-varying environments, the CSI may be outdated at the actual transmission time. One of the solutions to this issue is channel prediction. The authors have proposed the prediction method using FISTA, a compressive sensing technique, for OFDM systems in a millimeter-wave band. Unfortunately, in realistic multipath environments, the prediction performance of the proposed technique degrades. In this letter, we examine the prediction performance in wider OFDM systems. It will be shown that FISTA reveals excellent performance in a sufficiently wide band case.
  • 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2020-  2020
  • 登坂紫織, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2020-  2020
  • DONG Bowen, 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (74(RCS2020 23-57))  2020
  • 安藤ダニエル明, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (74(RCS2020 23-57))  2020
  • 松村和士, 萩原淳一郎, 西村寿彦, 大鐘武雄, 小川恭孝, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (74(RCS2020 23-57))  2020
  • 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (74(RCS2020 23-57))  2020
  • 大塚達樹, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (74(RCS2020 23-57))  2020
  • YAMAMOTO Jumpei, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, TAKEDA Daiki, KISHIYAMA Yoshihisa  IEICE Transactions on Communications (Web)  E103.B-  (6)  2020
  • KASE Yuya, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, KITAYAMA Daisuke, KISHIYAMA Yoshihisa  IEICE Transactions on Communications (Web)  E103.B-  (10)  2020
  • 加瀬裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 来山大祐, 岸山祥久  電子情報通信学会大会講演論文集(CD-ROM)  2020-  2020
  • 加瀬裕也, 佐藤孝憲, 西村寿彦, 大鐘武雄, 小川恭孝, 来山大祐, 岸山祥久  電子情報通信学会技術研究報告(Web)  120-  (87(RCC2020 2-10))  2020
  • 松村和士, 萩原淳一郎, 西村寿彦, 大鐘武雄, 小川恭孝, 佐藤孝憲  電子情報通信学会技術研究報告(Web)  120-  (298(RCS2020 134-153))  2020
  • 宇津野太一, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎, 佐藤孝憲  電子情報通信学会大会講演論文集(CD-ROM)  2020-  2020
  • 加瀬 裕也, 西村 寿彦, 大鐘 武雄, 小川 恭孝, 来山 大祐, 岸山 祥久  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  119-  (106)  133  -138  2019/07
  • 高野裕太, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会技術研究報告  118-  (433(IT2018 35-74))  2019
  • 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  119-  (90(RCS2019 37-100)(Web))  2019
  • 登坂紫織, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会技術研究報告  119-  (90(RCS2019 37-100)(Web))  2019
  • 島屋早希, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  119-  (90(RCS2019 37-100)(Web))  2019
  • 中島亮太, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  119-  (90(RCS2019 37-100)(Web))  2019
  • LI Renjie, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  119-  (176(RCS2019 146-177)(Web))  2019
  • 辻本若葉, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  119-  (296(RCS2019 203-236)(Web))  2019
  • 中都正義, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電気・情報関係学会北海道支部連合大会講演論文集(CD-ROM)  2019-  2019
  • 高野裕太, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 高野裕太, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 中島亮太, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 齋藤剣聖, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 渡部泰成, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • LI Renjie, 大鐘武雄, 西村寿彦, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 登坂紫織, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 鈴木裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 島屋早希, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 福田健太郎, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 加瀬裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 来山大祐, 岸山祥久  電子情報通信学会技術研究報告  119-  (8(RCS2019 1-19)(Web))  2019
  • 加瀬裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 来山大祐, 岸山祥久  電子情報通信学会技術研究報告  119-  (106(RCC2019 11-52))  2019
  • 加瀬裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 来山大祐, 岸山祥久  電子情報通信学会大会講演論文集(CD-ROM)  2019-  2019
  • 加瀬 裕也, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  118-  (123)  51  -55  2018/07/11  [Not refereed][Not invited]
  • 木原 光太郎, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (456)  25  -29  2018/02/28  [Not refereed][Not invited]
  • 奥村 香菜子, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (456)  179  -184  2018/02/28  [Not refereed][Not invited]
  • 山本 順平, 西村 寿彦, 大鐘 武雄, 小川 恭孝, 岸山 祥久, 武田 大樹  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (394)  125  -130  2018/01/22  [Not refereed][Not invited]
  • 星川豊希, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 齋藤剣聖, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 鈴木裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 中村駿太, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  118-  (101(RCS2018 35-79)(Web))  2018
  • 福田健太郎, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  118-  (101(RCS2018 35-79)(Web))  2018
  • 中村駿太, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 高野裕太, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 星川豊希, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 齋藤剣聖, 小川恭孝, 西村寿彦, 大鐘武雄, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 鈴木裕也, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 渡部泰成, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 福田健太郎, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • LI Renjie, 西村寿彦, 大鐘武雄, 小川恭孝, 萩原淳一郎  電子情報通信学会技術研究報告  118-  (125(RCS2018 80-130)(Web))  2018
  • 山本順平, 西村寿彦, 大鐘武雄, 小川恭孝, 武田大樹, 岸山祥久  電子情報通信学会大会講演論文集(CD-ROM)  2018-  2018
  • 齋藤 剣聖, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (352)  101  -106  2017/12/14  [Not refereed][Not invited]
  • 星川 豊希, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (283)  161  -165  2017/11/08  [Not refereed][Not invited]
  • 井上 航一, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (284)  117  -122  2017/11/08  [Not refereed][Not invited]
  • 渡部 泰成, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (246)  19  -24  2017/10/19  [Not refereed][Not invited]
  • 奥村 香菜子, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (132)  61  -66  2017/07/19  [Not refereed][Not invited]
  • 山本 順平, 西村 寿彦, 大鐘 武雄, 小川 恭孝, 武田 大樹, 岸山 祥久  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (103)  31  -36  2017/06/21  [Not refereed][Not invited]
  • 齋藤 剣聖, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (103)  121  -126  2017/06/21  [Not refereed][Not invited]
  • 鈴木 裕也, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (103)  127  -132  2017/06/21  [Not refereed][Not invited]
  • 井上 航一, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  117-  (11)  155  -159  2017/04/24  [Not refereed][Not invited]
  • 山本順平, 西村寿彦, 大鐘武雄, 小川恭孝, 武田大樹, 岸山祥久  電子情報通信学会大会講演論文集(CD-ROM)  2017-  2017
  • 山本 順平, 西村 寿彦, 大鐘 武雄, 小川 恭孝, 武田 大樹, 岸山 祥久  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  116-  (383)  147  -152  2016/12/21  [Not refereed][Not invited]
  • 西崎 隼, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  116-  (318)  79  -84  2016/11/24  [Not refereed][Not invited]
  • Sanada Yukitoshi, Denno Satoshi, Murata Hidekazu, Nishimura Toshihiko, Tandai Tomoya, Okazaki Akihiro, Suyama Satoshi, Mashino Jun, Yamamoto Tetsuya, Taromaru Makoto  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  116-  (147)  177  -182  2016/07/20
  • 西村 寿彦, 西崎 隼, 小川 恭孝, 大鐘 武雄  映像情報メディア学会技術報告 = ITE technical report  40-  (23)  51  -54  2016/07  [Not refereed][Not invited]
  • 木原 光太郎, 西村 寿彦, 大鐘 武雄, 小川 恭孝  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  116-  (110)  47  -52  2016/06/22  [Not refereed][Not invited]
  • 奥村 香菜子, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  116-  (110)  81  -86  2016/06/22  [Not refereed][Not invited]
  • 阿部 大輔, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (506)  69  -74  2016/03/10  [Not refereed][Not invited]
  • 上橋 俊介, 小川 恭孝, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (472)  357  -362  2016/03/02  [Not refereed][Not invited]
  • Endo Taiki, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  2016-  (1)  194  -194  2016/03/01  [Not refereed][Not invited]
  • Yuki Shuto, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2016-  (1)  436  -436  2016/03/01  [Not refereed][Not invited]
  • Hagiwara Mitsuyoshi, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2016-  (1)  495  -495  2016/03/01  [Not refereed][Not invited]
  • Tanno Shuhei, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2016-  (1)  496  -496  2016/03/01  [Not refereed][Not invited]
  • Uehashi Shunsuke, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2016-  (1)  512  -512  2016/03/01  [Not refereed][Not invited]
  • Suzuki Kosuke, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2016-  (1)  546  -546  2016/03/01  [Not refereed][Not invited]
  • 阿部 大輔, 小川 恭孝, 西村 寿彦  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (390)  77  -82  2016/01/14
  • Ohgane Takeo, Nishimura Toshihiko, Ogawa Yasutaka  The Journal of The Institute of Image Information and Television Engineers  70-  (1)  17  -22  2016  [Not refereed][Not invited]
  • 大鐘 武雄, 西村 寿彦, 小川 恭孝  映像情報メディア学会誌 = The journal of the Institute of Image Information and Television Engineers  70-  (1)  17  -22  2016/01  [Not refereed][Not invited]
  • 上橋 俊介, 小川 恭孝, 西村 寿彦  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (288)  299  -304  2015/11/04
  • 阿部 大輔, 小川 恭孝, 西村 寿彦  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (286)  99  -104  2015/11/04  [Not refereed][Not invited]
  • 萩原 光義, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (288)  7  -12  2015/11/04  [Not refereed][Not invited]
  • 丹野 柊平, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (288)  37  -42  2015/11/04  [Not refereed][Not invited]
  • 宇佐美 友也, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (288)  43  -48  2015/11/04  [Not refereed][Not invited]
  • 西崎 隼, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (288)  127  -132  2015/11/04  [Not refereed][Not invited]
  • Abe Daisuke, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2015-  (1)  142  -142  2015/08/25  [Not refereed][Not invited]
  • Uehashi Shunsuke, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2015-  (1)  272  -272  2015/08/25  [Not refereed][Not invited]
  • Yuki Shuto, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2015-  (1)  288  -288  2015/08/25  [Not refereed][Not invited]
  • Nishizaki Shun, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2015-  (1)  343  -343  2015/08/25  [Not refereed][Not invited]
  • Tanno Shuhei, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2015-  (1)  344  -344  2015/08/25  [Not refereed][Not invited]
  • Hagiwara Mitsuyoshi, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2015-  (1)  345  -345  2015/08/25  [Not refereed][Not invited]
  • Nishimura Toshihiko, Nishizaki Shun, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2015-  (1)  "S  -39"-"S-40"  2015/08/25  [Not refereed][Not invited]
  • 遠藤 大樹, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (164)  107  -112  2015/07/30  [Not refereed][Not invited]
  • 結城 嵩仁, 小川 恭孝, 西村 寿彦  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (113)  247  -252  2015/06/24  [Not refereed][Not invited]
  • 西崎 隼, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (113)  241  -246  2015/06/24  [Not refereed][Not invited]
  • 丹野 柊平, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (113)  257  -261  2015/06/24  [Not refereed][Not invited]
  • 萩原 光義, 西村 寿彦, 大鐘 武雄  電子情報通信学会技術研究報告 = IEICE technical report : 信学技報  115-  (113)  263  -267  2015/06/24  [Not refereed][Not invited]
  • Kusano Kaoru, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2015-  (1)  193  -193  2015/02/24  [Not refereed][Not invited]
  • Uehashi Shunsuke, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2015-  (1)  374  -374  2015/02/24  [Not refereed][Not invited]
  • Suzuki Kosuke, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2015-  (1)  408  -408  2015/02/24  [Not refereed][Not invited]
  • Usami Tomoya, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2015-  (1)  466  -466  2015/02/24  [Not refereed][Not invited]
  • Sugita Masatomo, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2015-  (1)  522  -522  2015/02/24  [Not refereed][Not invited]
  • Endo Taiki, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  2015-  (1)  "S  -1"-"S-2"  2015/02/24  [Not refereed][Not invited]
  • Ohgane Takeo, Ogawa Yasutaka, Nishimura Toshihiko  Proceedings of the IEICE General Conference  2015-  (1)  "SS  -9"-"SS-10"  2015/02/24  [Not refereed][Not invited]
  • UEHASHI Shunsuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Signal processing  114-  (394)  55  -60  2015/01/22  [Not refereed][Not invited]
     
    In multi-user MIMO systems, a base station needs downlink channel state information (CSI) to each user to suppress inter-user interference and inter-stream interference. In wireless communication, however, signal propagation environments are time-varying, and CSI obtained at the base station is different from the channel at the actual transmission time because we have delay. This deteriorates communication quality. To solve this problem, some channel prediction schemes have been developed. So far, we have proposed a channel prediction scheme using a compressed sensing technique. This scheme can predict channel with high accuracy even when the number of arrival waves is large. In this paper, we evaluate the effect of the proposed method in multi-user MIMO systems.
  • NAKANISHI Yuki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  IEICE technical report. Signal processing  114-  (394)  61  -66  2015/01/22  [Not refereed][Not invited]
     
    When a base station has many transmit antennas such as a massive MIMO system, we need as many pilot resources as the transmit antennas to estimate channel state information (CSI) and its feedback in an FDD system, and thus transmission efficiency degrades. In our previous study, we have proposed an over-distributed antenna system (O-DAS) with much more transmit antennas than limited pilot resources, and have shown an improvement of the peak throughput under a perfect CSI assumption. However, the CSI is outdated if control delay exists, and thus it may cause the inter-user-interference which seriously degrades the transmission performance. In this paper, we evaluate the throughput performance of the O-DAS for two transmission methods, namely, signal distributing and switching, in time-varying environments with a control delay. Compared with the case in non time-varying environments, it is shown that the performance degradation of signal switching is not serious and that the signal distributing still provides sufficient gain although the profitable range becomes narrow.
  • USAMI Tomoya, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report. Signal processing  114-  (394)  163  -168  2015/01/22  [Not refereed][Not invited]
     
    With the rapid traffic growth, a massive multiple-input multiple-output (MIMO) system with an order of 100 elements has been discussed recently. Increasing the number of both transmit and receive antennas improves peak data rate and capacity, but requires the complexity proportional to at least the third power of the number of antenna elements to detect spatially-multiplexed signals in general. Thus, the implementation of a fully massive MIMO system becomes very difficult. To solve this problem, detection based on the belief propagation has been developed and studied. It has been shown that the belief propagation is implementable in the order of the second power of the number of elements and achieves very good BER performance in a QPSK modulated massive MIMO system. But it is essential to study a multi-level QAM modulated massive MIMO system in the viewpoint of peak throughput. In this paper, we apply the belief propagation to a 16-QAM modulated massive MIMO system and have shown that starting the process from error-tolerant bit nodes improves the BER performance.
  • UEHASHI Shunsuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  114-  (395)  55  -60  2015/01/22  [Not refereed][Not invited]
     
    In multi-user MIMO systems, a base station needs downlink channel state information (CSI) to each user to suppress inter-user interference and inter-stream interference. In wireless communication, however, signal propagation environments are time-varying, and CSI obtained at the base station is different from the channel at the actual transmission time because we have delay. This deteriorates communication quality. To solve this problem, some channel prediction schemes have been developed. So far, we have proposed a channel prediction scheme using a compressed sensing technique. This scheme can predict channel with high accuracy even when the number of arrival waves is large. In this paper, we evaluate the effect of the proposed method in multi-user MIMO systems.
  • 中西裕基, 西村寿彦, 大鐘武雄, 小川恭孝, 大渡裕介, 岸山祥久  電子情報通信学会技術研究報告  114-  (395(RCS2014 269-300))  61  -66  2015/01/22  [Not refereed][Not invited]
     
    When a base station has many transmit antennas such as a massive MIMO system, we need as many pilot resources as the transmit antennas to estimate channel state information (CSI) and its feedback in an FDD system, and thus transmission efficiency degrades. In our previous study, we have proposed an over-distributed antenna system (O-DAS) with much more transmit antennas than limited pilot resources, and have shown an improvement of the peak throughput under a perfect CSI assumption. However, the CSI is outdated if control delay exists, and thus it may cause the inter-user-interference which seriously degrades the transmission performance. In this paper, we evaluate the throughput performance of the O-DAS for two transmission methods, namely, signal distributing and switching, in time-varying environments with a control delay. Compared with the case in non time-varying environments, it is shown that the performance degradation of signal switching is not serious and that the signal distributing still provides sufficient gain although the profitable range becomes narrow.
  • USAMI Tomoya, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  114-  (395)  163  -168  2015/01/22  [Not refereed][Not invited]
     
    With the rapid traffic growth, a massive multiple-input multiple-output (MIMO) system with an order of 100 elements has been discussed recently. Increasing the number of both transmit and receive antennas improves peak data rate and capacity, but requires the complexity proportional to at least the third power of the number of antenna elements to detect spatially-multiplexed signals in general. Thus, the implementation of a fully massive MIMO system becomes very difficult. To solve this problem, detection based on the belief propagation has been developed and studied. It has been shown that the belief propagation is implementable in the order of the second power of the number of elements and achieves very good BER performance in a QPSK modulated massive MIMO system. But it is essential to study a multi-level QAM modulated massive MIMO system in the viewpoint of peak throughput. In this paper, we apply the belief propagation to a 16-QAM modulated massive MIMO system and have shown that starting the process from error-tolerant bit nodes improves the BER performance.
  • NAKANISHI Yuki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  IEICE Transactions on Communications (Web)  E98.B-  (8)  2015
  • SUZUKI Kosuke, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  114-  (372)  135  -140  2014/12/18  [Not refereed][Not invited]
     
    In a wireless mesh network, the interference between nearby links is not negligible and thus degrades the area spectral efficiency. There have been many works on a use of directional antennas capable of forming a narrow beam to a destination node. An adaptive array capable of controlling not only beams but also nulls is more effective for reducing interference, and thereby the possibility to establish new links increases. Here, an alternative route enables avoiding resource competitions and improves the possibility of new link establishment. In the paper, we evaluate the system throughput performance in a wireless mesh network consisting of nodes having alternative routes and an adaptive array function.
  • SUGITA Masatomo, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  114-  (295)  37  -42  2014/11/12  [Not refereed][Not invited]
     
    Frequency-domain equalization is well known as a countermeasure for inter-symbol interference in a single carrier transmission system in terms of light weight and reasonably high performance. Frequency-domain turbo equalization with iterative processing has been developed as the extension to provide very high performance. In this paper, we consider a channel equalizer using a belief propagation (BP) algorithm in the time domain. In multiple-input multiple-output multi-path environments, it has been reported that this algorithm achieves a near-optimum BER performance. However, in single-input single-output (SISO) multi-path environments, the normal BP algorithm does not work. We show the problems and a solution against that. And we evaluate the BER performance with our proposal in a SISO multi-path environment.
  • UEHASHI Shunsuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  114-  (245)  1  -6  2014/10/15  [Not refereed][Not invited]
     
    In wireless communication, channel estimation using pilot symbols is essential. If we need to transmit many pilot symbols in time-varying environments, the transmission efficiency is lowed. Also, channel state information (CSI) obtained by the pilot symbols is different from the channel at the actual transmission time because we have delay. This deteriorates communication quality. To solve this problem, some channel prediction schemes have been developed. In this paper, we propose a channel prediction scheme which combines a sum-of-sinusoids (SOS) method and direction-of-arrival (DOA) estimation using a compressed sensing technique. Using simulation, it is shown that the proposed method realizes highly precise channel prediction.
  • ENDO Taiki, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report. Antennas and propagation  114-  (245)  7  -12  2014/10/15  [Not refereed][Not invited]
     
    In recent years, much attention has been paid to DOA estimation using a compressed sensing technique. We have studied a DOA estimation method of multi-band signals with frequency characteristics. Using multi-band signals, we can achieve higher probability of correct estimation that using single-band signals and estimate more waves than the number of antenna elements. The half-quadratic regularization (HQR) method is a technique to solve a linear programming problem of the compressed sensing technique. In this paper, we study dependence property of three parameters in the HQR method for probability of correct estimation and obtaine adequate values of the parameters.
  • Endo Taiki, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2014-  (1)  172  -172  2014/09/09  [Not refereed][Not invited]
  • Uehashi Shunsuke, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2014-  (1)  321  -321  2014/09/09  [Not refereed][Not invited]
  • Fukuda Hayato, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2014-  (1)  322  -322  2014/09/09  [Not refereed][Not invited]
  • NISHIMURA T., ENDO T., OGAWA Y., OHGANE T.  Technical report of IEICE. SANE  114-  (194)  65  -70  2014/08/28  [Not refereed][Not invited]
     
    It has been proposed to apply compressed sensing methods to problems estimating the direction of arrival angles of radio waves. Using the proposed method, angular resolution can be more precise than the traditional methods such as the MUSIC. If the arrival waves are multiband signal spread over a wide-frequency-band, the performance can be improved. Furthermore, the performance enhancement can be expected by using the Khatri-Rao product and normalization of power even when the arrival waves have frequency dependency. We show how the compressed sensing method is applied, and then we explain how the method using the Khatri-Rao product and normalization of power is applied. The effectiveness of our proposal is confirmed by some simulation results.
  • NISHIMURA T., ENDO T., OGAWA Y., OHGANE T.  IEICE technical report. Antennas and propagation  114-  (193)  79  -84  2014/08/28  [Not refereed][Not invited]
     
    It has been proposed to apply compressed sensing methods to problems estimating the direction of arrival angles of radio waves. Using the proposed method, angular resolution can be more precise than the traditional methods such as the MUSIC. If the arrival waves are multiband signal spread over a wide-frequency-band, the performance can be improved. Furthermore, the performance enhancement can be expected by using the Khatri-Rao product and normalization of power even when the arrival waves have frequency dependency. We show how the compressed sensing method is applied, and then we explain how the method using the Khatri-Rao product and normalization of power is applied. The effectiveness of our proposal is confirmed by some simulation results.
  • FUKUDA Hayato, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  Technical report of IEICE. RCS  114-  (180)  1  -6  2014/08/19  [Not refereed][Not invited]
     
    In order to realize high capacity communication, massive multiple-input multiple-output (MIMO) systems which have a very large number of antenna elements at a base station (BS) or an access point (AP) have been studied for future cellular systems. It is, however, difficult to build the massive MIMO system because the installation space is limited. To cope with this limitation, a full-dimension MIMO (FD-MIMO) system where antenna elements are placed on a 2D grid at the BS or AP for MIMO transmission is proposed. The 2D antenna array saves the space and allows elevation beamforming as well as azimuth beamforming. In this paper, we evaluate performance of the FD-MIMO in indoor Line-of-Sight environments compared with that of a ID antenna arrangement using a ray tracing technique which enables to obtain channel matrices between BS and user terminals. It has been shown that FD-MIMO with a small rectangular antenna array performs better than ID antenna array when users are located near the BS.
  • NAKANISHI Yuki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  114-  (180)  7  -12  2014/08/19  [Not refereed][Not invited]
     
    A distributed antenna system, where antennas of a base station are spatially distributed over the cell, can improve throughput at the cell edge compared to a centralized antenna system but reduces peak throughput. Therefore, it is expected that we can obtain higher throughput by increasing the number of antennas per remote antenna unit. In general, we need to send as many pilot sequences as transmit antennas to estimate channel state information and thus transmission efficiency degrades. In this paper, we present a novel system where we distribute the same signal to several antennas to increase the number of antennas without increasing the number of pilot sequences. We show the throughput improvement with signal distribution and evaluate the effect of weighted signal distribution.
  • OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  The Journal of the Institute of Electronics, Information, and Communication Engineers  97-  (4)  285  -289  2014/04  [Not refereed][Not invited]
     
