Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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A novel contention-free medium access control protocol for inter-vehicle communication systems Reviewed

Masamura Mitsuru, Okada Hiraku, Makido Satoshi, Yamazato Takaya, Katayama Masaaki

2007 IEEE INTERNATIONAL CONFERENCE ON MOBILE AD-HOC AND SENSOR SYSTEMS, VOLS 1-3 page： 995 - + 2007

Iterative channel decoding scheme using the correlation of transmitted information sequences in sensor networks Reviewed

K. Kobayashi, T. Yamazato, H. Okada and M. Katayama

IEICE Transaction on Fundamentals of Electronics, Communications and Computer Sciences Vol. J89-A ( 12 ) page： 1044-1056 2006.12

Language：Japanese Publishing type：Research paper (scientific journal)

In sensor networks, many sensor nodes are densely deployed and observation data obtained by each sensor node are correlated. The observation data are encoded and transmitted from each sensor node. Such observation data are collected at a fusion center. In this paper, we extend the iterative channel decoding scheme using the correlation of transmitted information sequences to the case of more than two sensor nodes. An approach to use practical channel codes for more than two correlated data is still not presented. A problem in the extension to cases of more than two sensor nodes is how to use the information of correlation obtained from observation data. In this paper, we propose an iterative channel decoding scheme that uses them with weighting. We show that when the number of sensor nodes is increased, decoding performance improvement cannot be achieved by simple weighting, and so a more appropriate weight is needed. We find the weight that minimizes the bit error rate from the analytical formula for uncoded BPSK and apply it to the case of Turbo code.

Influence of ADC Nonlinearity on the Performance of an OFDM Receiver Reviewed

M. Sawada, H. Okada, T. Yamazato, M. Katayama

IEICE Transactions on Communications Vol. E89-B ( 12 ) page： 3250-3256 2006.12

Language：English Publishing type：Research paper (scientific journal)

This paper discusses the influence of the nonlinearity of analog-to-digital converters (ADCs) on the performance of orthogonal frequency division multiplexing (OFDM) receivers. We evaluate signal constellations and bit error rate performances while considering quantization errors and clippings. The optimum range for an ADC input amplitude is found as a result of the trade-off between quantization error and the effects of clipping. In addition, it is shown that the peak-to-average power ratio (PAPR) of the signal is not a good measure of the bit error rate (BER) performance, since the largest peaks occur only with very low probabilities. The relationship between the location of a subcarrier and its performance is studied. As a result, it is shown that the influence of the quantization error is identical for all subcarriers, while the effects of clipping depend on the subcarrier frequency. When clipping occurs, the BER performance of a subcarrier near the center frequency is worse than that near the edges.

Iterative Channel Decoding Scheme Using Correlation between Transmitting Data Sequences for Fading Channels

K. Kobayashi, T. Yamazato, H. Okada and M. Katayama

Technical Report of IEICE Vol. SN2006-45 page： 45-51 2006.12

Language：Japanese

In sensor networks, many sensor nodes are densely deployed and observation data obtained by each sensor node is correlated. The observation data is encoded and transmitted from each sensor node. Such observation data are collected at a fusion center. We consider a channel decoding scheme using the correlation of observation data at the fusion center. In our previous work, we have proposed an iterative joint channel decoding scheme for more than two sensor nodes. In this paper, based on our previous work in AWGN channels, we show that our proposed joint decoding scheme is effective in fading channels, too. As a result, we can obtain larger performance improvement than that in AWGN channel.

Influence of Characteristics of Wireless Channels on Quality of Wireless Control Systems Reviewed

R. Uchida, H. Okada, T. Yamazato, M. Katayama

IEICE Transaction on Fundamentals of Electronics, Communications and Computer Sciences Vol. J89-A ( 12 ) page： 1104-1107 2006.12

Language：Japanese Publishing type：Research paper (scientific journal)

In this manuscript, the employment of wireless data transmission for control of industrial machines in an indoor fading environment is considered. The relationship between the performance of the wireless control and that of the wireless transmission is studied in two types of the systems: the system with wireless transmission both for a control signal to a controlled target and a feedback signal from a sensor at the target; and the system that employs wireless transmission only for a control signal. As a result, it is shown that the performance of the systems can be improved by increasing the transmission rate as well as decreasing the error rate. The fact suggests how the wireless transmission should be designed to maintain high quality in wireless-controlled systems.

