Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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Improvement of transmission quality using correlation of observational data in sensor networks Reviewed

Kentaro Kobayashi, Takaya Yamazato, Hiraku Okada, Masaaki Katayama

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART III-FUNDAMENTAL ELECTRONIC SCIENCE Vol. 90 ( 11 ) page： 1 - 10 2007

Language：English Publishing type：Research paper (scientific journal) Publisher：SCRIPTA TECHNICA-JOHN WILEY & SONS

In sensor networks, many of the sensor nodes are often positioned in clusters, and there is a correlation between the data obtained at the various sensor nodes by observation. This kind of observational data is collected at fusion centers. In this paper, we study the observation precision at fusion centers from the viewpoint of the Kullback-Leibler (KL) information. In particular, we consider transmission path errors arising when transmission is made from each sensor node via wireless communication paths, as a factor in the deterioration of the KL information, or in other words, observation precision, and study its effects and methods for reducing it. In this paper, We Study the KL information obtained in fusion centers when there have been transmission path errors in cases where the correlation between observational data is all equal, and where the correlation is random. We show that the deterioration of the KL information can be reduced in fusion centers by using the correlation of observational data in the estimates of error data. In addition, we present examples of estimating the correlation between observational data in fusion centers that use correlation, and of estimating error data using correlation. (C) 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3. 90(11): 1-10, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).

DOI： 10.1002/ecjc.20250

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Performance analysis of UWB impulse radar receiver using parallel IPCP Reviewed

Hatano Hiroyuki, Yamazato Takaya, Okada Hiraku, Katayama Masaaki

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART III-FUNDAMENTAL ELECTRONIC SCIENCE Vol. 90 ( 7 ) page： 1 - 14 2007

Route diversity effect of joint decoding using correlation between observed data sequences in sensor networks Reviewed

Hiraku Okada, Kentaro Kobayashit, Takaya Yamazato, Kenichi Mase

2007 IEEE 65TH VEHICULAR TECHNOLOGY CONFERENCE, VOLS 1-6 page： 217 - 221 2007

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

In sensor networks, because of densely deployment of sensor nodes, sensing area of each sensor node is overlapped with each other and its observed data sequence is correlated. The joint decoding scheme that uses the correlation between the observed data sequences can reduce bit errors in the wireless channel. In this paper, we extend the joint decoding to the case of more than two-hop transmission. For such extension, selection of fusion scheme is very important issue. If the global fusion scheme is employed and the observed data sequence of each sensor node is transmitted on an independent route, route diversity effect could be obtained by using the correlation between observed data sequences. We compare the bit error rate performance of local and global fusion schemes and clarify the route diversity effect.

DOI： 10.1109/VETECS.2007.57

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Throughput comparison of CSMA and CDMA slotted ALOHA in inter-vehicle communication Reviewed

Sakata Atsunori, Yamazato Takaya, Okada Hiraku, Katayama Masaaki

2007 7TH INTERNATIONAL CONFERENCE ON ITS TELECOMMUNICATIONS, PROCEEDINGS page： 52 - + 2007

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 Open Access

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.

Open Access

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 Open Access

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

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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

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Papers - YAMAZATO Takaya