    マルチユーザMIMOシステムの下り回線においては,通常,ユーザ間の干渉,及び,同一ユーザの複数ストリーム間の干渉がなくなるように基地局は送信ウェイトを決定し,それを信号に乗算して伝送が行われる.一方,ユーザ端末や周囲の散乱体の移動により,一般に,チャネルは時間変動する.このような環境では,送信ウェイトを決定したときのチャネルと実際に送信を行うときのチャネルに変動があるため干渉が発生し,特性が劣化する.この問題はチャネルを予測することにより軽減が可能である.本稿では,時変動チャネルがマルチユーザMIMOシステムに与える影響とチャネル予測の効果を明らかにする.
  • Ohgane Takeo, Usami Tomoya, Fukuda Wataru, Ogawa Yasutaka, Nishimura Toshihiko  Proceedings of the IEICE General Conference  2014-  "S  -54"-"S-55"  2014/03/04  [Not refereed][Not invited]
  • Yamaguchi Kanako, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2014-  (1)  216  -216  2014/03/04  [Not refereed][Not invited]
  • SHIRAI Satoshi, YAMADA Hiroyoshi, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo, YAMAGUCHI Yoshio  Proceedings of the IEICE General Conference  2014-  (1)  228  -228  2014/03/04  [Not refereed][Not invited]
  • Terada Tsubasa, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo, Yamada Hiroyoshi  Proceedings of the IEICE General Conference  2014-  (1)  231  -231  2014/03/04  [Not refereed][Not invited]
  • Tanaka Tomoki, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2014-  (1)  416  -416  2014/03/04  [Not refereed][Not invited]
  • Fukuda Wataru, Abiko Takashi, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Ohwatari Yusuke, Kawamura Teruo, Kishiyama Yoshihisa  Proceedings of the IEICE General Conference  2014-  (1)  428  -428  2014/03/04  [Not refereed][Not invited]
  • Abiko Takashi, Fukuda Wataru, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Ohwatari Yusuke, Kawamura Teruo, Kishiyama Yoshihisa  Proceedings of the IEICE General Conference  2014-  (1)  430  -430  2014/03/04  [Not refereed][Not invited]
  • Harada Keita, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2014-  (1)  473  -473  2014/03/04  [Not refereed][Not invited]
  • Nakanishi Yuki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2014-  (1)  475  -475  2014/03/04  [Not refereed][Not invited]
  • Sugita Masatomo, Fukuda Wataru, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2014-  (1)  495  -495  2014/03/04  [Not refereed][Not invited]
  • Izumo Kyousuke, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2014-  (1)  553  -553  2014/03/04  [Not refereed][Not invited]
  • Ohgane Takeo, Usami Tomoya, Fukuda Wataru, Ogawa Yasutaka, Nishimura Toshihiko  Proceedings of the IEICE General Conference  2014-  (1)  "S  -54"-"S-55"  2014/03/04  [Not refereed][Not invited]
  • Ohgane Takeo, Usami Tomoya, Fukuda Wataru, Ogawa Yasutaka, Nishimura Toshihiko  Proceedings of the IEICE General Conference  2014-  "S  -54"-"S-55"  2014/03/04  [Not refereed][Not invited]
  • Tanaka Tomoki, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2014-  (1)  416  -416  2014/03/04  [Not refereed][Not invited]
  • Yamaguchi Kanako, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2014-  (1)  216  -216  2014/03/04  [Not refereed][Not invited]
  • Nakanishi Yuki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2014-  (1)  475  -475  2014/03/04  [Not refereed][Not invited]
  • Fukuda Wataru, Abiko Takashi, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Ohwatari Yusuke, Kawamura Teruo, Kishiyama Yoshihisa  Proceedings of the IEICE General Conference  2014-  (1)  428  -428  2014/03/04  [Not refereed][Not invited]
  • SHIRAI Satoshi, YAMADA Hiroyoshi, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo, YAMAGUCHI Yoshio  Proceedings of the IEICE General Conference  2014-  (1)  228  -228  2014/03/04  [Not refereed][Not invited]
  • Terada Tsubasa, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo, Yamada Hiroyoshi  Proceedings of the IEICE General Conference  2014-  (1)  231  -231  2014/03/04  [Not refereed][Not invited]
  • Abiko Takashi, Fukuda Wataru, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Ohwatari Yusuke, Kawamura Teruo, Kishiyama Yoshihisa  Proceedings of the IEICE General Conference  2014-  (1)  430  -430  2014/03/04  [Not refereed][Not invited]
  • Izumo Kyousuke, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2014-  (1)  553  -553  2014/03/04  [Not refereed][Not invited]
  • Sugita Masatomo, Fukuda Wataru, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2014-  (1)  495  -495  2014/03/04  [Not refereed][Not invited]
  • Harada Keita, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2014-  (1)  473  -473  2014/03/04  [Not refereed][Not invited]
  • SAI Seii, DOI Yoshiharu, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  113-  (456)  169  -174  2014/03/03  [Not refereed][Not invited]
     
    In Japan, 700MHz-band ITS has been promoted to improve not only the "environment", "comfort and convenient", but also the "road safety" over recent years. The idea is to exchange safety-related information between neighboring vehicles to extend the driver's view and provide more information to drivers by using the wireless communication. In the near future, it is expected that neighboring vehicles may even directly exchange critical control-relevant information without driver involved to realize safer road environments. Therefore, it is necessary to improve the reliability of vehicle-to-vehicle commutation. In the paper, we propose a new communication method for high reliability vehicle-to-vehicle communication and show the initial performance evaluation results through computer simulations.
  • SAI SEII, DOI YOSHIHARU, NISHIMURA TOSHIHIKO, OGANE TAKEO, OGAWA YASUTAKA  電子情報通信学会技術研究報告  113-  (456(RCS2013 306-396))  169  -174  2014/02/24  [Not refereed][Not invited]
  • SHIRAI Satoshi, YAMADA Hiroyoshi, NISHIMURA Toshihiko, OGAWA Yasutaka, YAMAGUCHI Yoshio  IEICE technical report. Antennas and propagation  113-  (344)  35  -40  2013/12/12  [Not refereed][Not invited]
     
    Recently, research and communication using wideband signal have been investigated intensively. With the progress of wideband communications, wideband DOA estimation technique has been also required. The history of wideband DOA estimation has several decades, but standard approach does not still exist. In this report, we have proposed a new wideband DOA estimation method using the Khatri-Rao matrix product. This method enables a wideband DOA estimation using a simple conversion of sub-frequency band signals. Furthermore, it has the advantage of enhance the degrees-of-freedom of the array. In this paper, we evaluate the performance of the proposed method through simulations and experiments.
  • SHIRAI SATOSHI, YAMADA HIROYOSHI, NISHIMURA TOSHIHIKO, OGAWA YASUTAKA, YAMAGUCHI YOSHIO  電子情報通信学会技術研究報告  113-  (344(AP2013 124-133))  35  -40  2013/12/05  [Not refereed][Not invited]
  • FUKUDA Wataru, ABIKO Takashi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KAWAMURA Teruo, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  113-  (301)  55  -60  2013/11/20  [Not refereed][Not invited]
     
    The easiest way to improve the throughput performance of multiple-input multiple-output (MIMO) systems is increasing the number of both transmit and receive antennas. In general, however, algorithms detecting spatially-multiplexed signals require the complexity to be proportional to the third power of the number of antenna elements at least. Thus, the implementation of an antenna array with an order of 100 elements becomes very difficult. Several studies have shown that a detection based on the belief propagation with a parallel interference canceller is implementable in the order of the second power of the number of elements and achieves very good BER performance in uncorrelated MIMO channels. However, it is expected that the detection performance degrades in spatially correlated MIMO channels. In this paper, we propose applying node selection, and show the BER performance in correlated channels.
  • YAMAGUCHI Kanako, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  113-  (300)  43  -48  2013/11/20  [Not refereed][Not invited]
     
    A multi-user MIMO system uses block diagonalization and eigenbeam-space division multiplexing to suppress inter-user interference and inter-stream interference. In order to use these techniques, the transmitter needs to determine beamforming weights from channel state information (CSI). In time-varyinig environments, however, MIMO channels change during the time interval between transmission parameter determination and actual MIMO transmission. Therefore, the outdated CSI causes the interfernces and seriously affects the transmission performance. Channel prediction schemes have been developed to mitigate the effect of the outdated CSI. In this paper, we evaluate the prediction effects based on the autoregressive (AR) model and the Lagrange extrapolation such as linear extrapolation in time-varying environments.
  • TERADA Tsubasa, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo, YAMADA Hiroyoshi  IEICE technical report. Antennas and propagation  113-  (300)  93  -98  2013/11/20  [Not refereed][Not invited]
     
    Much attention has been paid to direction of arrival (DOA) estimation using a compressed sensing technique. In our previous study, we have proposed a method to estimate DOAs of multi-band signals using an array antenna at a receiver. As a result, we have produced an improvement of the probability of correct estimation. Moreover, the method can deal with waves exceeding the degrees of freedom of the array. However, we have assumed that incident waves have multi-bands where complex amplitudes are the same. First, in this paper, we propose a method that allows the estimation of DOAs when only the phases at the bands are different using not the complex amplitudes but powers of the signals. Second, we extend the technique in such a way that it can estimate DOAs of the signals having different amplitudes among bands.
  • TERADA TSUBASA, NISHIMURA TOSHIHIKO, OGAWA YASUTAKA, OGANE TAKEO, YAMADA HIROYOSHI  電子情報通信学会技術研究報告  113-  (300(AP2013 100-123))  93  -98  2013/11/13  [Not refereed][Not invited]
  • YAMAGUCHI KANAKO, OGAWA YASUTAKA, NISHIMURA TOSHIHIKO, OGANE TAKEO  電子情報通信学会技術研究報告  113-  (300(AP2013 100-123))  43  -48  2013/11/13  [Not refereed][Not invited]
  • 福田航, 安孫子卓史, 西村寿彦, 大鐘武雄, 小川恭孝, 大渡裕介, 川村輝雄, 岸山祥久  電子情報通信学会技術研究報告  113-  (301(RCS2013 174-205))  55  -60  2013/11/13  [Not refereed][Not invited]
  • Kusano Kaoru, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2013-  (1)  209  -209  2013/09/03  [Not refereed][Not invited]
  • Nakanishi Yuki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2013-  (1)  396  -396  2013/09/03  [Not refereed][Not invited]
  • KUSANO Kaoru, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  113-  (151)  43  -48  2013/07/23  [Not refereed][Not invited]
     
    A radar is a device for detecting scatterers by observing scattered electromagnetic waves. To enhance the precision, we need a wide frequencyband and/or more antennas. The frequency band and the number of antennas are, howerver, limited, and a higly accurate method is needed when the samples are not sufficient. In this paper, we formulate a method based on compressed sensing. Then, we consider the performance of cases of using a single transmit antenna and all of the transmit ones in the array.
  • KUSANO KAORU, OGAWA YASUTAKA, NISHIMURA TOSHIHIKO, OGANE TAKEO  電子情報通信学会技術研究報告  113-  (151(AP2013 46-61))  43  -48  2013/07/16  [Not refereed][Not invited]
  • HARADA Keita, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  113-  (93)  49  -54  2013/06/20  [Not refereed][Not invited]
     
    Multi-user multiple-input multiple-output (MU-MIMO) systems in which signals are simultaneously transmitted from a base station to multiple users are well known as a method to improve the throughput performance. In MU-MIMO systems, the block diagonalization scheme is used to eliminate inter-user interference and the eigenbeam-space division multiplexing (E-SDM) technique is used for channel capacity maximization. In this paper, a multi-user single-carrier E-SDM scheme in wideband transmissions is formulated. The transmit and receive weights are obtained in the frequency domain. The receive weights are based on the zero-forcing method, which simultaneously operates the spatial domain processing and frequency domain equalization. Then, the bit error rate performance is evaluated using computer simulations.
  • NAKANISHI Yuki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  113-  (93)  55  -60  2013/06/20  [Not refereed][Not invited]
     
    A distributed antenna system, where antennas of a base station are spatially distributed over the cell, can improve throughput at the cell edge compared to a centralized antenna system. In a multiuser multiple-input multiple-output (MIMO) system, we can obtain higher sum capacity by increasing the number of antennas per distributed base station. However, the large number of total antenna elements requires the same or larger number of pilot sequences to estimate the channel gains. In this paper, we propose pilot signal sharing to reduce the number of pilot signals, and the impact of the pilot signal sharing on the sum capacity is evaluated. From computer simulations, it is shown that inter-user interference due to the wrong channel information can be suppressed at a certain sharing condition.
  • YAMAGUCHI Kanako, NISHIMOTO Hiroshi, OKAZAKI Akihiro, SANO Hiroyasu, ISHIZU Fumio, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  113-  (93)  193  -198  2013/06/20  [Not refereed][Not invited]
     
    As a countermeasure for serious shortage of radio frequency resources, single-carrier block transmission (SCBT) techniques, which can achieve a low PAPR property and high spectral efficiency simultaneously, have attracted much attention. Further efficient spectral utilization can be yielded by incorporating multilevel modulation and MIMO spatial multiplexing into SCBT. In that case, however, the receiver requires accurate channel estimation in order to demultiplex and detect the spatially-multiplexed multilevel-modulated signal. So far, the authors have proposed core techniques for SCBT and verified their availability by computer simulations: (a) a frequency-domain scattered pilot multiplexing technique with maintenance of the low PAPR property of SCBT, and (b) a two-dimensional channel estimation technique using parameter table selection, which equivalently achieves an MMSE criterion with highly-reduced numerical complexity. Here, the authors construct a testbed of multilevelmodulated MIMO-SCBT using an FPGA-based prototype modem in order to demonstrate our techniques. This paper reports experimental performance evaluation of the 1024QAM-modulated 2 x 4 MIMO-SCBT.
  • YAMAGUCHI KANAKO, NISHIMOTO HIROSHI, OKAZAKI AKIHIRO, SANO HIROYASU, ISHIZU FUMIO, NISHIMURA TOSHIHIKO, OGANE TAKEO, OGAWA YASUTAKA  電子情報通信学会技術研究報告  113-  (93(RCS2013 37-77))  193  -198  2013/06/13  [Not refereed][Not invited]
  • NAKANISHI YUKI, NISHIMURA TOSHIHIKO, OGANE TAKEO, OGAWA YASUTAKA  電子情報通信学会技術研究報告  113-  (93(RCS2013 37-77))  55  -60  2013/06/13  [Not refereed][Not invited]
  • HARADA KEITA, OGAWA YASUTAKA, NISHIMURA TOSHIHIKO, OGANE TAKEO  電子情報通信学会技術研究報告  113-  (93(RCS2013 37-77))  49  -54  2013/06/13  [Not refereed][Not invited]
  • Terada Tsubasa, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  2013-  (1)  198  -198  2013/03/05  [Not refereed][Not invited]
  • Yamaguchi Kanako, Bui Huu Phu, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2013-  (1)  217  -217  2013/03/05  [Not refereed][Not invited]
  • MORITANI Kentaro, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  420  -420  2013/03/05  [Not refereed][Not invited]
  • Fukuda Wataru, Abiko Takashi, Nishimura Toshihiko, Ohgane Takeo, Ohwatari Yusuke, Kishiyama Yoshihisa, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  421  -421  2013/03/05  [Not refereed][Not invited]
  • Abiko Takashi, Fukuda Wataru, Nishimura Toshihiko, Ohgane Takeo, Ohwatari Yusuke, Kishiyama Yoshihisa, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  422  -422  2013/03/05  [Not refereed][Not invited]
  • KOBAYASHI Takuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2013-  (1)  440  -440  2013/03/05  [Not refereed][Not invited]
  • KIYOMI Naohito, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  580  -580  2013/03/05  [Not refereed][Not invited]
  • Terada Tsubasa, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  2013-  (1)  198  -198  2013/03/05  [Not refereed][Not invited]
  • Yamaguchi Kanako, Bui Huu Phu, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2013-  (1)  217  -217  2013/03/05  [Not refereed][Not invited]
  • KOBAYASHI Takuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2013-  (1)  440  -440  2013/03/05  [Not refereed][Not invited]
  • Harada Keita, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2013-  (1)  414  -414  2013/03/05  [Not refereed][Not invited]
  • KIYOMI Naohito, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  580  -580  2013/03/05  [Not refereed][Not invited]
  • Abiko Takashi, Fukuda Wataru, Nishimura Toshihiko, Ohgane Takeo, Ohwatari Yusuke, Kishiyama Yoshihisa, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  422  -422  2013/03/05  [Not refereed][Not invited]
  • MORITANI Kentaro, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  420  -420  2013/03/05  [Not refereed][Not invited]
  • Fukuda Wataru, Abiko Takashi, Nishimura Toshihiko, Ohgane Takeo, Ohwatari Yusuke, Kishiyama Yoshihisa, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2013-  (1)  421  -421  2013/03/05  [Not refereed][Not invited]
  • FUKUDA Wataru, ABIKO Takashi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  112-  (424)  225  -230  2013/01/31  [Not refereed][Not invited]
     
    The easiest way to improve the throughput performance of multiple-input multiple-output (MIMO) systems is to increase the number of both transmit and receive antennas. In general, however, algorithms detecting spatially-multiplexed signals require the complexity proportional to the third power of the number of antenna elements in the least case. Thus, the implementation of an antenna array with an order of 100 elements becomes very difficult. Several studies have shown that a detection based on the belief propagation with a parallel interference canceller is implementable in the order of the second power of the number of elements and achieves very good BER performance. In this paper, we apply three methods for the complexity reduction into the belief propagation with focus on the Tanner graph, and evaluate those BER performances.
  • ABIKO Takashi, FUKUDA Wataru, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  112-  (424)  231  -236  2013/01/31  [Not refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems are well known as a method to improve the throughput performance Recently, a concept of massive (or very large) MIMO using an antenna array with an order of 100 elements has been proposed. In general, the complexity order of signal detection in such a MIMO system becomes the third power of the number of antenna elements in the least case. The authors have evaluated the belief propagation based algorithm with parallel interference cancellers and shown that it is implementable in the order of the second power of the number of elements Here, we describe a method to use maximum ratio combining (MRC) for message fusion and evaluate BER performance. In addition, the convergence behavior is discussed by applying the extrinsic information transfer analysis.
  • FUKUDA Wataru, ABIKO Takashi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  112-  (424)  225  -230  2013/01/31  [Not refereed][Not invited]
     
    The easiest way to improve the throughput performance of multiple-input multiple-output (MIMO) systems is to increase the number of both transmit and receive antennas. In general, however, algorithms detecting spatially-multiplexed signals require the complexity proportional to the third power of the number of antenna elements in the least case. Thus, the implementation of an antenna array with an order of 100 elements becomes very difficult. Several studies have shown that a detection based on the belief propagation with a parallel interference canceller is implementable in the order of the second power of the number of elements and achieves very good BER performance. In this paper, we apply three methods for the complexity reduction into the belief propagation with focus on the Tanner graph, and evaluate those BER performances.
  • ABIKO Takashi, FUKUDA Wataru, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATARI Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  112-  (424)  231  -236  2013/01/31  [Not refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems are well known as a method to improve the throughput performance Recently, a concept of massive (or very large) MIMO using an antenna array with an order of 100 elements has been proposed. In general, the complexity order of signal detection in such a MIMO system becomes the third power of the number of antenna elements in the least case. The authors have evaluated the belief propagation based algorithm with parallel interference cancellers and shown that it is implementable in the order of the second power of the number of elements Here, we describe a method to use maximum ratio combining (MRC) for message fusion and evaluate BER performance. In addition, the convergence behavior is discussed by applying the extrinsic information transfer analysis.
  • 福田航, 安孫子卓史, 西村寿彦, 大鐘武雄, 小川恭孝, 大渡裕介, 岸山祥久  電子情報通信学会技術研究報告  112-  (424(RCS2012 238-283))  225  -230  2013/01/24  [Not refereed][Not invited]
  • 安孫子卓史, 福田航, 西村寿彦, 大鐘武雄, 小川恭孝, 大渡裕介, 岸山祥久  電子情報通信学会技術研究報告  112-  (424(RCS2012 238-283))  231  -236  2013/01/24  [Not refereed][Not invited]
  • Keita Harada, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane  2013 INTERNATIONAL SYMPOSIUM ON INTELLIGENT SIGNAL PROCESSING AND COMMUNICATIONS SYSTEMS (ISPACS)  2013-  (1)  240  -244  2013  [Not refereed][Not invited]
     
    Multi-user multiple-input multiple-output (MU-MIMO) systems in which signals are simultaneously transmitted from a base station to multiple users are well known as a method to improve the throughput performance. In MU-MIMO systems, the block diagonalization scheme is used to eliminate inter-user interference and the eigenbeam-space division multiplexing (E-SDM) technique is used for channel capacity maximization. In this paper, a multi-user single-carrier E-SDM scheme in wideband transmissions is formulated. The transmit and receive weights are obtained in the frequency domain. The receive weights are based on the zero-forcing method, which simultaneously operates on the spatial domain processing and frequency domain equalization. Then, the bit error rate performance is evaluated using computer simulations.
  • Wataru Fukuda, Takashi Abiko, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yusuke Ohwatari, Yoshihisa Kishiyama  2013 IEEE 77TH VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING)  1  -5  2013  [Refereed][Not invited]
     
    A very large MIMO system has a potential to achieve extremely-high system throughput. In general, however, algorithms detecting spatially-multiplexed signals require the complexity proportional to the cubed number of antenna elements in the least case. Thus, the implementation of an antenna array with an order of 100 elements becomes very difficult. In this paper, we focus on the algorithm which is based on belief propagation and implementable with the second-order calculations. The simulation results show that the algorithm provides very good BER performance in MIMO spatial multiplexing when the number of antenna elements is 100 and reasonably low complexity in comparison to the MMSE spatial filtering.
  • Takashi Abiko, Wataru Fukuda, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa, Yusuke Ohwatari, Yoshihisa Kishiyama  IEEE Vehicular Technology Conference  1  -5  2013  [Refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems are well known as a method to improve the throughput performance. Recently, a concept of massive (or very large) MIMO using an antenna array with an order of 100 elements has been proposed. In a demand for low-complexity detection method, belief-propagation based algorithm, which is implementable in the order of the second power of the number of elements, has been developed. In the paper, the extrinsic information transfer (EXIT) analysis is applied to clarify the validity of iterative processing capability and evaluate the convergence performance. The results show that the EXIT chart expresses the BER convergence behavior well when the number of antenna elements is 100. © 2013 IEEE.
  • Kobayashi Takuya, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Technical report of IEICE. RCS  112-  (351)  197  -202  2012/12/13  [Not refereed][Not invited]
     
    In future mobile communications, a higher frequency band will be used because we need a wider frequency bandwidth for high-speed transmission. However, the propagation loss increases in a higher frequency band.It causes the communication quality degradation. The power of terminals is supplied by the battery. Thus, this problem is serious in an uplink channel. The virtual MIMO system that a communication terminal cooperates with nearby terminals has been proposed to solve this problem. We evaluated the performance of the virtual MIMO-OFDM system in static channels in previous works. In this paper, we investigate the performance of the virtual MIMO-OFDM system in dynamic channels.
  • Kiyomi Naohito, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Technical report of IEICE. RCS  112-  (351)  203  -208  2012/12/13  [Not refereed][Not invited]
     
    A cooperative relay has been studied as a method to improve transmission quality. A half-duplex (HD) relay uses 2 time-intervals to avoid interference between the signals from source and relay nodes. In contrast, a full-duplex (FD) relay consumes less time resources than the HD relay because the source and relay nodes transmit each packet at the same time-interval. However, the destination node requires to suppress the inter-symbol interference caused by the signal via relay. In this paper, we evaluate the FD-AF relay performance using frequency domain equalization with multiple antennas at the destination node under the condition of perfectly-known channel information and no self-interference at the relay.
  • Moritani Kentaro, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Technical report of IEICE. RCS  112-  (351)  257  -262  2012/12/13  [Not refereed][Not invited]
     