Channel estimation for BFDM/OQAM system in dispersive time-varying channels Reviewed

Mongol B.

3rd International Symposium on Wireless Communication Systems 2006, ISWCS'06 page： 159 - 163 2006.12

Influence of ADC nonlinearity on the performance of an OFDM receiver Reviewed

Manabu Sawada, Hiraku Okada, Takaya Yamazato, Masaaki Katayama

IEICE TRANSACTIONS ON COMMUNICATIONS Vol. E89B ( 12 ) page： 3250 - 3256 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

DOI： 10.1093/ietcom/e89-b.12.3250

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Throughput evaluation of ARQ scheme for multi-route coding in wireless multi-hop networks Reviewed

Okada H.

IEEE Vehicular Technology Conference Vol. 2 page： 668 - 672 2006.12

Iterative channel decoding scheme using the correlation of transmitted information sequences in sensor networks Reviewed

K. Kobayashi, T. Yamazato, H. Okada, M. Katayama

IEICE Transaction on Fundamentals Vol. J89-A ( 12 ) page： 1044-1056 - 1056 2006.12

Influence of Characteristics of Wireless Channels on Quality of Wireless Control Systems Reviewed

R. Uchida, H. Okada, T. Yamazato, M. Katayama

IEICE Transaction on Fundamentals Vol. J89-A ( 12 ) page： 1104-1107 - 1107 2006.12

MIMO Zero-forcing Equalizer for BFDM/OQAM Systems in the Time-Frequency Dispersive Channels Reviewed

B. Mongol, T. Yamazato, H. Okada, M. Katayama

IEICE Transaction on Fundamentals of Electronics, Communications and Computer Sciences Vol. E89-A ( 11 ) page： 3114-3122 2006.11

Language：English Publishing type：Research paper (scientific journal)

Pulse-shaping OFDM is well-known that it performs well in a mobile environment compared with conventional OFDM. However, in a highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Proper channel equalization is needed for further improvement of the systems. In this paper, a more general case, namely Biorthogonal Frequency Division System based on Offset QAM (BFDM/OQAM) is considered. We propose a multi-input multi-output (MIMO) transversal filter to equalize the time-frequency dispersive channel. Tap weights are calculated using the zero-forcing (ZF) algorithm. We also propose maximum-likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of BFDM/OQAM systems in the highly mobile environment.

MIMO Zero-forcing Equalizer for BFDM/OQAM Systems in the Highly Mobile Environments Reviewed

B. Mongol, T. Yamazato, H. Okada, M. Katayama

IEEE Global Communications Conference page： - 2006.11

Language：English

Pulse-shaping OFDM is well-known that it performs well in a mobile environment comparing with conventional OFDM. However, in highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Proper channel equalization is needed for further improvement of the systems. In this paper, more general case, namely Biorthogonal Frequency Division System based on Offset QAM (BFDM/OQAM) is considered. We propose a multi-input multi-output (MIMO) transversal filter to equalize the time-frequency dispersive channel. Tap weights are calculated using the zero-forcing (ZF) algorithm. We also propose maximum-likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of BFDM/OQAM systems in the highly mobile environment.

Influence of Transmit and Receive Correlations on Performance of the MIMO System with Multiple Antennas and Relay Terminals

R. Uchida, H. Okada, T. Yamazato, M. Katayama

MObile Radio Interdisciplinary Workshop (MORI Workshop) page： - 2006.11

A study on the Method for Reducing the Influence of the Interference Considering ADC Nonlinearity in an OFDM Receiver

M. Sawada, T. Yamazato, M. Katayama

Symposium on Information Theory and Its Applications (SITA) Vol. 2 page： 691-694 2006.11

Language：Japanese

In this paper we propose an OFDM receiver that mitigates the performance degradation caused by interference. The mitigation process is done all in digital after ADCs. The receiver estimates the reliability of each OFDM symbol based on its number of out-of-range samples. This reliability is then used as the external information in soft Viterbi decoding process. The results of numerical simulations for 16QAM/OFDM show that the proposed receiver is robust to strong interference.