    Lattice reduction is known as a method improving detection performance for multiple-input multiple-output (MIMO) systems. The Lenstra, Lenstra, and Lovasz (LLL) algorithm, which is most-typically used for lattice reduction, has a problem that the maximum computational load is not a constant due to existence of exchanged steps. On the other hand, in coded MIMO systems, lattice reduction based detection requires reproduction of log-likelihood ratio (LLR) values for missing bits. In the paper, we discuss the computational complexity reduction and LLR estimation methods and evaluate the detection performance for various parameters for those methods.
  • MORITANI KENTARO, NISHIMURA TOSHIHIKO, OGANE TAKEO, OGAWA YASUTAKA  電子情報通信学会技術研究報告  112-  (351(RCS2012 184-237))  257  -262  2012/12/06  [Not refereed][Not invited]
  • KIYOMI NAOHITO, NISHIMURA TOSHIHIKO, OGANE TAKEO, OGAWA YASUTAKA  電子情報通信学会技術研究報告  112-  (351(RCS2012 184-237))  203  -208  2012/12/06  [Not refereed][Not invited]
  • KOBAYASHI TAKUYA, OGAWA YASUTAKA, NISHIMURA TOSHIHIKO, OGANE TAKEO  電子情報通信学会技術研究報告  112-  (351(RCS2012 184-237))  197  -202  2012/12/06  [Not refereed][Not invited]
  • 出雲恭輔, 西村寿彦, 大鐘武雄, 小川恭孝  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.118  2012/10/20  [Not refereed][Not invited]
  • 田中友基, 小川恭孝, 西村寿彦, 大鐘武雄  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.119  2012/10/20  [Not refereed][Not invited]
  • 原田佳太, 小川恭孝, 西村寿彦, 大鐘武雄  電気・情報関係学会北海道支部連合大会講演論文集(CD−ROM)  2012-  ROMBUNNO.117  2012/10/20  [Not refereed][Not invited]
  • FUKUDA Wataru, ABIKO Takashi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATAR Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  112-  (239)  7  -12  2012/10/10  [Not refereed][Not invited]
     
    The easiest way to improve the throughput performance of multiple-input multiple-output (MIMO) systems is increasing the number of both transmit and receive antennas. In general, however, algorithms detecting spatially-multiplexed signals require the complexity proportional to the third power of the number of antenna elements in the least case. Thus, the implementation of an antenna array with an order of 100 elements becomes very difficult. In this paper, we evaluate the algorithm based on belief propagation with parallel interference cancellers. This algorithm is implementable in the order of the second power of the number of elements, and it has been shown that the array with the order of 100 elements reveals very good BER performance.
  • ABIKO Takashi, FUKUDA Wataru, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, OHWATAR Yusuke, KISHIYAMA Yoshihisa  Technical report of IEICE. RCS  112-  (239)  13  -18  2012/10/10  [Not refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems are well known as a method to improve the throughput performance. Recently, a concept of massive (or very large) MIMO using an antenna array with an order of 100 elements has been proposed. In general, the complexity order of signal detection in such a MIMO system becomes the third power of the number of antenna elements in the least case. The authors have evaluated the belief propagation based algorithm with parallel interference cancellers and shown that it is implementable in the order of the second power of the number of elements. Here, the extrinsic information transfer analysis is applied to evaluate the convergence performance.
  • Terada Tsubasa, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2012-  (1)  203  -203  2012/08/28  [Not refereed][Not invited]
  • Terada Tsubasa, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2012-  (1)  203  -203  2012/08/28  [Not refereed][Not invited]
  • CHOI Heedong, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  112-  (149)  17  -22  2012/07/18  [Not refereed][Not invited]
     
    Time-reversal (TR) approach with multiple signal classification (MUSIC) has been developed for a remote sensing system due to super-resolution and statistical stability. Especially, TR-MUSIC imaging using the angle- and/or time-domain gating (filtering) technique in early papers provides a tremendous enhancement for the imaging results by reducing noise components and relaxing the antenna restriction. In this paper, we address the formulation of our approach, and discuss its performance in more detail.
  • CHOI Heedong, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  112-  (149)  17  -22  2012/07/18  [Not refereed][Not invited]
     
    Time-reversal (TR) approach with multiple signal classification (MUSIC) has been developed for a remote sensing system due to super-resolution and statistical stability. Especially, TR-MUSIC imaging using the angle- and/or time-domain gating (filtering) technique in early papers provides a tremendous enhancement for the imaging results by reducing noise components and relaxing the antenna restriction. In this paper, we address the formulation of our approach, and discuss its performance in more detail.
  • MAEDA Kyouhei, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report. Antennas and propagation  111-  (487)  25  -30  2012/03/08  [Not refereed][Not invited]
     
    Recently, due to the wide spread of wireless communications, importance of a precise direction-of-arrival (DOA) estimation technology has become greater in order to investigate propagation environments or determine terminal's positions. The authors have proposed the precise DOA estimation method of wide-band signals. First, coarse DOAs are estimated at the lowest frequency band where grating lobes do not appear. Next, precise DOA estimation is done at a higher frequency band in a narrower search range to prevent grating lobes. In this paper, to estimate DOA accurately under multipath environments, we use multiple antenna elements at a transmitter and apply spatial smoothing preprocessing (Transmit-SSP). The multiple signals transmitted from different positions cause correlation reduction effect. From computer simulations, we show the correlation suppression effect and high accuracy of the proposed method.
  • Maeda Kyouhei, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  2012-  (1)  186  -186  2012/03/06  [Not refereed][Not invited]
  • YAMAGUCHI Kanako, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2012-  (1)  224  -224  2012/03/06  [Not refereed][Not invited]
  • KOBAYASHI Takuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2012-  (1)  453  -453  2012/03/06  [Not refereed][Not invited]
  • MORITANI Kentaro, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2012-  (1)  479  -479  2012/03/06  [Not refereed][Not invited]
  • Takeda Daiki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2012-  (1)  565  -565  2012/03/06  [Not refereed][Not invited]
  • Ohgane Takeo, Ogawa Yasutaka, Nishimura Toshihiko  Proceedings of the IEICE General Conference  2012-  (1)  "SS  -7"-"SS-8"  2012/03/06  [Not refereed][Not invited]
  • 大鐘武雄, 小川恭孝, 西村寿彦  電子情報通信学会大会講演論文集  2012-  SS.7-SS.8  2012/03/06  [Not refereed][Not invited]
  • DAVIDESCU Cristian, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proc. IEEE VTC2612-Spring, May  111-  (451)  55  -60  2012/02/29  [Not refereed][Not invited]
     
    Single-carrier modulation combined with frequency-domain equalization (FDE) at the receiver has been proposed as an alternative to the OFDM system for the uplink transmission, in the case of severe frequency-selective fading channels. Furthermore, an eigenbeam-space division multiplexing (E-SDM) technique can be used to improve the spectrum efficiency. In order to reduce computational complexity at the transmitter, some techniques decreasing the number of singular value decompositions have been proposed. In this paper, we propose some reduced-complexity techniques that can improve the bit error rate (BER) performance. The evaluations of these techniques and the trade-off between complexity and BER are analyzed by computer simulations.
  • KOBAYASHI Takuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  111-  (451)  61  -66  2012/02/29  [Not refereed][Not invited]
     
    We need a wider frequency bandwidth for high-speed transmission, and thus a higher frequency band will be used in future mobile communications. However, the propagation loss increases in a higher frequency band. It causes degradation of communication quality especially for an uplink channel because the power is supplied by the terminal battery. Then, it has been proposed that a communication terminal cooperates with nearby terminals to solve this problem. However, different frequency offsets of the terminals cause different phase rotations. In this paper, we propose a frequency offset estimation and compensation scheme of them. We evaluate the performance of the virtual MIMO-based OFDM communications using the compensation scheme.
  • YAMAGUCHI Kanako, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  111-  (451)  67  -72  2012/02/29  [Not refereed][Not invited]
     
    In wireless communication channels, we have multipath propagation due to a large number of reflected and diffracted waves. When the delay difference between multipath waves is not negligible, we encounter frequency selective fading. Thus far, a frequency correlation defined for a single receive antenna has been used for evaluating the frequency selectivity. Recently, multiple antennas have been introduced to realize space diversity and/or spatial filtering. Then, the conventional frequency correlation defined for a single antenna cannot be used for a multiple-antenna system. In this paper, we extend the frequency correlation to a multiple-antenna system. Moreover, we compare the newly-introduced correlation with the conventional one and the error for signal detection under several propagation environments.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  International Conference on Advanced Communication Technology, ICACT  2012
  • WEBBER Julian, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  電子情報通信学会技術研究報告  111-  (345(RCS2011 232-266))  1  -6  2011/12/08  [Not refereed][Not invited]
     
    Very low error rates can be obtained using low-density parity-check (LDPC) codes and their use is now common in new communications standards such as the Long Term Evolution (LTE) Advanced. The decoders based on belief propagation offer excellent performance but have high complexity. Therefore simpler architectures based on the bit flipping algorithm have been researched. Over the last two years a few adaptive threshold algorithms have been proposed in which a bit is either inverted if it is below a threshold, or the threshold itself is lowered using a scaling factor. This work looks at how the scaling factor influences the iteration count and error performance. We propose an algorithm that switches between two scaling factors based on the syndrome sum on each branch. Using this technique we show that the error performance is comparable with that of a single scaling factor but the iteration count is significantly reduced. Further, if a non-transmitted codeword is detected, which corresponds to a trapped search point, an addition of a small noise perturbation can potentially provide an escape opportunity and this is experimentally investigated.
  • MAEDA Kyouhei, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report. Antennas and propagation  111-  (288)  1  -6  2011/11/16  [Not refereed][Not invited]
     
    Recently, with the spreading of wireless communication technology, importance of a precise direction of arrival (DOA) estimation technology becomes larger in order to investigate propagation environments or determine terminal's positions. An array antenna is used in general DOA estimation algorithms. In a case where antenna element positions of the array are fixed, the higher frequency signal is used, the higher resolution DOA estimation is obtained. However, calculation load increases because we must calculate MUSIC spectra with a narrow angle step. Also, grating lobes occur when using high frequency signals for a fixed element interval. The authors have proposed the DOA estimation method based on the MUSIC algorithm using wide-band signals to solve these problems. First, coarse DOA is estimated at the lowest frequency band where grating lobes do not appear. Next, precise DOA estimation is done at a higher frequency band in a narrower search range to prevent grating lobes and increase of calculation load. In this paper, to estimate DOA using higher frequency signals while avoiding grating lobes, we optimize the frequency, search range, step width.
  • MAEDA Kyouhei, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  電子情報通信学会技術研究報告. A・P, アンテナ・伝播  111-  (288)  1  -6  2011/11/09  [Not refereed][Not invited]
  • KOBAYASHI Takuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  111-  (289)  185  -190  2011/11/09  [Not refereed][Not invited]
     
    In future mobile communication, we need wider frequency bandwidth transmission in a higher frequency band. However, the propagation loss increases in a high frequency band. It causes a degradation of communication quality. Especially for an uplink channel, the transmission power is limited because the power is supplied by the battery. Then, it has been proposed that a communication terminal cooperates with nearby terminals to solve this problem. The virtual MIMO-based cooperative communication using a single carrier in a narrow bandwidth has been examined in detail. In this paper, we evaluate the characteristics of the virtual MIMO-based cooperative communication using OFDM.
  • KIYOMI Naohito, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  111-  (289)  203  -208  2011/11/09  [Not refereed][Not invited]
     
    Data transmission through relay nodes has been studied as a method to improve transmission quality in wireless mesh networks and cellular systems. Multiple antenna elements at a source node enable adaptive beamforming and thus improve total performance of the relay transmission. In this paper, we propose simple transmit beamforming at a source node when the source node has two or more antenna elements and knows all channel information in MISO/MIMO amplify-and-forward relay with direct link and evaluate the packet error rate.
  • WEBBER Julian, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  電子情報通信学会大会講演論文集  2011-  (1)  2011/08/30  [Not refereed][Not invited]
  • Davidescu Cristian, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2011-  (1)  2011/08/30  [Not refereed][Not invited]
  • KIYOMI Naohito, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  2011-  (1)  508  -508  2011/08/30  [Not refereed][Not invited]
  • Takeda Daiki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2011-  (1)  509  -509  2011/08/30  [Not refereed][Not invited]
  • CHOI Heedong, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the Society Conference of IEICE  2011-  (1)  "S  -27"-"S-28"  2011/08/30  [Not refereed][Not invited]
  • TAKEDA Daiki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  111-  (68)  1  -6  2011/05/19  [Not refereed][Not invited]
     
    The interference between nearby links in a wireless multihop network degrades the area spectral efficiency. Thus there have been many works on a use of narrow beam antenna or adaptive array capable of forming nulls. In specific, the adaptive array allows the multiple links within a limited area by suppressing the interference among those. However, efficient routing is required to exploit the benefit. In the paper, the system throughput performance is evaluated under a partially-ideal routing, and the potential ability of the adaptive array is indicated.
  • MAEDA Kyouhei, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report  111-  (29)  65  -70  2011/05/05  [Not refereed][Not invited]
     
    Recently, according to rapid spreading of cellular phones and wireless LAN equipment, importance of a precise direction of arrival (DOA) estimation technology becomes larger in order to investigate propagation environments or determine terminal's position. Generally, an array antenna with an estimation is used for the DOA estimation algorithm. In a case where the element position of array antenna is fixed, the higher frequency signal is used, the higher resolution DOA estimation is. However, calculation load increases because we must treat MUSIC spectra which have a narrow angle step and grating lobes occur by using high frequency signals for a fixed element interval. The authers have proposed the precise DOA estimation method using wide-band signals. In the beginning, coarse DOA is estimated at the lowest frequency band that grating lobes do not appear. Next, precise DOA estimation is done at higher frequency band in a narrower angle range in order to prevent grating lobes and calculation load. In this paper, we propose a method that can prevent grating lobes much effectively by changing adaptively the band in higher frequencies. We evaluated the performance of the technique using computer simulations. From the computer simulations, we show the highly accuracy of the proposed method.
  • Sada Tomoki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2011-  (1)  477  -477  2011/02/28  [Not refereed][Not invited]
  • SHIMODA Yusuke, KISHIYAMA Yoshihisa, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  110-  (433)  319  -323  2011/02/23  [Not refereed][Not invited]
     
    In the downlink of Long Term Evolution (LTE), it is planned to apply multiuser MIMO (MU-MIMO) systems for system capacity improvement. MU-MIMO transmission requires pre-coding at the transmitter side to decrease interference between users. In LTE, a code-book describing pre-coding matrices is defined. Thus, the user equipment is allowed to feed back the pre-coding matrix indicator only. In this paper, we consider a time-variant fading channel and evaluate the performance of pre-coding prediction to reduce degradation due to processing delay.
  • SADA Tomoki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  110-  (368)  7  -12  2011/01/13  [Not refereed][Not invited]
     
    In a downlink (broadcast channel) of multiuser MIMO systems, we need to suppress the inter-user interference (IUI). It is known that block diagonalization and MMSE precoding are typical schemes for IUI suppression. In addition, we have proposed generalized block diagonalization (GBD) to achieve both high transmit diversity gain and IUI space limiting with a partial nulling concept. In this paper, we evaluate the impact of channel estimation error on the these precoding methods by computer simulations for BER performance.
  • MATSUYA Sakiko, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  110-  (368)  173  -178  2011/01/13  [Not refereed][Not invited]
     
    Recently, wireless relay systems have been discussed to achieve a flexible network for connecting ubiquitous communication terminals. Network coding that encodes the packets using XOR in the relay node reduces the number of transmission packets and thus improves throughput performance in the network. In our previous papers, we investigated beamforming techniques at the relay node for multicasting the network-coded data and proposed the capacity-maximizing criterion. In this paper, we expand the system model to a MIMO relay and propose a simple beamforming criterion. The high performance has been numerically confirmed.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  APSIPA ASC 2011 - Asia-Pacific Signal and Information Processing Association Annual Summit and Conference 2011  2011
  • Kyouhei Maeda, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane  IEEE Antennas and Propagation Society, AP-S International Symposium (Digest)  835  -838  2011  [Not refereed][Not invited]
     
    The method to estimate direction of arrival (DOA) with multi-band signals is proposed in this paper. The MUSIC method, which is one of the conventional super-resolution DOA estimation methods, is applied to sets of snapshots filtered from the multi-band signal. In the beginning, a set of snapshots is extracted by the narrow-band filter (NBF) for the lowest frequency where the half wavelength of center frequency equals the array antenna spacing for a uniform linear array, and processed by the MUSIC method in order to avoid grating lobes. Next, using another set of snapshots in higher frequency, more precise DOA estimation is done in a narrower range with finer step angle. Therefore, this method can realize more accurate DOA estimation than the conventional method using a single set of snapshots. By examining RMSE and success probability of DOA detection, this method is compared with a conventional method. © 2011 IEEE.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  2011 the 14th International Symposium on Wireless Personal Multimedia Communications: Communications, Networking and Applications for the Internet of Things, WPMC'11  1  -5  2011  [Refereed][Not invited]
  • Takeda, Daiki, Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  2011 the 14th International Symposium on Wireless Personal Multimedia Communications: Communications, Networking and Applications for the Internet of Things, WPMC'11  1  -5  2011  [Refereed][Not invited]
  • ITO Tatsuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  110-  (339)  43  -48  2010/12/09  [Not refereed][Not invited]
     
    In future cellular radio, we need to transmit signals in a higher frequency band to accommodate a wider frequency bandwidth. The higher a frequency band is, the larger the propagation loss is. Also, a wider frequency bandwidth requires higher transmission power. For an uplink channel, however, the transmission power is limited because the power is supplied by the terminal battery. Thus, we will encounter a difficulty in sending uplink signals. The authors have proposed virtual MIMO-based cooperative communication to solve this problem. In this paper, we clarify bit error rate and packet error rate performances for various conditions. We evaluate the required transmission power. It has been shown that the virtual MIMO system requires lower transmission power than the conventional SIMO scheme.
  • BUI Huu Phu, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  110-  (267)  47  -52  2010/11/03  [Not refereed][Not invited]
     
    A downlink multi-user MIMO system uses a block diagonalization scheme to suppress inter-user interference. Furthermore, the system can realize efficient transmission using eigenbeam-space division multiplexing. In time-varying environments, however, bit error rate (BER) performance seriously degrades because MIMO channels change during the time interval between transmission parameter determination and actual MIMO transmission. Channel prediction techniques have been proposed to improve the BER performance in dynamic environments. In this paper, based on indoor measurement data, we evaluate the BER performance of the downlink multiuser MIMO system with linear extrapolation and second order extrapolation.
  • Sada Tomoki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2010-  (1)  367  -367  2010/08/31  [Not refereed][Not invited]
  • Shimoda Yusuke, Nishimura Yoshihisa, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2010-  (1)  371  -371  2010/08/31  [Not refereed][Not invited]
  • Ito Tatsuya, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2010-  (1)  "S  -9"-"S-10"  2010/08/31  [Not refereed][Not invited]
  • BUI Huu Phu, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  110-  (135)  7  -12  2010/07/14  [Not refereed][Not invited]
     
    A multi-user MIMO system which simultaneously accommodates multiple users uses a block diagonalization scheme to suppress inter-user interference. Also, it can use an eigenbeam-space division multiplexing technique for efficient transmission. However, in time-varying environments, we may have performance degradation because of a channel change during the time interval between multi-user MIMO parameter determination and actual transmission. In this paper, on the basis of time-varying indoor measurements, we show Doppler spectra and average bit error rates (BERs). We also show that time-varying channels seriously degrade the BER performance.
  • ITO Tatsuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  110-  (127)  125  -130  2010/07/08  [Not refereed][Not invited]
     
    In future cellular radio, we need to transmit signals in a higher frequency band to accommodate a wider frequency bandwidth. The higher a frequency band is, the larger the propagation loss is. Also, a wider frequency bandwidth requires higher transmission power. For an uplink channel, however, the transmission power is limited because the power is supplied by the terminal battery. Thus, we will encounter a difficulty in sending uplink signals. Virtual MIMO-based cooperative communication is expected to be a key technology to solve this problem. In this paper, we clarify bit error rate and packet error rate performances on the basis of a realistic propagation channel model. We evaluate the required transmission power. It has been shown that the virtual MIMO system requires lower transmission power than the conventional SIMO scheme.
  • SADA Tomoki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  110-  (127)  161  -166  2010/07/08  [Not refereed][Not invited]
     
    In the downlink(broadcast channel)of multiuser MIMO systems, we need to suppress the inter-user interference(IUI). Block diagonalization(BD)which achieves perfect nulling is noted as an effective solution. In addition, imperfect block diagonalization(IBD)has been proposed previously as one of the solutions. The IBD can obtain transmit diversity gain by partial nulling. In this paper, we unify approaches of BD and IBD into generalized BD(GBD). In the paper, the BER performance of the GBD is evaluated by computer simulations.
  • NOBA Toshihiro, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  110-  (1)  47  -51  2010/04/02  [Not refereed][Not invited]
     
    Some techniques using intelligent transport systems have been studied to prevent traffic accidents whose victims are a pedestrian. We have studied a scheme that informs a driver of a pedestrian's position using an electromagnetic wave radiated from the pedestrian's RFID tag. Although the direction-of-arrival (DOA) of a direct wave indicates the direction of the pedestrian, it is, however, difficult to estimate the DOA under multipath fading environments. Therefore, we have used a simple technique we proposed for DOA estimation. Using multiple antennas with the spacing of 1.5 wavelengths, we receive signals that experience different fading due to vehicle motion. If we beamform towards the direction of the direct wave, we can expect to compute the maximum average power because its signal is the largest and the multipath components are reduced by the array. Using received horizontally-polarized signals, we then beamform towards multiple directions, and the direction that gives the maximum average power indicates the direction of the pedestrian. Since the antenna spacing is larger than a half wavelength, we have grating lobes and may have false detections. In this paper, we propose a scheme to cope with the grating lobe problem.
  • MATSUYA Sakiko, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2010-  (1)  466  -466  2010/03/02  [Not refereed][Not invited]
  • Sada Tomoki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2010-  (1)  491  -491  2010/03/02  [Not refereed][Not invited]
  • Nishimoto H., Hirai H., Taira A., Kubo H., Nishimura T., Ohgane T., Ogawa Y.  Proceedings of the IEICE General Conference  2010-  (1)  501  -501  2010/03/02  [Not refereed][Not invited]
  • NOBA Toshihiro, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  109-  (440)  29  -34  2010/02/24  [Not refereed][Not invited]
     
    Information transmission between a controller and a machine is essential for reliable factory automation. To help facilitate this, wireless communication is useful in the building of flexible factory environments because it does not need cables. The wireless system can employ an OFDM LAN technique. However, in a case where a plurality of communication systems are used in a neighborhood, we may have mutual interference among them. This paper describes a smart antenna for the interference reduction. We examine two weight control schemes: one is based on channel estimation, and the other is the SMI algorithm. We show cumulative distributions of SINR and average BERs of the smart antenna.
  • SHIBATA Koji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  109-  (440)  427  -432  2010/02/24  [Not refereed][Not invited]
     
    OFDM has a problem of high peak to average power ratio (PAPR) whereas it is tolerant to the frequency selective fading. As a countermeasure for the high PAPR problem, partial transmit sequence (PTS) giving different phase rotation to segmented blocks has been proposed. However, PTS requires side information on the phase rotation. Previously, we proposed a simple blind detection based on the M-algorithm with very low complexity. The blind detection performance is highly affected by phase rotation candidates. In this paper, we propose the search technique of the proper phase rotation for blind detection. Also, we examine the impact of channel estimation error and signal distortion on the blind detection performance.
  • SAITO Keisuke, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  109-  (440)  443  -448  2010/02/24  [Not refereed][Not invited]
     
    Frequency-domain equalization (FDE) and frequency-domain turbo equalization (FDTE) based on iterative decoding have been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. To solve this problem, we have proposed a channel approximation and tri-diagonalizing approach to FDE and FDTE without strict calculation and ascertained the validity of our proposal by computer simulations. As a realistic scenario, in this paper, we introduce channel estimation and evaluate the impact of the channel estimation error on the equalizing performance.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  APSIPA ASC 2010 - Asia-Pacific Signal and Information Processing Association Annual Summit and Conference  2010
  • Huu Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane  2010 IEEE 72ND VEHICULAR TECHNOLOGY CONFERENCE FALL  1  -5  2010  [Refereed][Not invited]
     
    In the paper, we examine Doppler spectrum and bit-error rate (BER) performance of multiuser MIMO systems in an indoor time-varying environment based on our measured data conducted in a meeting room. Simulation results show that both Doppler spectrum and the BER performance are much dependent on the array orientation and the direction of the receiver motion. In the non-line-of-sight environment, the actual Doppler spectrum is quite different from the theoretical U-shaped spectrum in the Jakes' model. In addition, it has been shown that the BER performance is much degraded due to a channel change.
  • Sakiko Matsuya, Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa  2010 IEEE 21ST INTERNATIONAL SYMPOSIUM ON PERSONAL INDOOR AND MOBILE RADIO COMMUNICATIONS (PIMRC)  2093  -2098  2010  [Refereed][Not invited]
     
    Wireless relay is an essential technology to achieve a flexible network for ubiquitous communication. To improve throughput performance in the network, network coding (NC) has been proposed for a two-user relay node. NC is a concept encoding both users' data into one packet and multicasting it simultaneously. However, if the relay node has two or more antenna elements, antenna pattern control is additionally required to send the packet efficiently to both users. In this paper, we formulate several transmit-beamforming techniques in the interactive wireless relay system and compare the performance with each other and with non-NC systems. Numerical analysis has shown that the method maximizing the total capacity in NC provides the best performance.
  • Tomoki Sada, Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa  2010 IEEE 21ST INTERNATIONAL SYMPOSIUM ON PERSONAL INDOOR AND MOBILE RADIO COMMUNICATIONS (PIMRC)  504  -509  2010  [Refereed][Not invited]
     
    In multiple input multiple output (MIMO) systems, multiuser enhancement is in the implementation phase. Block diagonalization (BD) is known as the safest technique for the multiuser MIMO downlink since it suppresses the inter-user interference (IUI) perfectly. However, BD consumes most of the transmit antenna resource to form many nulls. Thus, it is very difficult to obtain the transmit diversity gain. In the paper, the adaptive selection of the number of layers is considered. Such approaches have been limited to iterative beamforming. Here, we formulate deterministic transmit beamforming as a generalized approach to the BD (GBD), based on a concept of projecting the IUI to a limited vector space. Our proposal can efficiently utilize the extra degrees of freedom, which are obtained in exchange for reducing the number of layers, to provide the diversity gain in the transmit beamforming. The high capability of the GBD is confirmed by computer simulations.
  • ITO Tatsuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  109-  (305)  73  -78  2009/11/19  [Not refereed][Not invited]
     
    A higher frequency band is considered to be used for future mobile communications for broadband transmission. However, propagation loss increases at a higher frequency band. The transmission will be difficult in an uplink channel because of limited transmit power of terminals. To solve the problem, cooperative communication has drawn attention. We have proposed a virtual MIMO system where neighboring terminals cooperate each other and form transmit beams as a distributed antenna system. In this paper, we examine frequency offset estimation performance and BER versus transmit power in dynamic fading environments. It has been clarified that the advantage of the virtual MIMO system decreases in dynamic fading environments. The reason for this is considered to be that transmit parameters cannot be determined properly because the channel at transmission time is not obtained exactly.
  • MATSUYA Sakiko, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  109-  (305)  25  -30  2009/11/19  [Not refereed][Not invited]
     
    Recently, wireless relay systems have been investigated to achieve a flexible network for ubiquitous communication. Network coding that encodes the packets using XOR in the relay node is expected to reduce the number of transmission packets and to improve throughput performance in the network. In this paper, we propose the transmit beamforming technique when the relay node has two or more antenna elements in the interactive wireless relay system and evaluate the packet error rate and throughput performance.
  • ITO Tatsuya, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  109-  (305)  73  -78  2009/11/19  [Not refereed][Not invited]
     
    A higher frequency band is considered to be used for future mobile communications for broadband transmission. However, propagation loss increases at a higher frequency band. The transmission will be difficult in an uplink channel because of limited transmit power of terminals. To solve the problem, cooperative communication has drawn attention. We have proposed a virtual MIMO system where neighboring terminals cooperate each other and form transmit beams as a distributed antenna system. In this paper, we examine frequency offset estimation performance and BER versus transmit power in dynamic fading environments. It has been clarified that the advantage of the virtual MIMO system decreases in dynamic fading environments. The reason for this is considered to be that transmit parameters cannot be determined properly because the channel at transmission time is not obtained exactly.
  • SADA Tomoki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  109-  (229)  37  -42  2009/10/08  [Not refereed][Not invited]
     
    In the downlink (broadcast channel) of the multiuser MIMO system, suppression of inter-user interference (IUI) is an important issue to be solved. Due to the limitated antenna resources, it is difficult to implement the IUI cancellation at the terminal side. Thus, reduction of undesired radiation by a certain beam-control is preferable. The imperfect block diagonalization (IBD) has been proposed previously as one of the solutions. In the paper, we extend the IBD to be capable of multi-stream transmission per user and evaluate the BER performance using computer simulations.
  • Webber Julian, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings : APSIPA ASC 2009 : Asia-Pacific Signal and Information Processing Association, 2009 Annual Summit and Conference  684  -687  2009/10/04  
    APSIPA ASC 2009: Asia-Pacific Signal and Information Processing Association, 2009 Annual Summit and Conference. 4-7 October 2009. Sapporo, Japan. Poster session: Signal Processing and Implementations in Communications (6 October 2009).
  • Sada Tomoki, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2009-  (1)  398  -398  2009/09/01  [Not refereed][Not invited]
  • Ito Tatsuya, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2009-  (1)  399  -399  2009/09/01  [Not refereed][Not invited]
  • MATSUYA Sakiko, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  2009-  (1)  404  -404  2009/09/01  [Not refereed][Not invited]
  • Shibata Koji, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2009-  (1)  411  -411  2009/09/01  [Not refereed][Not invited]
  • Saito Keisuke, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2009-  (1)  437  -437  2009/09/01  [Not refereed][Not invited]
  • SHIBATA Koji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  109-  (130)  125  -130  2009/07/09  [Not refereed][Not invited]
     
    OFDM has a problem of high peak to average power ratio (PAPR) whereas it is tolerant to the frequency selective fading. As a countermeasure for the high PAPR problem, partial transmit sequence (PTS) giving different phase rotation to segmented blocks has been proposed. However, PTS requires side information on the phase rotation. Previously, we proposed a simple blind detection based on the M-algorithm with very low complexity. However, some degradation has been observed when the constraint length of the convolutional code is long. In the paper, as the countermeasure we evaluate the case with two survivor paths in M-algorithm in addition to the bi-directional search.
  • SAITO Keisuke, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  109-  (130)  119  -124  2009/07/09  [Not refereed][Not invited]
     
    Frequency-domain equalization (FDE) and frequency-domain turbo equalization (FDTE) based on iterative decoding have been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. To solve this problem, we propose a tri-diagonalizing approach to FDE and FDTE without strict calculation and evaluate our proposal by computer simulations.
  • NOBA Toshihiro, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo, TANAKA Makoto, SASAKI Kunihiko  IEICE technical report  109-  (117)  177  -182  2009/07/01  [Not refereed][Not invited]
     
    Some techniques using intelligent transport systems have been studied to prevent traffic accidents whose victims are a pedestrian. We have studied a scheme that informs a driver of a pedestrian's position using an electromagnetic wave radiated from the pedestrian's RFID tag. Although the direction-of-arrival (DOA) of a direct wave indicates the direction of the pedestrian, it is, however, difficult to estimate the DOA under multipath fading environments. This paper proposes a simple technique for DOA estimation. Using multiple antennas, we receive signals that experience different fading due to vehicle motion. If we beamform towards the direction of the direct wave, we can expect to compute the maximum average power because its signal is the largest and the multipath components are reduced by the array. Using the received data, we then beamform towards multiple directions, and the direction that gives the maximum average power indicates the direction of the pedestrian. Conducting computer simulations, we show the performance of the proposed scheme.
  • Shibata Koji, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2009-  (1)  503  -503  2009/03/04  [Not refereed][Not invited]
  • Nishimoto Hiroshi, Sogabe Yasushi, Shibuya Akihiro, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2009-  (1)  489  -489  2009/03/04  [Not refereed][Not invited]
  • Saito Keisuke, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2009-  (1)  484  -484  2009/03/04  [Not refereed][Not invited]
  • SAITO Yuta, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko  IEICE technical report  108-  (445)  65  -70  2009/02/25  [Not refereed][Not invited]
     
    A higher frequency band is considered to be used for future mobile communications. However, reliable transmission may not be possible in an uplink channel because of limited transmit power of terminals. We can improve uplink transmission performance using a virtual antenna array which is formed by multiple terminals cooperating with each other. However, because we have neglected the power for sharing data among the terminals in our previous studies, a fair comparison with a non-cooperating system has not been done. In this paper, we consider total transmit power required for a virtual MIMO system and compare the characteristic with that of non-cooperating system in variety of propagation environments.
  • QIN Fei, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  108-  (390)  201  -205  2009/01/15  [Not refereed][Not invited]
     
    Frequency domain turbo equalization with soft canceller is a powerful way to reduce the inter-symbol interference in a frequency selective fading channel for single-carrier systems. When applying the frequency domain turbo equalization to a Type-I HARQ system, chase combining with parallel turbo-equalizers using multiple received packets achieves a significant improvement of throughput performance at a cost of heavy load. In the paper, the performance of the complexity reduction method previously proposed by the authors is analyzed. And, improved methods for complexity reduction is proposed.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  APSIPA ASC 2009 - Asia-Pacific Signal and Information Processing Association 2009 Annual Summit and Conference  2009
  • Noba Toshihiro, Ogawa Yasutaka, Nishimura Toshiihko, Ohgane Takeo, Tanaka Makoto, Sasaki Kunihiko  Proceedings of the IEICE General Conference  228  -228  2009  [Not refereed][Not invited]
  • Morikawa Hiroaki, Nishimura Toshihiko, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  209  -209  2009  [Not refereed][Not invited]
  • 小川 恭孝, 大鐘 武雄, 西村 寿彦  B-plus  (11)  12  -49,1  2009  [Not refereed][Not invited]
  • Koji Shibata, Julian Webber, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa  GLOBECOM 2009 - 2009 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, VOLS 1-8  2705  -2710  2009  [Refereed][Not invited]
     
    PAPR reduction is an important issue in wireless OFDM transmission. Partial transmit sequence (PTS) is one of the distortionless methods. However, PTS requires side information on the phase rotation. This impacts not only the transmit efficiency but also the standardization process. Thus, blind detection without side information is expected as a solution to implement PTS. In the paper, simple blind detection with very low complexity is proposed. The computer simulation results indicate that the proposal gives almost the same performance as one with perfect side information by selecting a proper set of phase rotation candidates.
  • Webber, Julian, Nishimura, Toshihiko, Ohgane, Takeo, Ogawa, Yasutaka  2009 IEEE 20TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS  1039  -1043  2009  [Refereed][Not invited]
     
    System performance can be improved when channel state information is fed-back to the transmitter, and multiple-input multiple-output (MIMO) systems can realize eigenbeam-space division multiplexing (E-SDM). Pseudo E-SDM offers both reduced complexity (the mean number of multiplications is reduced to about 1/10 for 4x4 MIMO) and a reduction in the effective channel delay spread compared to E-SDM. This work describes a real-time MIMO orthogonal frequency division multiplexing (OFDM) system based on the IEEE802.11n standard. A channel emulator developed using the modified Jakes model provides the fading channels to appraise the algorithm.
  • Huu Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane  2009 IEEE 20TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS  2459  -2463  2009  [Refereed][Not invited]
     
    In the paper, performance of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) eigenbeam-space division multiplexing (E-SDM) systems using uniform circular antenna arrays is evaluated. We conducted a MIMO channel measurement campaign at a 5.2 GHz frequency band in an indoor fading environment. Simulation results based on the measured data have shown that differently from the linear array, the BER performance of the circular array is almost the same for the array orientation. It is also shown that the performance can be degraded due to a channel change during the time delay between the transmit weight matrix determination and the actual data transmission. To compensate for the channel change, we have proposed two methods of channel extrapolation. Applying the proposed methods, robust performance can be obtained.
  • Yuta Saito, Yasutaka Ogawa, Takeo Ohgane, Toshihiko Nishimura  2009 IEEE VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5  1084  -1088  2009  [Refereed][Not invited]
     
    In future cellular radio such as IMT-advanced systems, we will encounter a difficulty in sending uplink signals. This is because transmit power is limited by a battery in a terminal and we need higher transmit power to accommodate a wider frequency bandwidth in a higher frequency band. Virtual MIMO-based cooperative communication is expected to be a key technology to solve this problem. Especially, if we have a feedback path from the basestation to send the transmit parameters, we can achieve much better performance. However, each terminal has an independent oscillator, and we have inevitably carrier frequency offsets. This causes performance degradation. This paper proposes a transmission scheme compensating for the frequency offsets and multi-stream transmission using eigenbeam space division multiplexing (E-SDM). Furthermore, this paper describes the reduction of feedback amount from a basestation. From computer simulation results, it will be shown that the proposed transmission technique has excellent performance.
  • SHIBATA Koji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  108-  (249)  7  -12  2008/10/15  [Not refereed][Not invited]
     
    OFDM has a problem of high peak to average power ratio (PAPR) whereas it is tolerant to the frequency selective fading. As a countermeasure for high PAPR problem, partial transmit sequence (PTS) giving different phase rotation to segmented blocks has been proposed. However, PTS requires inverse phase rotation at the receiver side for corrent detection. Thus, an extra subchannel for side information transmission is needed. in the paper, a blind detection based on the parallel trellis decoding under the use of a convolutional code is proposed. And, its high performance has been confirmed by computer simulations.
  • SAITO Yuta, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the Society Conference of IEICE  2008-  (1)  "S  -3"-"S-4"  2008/09/02  [Not refereed][Not invited]
  • QIN Fei, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  2008-  (1)  371  -371  2008/09/02  [Not refereed][Not invited]
  • BUI Huu Phu, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  108-  (188)  19  -24  2008/08/27  [Not refereed][Not invited]
     
    In the paper, we present our measurement campaigns in a typical meeting room to get multiuser multiple-input multiple-output (MIMO) channels. Based on the data, the performance of multiuser MIMO systems employing the block-diagonalization (BD) scheme and the eigenbeam-space division multiplexing (E-SDM) technique for downlink transmission is evaluated in actual time-varying fading environments. Simulation results show that due to a channel change during the time interval between the transmit weight matrix determination and the actual downlink data transmission, the performance is much degraded because of inter-user and inter-substream interference. Here, we propose two methods of channel extrapolation, linear extrapolation and second-order extrapolation, to compensate for the channel change. Simulation results show that applying the proposed methods to the systems, much better performance can be obtained.
  • SAITO Yuta, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  108-  (188)  25  -30  2008/08/27  [Not refereed][Not invited]
     
    A higher frequency band is considered to be used for future mobile communications. However, reliable transmission may not be possible in an uplink channel because of limited transmit power of terminals. We can improve uplink transmission performance using a virtual antenna array which is formed by multiple terminals cooperating with each other. However, in this system, the terminals need information about transmit weight, frequency offset, and transmit power ratio from a base station. The feedback of the information from a base station limits downlink transmission. In this paper, we propose a codebook for transmit weight, and quantization of frequency offset and transmit power ratio. We examine the impact of them on the bit error rate performance.
  • QIN Fei, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  108-  (188)  151  -156  2008/08/27  [Not refereed][Not invited]
     
    Frequency domain turbo equalization with soft canceller is a powerful way to reduce the inter-symbol interference in a frequency selective fading channel for single-carrier systems. In the paper, the frequency domain turbo equalization is applied to an HARQ system and its throughput performance is confirmed. In addition, several simplified methods of chase combining for multiple received packets is proposed. The computer simulation results show that the performance degradation due to simplifying is not significant.
  • BUI Huu Phu, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  108-  (148)  129  -134  2008/07/16  [Not refereed][Not invited]
     
    The main contribution of the paper is to investigate channel charateristics based on measured data in a typical meeting room and to evaluate the performance of MIMO systems using an eigenbeam-space division multiplexing (E-SDM) technique in actual time-varying fading environments. Results based on the measured channel data show that channel auto-correlation and Doppler spectrum are much dependent not only on the direction of terminal motion, but also on the antenna configuration. Even in the non-line-of-sight environment, observed Doppler spectrum is quite different from the theoretical U-shaped Jakes one. In addition, it has been also shown that a channel change during the time interval between the transmit weight matrix determination and the actual data transmission can degrade the performance of MIMO E-SDM systems.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  107-  (518)  193  -198  2008/03/05  [Not refereed][Not invited]
     
    When the transmitter maps a bit-interleaved coded sequence into DPSK symbols, turbo (iterative) decoding is applicable at the receiver by regarding a differential encoder in DPSK as an inner encoder, i.e., serial concatenation of two encoders. In this paper, we examine blind iterative decoding in a bit-interleaved coded DPSK system. We also propose a blind channel estimation scheme based on decision feedback because coherent detection is required for the iterative decoding. The result obtained by computer simulations shows that performance of the iterative decoding significantly outperforms that of coherent PSK with perfect CSI. In addition, it is demonstrated that the proposed channel estimation scheme provides the performance approaching to that of the perfect CSI case by 0.1dB and 0.9dB in no fading and dynamic fading environments, respectively, at BLER of 10^<-2>.
  • KATO Shohei, NISHIMOTO Hiroshi, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko  IEICE technical report  107-  (518)  329  -334  2008/03/05  [Not refereed][Not invited]
     
    Recently, a multiuser MIMO system has attracted much attention. In the downlink of the multiuser MIMO system, since the base station simultaneously transmits signals to terminals, there is inter-user interference (IUI) at each terminal. Block diagonalization, which can achieve perfect IUI supression, has been extensively studied to solve the issue. However, with the scheme we cannot obtain sufficient diversity gain due to the null steering at the base station. In this paper, we propose imperfect block diagonalization based on maximum eigenvectors of users and Gram-Schmidt orthonormalization, and its error rate performance is evaluated using computer simulation. The result shows that, despite its low complexity, the proposed scheme provides excellent performance, especially in many user environments.
  • KIM Sang-Woo, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  107-  (438)  85  -90  2008/01/17  [Not refereed][Not invited]
     
    OFDM is an attractive system for high spectral efficiency and capability of multipath fading compensation. In high-speed fading environments, however, channel tracking during the data period becomes a substantial technique to maintain good BER performance since channel change from the initial estimate using preamble symbols cannot be ignored. In this paper, we focus on the decision feedback channel tracking and propose a way to generate more accurate replicas by switching the decoder output based on a property of concatenated codes. In addition, we introduce a linear prediction method with two different techniques for the estimate of prediction coefficients. The simulation results show the effectiveness of these proposed methods under an IEEE 802.16e-OFDM model with 250Hz and higher Doppler frequency.
  • WEBBER Julian, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka  光電技報  (24)  2008
  • Huu Phu Bui, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane  GLOBECOM 2008 - 2008 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE  3303  -3307  2008  [Refereed][Not invited]
     
    In the paper, performance of multiuser multiple-input multiple-output eigenbeam-space division multiplexing (ESDM) systems in the downlink transmission is evaluated in both uncorrelated and correlated time-varying fading environments based on computer-generated data. In the ideal case, using the block diagonalization (BD) scheme, inter-user interference can be completely eliminated at each user; and using the E-SDM technique for each user, optimal resource can be allocated, and spatially orthogonal substreams can be obtained. In realistic environments, however, due to the dynamic nature of the channel and the processing delay at both the transmitter and the receiver, the channel change during the delay may cause existence of inter-user interference even if the BD scheme is used. In addition, the change may also result in large inter-substream interference and no longer lead the allocated data resource for each user to the optimal condition. As a result, system performance may be degraded seriously. To overcome the problem, we propose a method of channel extrapolation to compensate for the channel change. Applying our proposed method, simulation results show that much better system performance can be obtained than the conventional case.
  • Hiroshi Nishimoto, Shohei Kato, Yasutaka Ogawa, Takeo Ohgane, Toshihiko Nishimura  IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC  1  -5  2008  [Refereed][Not invited]
     
    Recently, a multiuser MIMO system has attracted much attention. In the downlink of the multiuser MIMO system, since the base station simultaneously transmits signals to terminals, there is inter-user interference (IUI) at each terminal. Block diagonalization, which can achieve perfect IUI suppression, has been extensively studied to solve the issue. However, with the scheme we cannot obtain extra diversity gain due to the null steering at the base station. In this paper, we propose imperfect block diagonalization based on maximum eigenvectors of users and Gram-Schmidt orthonormalization, and its error rate performance is evaluated using computer simulations. The result shows that, despite its low complexity, the proposed scheme provides excellent performance, especially in many-user environments. © 2008 IEEE.
  • KAMBARA Keiichi, NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  107-  (402)  37  -42  2007/12/13  [Not refereed][Not invited]
     
    Frequency-domain equalization (FDE) has been studied as a very simple countermeasure against frequency selective fading in a single carrier transmission system. In a fast fading environment, however, the equalization performance degrades since periodicity of the channel within an FDE block is lost. Therefore, we have proposed a method dividing a received data block into multiple subblocks to decrease the channel transition within the block in such an environment. In this method, the performance is degraded by inaccuracies of pseudo CP processing, which is introduced to satisfy periodicity in each subblock. In this paper, we study the application of frequency-domain turbo equalization (FDTE) to subblock processing for improving the accuracy of pseudo CP. The simulation results show that FDTE with subblock processing yields remarkable performance improvements.
  • SAITO Yuta, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko  IEICE technical report  107-  (305)  31  -36  2007/11/01  [Not refereed][Not invited]
     
    Recently, a virtual antenna array, which is formed by multiple terminals cooperating each other, has attracted attention because it can potentially improve uplink capacity in high-frequency-band communications. However, since it is difficult in practice to accurately synchronize carrier frequencies at the terminals, performance is degraded due to frequency offsets. In this paper, we propose a method to estimate frequency offsets and to conpensate them at the terminals. Also, this paper describes a receive weight tracking scheme by the RLS algorithm at a basestation. Then, we evaluate the BER performance by computer simulations. The simulation results show performance improvements by applying these techniques.
  • HIGASHINAKA Masatsugu, KUBO Hiroshi, SHIBUYA Akihiro, OKAZAKI Akihiro, OGAWA Yasutata, OHGANE Takeo, NISHIMURA Toshihiko  IEICE technical report  107-  (262)  1  -6  2007/10/11  [Not refereed][Not invited]
     
    This paper proposes a channel estimation method with ordered interference cancellation for a MIMO receiver using iterative equalization and decoding. In the iterative receiver, channel estimation can be performed in every iteration by using symbol estimates composed of extrinsic information from a soft-output decoder. In the MIMO case, however, data sequences transmitted from each transmit antenna are not always applicable to the iterative channel estimation because the transmitted data sequences may be not suitable for the channel estimation. The proposed channel estimation method performs ordered interference cancellation and then estimates the channel state information for a residual stream, reffering to a decoder output. Computer simulation confirms that the proposed method has excellent frame error rate performance.
  • NAITO A., NISHIMURA T., OHGANE T., OGAWA Y.  IEICE technical report  107-  (262)  19  -24  2007/10/11  [Not refereed][Not invited]
     
    We can realize high-speed communications with MIMO systems that have multiple antennas at both transmitter and receiver. For a downlink channel in a MIMO system, we apply E-SDM using adaptive modulation in which communication speed is changed according to the channel condition. In this case, assuming packet transmission, we apply a maximum throughput criterion for the adaptive modulation. In this paper, we evaluate the throughput performance of E-SDM transmission with adaptive modulation by using an indoor testbed. Because computation load with conventional adaptive modulation is heavy, it is reduced by simplification. Additionally, we show that linear extrapolation that compensates errors caused by channel fluctuation works in dynamic fading environments.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  2007-  (1)  439  -439  2007/03/07  [Not refereed][Not invited]
  • OGAWA Kenta, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko  IEICE technical report  106-  (555)  65  -68  2007/02/28  [Not refereed][Not invited]
     