MIMO zero-forcing equalizer for BFDM/OQAM systems in time-frequency dispersive channels Reviewed

Bayarpurev Mongol, Takaya Yamazato, Hiraku Okada, Masaaki Katayama

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E89A ( 11 ) page： 3114 - 3122 2006.11

Language：English Publishing type：Research paper (scientific journal) Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

DOI： 10.1093/ietfec/a89-a.11.3114

Web of Science

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MIMO zero-forcing equalizer for BFDM/OQAM systems in time-frequency dispersive channels Reviewed

Mongol Bayarpurev, Yamazato Takaya, Okada Hiraku, Katayama Masaaki

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E89A ( 11 ) page： 3114 - 3122 2006.11

A study on route selection metrics for the multiple-route packet combining scheme in wireless multihop networks Reviewed

Y. Hirayama, H. Okada, T. Yamazato, M. Katayama

IEICE Transactions on Communications Vol. J89-B ( 10 ) page： 2047-2051 2006.10

Iterative Joint Channel-Decoding Scheme Using the Correlation of Transmitted Information Sequences Reviewed

K. Kobayashi, T. Yamazato, H. Okada, M. Katayama

The 2006 International Symposium on Information Theory and Its Applications page： 808-813 2006.10

Language：English

In this study, we consider joint channel decoding of Turbo code for multiple correlated data that are observed by sensor nodes densely deployed in a sensor field. We focus on the correlation properties of observation data and try to reduce decoding error by an iterative procedure. An approach to use practical channel codes for more than two correlated data is still not presented. A problem in the extension to cases of more than two sensor nodes is how to use the information of correlation obtained from observation data. In this study, we propose an iterative channel decoding scheme that uses them with weighting. We show that when the number of sensor nodes is increased, decoding performance improvement cannot be achieved by simple weighting, and so a more appropriate weight is needed. We find the optimum weight that minimizes the bit error rate from the analytical formula for uncoded BPSK and apply it to the case of Turbo code.

Influence of Transmit and Receive Correlations on Performance of the MIMO System with Multiple Antennas and Relay Terminals Reviewed

R. Uchida, H. Okada, T. Yamazato, M. Katayama

The 2006 International Symposium on Information Theory and Its Applications page： 454-459 2006.10

Language：English

In this manuscript, spatial diversity for in-factory environments is considered. The proposed scheme uses multiple antennas at a transmitter and a receiver, and also multiple relay terminals to provide diversity gain against fading and shadowing. If the separation of antennas at the transmitter or the receiver is not enough, then diversity gain is influenced by correlation at the transmitter or the receiver. This manuscript shows the analytical and numerical results of the effects of transmit and receive correlations on bit error performance of the proposed spatial diversity scheme.

A Study on Blind Cooperative Relaying Scheme with Space-Time Block Coding

R. Uchida, H. Okada, T. Yamazato, M. Katayama

Technical Report of IEICE Vol. RCS2006-142 page： 55-60 2006.10

Language：Japanese

In this manuscript, a spatial diversity scheme with multiple transmit and receive antennas together with multiple relay terminals for packet radio is considered. Correctly received signals at relay terminals are re-transmitted to the base station with the spatial diversity by STBC cooperative relaying scheme. To achieve high diversity order with the conventional STBC cooperative relaying scheme, the relay terminals are required to exchange signaling information with each other. In this manuscript, a novel signaling scheme for the STBC cooperative relaying is proposed. The proposed scheme releases relay terminals exchanging of the signaling information and saves the communication rosource to provide flexibility for installation of relay terminals. As a benchmark to the proposed scheme, optimum signaling case is also considered.

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Papers - YAMAZATO Takaya