    Recently, the virtual antenna array, which is formed by multiple terminals cooperating each other, has attracted attention because it can potentially improve capacity in high-frequency-band communications. However, since it is difficult in practice to accurately synchronize the terminals, performance may be affected by phase and frequency offsets, which are caused by the imperfect synchronization. In this paper, we evaluate effects of the offsets and channel estimation errors on the system performance by computer simulations. The results show that degradation of performance can be reduced by using the equivalent channel, which includes both the actual channel and offsets, in processing at the receiver, and that performance in multi-beam transmission is more affected by the frequency offset compared with that in single-beam transmission.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  電子情報通信学会技術研究報告. RCS, 無線通信システム  106-  (480)  67  -72  2007/01/26  [Not refereed][Not invited]
  • OHWATARI Yusuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  電子情報通信学会技術研究報告. RCS, 無線通信システム  106-  (480)  73  -78  2007/01/26  [Not refereed][Not invited]
  • KAMBARA Keiichi, NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report  106-  (480)  7  -12  2007/01/26  [Not refereed][Not invited]
     
    Frequency domain equalization (FDE) has been studied for preventing performance degradation due to frequency selective fading in single carrier transmission. In fast fading environments, however, another problem occurs since cyclicity in the FDE block is lost. Thus, we have proposed subblock processing at the receiver side with pseudo cyclic prefix (CP) generation. The performance highly depends on the CP accuracy. Therefore, here, we apply a higher order interpolation method for more accurate channel estimation. In addition, overlapped subblock processing is used to reduce an effect of degradation in pseudo CP accuracy. The simulation results show performance improvements by applying these techniques to the subblock processing.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (480)  67  -72  2007/01/26  [Not refereed][Not invited]
     
    In a MIMO system with space-frequency domain beamforming under frequency selective fading scenarios, a pseudo eigenvector decomposition has been proposed to reduce the calculation load at the transmitter and to maintain frequency continuity of the effective channel observed at the receiver. It has been reported that a pseudo eigenbeam space division multiplexing (PE-SDM) technique can provide almost the same or better performance compared with eigenbeam space division multiplexing when the receiver employs a simple channel estimator exploiting pseudo-eigenvector properties. In this paper, focusing on the calculating process of pseudo eigenvectors, we propose a new scheme improving the accuracy of the effective channel estimates. The simulation results show that the accuracy in the PE-SDM is improved by combining the proposed scheme with the conventional one.
  • OHWATARI Yusuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  106-  (480)  73  -78  2007/01/26  [Not refereed][Not invited]
     
    In a multiple-input multiple-output system for OFDM (MIMO-OFDM), eigenbeam-space division multiplexing (E-SDM) which is also called a singular value decomposition (SVD) algorithm can provide maximum throughput in MIMO channels when channel state information (CSI) or transmit weight matrix is available at the transmitter. We have proposed a technique that only dominant time-domain CSI is fed back in order to reduce the amount of feedback. In this paper, we compare the proposed method to the scheme which feeds back the transmit weight matrix with a codebook.
  • K. Kambara, H. Nishimoto, T. Nishimura, Y. Ogawa, T. Ohgane  IEEE Vehicular Technology Conference  2190  -2194  2007  [Not refereed][Not invited]
     
    Frequency domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) caused by frequency selective fading in single carrier systems. When a high-mobility terminal exists in the system, channel state changes within a DFT block. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. Here, we propose to divide received data block into multiple subblocks to decrease the channel transition within the DFT block in fast fading environments. Also, to satisfy periodicity of the received signal in each subblock, we introduce a pseudo cyclic prefix technique. The results of numerical analysis show that the proposed method provides 1.3-fold increase in tolerable Doppler frequency for FER of 0.01. © 2007 IEEE.
  • SAITO Yuta, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko  Proceedings of the Society Conference of IEICE  201  -201  2007  [Not refereed][Not invited]
  • Kato Shohei, Nishimoto Hiroshi, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  202  -202  2007  [Not refereed][Not invited]
  • Kim Sang-Woo, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  337  -337  2007  [Not refereed][Not invited]
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa  2007 IEEE 66TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5  541  -545  2007  [Refereed][Not invited]
     
    In a frequency-selective MIMO channel, the optimum beamforming is achieved by using eigenvectors, i.e., eigenbeam-space division multiplexing (E-SDM), in the frequency domain. However, the calculation load of eigenvalue decomposition increases in proportion to the number of FFT points. In addition, eigenvectors without consideration of frequency continuity increase the delay spread of the effective channel observed at the receiver. To solve these issues, a pseudo eigenvector technique has been proposed. It has also been reported that a pseudo E-SDM (PE-SDM) technique can provide almost the same or better performance compared with the E-SDM when the receiver employs a simple channel estimator with time windowing. In this paper, focusing on the calculating process of pseudo eigenvectors, we propose a spatial windowing scheme improving the accuracy of the effective channel estimates. The simulation results show that the accuracy in the PE-SDM can be improved by combining the proposed scheme with the conventional time windowing scheme.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa  2007 IEEE 18TH INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1-9  1852  -1856  2007  [Refereed][Not invited]
     
    In a frequency-selective MIMO channel, the optimum beam-forming is achieved by using eigenvectors, i.e., eigenbeam-space division multiplexing (E-SDM), in the frequency domain. However, the calculation load of eigenvalue decomposition increases in proportion to the number of FFT points. In addition, eigenvectors without consideration of frequency continuity increase the delay spread of the effective channel observed at the receiver. Addressing these issues, we have proposed a pseudo eigenvector scheme for the purpose of mitigating the calculation load and maintaining frequency continuity (or decreasing the delay spread). In this paper, we present the PE-SDM performance in a MIMO single-carrier system with MMSE-FDE. The simulation results show that PE-SDM single-carrier transmission provides almost the same or better throughput performance with less complexity in comparison to E-SDM.
  • Bui Huu Phu, Toshihiko Nishimura, Hiroshi Nishimoto, Yasutaka Ogawa, Takeo Ohgane  2007 IEEE 65TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6  1460  -1464  2007  [Refereed][Not invited]
     
    Performance of Multiple-Input Multiple-Output (MIMO) systems applying the Eigenbeam-Space Division Multiplexing (E-SDM) technique may be degraded in time-varying fading environments due to a channel change during the time interval between the transmit weight matrix determination and the actual data transmission. We have proposed some channel prediction methods to compensate for the channel change. Simulation results based on computer generated channels showed better performance when using the prediction methods in rich scatterer environments assuming the Jakes model. However, actual MIMO systems may be used in line-of-sight (LOS) environments, and even in a non-LOS (NLOS) case scatterers may not be uniformly distributed around a receiver and/or a transmitter. In addition, mutual coupling between antenna elements should be considered in actual implementation since it affects the system performance. We conducted MIMO measurement campaigns at a 5.2 GHz frequency band to evaluate the channel prediction techniques. In this paper, we present the experiment and simulation results using the measured channel data. It is shown that robust BER performance is obtained when using the channel prediction methods, and that the performance in LOS environments is better than that in NLOS ones.
  • Bui Huu Phu, Toshihiko Nishimura, Hiroshi Nishimoto, Takeo Ohgane, Yasutaka Ogawa  2007 IEEE 66TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-5  1322  -1326  2007  [Refereed][Not invited]
     
    The performance of MIMO-OFDM E-SDM systems may be seriously degraded in time-varying fading environments due to a channel transition. In the paper, we propose two methods of channel extrapolation to compensate for the channel change. Futhermore, we also consider a method to reduce the amount of header signal and the computational complexity for the systems. We conducted MIMO measurement campaigns at a 5.2 GHz frequency band to evaluate the system performance. Simulation results based on the measured channel data show that robust bit-error rate performance can be obtained by using our channel prediction methods in both line-of-sight (LOS) and non-LOS environments. It is also shown that the method of reducing the amount of header signal and the computational complexity may be used in the practical implementation point of view.
  • K. Kambara, H. Nishimoto, T. Nishimura, Y. Ogawa, T. Ohgane  2007 IEEE 65TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6  2190  -2194  2007  [Refereed][Not invited]
     
    Frequency domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) caused by frequency selective fading in single carrier systems. When a high-mobility terminal exists in the system, channel state changes within a DFT block. Then, the ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. Here, we propose to divide received data block into multiple subblocks to decrease the channel transition within the DFT block in fast fading environments. Also, to satisfy periodicity of the received signal in each subblock, we introduce a pseudo cyclic prefix technique. The results of numerical analysis show that the proposed method provides 1.3-fold increase in tolerable Doppler frequency for FER of 0.01.
  • Hiroshi Nishimoto, Toshihiko Nishimura, Takeo Ohgane, Yasutaka Ogawa  2007 IEEE 65TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6  2068  -2072  2007  [Refereed][Not invited]
     
    In a frequency-selective MIMO channel, the optimum transmission is beamforming based on eigenvectors, i.e., eigenbeam-space division multiplexing (E-SDM), at each frequency point. However, the calculation load of eigenvalue decomposition at the transmitter increases in proportion to the number of frequency points. In addition, frequency-independent eigenvectors increase the delay spread of the effective channel observed at the receiver. In this paper, we propose pseudo eigenvectors for the purpose of reducing the calculation load at the transmitter and maintaining frequency continuity of the effective channel. First, we demonstrate that pseudo eigenvectors decrease the delay spread of the effective channels. Next, the practical performance of the pseudo E-SDM (PE-SDM) transmission in MIMO-OFDM systems is evaluated. The simulation results show that PE-SDM with an interference canceller provides better performance than E-SDM when an estimated effective channel is used to detect the substreams at the receiver.
  • Masaki Takanashi, Toshihiko Nishimura, Yasutaka Ogawa, Takeo Ohgane  2007 IEEE WIRELESS COMMUNICATIONS & NETWORKING CONFERENCE, VOLS 1-9  1601  -1605  2007  [Refereed][Not invited]
     
    The UWB-IR ((U) under bar ltra (W) under bar ide (b) under bar and-(I) under bar mpulse (R) under bar adio) technology and MIMO system have attracted interest for next generation high rate radio communications. We have researched MIMO-UWB systems using the FDE (Frequency Domain Equalization) technique with the MMSE spatial filtering technique. The UWB system will be used in short range wireless transmissions. Then, we usually have line-of-sight (LOS) environments in the MIMO-UWB systems. We conducted propagation measurement and evaluated the transmission performance of MIMO-UWB systems in LOS environments. Then, we proposed a timing control scheme for performance improvement. SIC (Successive Interference Canceller) and PIC (Parallel Interference Canceller) are known as better signal separation techniques in MIMO systems. In these techniques, we can obtain diversity gain subtracting the data detected by a spatial filtering technique from the received signal. Therefore, we can achieve better signal separation performance by the diversity gain. We found that the timing control scheme is also needed for the SIC and PIC techniques in LOS MIMO-UWB environments by bit error rate (BER) evaluation. In this paper, we show the signal separation performance applying the SIC and PIC techniques with the timing control scheme in LOS environments.
  • BUI Huu Phu, NISHIMURA Toshihiko, NISHIMOTO Hiroshi, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report  106-  (395)  97  -104  2006/11/22  [Not refereed][Not invited]
     
    In time-varying fading environments, a channel prediction method should be used to reduce channel errors due to the channel changes between the transmit weight matrix determination time and the actual data transmission time, so that the performance of MIMO E-SDM (Eigenbeam-Space Division Multiplexing) system can be improved. Here, we present an experimental measurement setup to evaluate the performance in actual environments. Based on the measured data, simulation results show that by using our proposed prediction methods much better performance can be obtained in both actual line-of-sight (LOS) and non-LOS (NLOS) communications environments. We can also see that the performance in LOS environments is better than that in NLOS ones.
  • KAMBARA Keiichi, NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report  106-  (305)  95  -100  2006/10/12  [Not refereed][Not invited]
     
    Frequency domain equalization (FDE) has been studied for suppressing inter-symbol interference (ISI) due to frequency selective fading in single carrier systems. When a high-mobility terminal is assumed in the system, channel transition within a FFT block can not be ignored. Then, ISI reduction performance of FDE degrades since cyclicity of the channel matrix is lost. Here, we propose a method dividing a received data block into multiple subblocks to decrease the channel transition within the FFT block in fast fading environments. In addition, we propose a method generating pseudo cyclic prefix to satisfy periodicity of the received signal in each subblock.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  2006-  (1)  217  -217  2006/09/07  [Not refereed][Not invited]
     
    周波数選択性フェージング環境下のMIMOシステムでは,各周波数において固有ビーム形成を行うことで最適伝送を実現できるが[1],周波数毎の固有ウェイトの算出は大きな計算負荷となり,周波数連続性のない送信ウェイトは受信側で観測される実効チャネルのインパルス応答に大きな遅延広がりを生じさせる.これらの問題を解決するため,筆者らは文献[2]において疑似固有ベクトル手法を提案し,これにより演算量削減,及び,実効チャネルの周波数連続性を実現できることを示した.本稿では.文献[3]の屋内伝搬実験に基づき,疑似固有ベクトルを用いるPE-SDM (Pseudo Eigenbeam-Space Division Multiplexing)について,実環境におけるMIMO-OFDM伝送特性を評価する.
  • ISHIDA Takahiro, NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  2006-  (1)  368  -368  2006/09/07  [Not refereed][Not invited]
  • Iwazaki Kiyoto, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2006-  (1)  400  -400  2006/09/07  [Not refereed][Not invited]
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (223)  1  -6  2006/08/24  [Not refereed][Not invited]
     
    In a MIMO system with space-frequency domain beamforming under frequency selective fading scenarios, a pseudo eigenvector decomposition has been proposed to reduce the calculation load at the transmitter and to maintain frequency continuity of the effective channel observed at the receiver. It has been reported that pseudo eigenbeam space division multiplexing (PE-SDM) technique can provide almost the same or better performance compared with eigenbeam space division multiplexing (E-SDM) when the receiver employs a simple channel estimator exploiting pseudo-eigenvector properties. In this paper, under various multipath delay profiles, we evaluate performance of the PE-SDM in MIMO-OFDM with an interference canceller and compare it with E-SDM perfor-mance. The simulation results show that the accuracy of the estimated effective channel in the PE-SDM can be improved more under lower delay spread multipath environments, and that the receiver incorporating a parallel interference canceller can make the performance of the PE-SDM better than that of the E-SDM.
  • ISHIDA Takahiro, NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (223)  7  -12  2006/08/24  [Not refereed][Not invited]
     
    In frequency selective MIMO channels, frequency-flat E-SDM (FFE-SDM) with MMSE-FDE suffers from co-channel interference (CCI). Thus it has been shown that resource adaptation based on both inter-symbol interference and CCI measures gives good performance. In this paper, we apply a parallel interference canceller (PIC) to this system for reducing CCI effectively and evaluate performance with resource adaptation based on three criteria. In comparison with the conventional SDM, the results show that the FFE-SDM technique is more robust to fading correlation and that an eigenvalue criterion which can be easily calculated is practical.
  • OHWATARI Yusuke, NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  106-  (168)  31  -36  2006/07/12  [Not refereed][Not invited]
     
    In a multiple-input multiple-output system for OFDM (MIMO-OFDM), eigenbeam-space division multiplexing (E-SDM) which is also called a singular value decomposition (SVD) algorithm can provide maximum throughput in the MIMO channel when channel state information (CSI) is available at the transmitter. We have proposed reduction of the CSI feedback using the minimum mean square error method in the time domain, and clarified good bit error rate performance. In this paper, we propose a novel technique that only dominant time-domain CSI is fed back in order to reduce the amount of feedback compared to the conventional scheme.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (168)  61  -66  2006/07/12  [Not refereed][Not invited]
     
    In a MIMO system with space-frequency domain beamforming under frequency selective fading scenarios, a pseudo eigenvector decomposition has been proposed to reduce the calculation load at the transmitter and maintain frequency continuity of the effective channel observed at the receiver. In this paper, we evaluate the performance of the pseudo E-SDM (PE-SDM) transmission in MIMO single carrier systems with MMSE-FDE, and compare three substream quality measures for transmit resource control and two encoding schemes. The simulation results show that difference among the three criteria becomes smaller as the number of antennas increases. Moreover, the scheme, in which each data sequence is encoded and interleaved over all substreams, makes the difference smaller so that a simple resource control is practically applicable.
  • IWAZAKI Kiyoto, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (168)  73  -78  2006/07/12  [Not refereed][Not invited]
     
    In frequency-selective channels, the performance of a direct sequence code division multiplexing (DS-CDM) system is severely degraded by inter-code interference since code orthogonality is no longer satisfied. However, the inter-code interference can be suppressed by frequency domain equalization (FDE). On the other hand, multicode transmission in DS-CDM causes an increase of peak-to-average-power-ratio (PAPR). For PAPR reduction, it is known that selection or multiplexed symbol combination from a limited group is effective. Here, side information on the selection must be transmitted. In this paper, we propose to use the side information as a code redundancy and to apply turbo type decoding. As the first step, the performance of multicode transmission with a simple even parity is evaluated. The resutls show that, using turbo type decoding and MMSE-FDE in a frequency selective channel, the obtained gain at FER of 10^<-3> is about 3dB.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (119)  125  -130  2006/06/15  [Not refereed][Not invited]
     
    In frequency selective MIMO channels, the optimum transmission is achieved by beamforming based on eigenvectors (i.e., E-SDM) at each frequency point. However, the calculation load of eigenvalue decomposition at the transmitter increases in proportion to the number of frequency points. In addition, frequency-independent eigenvectors enlarge delay spread of the effective channel observed at the receiver. In this paper, we propose pseudo eigenvectors for the purpose of maintaining frequency continuity of the effective channel and reducing the calculation load at the transmitter. First, we demonstrate that pseudo eigenvectors decrease delay spread of effective channels. Next, the performance of the pseudo E-SDM (PE-SDM) transmission in MIMO-OFDM systems is evaluated. The simulation results show that PE-SDM provides almost the same or better performance compared with E-SDM when an estimated effective channel is used to detect the substreams at the receiver.
  • OHWATARI Yusuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report  106-  (25)  37  -42  2006/04/14  [Not refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system (MIMO-OFDM) can achive high-data-rate transmission without additional frequency spectra. Furthermore, eigenbeam-space division multiplexing (E-SDM) which is also called the singular value decomposition (SVD) algorithm can provide maximum throughput in the MIMO channel when channel state information (CSI) is available at the transmitter. When the uplink and downlink channels are not reciprocal as in a FDD system, we need to feed back the CSI from the receiver to the transmitter. However, capacity is limited because CSI feedback is needed for each subcarrier in an OFDM system. This paper proposes the feedback of the time-domain channel estimated using the minimum mean square error method. The proposed method can reduce the amount of feedback information, and reveals better bit error rate performance than the other schemes.
  • ISHIDA Takahiro, NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  106-  (25)  55  -60  2006/04/14  [Not refereed][Not invited]
     
    In frequency selective multiple-input multiple-output (MIMO) channels, equalization for suppressing inter-symbol interference is necessary as well as spatial-demultiplexing. When MMSE frequency domain equalization (MMSE-FDE) is applied to a single carrier system in eigenbeam-space division multiplexing with frequency-flat transmit weights, resource adaptation based on the extended MIMO channel does not give expected performance due to not considering less detection capability of MMSE-FDE. In this paper, we propose two criteria and evaluate their performance compared with the conventional space division multiplexing transmission. The results show that a new criterion incorporating the amount of interference in the MMSE-FDE output gives better performance than the others.
  • BUI Huu-Phu, OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko  Proceedings of the IEICE General Conference  2006-  (1)  428  -429  2006/03/08
  • OHWATARI Yusuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2006-  (1)  420  -420  2006/03/08  [Not refereed][Not invited]
  • MIYAZAWA Makoto, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2006-  (1)  450  -450  2006/03/08  [Not refereed][Not invited]
  • Takanashi Masaki, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2006-  141  -141  2006/03/08  [Not refereed][Not invited]
  • OHKAWARA Junya, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  105-  (559)  65  -70  2006/01/19  [Not refereed][Not invited]
     
    In this paper, we discuss methods of transmit-antenna selection for uplink multiuser MIMO-SDM systems. In multiuser MIMO-SDM systems, signal detection quality at a basestation is degraded by cochannel interference, and depends on the number of transmit antennas of each user. In this paper, we propose a novel method for antenna selection to increase diversity gain. The criterion of antenna selection is based on capacity using spatial filter output. Simulation results show that frame error rate performance in the multiuser MIMO-SDM systems is improved by the proposed method. In addition, we show the advantage of diversity gain to select the number of transmit antennas at each user.
  • Toshihiko Nishimura, Yasuo Hata, Takeo Ohgane, Yasutaka Ogawa  IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC  105-  (559)  89  -94  2006  [Refereed][Not invited]
     
    Eigenbeam space division multiplexing systems in a multiple-input multiple-output channel require resource adaptation (a modulation scheme and transmit power allocation for each stream) optimized based on criteria such as throughput maximization. We propose a technique to simplify transmit resource control for the purpose of implementing the algorithm on an actual system. The proposed technique uses simple calculations with eigenvalues derived from the channel information and noise power of a receiver to achieve the most appropriate transmit resource control. By contrast, the conventional technique requires complex calculations of throughput for all possible combinations of modulation schemes. Additionally, our technique can accommodate any number of antenna elements. The results of computer simulation show that the performance of the proposed technique is almost the same as conventional performance throughout the signal-to-noise ratio (SNR) region, although the simplification is analytically valid only for high SNR. © 2006 IEEE.
  • Bui Huu Phu, Yasutaka Ogawa, Takeo Ohgane, Toshihiko Nishimura  2006 IEEE 63RD VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6  1748  -1752  2006  [Refereed][Not invited]
     
    Multiple-input multiple-output (MIMO) systems using eigenbeam space division multiplexing (E-SDM) perform well and have increased channel capacities. However, channel state information (CSI) is required at a transmitter, and the performance of the systems depends much on the accuracy of the CSI at a transmitter and a receiver. In time-varying fading environments, the channel change between the transmission weight matrix determination time and the actual data transmission time causes the system performance to degrade. To compensate for the channel error, a linear extrapolation method has been proposed for a time division duplexing system. Unfortunately, the performance still deteriorates as the maximum Doppler frequency increases. Here, two new techniques of channel extrapolation are proposed. One is second order extrapolation, and the other is exponential extrapolation. Simulation results for 4tx 4rx MIMO systems show that using the proposed methods, E-SDM system performs better in a higher Doppler frequency region.
  • Yusuke Ohwatari, Bui Huu Phu, Yasutaka Ogawa, Toshihiko Nishimura, Takeo Ohgane  2006 IEEE 64TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6  401  -405  2006  [Refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system (MIMO-OFDM) can achive high-data-rate transmission without additional frequency spectra. Furthermore, eigenbeam-space division multiplexing (E-SDM) which is also called the singular value decomposition (SVD) algorithm can provide maximum throughput in the MIMO channel when channel state information (CSI) is available at the transmitter. When the uplink and downlink channels are not reciprocal as in a FDD system, we need to feed back the CSI from the receiver to the transmitter. However, capacity, is limited because CSI feedback is needed for each subcarrier in an OFDM system. This paper proposes the feedback of the time-domain channel estimated using the minimum mean square error method. The proposed method can reduce the amount of feedback information, and reveals better bit error rate performance than the other schemes.
  • Toshihiko Nishimura, Yasuo Hata, Takeo Ohgane, Yasutaka Ogawa  2006 IEEE 63RD VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6  2285  -2289  2006  [Refereed][Not invited]
     
    This paper deals with experimental considerations for an eigenbeam-space division multiplexing (E-SDM) system with time division duplex downlink in multiple-input multiple-output channels. Channel information in E-SDM is necessary for a transmitter. If the time difference between the transmit weight calculation from the channel information at a transmitter and the actual transmission is large, E-SDM performance degrades because channel orthogonality is not maintained. In this study, indoor experiments of the E-SDM were performed to evaluate channel error compensation using first order extrapolation. Furthermore, simplification of transmit resource control and reduction of calculation load were proposed. Experimental results showed that channel estimation error compensation by first order extrapolation was very effective and improved bit error rate performance.
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  105-  (355)  127  -132  2005/10/13  [Not refereed][Not invited]
     
    A multiple input multiple output (MIMO) system in which multiple antennas are placed at both the transmitter and receiver end can potentially meet the growing demand for higher capacity in wireless communications. When information on the channel state is available at the transmitter end, eigenbeam-space division multiplexing (E-SDM) which can provide maximum throughput in the MIMO channel is more efficient technique in order to achieve higher speed transmission compared with the conventional space division multiplexing (SDM). This paper shows MIMO channel measurement campaigns conducted in indoor line-of-sight (LOS) and non line-of-sight (NLOS) environments. Using the measured data, we present the bit error rate performance of 2×2 and 4×4 E-SDM. The results shows that, E-SDM generally gives better performance than SDM, and LOS environments provide more excellent performance of E-SDM compared with NLOS ones. However, we can see that the performance of E-SDM in LOS environments strongly depends on the array configuration.
  • OHWATARI Yusuke, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  IEICE technical report  105-  (356)  61  -66  2005/10/13  [Not refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system (MIMO-OFDM) can achive high-data-rate transmission without inter-symbol interference in frequency selective fading channels. In a receiver, however, spatial filtering is needed to separate and detect transmitted signals because the signals sent from all the transmit antennas interfere each other. It has been reported that precise channel estimation is possible and the performance of MIMO-OFDM using MMSE-OSD is improved by an evaluation system experimentaly. In this paper, we introduce a coded MIMO-OFDM system in order to improve the performance. Also, we show the experimental results of performance of BER and FER.
  • Phu Bui Huu, Ogawa Yasutaka, Ohgane Takeo, Nishimura Toshihiko  Proceedings of the Society Conference of IEICE  2005-  (1)  424  -424  2005/09/07
  • TANAKA Toyohisa, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2005-  (1)  431  -431  2005/09/07  [Not refereed][Not invited]
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the Society Conference of IEICE  2005-  (1)  "S  -7"-"S-8"  2005/09/07  [Not refereed][Not invited]
  • Takanashi Masaki, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the Society Conference of IEICE  2005-  "S  -19"-"S-20"  2005/09/07  [Not refereed][Not invited]
  • OHKAWARA Junya, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  105-  (121)  53  -58  2005/06/10  [Not refereed][Not invited]
     
    In this paper, we discuss effects of transmit-antenna selection for uplink multiuser MIMO-SDM systems. In multiuser MIMO-SDM systems, signal detection quality at a basestation is degraded by cochannel interference and depends on the number of transmit antennas. To reduce cochannel interference, we consider limiting the number of transmit-antennas and antenna selection at each or target mobile station. Computer simulation results show that frame error rate performance in multiuser MIMO-SDM systems is improed by transmit-antena selection.
  • HATA Y., NISHIMURA T., OHGANE T., OGAWA Y.  Technical report of IEICE. RCS  105-  (121)  65  -70  2005/06/10  [Not refereed][Not invited]
     
    Applying E-SDM system is evaluated for a TDD uplink in MIMO (Multiple-Input Multiple-Output) channels when a channel response matrix is known at a transmitter. If time difference between transmit weight calculation from channel information at a transmitter and actual transmission is large, performance of E-SDM degrades because channel orthogonality is not kept. In this study, indoor experiments of E-SDM are done using fading simulators to evaluate the channel estimation error compensation by the first order extrapolation, which has been proposed. Furthermore, simplification of transmission resource control and reduction of calculation load are proposed. Experimental results show that the channel estimation error compensation by the first order extrapolation is very effective and improves BER performance.
  • NISHIMOTO H.  IEICE Technical Report  105-  (121)  RCS2005  -39  2005/06/10  [Not refereed][Not invited]
     
    Recently a MIMO system, which promises very high-speed data transmission, has attracted great attention to wireless communications. In multipath-rich environments, it is considered that strong cross-polarization components also arrive at a receiver. We measured 3×3 MIMO channels in a multipath-rich room using tripole antennas. The tripole antenna is composed of three orthogonal omni-directional antennas. It is shown that the tripole antennas give lower fading correlations. However, we cannot find clear differences of the performance in array configurations.
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2005-  (1)  244  -244  2005/03/07  [Not refereed][Not invited]
  • HOSHINO Masayuki, TAKAKUSAKI Keiji, OHGANE Takeo, OGAWA Yasutaka, NISHIMURA Toshihiko  Proceedings of the IEICE General Conference  2005-  (1)  533  -533  2005/03/07  [Not refereed][Not invited]
  • Takanashi Masaki, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2005-  121  -121  2005/03/07  [Not refereed][Not invited]
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  104-  (679)  123  -128  2005/02/24  [Not refereed][Not invited]
     
    A MIMO measurement campaign was conducted in indoor multipath-rich line-of-sight (LOS) and non-LOS (NLOS) environments. In this paper, for various antenna array configurations, we examined the performance of bit error rate (BER) for 2×2 and 4×4 MIMO-SDM systems using the actual channel state data with mutual coupling of antennas, and considered the effects of channel correlations and eigenvalue distributions. Results showed that MIMO channels in LOS generally give better BER performance than those in NLOS. Meanwhile, we also found that the performance in LOS tends to change largely depending on an array configuration.
  • MATSUNOSHITA Masahiro, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (679)  81  -86  2005/02/24  [Not refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system (MIMO-OFDM) can achive high-data-rate transmission without inter-symbol interference in frequency selective fading channels. In a receiver, however, spatial filtering must be needed to separate and detect transmitted signal, because received signals include transmitted signals from all the transmit antennas. We constructed an evaluation system with fading simulators in order to verify the MIMO-OFDM spatial division multiplexing system experimentaly. In this paper, we show some improvements of the hardware and processing software.
  • TAKANASHI Masaki, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  電子情報通信学会技術研究報告. A・P, アンテナ・伝播  104-  (675)  207  -212  2005/02/23  [Not refereed][Not invited]
  • SHIBAHARA Koji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (678)  37  -42  2005/02/23  [Not refereed][Not invited]
     
    In this paper, it is considered to apply a parallel interference canceller (PIC) to a coded MIMO-OFDM system. In a hard canceller with a simple configuration, a cancelling factor is generally introduced to reduce the effect of error propagation due to low reliability replicas. Here, a novel hard canceller using a spatial filtering factor is proposed. In addition, a symbol-by-symbol PIC is also applied to reduce the packet processing delay. The simulation results show that it achieves low computational complexity and short packet processing delay, and that the performance degradation compared to soft PIC is reasonably small.
  • SUMII Kenji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (678)  43  -48  2005/02/23  [Not refereed][Not invited]
     
    A turbo-coded MIMO-SDM system requires a soft-output MIMO detector. Although MAP-based soft-output detection is optimum, its hardware implementation is very difficult since its computational complexity increases exponentially with the antennas and constellations. Sphere decoding (SD) is one of promising ways to reduce the computational complexity effectively. In SD, however, it occasionally excludes signal points required for the likelihood estimation in turbo decoding. In this paper, we propose a method recovering the signal points outside the sphere, and its error performance is evaluated. The simulation results reveal its extremely low complexity.
  • TANAKA Toyohisa, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (599)  37  -42  2005/01/21  [Not refereed][Not invited]
     
    W-CDMA has already been operated as the 3rd generation mobile communication system. Continuously the 3rd Generation Partnership Project (3GPP) has been worked for enhancing the 3G systems. A specification of High Speed Downlink Packet Access (HSDPA), which enables up to 14.4Mbps data rate for downlink, was completed so far. In addition to the HSDPA, MIMO has been proposed to apply for further enhancement. We studied MIMO for W-CDMA uplink by using a computer simulation in this report.
  • Nishimura Toshihiko, Nishimoto Hiroshi, Ogawa Yasutaka, Ohgane Takeo  Proceedings of the IEICE General Conference  241  -241  2005  [Not refereed][Not invited]
  • HATA Yasuo, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  423  -423  2005  [Not refereed][Not invited]
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  104-  (399)  53  -58  2004/10/29  [Not refereed][Not invited]
     
    We measured MIMO channels with mutual coupling of antennas in indoor line-of-sight (LOS) and non-LOS (NLOS) environments where we have rich multipath signals. Using the measured data, we examined bit error rate performance, channel correlations, and eigenvalue distributions for 2x2 MIMO space division multiplexing (SDM) systems to evaluate effects of mutual coupling on the performance. We show that t,he MIMO-SDM is useful also in an indoor LOS environment, whereas the performance in the LOS environment tends to change significantly depending on an array configuration. Moreover, it is shown that the mutual coupling tends to effect on LOS channel data more largely than on NLOS ones.
  • NAMKAMURA Yuichiro, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  104-  (258)  79  -84  2004/08/20  [Not refereed][Not invited]
     
    An OFDM system has been used also for wireless local area networks. MIMO space division multiplexing in an OFDM system has been studied to achive high-speed transmission over lOOMbps. In this paper, we compare three methods of channel estimation using a few training symbols. We show that the time-domain minimum square error method that the authors have proposed enables accurate channel estimation. Furthermore, we develop this scheme to estimation of channel and frequency offset between a transmitter and a receiver. We show that the proposed method can estimate them using a preamble that have the same duration as that of the IEEE802.11 a standard.
  • MATSUNOSHITA Masahiro, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (258)  103  -107  2004/08/20  [Not refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system (MIMO-OFDM) can achive high-data-rate transmission without inter-symbol interference in frequency-selective fading channels. It has been reported that precise channel estimation is possible by using the training symbols with a low condition number even though the number of training symbols in an OFDM system (for example, IEEE802.ila) is small. In this paper, we evaluate sensitivity of channel estimation acculacy and BER performance to the condition number depending on the training symbols, experimentary, using a DSP-based MIMO-OFDM system.
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  IEICE technical report. Antennas and propagation  104-  (202)  25  -30  2004/07/15  [Not refereed][Not invited]
     
    We measured MIMO channels in a line-of-sight (LOS) environment where channels may be correlated, then examined bit error rate performance for 2 × 2 MIMO-SDM and eigenvalue distributions to compare with channels, in a non-LOS (NLOS) environment. Furthermore, we analyzed channel data with mutual coupling between antennas, and evaluated its effect on the performance. We show that the performance of MIMO-SDM is useful also in a LOS environment where there are rich multipath signals, and that the performance in the LOS environment changes significantly depending on antenna spacing and array configuration. Moreover, it is shown that the presence of mutual coupling tends to effect on LOS channel data more largely than NLOS ones.
  • SHIBAHARA Koji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (123)  31  -35  2004/06/11  [Not refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system can achieve very high-speed transmission. In this paper, a parallel interference canceller (PIC) is considered for coded MIMO-OFDM based on the IEEE standard 802.11a, and its performance is evaluated. In addition, we propose PIC processing symbol by symbol to reduce a processing delay. Numerical analysis shows that PIC has better PER performance compared to spatial filtering, and that severe degradation is not observed in the symbol PIC.
  • SUMII Kenji, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  104-  (123)  37  -42  2004/06/11  [Not refereed][Not invited]
     
    A soft output MIMO decoder is required for turbo-coded MIMO-SDM. Although soft output maximum likelihood detection (MLD) is optimal, its computational complexity prevents application to iterative decoding of turbo decoding and soft output MIMO decoding. We propose a complexity reduction method for soft output MLD in iterative decoding, and also consider the application to partial search MLD. Computer simulation results show that the proposed method reduces complexity effectively.
  • Shibahara Koji, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2004-  (1)  519  -519  2004/03/08  [Not refereed][Not invited]
  • Nishio Keisuke, Ogawa Yasutaka, Nishimura Toshihiko, Ohgane Takeo  Proceedings of the IEICE General Conference  2004-  (1)  "S  -27"-"S-28"  2004/03/08  [Not refereed][Not invited]
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Proceedings of the IEICE General Conference  2004-  (1)  "S  -33"-"S-34"  2004/03/08  [Not refereed][Not invited]
  • FURUTA Takayuki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  103-  (680)  49  -54  2004/02/25  [Not refereed][Not invited]
     
    In a frequency selective MIMO channel, a maximum likelihood receiver performing both joint detection and sequence estimation is optimum. However, an increase of the number of delayed waves and substreams complicates the receiver process exponentially. We applied sphere decoding (SD) and M-algorithm (MA) for complexity reduction to the receiver in convolutional-coded SDM and E-SDM systems. In this paper, we evaluate effects of those algorithms in both complexity reduction and performance degradation.
  • SUMII Kenji, NISHIMURA Toshihiko, OHGANE Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  516  -516  2004  [Not refereed][Not invited]
  • Y Ogawa, K Nishio, T Nishimura, T Ohgane  VTC2004-FALL: 2004 IEEE 60TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-7  1523  -1527  2004  [Refereed][Not invited]
     
    An OFDM technique has been utilized for wireless local area networks (WLANs). Spatial division multiplexing using a multiple-input multiple-output (MIMO) technique has been studied to increase the transmission rate over 100 Mbps. Before we detect transmitted data, we need AGC adjustment, timing synchronization, frequency offset estimation, and channel estimation using a preamble. The current WLAN system with a single transmit antenna based on the IEEE 802.11a standard uses the four OFDM symbol duration preamble. However, the preamble period proposed so far for the MIMO-OFDM system grows linearly with the transmit antenna number. This results in an increased overhead, and the conventional technique is not efficient. In this paper, we present the channel and frequency offset estimation scheme using a preamble with four OFDM symbol duration for the MIMO-OFDM system in WLANs. This preamble has the same duration as that of the IEEE 802.11a standard. and does not increase the overhead. Computer simulation results are provided to demonstrate the performance of the proposed scheme.
  • NISHIMOTO Hiroshi, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  103-  (460)  139  -144  2003/11/21  [Not refereed][Not invited]
     
    Independent and identically distributed (i. i. d.) Rayleigh channels between transmit and receive antennas have been assumed in many studies on MIMO space division multiplexing (MIMO-SDM). In this case, transmitted streams can be separated and detected by processing at a receiver end. However, channels may be correlated in a line-of-sight (LOS) environment. We measured MIMO channels in a very rich multipath environment, and showed that the performance of LOS channels is more excellent than that of NLOS (Non-LOS) ones. We also evaluated the performance of channels measured in an an-echoic chamber where we do not have rich multipath propagation.
  • NISHIMOTO Hiroshi, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  Proceedings of the Society Conference of IEICE  2003-  (1)  236  -236  2003/09/10  [Not refereed][Not invited]
  • HOSHINO Masayuki, UESUGI Mitsuru, OHGANE Takeo, OGAWA Yasutaka, NISHIMURA Toshihiko  Proceedings of the Society Conference of IEICE  2003-  (1)  390  -390  2003/09/10  [Not refereed][Not invited]
  • Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Takatori Yasushi, Cho Keizo  Proceedings of the Society Conference of IEICE  2003-  (1)  408  -408  2003/09/10  [Not refereed][Not invited]
  • Ohgane Takeo, Ogawa Yasutaka, Nishimura Toshihiko  Proceedings of the Society Conference of IEICE  2003-  (1)  "SS  -34"-"SS-35"  2003/09/10  [Not refereed][Not invited]
  • FURUTA Takayuki, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  103-  (253)  7  -12  2003/08/21  [Not refereed][Not invited]
     
    In a frequency selective MIMO channel, the maximum likelihood receiver performing both joint detection and sequence estimation is optimum. However, an increase of the number of delayed waves and substreams complicates the receiver process, exponentially. In this paper, we apply Sphere Decoding (SD) to the receiver. SD limits the number of constellation points to be searched by setting a sphere around a received signal. Here, we evaluate effects of sequence estimation to SD and the performance.
  • TSUTSUMI Takahiko, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  103-  (204)  13  -18  2003/07/18  [Not refereed][Not invited]
     
    For some SDM applications, performance degradation due to error in channel state information is numerically analyzed. In addition, a channel prediction method using first order extrapolation is proposed. The computer simulation results show that SDM using a joint detector outperforms E-SDM and w-SDM which requires channel state information at the transmitter in fast fading condition. However, by using the channel prediction, the performance of E-SDM and w-SDM is improved.
  • NISHIO Keisuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  103-  (66)  83  -90  2003/05/23  [Not refereed][Not invited]
     
    MIMO space division multiplexing in an OFDM system can achieve very high-speed transmission. This paper nresents signal separation techniques for spatially multiplexed signals. We consider a channel estimation scheme using a very few training symbols. Then, we investigate reasons for degradation of channel estimation accuracy, and propose training symbol selection for better channel estimation. Also, we examine several MIMO reception techniques.
  • Furuta Takayuki, Ohgane Takeo, Nishimura Toshihiko, Ogawa Yasutaka, Tomisato Shigeru  Proceedings of the IEICE General Conference  2003-  (1)  775  -775  2003/03/03  [Not refereed][Not invited]
  • Tsutsumi Takahiko, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2003-  (1)  776  -776  2003/03/03  [Not refereed][Not invited]
  • HOSHINO Masayuki, EBIKO Keisuke, UESUGI Mitsuru, OHGANE Takeo, OGAWA Yasutaka, NISHIMURA Toshihiko  Proceedings of the IEICE General Conference  2003-  (1)  "S  -49"-"S-50"  2003/03/03  [Not refereed][Not invited]
  • Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka, Takatori Yasushi, Cho Keizo  Proceedings of the IEICE General Conference  2003-  (1)  "S  -55"-"S-56"  2003/03/03  [Not refereed][Not invited]
  • KIMURA Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  102-  (675)  1  -5  2003/02/27  [Not refereed][Not invited]
     
    In multiple-input multiple-output channels, channel capacity is highly improved by eigenbeam space division multiplexing (E-SDM), when the channel response is known at a transmitter. In this paper, we introduce FEC (turbo codes, in specific) to the E-SDM and evaluate its performance. Computer simulations show the results on performance improvement due to coding gain. However, the improvement is larger in the SDM case. Thus, the performance of E-SDM and SDM becomes very close.
  • NISHIO Keisuke, OGAWA Yasutaka, NISHIMURA Toshihiko, OHGANE Takeo  Technical report of IEICE. RCS  102-  (551)  121  -126  2003/01/10  [Not refereed][Not invited]
     
    OFDM is useful for high-speed transmission in a multipath environment. Space division multiplexing in a MIMO system can increase a transmission rate because different transmit antennas radiate indivisual signals. This paper describes an adaptive antenna configuration and weight control method for the OFDM system. Then, the authors propose MIMO-OFDM space division multiplexing based on the adaptive antenna. It is shown from computer simulations that the proposed system reveals excellent performance.
  • NISHIMURA T., OHGANE T., OGAWA Y., TAKATORI Y., CHO K.  Technical report of IEICE. RCS  102-  (551)  127  -132  2003/01/10  [Not refereed][Not invited]
     
    In this paper, two schemes to improve channel capacity, weighted-BLAST and E-SDMA, are evaluated in multiple-input multiple-output (MIMO) channels, when the channel response matrix is known at a transmitter. In the paper, we describe transmitting power and bit rate controls for each scheme, and three receiving methods for weighted-BLAST is examined by numerical simulations. Also, bit error rates of weighted-BLAST and E-SDM are computed and compared. The results show that the weighted BLAST is a promising scheme for some applications because of less feedback data and less terminal load even though bit error rate is higher than E-SDM.
  • TAKANASHI Masaki, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report. Antennas and propagation  102-  (230)  77  -82  2002/07/17  [Not refereed][Not invited]
     
    A uniform linear array (ULA) has been mainly used for DOA estimation of coherent signals because we can apply the spatial smoothing preprocessing (SSP) technique. However, the ULA has ambiguity due to the symmetry, and the estimation accuracy depends on the DOA. Although these problems can be solved by using a uniform circular array (UCA), we cannot estimate the DOA of coherent signals because the SSP technique cannot be employed for the UCA. In this paper, we propose to estimate 2-dimensional DOA (polar angle and azimuth angle) of the coherent signals using a cylindrical array which is composed of stucked UCAs.
  • KIMURA Hiroshi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  102-  (204)  19  -24  2002/07/10  [Not refereed][Not invited]
     
    The performance of Turbo Codes in MIMO systems was evaluated. When the channel state information is not known at a transmitter, the BER performance of Turbo codes using space division multiplexing (SDM) was numerically analyzed in comparison to Turbo codes with space-time block codes (STBC). When the channel state information is known at a transmitter in a MIMO system, we evaluated the BER performance combining Turbo Codes and E-SDM/transmit MRC. The simulation results for an unknown channel assuming 4-tx and 2-rx antennas show that Turbo codes using SDM have better BER performance than Turbo codes with STBC. For a known channel, the performance of Turbo codes with MRC is better.
  • NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, TAKATORI Yasushi, CHO Keizo  Technical report of IEICE. RCS  102-  (204)  25  -30  2002/07/10  [Not refereed][Not invited]
     
    Eignebeam-space division multiplexing (E-SDM) in the MIMO channel is effective when a receiver has less number of elements. In this paper, we evaluate E-SDM performance in the presence of chanel estimation error between channel response matrices used for determining transmit weights and actual channel responce ones. Average BER performance for maximal ratio combining has error floor because eigenbeams are not formed perefectly orthogonal. Therfore, zero-forcing method or joint detection are needed. The results of computer simulation show that the E-SDM method is superiour to normal SDM while channel correlation is over 0.8 with the joint detector.
  • MIYASHITA Kazumi, NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka, TAKATORI Yasushi, CHO Keizo  Technical report of IEICE. RCS  102-  (86)  13  -18  2002/05/17  [Not refereed][Not invited]
     
    In MIMO systems, when the channel state information is known at transmitter, the optimum capacity is given by eigenmode channel division with the water filling power control. In this paper, eigenbeam-space division multiplexing (E-SDM) is proposed based on that concept, and the BER performance is numerically analyzed in comparison to the conventional SDM. The simulation results assuming 5-tx and 2-rx antennas show that the E-SDM provides about 10 dB gain compared to the conventional SDM at average BER of 10^-3.
  • NISHIMURA Toshihiko, TAKATORI Yasushi, OHGANE Takeo, OGAWA Yasutaka, CHO Keizo  Technical report of IEICE. SST  101-  (677)  17  -22  2002/03/07  [Not refereed][Not invited]
     
    In this paper, we propose a novel downlink nullforming technique for space division multiple access (SDMA) in a multi-input multi-output (MIMO) channel where a basestation and all terminal stations have multiple antennas. In the SDMA system, simple beamforming is not efficient to achieve a good performance due to cochannel interference (CCI). Proposed method is based on nullforming and characterized by an antenna element selection at each terminal where the selected antenna pair satisfies the lowest spatial correlation condition in all combinations. The results obtained by the computer simulations show the selective diversity gain of the proposed method and its performance improvement due to joint detection at each terminal.
  • TANABE Yasuhiko, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, ASAI Takahiro, TOMISATO Shigeru  Technical report of IEICE. SST  101-  (677)  23  -30  2002/03/07  [Not refereed][Not invited]
     
    In this paper, we discuss a cascaded connection of an adaptive array antenna, in which each antenna contains a feedforward filter, and the Viterbi equalizer. When using the feedforward filter, MMSE tap coefficients degrade the system performance because noise correlation in an array output becomes high. computer simulations show that proposed methods have better BER performance under a large delay spread condition and when the feedforward filters have few taps. In addition, we propose a method applying a multi-input Viterbi algorithm with a multi-beam adaptive array antenna. As a result, the proposed method improves BER performance significantly.
  • NISHIMURA Toshihiko, TAKATORI Yasushi, OHGANE Takeo, OGAWA Yasutaka, CHO Keizo  Technical report of IEICE. RCS  101-  (683)  17  -22  2002/02/28  [Not refereed][Not invited]
     
    In this paper, we propose a novel downlink nullforming technique for space division multiple access (SDMA) in a multi-input multi-output (MIMO) channel where a basestation and all terminal stations have multiple antennas. In the SDMA system, simple beamforming is not efficient to achieve a good performance due to cochannel interference (CCI). Proposed method is based on nullforming and characterized by an antenna element selection at each terminal where the selected antenna pair satisfies the lowest spatial correlation condition in all combinations. The results obtained by the computer simulations show the selective diversity gain of the proposed method and its performance improvement due to joint detection at each terminal.
  • TANABE Yasuhiko, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, ASAI Takahiro, TOMISATO Shigeru  Technical report of IEICE. RCS  101-  (683)  23  -30  2002/02/28  [Not refereed][Not invited]
     
    In this paper, we discuss a cascaded connection of an adaptive array antenna, in which each antenna contains a feedforward filter, and the Viterbi equalizer. When using the feedforward filter, MMSE tap coefficients degrade the system performance because noise correlation in an array output becomes high. Computer simulations show that proposed methods have better BER performance under a large delay spread condition and when the feedforward filters have few taps. In addition, we propose a method applying a multi-input Viterbi algorithm with a multi-beam adaptive array antenna. As a result, the proposed method improves BER performance significantly.
  • NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Technical report of IEICE. RCS  101-  (371)  23  -30  2001/10/13  [Not refereed][Not invited]
     
    SDMA 方式の下り回線ビーム形成において, MISO(Multi-Input-Single-Output)およびMIMO(Multi-Input Multi-Output)チャンネルを想定した場合に, 結合推定機能をもつ端末での受信特性について考察する.希望信号の電力がそれぞれの端末で最大となる送信最大比合成ダイバーシチと, 干渉信号電力を最小とするヌル制御の概念から導出した下り回線でのビーム形成法について評価する.計算機シミュレーションから, 結合推定機能を持つ端末を用いた場合, ヌル制御によるビーム形成法は送信最大比合成ダイバーシチとなるビーム形成法より特性が優れているという結果が得られた.
  • Nakao Seigo, Kitakado Jun, Doi Yoshiharu, Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the Society Conference of IEICE  2001-  (1)  374  -374  2001/08/29  [Not refereed][Not invited]
  • SAITO Hiroyuki, NISHIMURA Toshihiko, YAMAMOTO Manabu, ITOH Kiyohiko  IEICE technical report. Antennas and propagation  101-  (231)  89  -96  2001/07/27  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms RF signal into intermediate frequency signal as soon as the system receives the RF signal and local oscillator's signal spatially. Using this system, we can reduce transmission loss, which causes serious problem in the millimeter-wave band. A simple Quasi-Optical Antenna-Mixer (QOAM) have been proposed using a magnetic loop antenna in our former study, and we have confirmed experimentally the performance of beam scanning with the arrayed QOAM in the 3GHz-band. In this report, we explore possibility for our proposal of application in the high-frequency band, verifying experimentally the behavior of the arrayed QOAM in the 10GHz band. Furthermore, we show that the RF signal the local oscillator's signal output are canceled out respectively by a symmetric arrangement of the QOAM.
  • MIYASHITA Kazumi, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  101-  (197)  31  -36  2001/07/12  [Not refereed][Not invited]
     
    Recently, with the demand on capacity increase, space division multiple access(SDMA) has been studied in order to improve channel efficiency. In TDD/SDMA using an adaptive array for a base station, weight control using a channel response estimated by first-order extrapolation is known as improving the BER performance in downlink. However, the performance degrades with increase of the fading speed. In this paper, we propose a channel response estimation method using exponential function approximation and evaluate its performance.
  • OYANE Hidehiko, NISHIMURA Toshihiko, ITOH Kiyohiko  The Transactions of the Institute of Electronics,Information and Communication Engineers B  84-  (5)  954  -957  2001/05/01  [Not refereed][Not invited]
     
    準光学アンテナ・ミキサ[1]〜[5]は, 高周波信号(RF)と局部発振周波(LO)を空間的に受信すると同時に中間周波数(IF)信号へ変換する。本研究では, 3GHz帯で動作する磁流ループアンテナを試作し, 以前提案した準光学アンテナ・ミキサアレーによるビーム走査法[6]〜[11]の実験を行って理論と比較する。
  • Nishimura Toshihiko, Ohgane Takeo, Ogawa Yasutaka  Proceedings of the IEICE General Conference  2001-  (1)  400  -400  2001/03/07  [Not refereed][Not invited]
  • 西村寿彦  信学技報  2001-  23  -30  2001
  • YONEZAWA N., OGAWA Y., NISHIMURA T., OHGANE T., DOI Y.  Technical report of IEICE. RCS  100-  (347)  29  -35  2000/10/07  [Not refereed][Not invited]
     
    Timing synchronization of a reference signal with an incident desired signal is required to control an adaptive antenna based on the MMSE criterion. This paper proposes to use nsrrow-band filters whose bandwidth is narrower than that of the root Nyquist filter. In the first weight control, the adaptive antenna weights are determined almost properly, since the narrow-band filter increases the correlation between the incident desired signal and the reference signal with timing error. The second synchronization of the reference signal at the array output is accurate, and the adaptive antenna can determine the weights more precisely. The computer simulation results show the improvement of the synchronization accuracy, SINR, and the BER performance.
  • KIMURA Masatoshi, TANABE Yasuhiko, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  IEICE technical report. Antennas and propagation  100-  (218)  23  -28  2000/07/27  [Not refereed][Not invited]
     
    Time-domain measurements are widely spread, which estimate time delays of signals applying the inverse Fourier transform to frequency-domain data measured by a networkanalyzer. We can use the MUSIC algorithm for separating closely located signals. However, the performance of the MUSIC algorithm deteriorates under multiple signal environment. In this paper, we propose the beamspace MUSIC algorithm for the above environment. We also compare the results of the beamspace MUSIC with those of the gating technique. The beamspace MUSIC tends to show better performance than the gating technique.
  • NISHIMURA T., CHIBA T., TANABE Y., OHGANE T., OGAWA Y., KITAKADO J., DOI Y.  Proceedings of the IEICE General Conference  2000-  (1)  412  -412  2000/03/07  [Not refereed][Not invited]
  • TANABE Yasuhiko, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  Proceedings of the IEICE General Conference  2000-  (1)  492  -492  2000/03/07  [Not refereed][Not invited]
  • TANABE Y., FUJISHIMA K., NISHIMURA T., OGAWA Y., OHGANE T.  Technical report of IEICE. RCS  99-  (638)  15  -20  2000/02/18  [Not refereed][Not invited]
     
    In a high speed TDMA system, frequency-selective fading is a serious problem.A spatial-domain path-diversity system using multibeam adaptive antenna has been proposed to reduce the frequency-selective fading, and to realize diversity.In this system, we need to estimate the time delays of multipath signals.If the estimation is not accurate, the system performance degrades.For this reason, the MUSIC algorithm has been proposed for the time delays estimation.However, the MUSIC algorithm needs a large quantity of operations.In this paper, we propose to use another scheme which is called an orthogonal vectors method.It needs much less operations, but the BER performance is almost the same as that of the MUSIC algorithm.
  • 田辺 康彦, 藤嶋 堅三郎, 西村 寿彦  電子情報通信学会技術研究報告  99-  (638)  15  -20  2000/02/18  [Not refereed][Not invited]
  • OYANE Hidehiko, NISHIMURA Toshihiko, ITOH Kiyohiko  電子情報通信学会技術研究報告. ITS  99-  (631)  111  -116  2000/02/17  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms RF signal into intermediate frequency signal as soon as the system receives the RF signal and local oscillator's signal spatially. Using this system, we can reduce transmission loss, which causes serious problem in the millimeter-wave band. We presented a dual frequency operating microstrip antenna fed by coplanar waveguide as an essential part of the quasi-optical antenna-mixer before. Its manufacturing error was considerable, however, because it was a stacked-configuration. In this report, we make up a simple Quasi-Optical Antenna-Mixer using a magnetic loop antenna. In addition, the antenna that performs in 3.0GHz band is made and performance of beam scanning is confirmed experimentally with the arrayed ones.
  • OYANE Hidehiko, NISHIMURA Toshihiko, ITOH Kiyohiko  Technical report of IEICE. RCS  99-  (637)  111  -116  2000/02/17  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms RF signal into intermediate frequency signal as soon as the system receives the RF signal and local oscillator's signal spatially. Using this system, we can reduce transmission loss, which causes serious problem in the millimeter-wave band. We presented a dual frequency operating microstrip antenna fed by coplanar waveguide as an essential part of the quasi-optical antenna-mixer before. Its manufacturing error was considerable, however, because it was a stacked-configuration. In this report, we make up a simple Quasi-Optical Antenna-Mixer using a magnetic loop antenna. In addition, the antenna that performs in 3.0GHz band is made and performance of beam scanning is confirmed experimentally with the arrayed ones.
  • OYANE Hidehiko, NISHIMURA Toshihiko, ITOH Kiyohiko  Technical report of IEICE. RCS  99-  (637)  111  -116  2000/02/17  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms RF signal into intermediate frequency signal as soon as the system receives the RF signal and local oscillator's signal spatially. Using this system, we can reduce transmission loss, which causes serious problem in the millimeter-wave band. We presented a dual frequency operating microstrip antenna fed by coplanar waveguide as an essential part of the quasi-optical antenna-mixer before. Its manufacturing error was considerable, however, because it was a stacked-configuration. In this report, we make up a simple Quasi-Optical Antenna-Mixer using a magnetic loop antenna. In addition, the antenna that performs in 3.0GHz band is made and performance of beam scanning is confirmed experimentally with the arrayed ones.
  • OYANE Hidehiko, NISHIMURA Toshihiko, ITOH Kiyohiko  Technical report of IEICE. SST  99-  (628)  111  -116  2000/02/17  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms RF signal into intermediate frequency signal as soon as the system receives the RF signal and local oscillator's signal spatially. Using this system, we can reduce transmission loss, which causes serious problem in the millimeter-wave band. We presented a dual frequency operating microstrip antenna fed by coplanar waveguide as an essential part of the quasi-optical antenna-mixer before. Its manufacturing error was considerable, however, because it was a stacked-configuration. In this report, we make up a simple Quasi-Optical Antenna-Mixer using a magnetic loop antenna. In addition, the antenna that performs in 3.0GHz band is made and performance of beam scanning is confirmed experimentally with the arrayed ones.
  • OYANE Hidehiko, NISHIMURA Toshihiko, ITOH Kiyohiko  Technical report of IEICE. RCS  99-  (637)  111  -116  2000/02/17  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms RF signal into intermediate frequency signal as soon as the system receives the RF signal and local oscillator's signal spatially. Using this system, we can reduce transmission loss, which causes serious problem in the millimeter-wave band. We presented a dual frequency operating microstrip antenna fed by coplanar waveguide as an essential part of the quasi-optical antenna-mixer before. Its manufacturing error was considerable, however, because it was a stacked-configuration. In this report, we make up a simple Quasi-Optical Antenna-Mixer using a magnetic loop antenna. In addition, the antenna that performs in 3.0GHz band is made and performance of beam scanning is confirmed experimentally with the arrayed ones.
  • 大矢根 秀彦, 西村 寿彦, 伊藤 精彦  電子情報通信学会技術研究報告  99-  (631)  111  -116  2000/02/17  [Not refereed][Not invited]
  • 大矢根 秀彦, 西村 寿彦, 伊藤 精彦  電子情報通信学会技術研究報告  99-  (637)  111  -116  2000/02/17  [Not refereed][Not invited]
  • KISHIYAMA Yoshihisa, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. SAT  99-  (567)  17  -24  2000/01/21  [Not refereed][Not invited]
     
    Recently, with the demand on capacity increase, space division multiple access (SDMA) has been studied in order to improve the channel efficiency. The SDMA requires high performance interference canceller such as an adaptive array which reduces the interference signals by steering nulls to those. In this paper, we propose a channel response assisted adaptive array (CRA-AA), and compare its performance with MMSE adaptive array and joint detection. We also discusse degradation due to carrier frequency offset and its compensation. The computer simulations show that the CRA-AA provides a good performance in the situation having fast fading and carrier frequency offset.
  • KISHIYAMA Yoshihisa, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  99-  (569)  17  -24  2000/01/21  [Not refereed][Not invited]
     
    Recently, with the demand on capacity increase, space division multiple access (SDMA) has been studied in order to improve the channel efficiency. The SDMA requires high performance interference canceller such as an adaptive array which reduces the interference signals by steering nulls to those. In this paper, we propose a channel response assisted adaptive array (CRA-AA), and compare its performance with MMSE adaptive array and joint detection. We also discusse degradation due to carrier frequency offset and its compensation. The computer simulations show that the CRA-AA provides a good performance in the situation having fast fading and carrier frequency offset.
  • KISHIYAMA Yoshihisa, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  99-  (569)  17  -24  2000/01/21  [Not refereed][Not invited]
     
    Recently, with the demand on capacity increase, space division multiple access (SDMA) has been studied in order to improve the channel efficiency. The SDMA requires high performance interference canceller such as an adaptive array which reduces the interference signals by steering nulls to those. In this paper, we propose a channel response assisted adaptive array (CRA-AA), and compare its performance with MMSE adaptive array and joint detection. We also discusse degradation due to carrier frequency offset and its compensation. The computer simulations show that the CRA-AA provides a good performance in the situation having fast fading and carrier frequency offset.
  • 岸山 祥久, 大鐘 武雄, 西村 寿彦  電子情報通信学会技術研究報告  99-  (565)  17  -24  2000/01/21  [Not refereed][Not invited]
  • NISHIMURA Toshihiko, DOI Yoshiharu, OHGANE Takeo, OGAWA Yasutaka, KITAKADO Jun  Technical report of IEICE. RCS  99-  (357)  103  -108  1999/10/15  [Not refereed][Not invited]
     
    It is a serious problem that interference is not efficiently canceled when the interference signals arrive from close directions to that of desired signal in an SDMA system, in which an adaptive array is used as the interference canceler. In this paper, we propose space domain-multistage interference canceler for the SDMA as a method to overcome the problem. The performance of this method is evaluated by computer simulations considering the PHS reverse link environment. The results show the remarkable improvement in high spatial-correlation situations.
  • NISHIMURA Toshihiko, DOI Yoshiharu, OHGANE Takeo, OGAWA Yasutaka, KITAKADO Jun  Technical report of IEICE. RCS  99-  (357)  103  -108  1999/10/15  [Not refereed][Not invited]
     
    It is a serious problem that interference is not efficiently canceled when the interference signals arrive from close directions to that of desired signal in an SDMA system, in which an adaptive array is used as the interference canceler. In this paper, we propose space domain-multistage interference canceler for the SDMA as a method to overcome the problem. The performance of this method is evaluated by computer simulations considering the PHS reverse link environment. The results show the remarkable improvement in high spatial-correlation situations.
  • TANABE Yasuhiko, FUJISHIMA Kenzaburoh, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  Technical report of IEICE. RCS  99-  (356)  89  -95  1999/10/14  [Not refereed][Not invited]
     
    In high speed TDMA mobile communications, frequency-selective fading is a serious problem because a delay difference between multipath signals is large in comparison with symbol duration. We have proposed spatial-domain path-diversity using a multibeam adaptive antenna. In the spatial-domain path-diversity system, the multibeam adaptive antenna resolves multipath signals in the spatial domain, and the system combines array outputs aligning the delay time. In this paper, we propose the application of MUSIC algorithm to estimate the delay time. Because estimation of the delay time using the MUSIC algorithm is precise, the BER (Bit Error Rate) performance of the proposed scheme is improved. Furthermore, we propose weighting factors which easily realize the maximal ratio combining.
  • TANABE Yasuhiko, FUJISHIMA Kenzaburoh, NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo  Technical report of IEICE. RCS  99-  (356)  89  -95  1999/10/14  [Not refereed][Not invited]
     
    In high speed TDMA mobile communications, frequency-selective fading is a serious problem because a delay difference between multipath signals is large in comparison with symbol duration. We have proposed spatial-domain path-diversity using a multibeam adaptive antenna. In the spatial-domain path-diversity system, the multibeam adaptive antenna resolves multipath signals in the spatial domain, and the system combines array outputs aligning the delay time. In this paper, we propose the application of MUSIC algorithm to estimate the delay time. Because estimation of the delay time using the MUSIC algorithm is precise, the BER (Bit Error Rate) performance of the proposed scheme is improved. Furthermore, we propose weighting factors which easily realize the maximal ratio combining.
  • 田辺 康彦, 藤嶋 堅三郎, 西村 寿彦  電子情報通信学会技術研究報告  99-  (354)  89  -95  1999/10/14  [Not refereed][Not invited]
  • 田辺 康彦, 藤嶋 堅三郎, 西村 寿彦  電子情報通信学会技術研究報告  99-  (356)  89  -95  1999/10/14  [Not refereed][Not invited]
  • NISHIMURA Toshihiko, TANABE Yasuhiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the Society Conference of IEICE  1999-  (1)  314  -314  1999/08/16  [Not refereed][Not invited]
  • NISHIMURA Toshihiko, TANABE Yasuhiko, OHGANE Takeo, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  99-  (141)  61  -66  1999/06/24  [Not refereed][Not invited]
     
    Since the preamble in PHS is common for all users, it can not be used for training the adaptive array weight as it is. Considering the PHS/SDMA system, only one solution is to provide the transmission timing difference between the users accommodated in the same channel. Then, the timing detection is required. For the first user, it is easy to estimate it since there is no interference. However, the timing of the second user must be estimated in rich interfered situation. In this paper, with some estimation methods the estimation performance is evaluated.
  • KISHIYAMA Yoshihisa, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  99-  (141)  67  -72  1999/06/24  [Not refereed][Not invited]
     
    In TDD/SDMA employing an adaptive array at a base station, generally, the array pattern for down-link is calculated from that for up-link. Considering the angle spread in the Rayleigh fading channel, time difference between up and down-link causes null position changes on the optimum array pattern. In this paper, we propose the weight estimation method for the down-link null forming. It is based on that the weight is uniquely determined by the array response vector. Here, we discuss the array response estimation and the performance of the down-link null forming.
  • NISHIMURA Toshihiko, TANABE Yasuhiko, OHGANE Takeo, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  99-  (141)  61  -66  1999/06/24  [Not refereed][Not invited]
     
    Since the preamble in PHS is common for all users, it can not be used for training the adaptive array weight as it is. Considering the PHS/SDMA system, only one solution is to provide the transmission timing difference between the users accommodated in the same channel. Then, the timing detection is required. For the first user, it is easy to estimate it since there is no interference. However, the timing of the second user must be estimated in rich interfered situation. In this paper, with some estimation methods the estimation performance is evaluated.
  • KISHIYAMA Yoshihisa, OHGANE Takeo, NISHIMURA Toshihiko, OGAWA Yasutaka, DOI Yoshiharu  Technical report of IEICE. RCS  99-  (141)  67  -72  1999/06/24  [Not refereed][Not invited]
     
    In TDD/SDMA employing an adaptive array at a base station, generally, the array pattern for down-link is calculated from that for up-link. Considering the angle spread in the Rayleigh fading channel, time difference between up and down-link causes null position changes on the optimum array pattern. In this paper, we propose the weight estimation method for the down-link null forming. It is based on that the weight is uniquely determined by the array response vector. Here, we discuss the array response estimation and the performance of the down-link null forming.
  • KAICHIDA Tsuyoshi, ISHII Nozomu, YAMAMOTO Manabu, NISHIMURA Toshihiko, ITOH Kiyohiko  The Transactions of the Institute of Electronics,Information and Communication Engineers B  82-  (6)  1177  -1184  1999/06  [Not refereed][Not invited]
     
    ミリ波帯においては，伝送線路による損失が大きいという問題が生じる．そこで，アンテナとミキサを一体化し，伝送損失を軽減することのできる準光学アンテナミキサがある．これは，高周波と局部発信周波の異なる二つの周波数を空間的に受信し，直後に中間周波数に変換するものである．これを実現することのできるアンテナとして，コプレーナ導波路給電による2周波動作可能なマイクロストリップアンテナがある．本論文においては，スペクトル領域モーメント法を用い，このアンテナの周波数1/20スケールモデルの入力特性をマイクロ波帝で解析し，異なる二つの周波数で独立に動作可能であることを示す．更に，本アンテナの放射指向性を絶対利得により評価する．
  • NISHIMURA Toshihiko, OHGANE Takeo, OGAWA Yasutaka  Proceedings of the IEICE General Conference  1999-  (1)  399  -399  1999/03/08  [Not refereed][Not invited]
  • OYANE Hidehiko, NISHIMURA Toshihiko, ISHII Nozomu, ITOH Kiyohiko  IEICE technical report. Microwaves  98-  (198)  1  -6  1998/07/24  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms the RF signal into the intermediate frequency signal (IF) as soon as the system receives the RF and the local oscillator's signal (LO) signals spatially. Using thes system, we can remove transmission loss that causes great problem in the millimeter-wave band. Generally, a low-pass-filter needs to prevent the RF and LO from mixer output. In this report, we propose a new configuration for canceling the RF and LO from total output on the quasi-optical antenna mixer without the filter. We fabricate a microwave band model to prove that the RF and LO are canceled from the output experimentally.
  • ITOH Kiyohiko, OGAWA Yasutaka, NISHIMURA Toshihiko, FUKUCHI Hisanao  Proceedings of the IEICE General Conference  1998-  (2)  267  -268  1998/03/06  [Not refereed][Not invited]
  • NISHIMURA Toshihiko, TSUCHIDA Katsumi, ISHII Nozomu, ITOH Kiyohiko  The Transactions of the Institute of Electronics,Information and Communication Engineers. B-(0xF9C2)  80-  (12)  1076  -1083  1997/12  [Not refereed][Not invited]
     
    準光学アンテナ・ミキサは，高周波信号（RF）と局部発振周波（LO）を空間的に受信し，直後に中間周波数の信号に変換するシステムである．このシステムを用いることで，高周波回路は不要となり，特に周波数が高いときには，損失を大きく低減することができる．本論文では，準光学アンテナ・ミキサを実現するシステムとして，ミキサダイオードを装荷したコプレーナ導波路給電による2周波マイクロストリップアンテナを提案する．従来，準光学アンテナ・ミキサに用いられてきた受信部において，一方向からRFとLOを合成して入力していたため，LOの入射がRFの入射に干渉するという問題があった．そこで本論文では，基板の両側でRFとLOを独立して受信することができる構造を用いて準光学アンテナ・ミキサを構成した．まずミリ波帯において，受信部の設計を行い，電磁界シミュレータを用いてその特性を明らかにした．更に，マイクロ波帯において，本システムを試作し，受信部の2周波動作およびミキシング動作に関する実験を行った．その結果，本システムが準光学アンテナ・ミキサとして機能することが確認された.
  • NISHIMURA Toshihiko, TSUCHIDA Katsumi, ISHII Nozomu, ITOH Kiyohiko  IEICE technical report. Antennas and propagation  97-  (382)  73  -78  1997/11/20  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms the RF signal and the local oscillator's signal (LO) into the intermediate frequency signal as soon as the system receives the RF and LO signals spatially. We have proved a novel beam scanning system with the quasi-optical antenna-mixer array. In the report, we describe experimental results in the microwave band. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters in the phased array. Therefore, not only losses in RF circuits are reduced but also the system is easily designed because of its simple structure.
  • NISHIMURA Toshihiko, TSUCHIDA Katsumi, ISHII Nozomu, ITOH Kiyohiko  Technical report of IEICE. RCS  96-  (531)  25  -32  1997/02/21  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms the RF signal and the local oscillator's signal (LO) into the intermediate frequency signal as soon as the system receives the RF and the LO spatially. In the report, we propose a novel receiving system with the multi-element quasi-optical antenna-mixer. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters in the phased array. Therefore, not only losses in RF circuits are reduced but also the system is designed easily because of its simple structure. We made this system in the microwave band, and verified that experimental results agree with analytical ones very much.
  • NISHIMURA Toshihiko, TSUCHIDA Katsumi, ISHII Nozomu, ITOH Kiyohiko  IEICE technical report. Microwaves  96-  (534)  25  -32  1997/02/21  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms the RF signal and the local oscillator's signal (LO) into the intermediate frequency signal as soon as the system receives the RF and the LO spatially. In the report, we propose a novel receiving system with the multi-element quasi-optical antenna-mixer. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters in the phased array. Therefore, not only losses in RF circuits are reduced but also the system is designed easily because of its simple structure. We made this system in the microwave band, and verified that experimental results agree with analytical ones very much.
  • NISHIMURA Toshihiko, TSUCHIDA Katsumi, ISHII Nozomu, ITOH Kiyohiko  IEICE technical report. Antennas and propagation  96-  (525)  25  -32  1997/02/21  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms the RF signal and the local oscillator's signal (LO) into the intermediate frequency signal as soon as the system receives the RF and the LO spatially. In the report, we propose a novel receiving system with the multi-element quasi-optical antenna-mixer. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters in the phased array. Therefore, not only losses in RF circuits are reduced but also the system is designed easily because of its simple structure. We made this system in the microwave band, and verified that experimental results agree with analytical ones very much.
  • NISHIMURA Toshihiko, TSUCHIDA Katsumi, ISHII Nozomu, ITOH Kiyohiko  Technical report of IEICE. RCS  96-  (531)  25  -32  1997/02/21  [Not refereed][Not invited]
     
    The quasi-optical antenna mixer system transforms the RF signal and the local oscillator's signal (LO) into the intermediate frequency signal as soon as the system receives the RF and the LO spatially. In the report, we propose a novel receiving system with the multi-element quasi-optical antenna-mixer. The arrival direction of the RF signal can be controlled by the system without RF circuits such as phase shifters in the phased array. Therefore, not only losses in RF circuits are reduced but also the system is designed easily because of its simple structure. We made this system in the microwave band, and verified that experimental results agree with analytical ones very much.
  • KURIBAYASHI Masashi, OHSHIMA Kenji, NISHIURA Toshihiko, ITOH Kiyohiko  Technical report of IEICE. SAT  96-  (168)  67  -73  1996/07/22  [Not refereed][Not invited]
     
    Complex conductivity of superconductor (CCS) is a principal parameter in the case of estimation for surface impedance of superconductor. Usual investigation on CCS is based on two fluid model, which is constructed on the assumption that electron pair has not collission with phonon. However, real part of CCS and surface impedance that derived from above two fluid model are not agree with measured values. We formulate modified two fluid model provided that moving electron pair has characteristic of equivalent loss which depend on high frequency electric field, and both density of super and normal electron are related by Rate equation. Furthermore, CCS and surface impedance are formulated by using modified two fluid model. Finally, numerical results of real part of CCS and surface impedance which obtained by modified two fluid model are agree with measured values.
  • NISHIMURA Toshihiko, ISHII Nozomu, ITOH Kiyohiko  IEICE technical report. Antennas and propagation  96-  (35)  27  -34  1996/05/16  [Not refereed][Not invited]
     
    In mm wave band, there is serious problem on the transmission line loss. The loss can be omitted by using the quasi-optical antenna mixer system, which can transfer RF and LO to IF without the transmission line. In this report, we propose "a dual frequency operation microstrip antenna system fed by coplanar waveguide" for the above system, and calculate its RF characteristics numerically. As a result, we find that the matching for two patches can be easily achieved by using the coplanar waveguide, because of the flexibility of the line design. The front to back ratio is better, because the patches are located on both side of the grand plane. And the antenna system can be operated at the two different frequencies when the resonant frequencies are somewhat separated.
  • Murata Tomohiro, Nishimura Toshihiko, Ishii Nozomu, Itoh Kiyohiko  IEICE technical report. Electromagnetic compatibility  95-  (134)  29  -34  1995/06/29  [Not refereed][Not invited]
     
    In this paper, we analyze resonance frequency and quality factor(Q-factor) of superconducting circular patch antennas. Superconductors have lower surface impedance than cuppers at the range of low frequency. On account of this, we expect application of superconductors to microwave devices to become characteristics better. We use the two-fluid model to consider frequency dependency of superconductors surface impedance. We use spectral-domain method to analyze the antennas. We find current expand function on circular patch on Fourier transform domain, in general we should use Hankel transform domain on circular, and formulate this process.
  • Nishimura T., Suzuki F., Nozaki R., Shiozaki Y.  Abstracts of the meeting of the Physical Society of Japan. Annual meeting  48-  (2)  113  -113  1993/03/16  [Not refereed][Not invited]
  • Ando K, Nishimura T, Nozaki R, Shiozaki Y  秋の分科会講演予稿集  1992-  (2)  64  -64  1992/09/14  [Not refereed][Not invited]

Presentations

  • [Tutorial] Orbital Angular Momentum for Wireless Communications: From Fundamentals to Implementation and Extension,  [Not invited]
    T. Nishimura, F. Maehara, E. Sasaki, D. Lee
    IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC2022)  2022/09

Teaching Experience

  • Communication SystemsCommunication Systems Hokkaido University

Association Memberships

  • The Institute of Electrical and Electronics Engineers (IEEE)   Institute of Electronics, Information and Communication Engineers (IEICE)   

Research Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2027/03 
    Author : 村田 英一, 岡本 英二, 井田 悠太, 丸田 一輝, 岡田 啓, 實松 豊, 西村 寿彦, 牟田 修, 田野 哲, 眞田 幸俊
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2023/04 -2027/03 
    Author : 大鐘 武雄, 筒井 弘, 西村 寿彦
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2020/04 -2023/03 
    Author : 西村 寿彦, 大鐘 武雄
     
    マルチユーザ大規模MIMOシステムでは, 基地局に100 素子以上の送信アンテナ素子を配置することに伴い, ウェイト形成の計算量が著しく増大する. このため,送信に使用するアンテナを選択するのみでウェイトを生成するルースビームフォーミングという手法が提案されている. 今年度は, 主に以下の2点について検討を行った． 一つ目は，ルースビームフォーミングの送信アンテナ選択について，前年度は機械学習や遺伝的アルゴリズムを用いて準最適解を得ていたが，新たに量子アニーリングを導入した．量子アニーリングは，組み合わせ最適化問題に特化したクラウドソルバーとして商用利用されるようになり，近年その用途について多くの検討が始まってきた．ルースビームフォーミングは送信アンテナを使うか使わないかの2値のベクトルを通信容量が最大となるように最適化することで実現できることから，この量子アニーリングが有用なソルバーとなりえると考えた．検討の結果，前年度に用いた機械学習や遺伝的アルゴリズムに比べて，極めて短時間で同程度の性能を得られる可能性を確認した． 二つ目は，マルチユーザ大規模MIMOシステムについて，ルースビームフォーミングと分散アンテナシステムの類似性から，分散大規模MIMOシステムにおけるアンテナ選択及びユーザ選択の検討を行った．屋内環境における大規模分散アンテナシステムを想定し，ユーザ選択及びアンテナ選択の効果を評価した．検討したモデル内では，アンテナ選択については有意な改善は見られなかったものの，ユーザ選択の効果は示された．
  • 確率伝搬法による大規模・過負荷MIMO信号検出を用いた超多数IoTデバイスの収容
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2018/04 -2021/03 
    Author : 大鐘 武雄, 西村 寿彦, 林 和則, 衣斐 信介, 石橋 功至
     
    1000個程度までの超多数IoTデバイスを同時に収容し，多数のアンテナ，あるいは，サブキャリアを用いて多数信号の同時信号検出を信号数の2乗オーダーで実現することを目的としている． 2018年度は初年度であるため，具体的なIoTデバイス収容手法を新たに想定することとした．その結果，SCMA (sparse code multiple access), IDMA (interleave division multiple access) MIMO-OFDM, サブキャリアIQインデックス変調に着目し，ガウス確率伝搬法による検出を行なった．その結果，どの手法においても過負荷，すなわち，信号数が受信信号数より多くても検出可能であることがわかった． SCMAに関しては，LLRの適応スケーリング，LLRの非均質化の有効性や，サブキャリア間相関による最適利用率の変化など，新たな知見が得られた．また，MIMO-OFDMおよびサブキャリアIQインデックス変調では，信号の離散性とグループスパース性，プリプロセッシングによる近似メッセージ伝搬が十分に適用できることが確認された．特に，検出すべき信号が限られた値のみ取るという性質が近似メッセージ伝搬を始めとする圧縮センシング技術等で有効であることがわかった． これ以外の基礎的分野では，要素技術であるチャネル推定と，チャネル符号として注目されているPolar符号の繰り返し復号への応用も新たに検討が開始されている．
  • 大規模MIMOシステムにおけるアンテナ選択によるビーム制御
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2017/04 -2020/03 
    Author : 西村 寿彦, 大鐘 武雄
     
    送信側受信側双方に複数のアンテナ素子を搭載するMultiple-Input Multiple-Output (MIMO)システムを発展させた、大規模MIMOシステムの研究が進められている。一般にこのシステムでは、3次元的なユーザ分離が可能となり、複数ユーザと基地局が同時に通信するマルチユーザMIMOシステムを実現するのに有効で、システムのスループットを飛躍的に上げることができる。但し、アンテナ素子の全てに高性能な信号処理機能を持たせる必要があり、製造コスト上の問題がある。本研究では、圧縮センシング法と呼ばれる新しい信号処理手法などを用いて、マルチユーザアクセスを低コストで実現し、第5世代以降の通信システムに供することを目的とする。 昨年度は、主にFD-MIMOシステムでマルチユーザ分離を実現するためのアンテナ素子選択アルゴリズムの確立を目指した。遺伝的アルゴリズムを用いて、最適なビーム形成を可能とするアンテナ素子を選択する。各アンテナは、その位置の違いによりそれぞれ異なるチャネル応答を持つため、それらのいくつかを選び出して組み合わせることで、素子数と同じだけの送受信機を装備することなく柔軟なビーム形成が可能となることを示した。また、圧縮センシングを実装することを前提に、電波の到来方向推定を例にとって、各種アルゴリズムの比較を行った。 今年度は、昨年度のマルチユーザ分離を実現するためのアンテナ素子選択アルゴリズムの開発を進めつつ、よりユーザ分離能力を高めるため、大規模MIMOのアンテナ素子をサブアレー化して分散配置する方法について検討を進めた。また、圧縮センシングを実装する電波の到来方向推定のための実験環境を整えた。さらに、電波の到来方向推定については、深層学習を導入する方法についても検討を始めた．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2018/03 
    Author : Takeo Ohgane
     
    It is known that we can obtain the global solution of a complex problem by decomposing it into multiple sub-problems and solving the small problems with exchanging the partial solution (reliability information) among them. The correct solution may not be obtained when some reliability exchange loops exist. However, an exception, i.e., an appropriate convergence can be seen if the problem size is very large. In this project, we tried many tests under various situations and obtained the fact that the effect of incorrect reliability propagation decreases with the problem size. From this results, we have succeeded developing a method adjusting the reliability information. In addition, the validity of the obtained method has been confirmed by another optimization approach.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : OHGANE Takeo, OGAWA Yasutaka, NISHIMURA Toshihiko, WEBBER Julian
     
    Wireless mesh networks are considered as an efficient candidate for a substitution of communication infrastructure in disaster situations. Such a network is suffered by mutual interferences between nodes since all nodes are reachable. We studied a cross layer processing to exploit this overreach by using beam/null control at each node. Specifically, beam/null control and its experimental test using USRP in the layer 2 were carried out. In addition, we clarified that the alternative routing with beam/null control in the layer 3 improved the throughput performance.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011/04 -2014/03 
    Author : OGAWA YASUTAKA, OHGANE Takeo, NISHIMURA Toshihiko
     
    A transmitter side needs channel state information in multi-user MIMO downlinks. In time-varying environments, channels at the actual downlink transmission time are different from estimated channels, which situation causes interference and performance degradation. The purpose of this study was to improve the multi-user MIMO system performance predicting channels at the transmission time. As for the channel prediction scheme, we examined autoregressive (AR)-model-based prediction and Lagrange extrapolation. We evaluated the MIMO transmission performance using channels obtained in a measurement campaign in indoor environments. It has been shown that the Lagrange extrapolation that is easy to implement can predict channels in the range over 0.1 wavelengths without significant performance degradation.
  • 圧縮サンプリング手法を使用したマルチバンドMIMOレーダの検証実験
    総務省：戦略的情報通信研究開発推進制度 (SCOPE)
    Date (from‐to) : 2013/11 -2014/03 
    Author : 西村 寿彦
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2012 
    Author : OHSHIMA Kohzoh, MURASMOTO Mitsuru, OGAWA Yasutaka, KASHIWA Tatsuya, TAGUCHI Kenji, IMAI Suguru, OHGANE Takeo, NISHIMURA Toshihiko
     
    In this research, we tried to apply Genetic Algorithm, Immune Algorithm andParticle Swarm Optimization to high resolution direction of arrival estimation.When the incident wave in the near field sources becomes a spherical wave, the complex calculation is needed with theMUSIC method though the incident wave was assumed to be a plane wave in conventional ways ofDOA estimation.As results of simulations, we confirmed the accuracy of direction of arrival estimation with metaheuristics and have shown its effectiveness.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2012 
    Author : NISHIMURA Toshihiko, OGAWA Yasutaka, OHGANE Takeo
     
    In this research, the method of relative position detection oftransmission and reception terminals, i.e. realization of a multi-input-multi-output (MIMO) radar, has examined by using the MIMO system which carries multi antenna elements in both terminals. As a problem, when many terminals existed, or when a multipass wave existed, many interference waves will enter into a receiving side, and it was predicted that the position estimate became difficult. Then, the technique of the position estimate of the terminals was developed by using the broadband signals. The broadband signal is divided into multi narrow band signals. Then, a conventional direction of arrival estimation method is adopted by rising from low frequency without the influence of a grating robe to the high frequency from which high resolution is obtained
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009 -2011 
    Author : OHGANE Takeo, OGAWA Yasutaka, NISHIMURA Toshihiko, WEBBER Julian
     
    In the wireless mesh network with nodes capable beam-forming, we have obtained the following three major achievements. (1) The approximate solution for maximizing sum-capacity has been developed and its high performance has been shown in network-coded links. (2) An suboptimum routing has been proposed for a wireless mesh network with nodes capable beam-forming and its high throughput performance has been indicated. (3) We have derived an approximated solution for the optimum beam-forming at the source node in a two-step relay.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2007 -2009 
    Author : OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko
     
    Future mobile communications need to use a higher frequency band to accommodate a wider frequency bandwidth. In a higher frequency band, the attenuation of electromagnetic waves is severely large. In an uplink channel, we may have difficulties to realize reliable transmission because the transmit power of a user terminal is limited due to battery use. In this study, we have proposed a virtual antenna array in which plural user terminals cooperate with each other and operate as a single terminal. The virtual antenna array forms transmit beams toward a base station. We have proposed several elemental technologies to realize the virtual antenna array. It has been shown that when four user terminals cooperate each other, we can reduce transmit power by about 6dB comparing with a conventional single user terminal case.
  • 疑似固有ビーム伝送技術の研究開発
    総務省：戦略的情報通信研究開発推進制度 (SCOPE)
    Date (from‐to) : 2007 -2008 
    Author : 大鐘武雄
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2006 -2008 
    Author : NISHIMURA Toshihiko
     
    MIMO-UWB-IR(Multiple-Input Multiple-Output:多入力‐多出力- Ultra-Wide-Band:超広帯域- Impulse Radio)通信システムを用いて移動体の高精度位置検出を行うための基礎研究を行った。MIMO-UWB通信の実験装置の構築、MIMOチャネルの取り扱い(テストベット構築、実伝搬環境での実験、チャネル推定法の検討)、信号到来方向推定アルゴリズムの提案を行った。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
    Date (from‐to) : 2004 -2005 
    Author : 西村 寿彦
     
    1.昨年度は、市販のオムニアンテナによりトライポールアンテナを構成したが、指向性や物理的大きさに制限があり、本研究の目的を遂行するには十分でない部分があった。そこで、本年度は、小型のオムニアンテナを製作し、理想的なトライポールアンテナを試作した。さらに、比較のため、トライポールアンテナと同じ素子で構成した3素子リニアアレーアンテナ、3素子円アレーアンテナも試作した。 2.前述の3種類のアレーアンテナによるMIMOチャネル通信がどのような環境で有効に働くかに重点を置き、周囲の散乱状況の異なる環境で複数の測定を行って伝搬データを取得した。取得したデータを用いて、フェージング相関、平均ビット誤り率特性、チャネルによって生成される行列の固有値分布、および、通信容量について計算機による数値解析を行い、その結果を比較した。その結果、トライポールアンテナは低いフェージング相関を与えること、ビット誤り率等では同等の特性を示すことがわかった。実験環境のような見通し内環境では、フェージング相関よりも受信電力の絶対値がその特性に大きく作用するためと結論付けられる。反射による偏波回転の多い環境が存在すればトライポールアンテナの使用が効果的であると予想される。 3.MIMOチャネル通信を実現する有効な方式として注目されているE-SDM(Eigenbeam-Space Division Multiplexing)方式を実装したテストベットを構築した。さらに、本テストベットを使用してフェージングシミュレータを用いた3×2MIMOチャネル実験を行い、提案アルゴリズムのリアルタイム動作を検証した。また、前年度に、送信リソース制御による計算負荷を軽減する方法を提案したが、今年度は素子数(ストリーム数)の制限のない方式を提案し、更なる計算負荷の軽減に成功した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : OGAWA Yasutaka, OHGANE Takeo, NISHIMURA Toshihiko
     
    1. Evaluation of the channel estimation and BER performance using an experimental system : An OFDM demodulation system was built up using DSP boards. Experimentally, we validated the OFDM channel estimation scheme proposed by our group. The channel was calculated by FFT applying to the impulse response obtained by the minimum square error method in the time domain. Then, we evaluated the bit error rate (BER) performance of the proposed OFDM system. Also, we examined an ordered successive detection method and transmission with error correcting codes. 2. Joint estimation of channel and frequency offset : We proposed a joint estimation scheme of the channel and frequency offset using only 4 OFDM training symbols. It was shown that we can estimate them accurately and can obtain good BER performance. 3. Reduction of the amount of channel state information (CSI) feedback : Eigenbeam-space division multiplexing (E-SDM) requires the feedback of CSI in frequency division duplex systems. In order to reduce the amount of the feedback, we proposed a new scheme. The scheme estimates the impulse response using the minimum square error method in the time domain, and feedback the impulse response. This reduces the amount of CSI feedback comparing with the feedback of all the subcarrier channel. 4. Evaluation of MIMO propagation : The performance of MIMO systems depends on electromagnetic wave propagation environments. We conducted propagation measurement in line-of-sight (LOS) and nonline-of-sight (NLOS) environments. It was shown that the BER performance is better in LOS environments than that in NLOS ones. However, it was also shown that the performance depends highly on the MIMO configurations in LOS environments.
  • 固有ビーム分割多重方式の実現に関する研究
    総務省：戦略的情報通信研究開発推進制度 (SCOPE)
    Date (from‐to) : 2003 -2004 
    Author : 小川恭孝
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2001 -2003 
    Author : OHGANE Takeo, YAMAMOTO Manabu, NISHIMURA Toshihiko, OGAWA Yasutaka
     
    In multiple-input multiple-output systems, most common application is space division multiplexing (SDM) where individual data substreams are transmitted from multiple antennas with the same power and the same rate. SDM applications assume that MIMO channel information in not available at the transmitter. If we know all of MIMO channel information, it is possible to assign matched beam to each substream where the optimum weight for beamforming is obtained by singular value decomposition of MIMO channel matrix. We call SDM with eigenbeam-forming as E-SDM, hereafter. In E-SDM, we have to consider resource (transmit power and data rate) adaptation. In this research, we employed minimum brt error rate (BER) criterion as expansion of transmit power control per sucarrier previously used in OFDM systems. As a result, E-SDM with the resource adaptation obtained higher BER performance in comparison to conventional SDM. However, the MIMO channel information required at the transmitter includes estimation and tracking errors. Under such errors, we also evaluated the E-SDM performance. The results show that degradation due to the channel estimation error is almost the same to E-SDM and SDM applications. Although the channel tracking error caused by a time lag until transmission degrades E-SDM performace severely when the maximum Doppler frequency is very high, we have shown that it can be compensated by employing the first-order extrapolation of estimated channel.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
    Date (from‐to) : 2001 -2002 
    Author : 西村 寿彦
     
    第4世代の移動通信に必要不可欠な大容量高速通信を実現するために、送信側・受信側にそれぞれ複数のアンテナが存在する(Multiple-Input Multiple-Output : MIMO)環境での検討が進められている。本研究では、このように複雑な伝搬環境をシミュレーションし、その環境下で最も効率良く通信を行うための信号処理法式を開発することが目的であった。 本年度の研究では、MIMO環境に適した多重接続方式として、固有ビーム空間分割多重接続(Eigenbeam-Space Division Multiplexing : E-SDM)方式の提案を行った。この方式は、MIMO環境のチャネル情報をもとに送受信間で複数の固有ビームを形成し,それらに複数のストリームを対応させて通信を行うものである。固有ビームは直交しているため受信側で最大比合成を行うだけで干渉なく送信ストリームを取り出すことができる。ただし、その場合、送信側でMIMOチャネル情報を正確に知る必要があるが、実際のシステムではそれを完全に行うことが難しいため、チャネル情報の誤差の影響について考察し、また、一次外捜によってチャネル情報を推定した場合の特性についても調査した。 E-SDMでは、各ストリームの品質に応じて送信信号の電力と送信ビット数を調節して通信容量を最適化する。この手法は単純に各送信アンテナから異なるストリームを送信するSDM方式にも適用できるため、受信側でBLASTを用いる重みつきBLAST (w-BLAST)の特性と比較した。最後に、第4世代移動通信で用いられると予測されているパケット通信を、想定し、E-SDMとw-BLASTのスループット特性をシミュレーションし、特性を評価した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Exploratory Research
    Date (from‐to) : 1996 -1998 
    Author : 小川 恭孝, 西村 寿彦, 大鐘 武雄
     
    本研究は、種々の通信システムの最適化問題に人工生命の概念を導入することを目的としたものである。本研究においては、主に遺伝的アルゴリズムを用いた、移動通信の固定チャネル割り当て、ATM網のルーテイング、および、フェーズドアレーアンテナの低サイドローブ化について検討を行った。さらに、移動通信の最適受信法についても研究した。以下にその実施結果を述べる。 1. セルラー方式を用いた移動通信の固定チャネル割り当ては組み合わせ論的問題になるため、一般に膨大な演算が必要とされる。本研究では、まず、遺伝的アルゴリズムを適用することにより、チャネル割り当てを実現する方法の定式化を行った。ここで、遺伝的アルゴリズムの交鎖においてチャネル間干渉が生じない染色体構造を提案するなど、チャネル割り当てへの遺伝的アルゴリズムの適用にいくつかの新知見を得た。 2. ATM網のリンクコストを最小化する最適アルゴリズムも組み合わせ論的問題となる。このようなルーティングを遺伝的アルゴリズムにより実現する方法の定式化を行い、シミュレーションにより本アルゴリズムの評価を行った。 3. フェーズドアレーアンテナのサイドローブレベルを低減する励振位相を求めることは非線形最適化問題となる。各移相器の励振位相を連結したものを染色体とみなし、交鎖、突然変異、選択の遺伝的アルゴリズムの操作を適用した。これにより、短い演算時間でフェーズドアレーアンテナの低サイドローブ化が実現できることが分かった。 4. 多重伝搬波および干渉波が存在する環境下における移動通信の受信を最適化するアダプティブシステムを検討し、その特性の評価を行った。

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