Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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A Study on Cross-Correlation Property in Orthogonal Multi-Code CDMA Systems Reviewed Open Access

A. Fujiwara, T. Wada, T. Yamazato, M. Katayama and A. Ogawa

IEICE Transaction on Fundamentals of Electronics, Communications and Computer Sciences Vol. J83 ( 5 ) page： 589-593 2000

A Study on Constant Amplitude Transmission for Orthogonal Multicode Systems Reviewed

T. Wada, and T. Yamazato

International Symposium on Information Theory and Its Applications (ISITA) Vol. ISITA2000 page： 576-579 2000

Language：English

In this paper, we deal with the constant amplitude orthogonal multicode systems. The constant amplitude transmission has the advantage of the high power efficiency because the high power amplifier which has non-linear characteristic can be applied for the amplification of the signals. In this paper, we show the bent sequences can achieve the constant amplitude transmission and also show the effectiveness of the constant amplitude transmission in terms of symbol error rate.

A Study on Weight Control Scheme of Adaptive Array Antennas with Interference Canceler

Takayuki Suzuki, Masaaki Katayama, Takaya Yamazato, Akira Ogawa

Technical Report of IEICE Vol. RCS page： - 2000

Throughput Performance of CDMA Unslotted ALOHA System with Successive Interference Cancellation considering Detection Error of Packet Existance Reviewed

Y. Tadokoro, H. Okada, M. Saito, T. Yamazato, M. Katayama, A. Ogawa

International Symposium on Information Theory and Its Applications (ISITA) Vol. ISITA2000 page： 728-731 2000

Language：English

In CDMA ALOHA system, Multiple Access Interference(MAI) is in existence and it has large influence on the system performance. To suppress the influence, we proposed new system in which SIC is applied to CDMA Unslotted ALOHA. But because of random access and time-short packets, it is very difficult to detect packet existence perfectly. So, in this paper, we evaluate the influence of detection error of packet existence in proposed system by throughput performance.

A New Diversity Reception and Decoding Scheme for Convolutional Encoded Signal Reviewed

W.Z. Wang, T. Yamazato, C. Zheng, H. Okada, M. Katayama, and A. Ogawa

International Symposium on Information Theory and Its Applications (ISITA) Vol. ISITA2000 page： 964-967 2000

Language：English

In this paper, we propose a new diversity reception and decoding scheme for a convolutionally encoded signal. Aiming at obtaining an additional gain by combining diversity reception and decoding technique, we extend notion of space diversity technique to error correction coded signal and consider an iterative decoding. As a result, we have found $2.0$ dB coding gain in 2 path Rayleigh fading channels at BER $=10^{-5}$ after 6 iterations. This reception technique is particularly useful when used in mobile communications.

A Symbol Detection Scheme for OFDM Signals with Subtraction Operation Reviewed

Shibata T.

The Journal of The Institute of Image Information and Television Engineers Vol. 54 ( 12 ) page： 1788 - 1791 2000

An access control protocol for a heterogeneous traffic with a multi-code CDMA scheme Reviewed

Sandouk A., Yamazato T., Katayama M., Ogawa A.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E83-A ( 11 ) page： 2085 - 2092 2000

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences

In this paper, we discuss the access control in multimedia CDMA ALOHA protocol. We introduce a new algorithm for the access control based on Modified Channel Load Sensing Protocol (MCLSP) in an integrated voice and two different classes of data users, high bit rate and low bit rate, exist in a multi-code CDMA Slotted ALOHA system. With our new algorithm, we show that the throughput of high bit rate data users, as well as, the total throughput of the data medium can be optimized and take a maximum value even at high values of offered loads. We also investigate the performance when voice activity detection (VAD) is considered in voice transmission.

Scopus

Adaptive transmit permission probability control in CDMA cellular packet communications with site diversity Reviewed

Mori K., Kobayashi T., Yamazato T., Ogawa A.

IEICE Transactions on Communications Vol. E83-B ( 7 ) page： 1445 - 1452 2000

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEICE Transactions on Communications

Site diversity causes unfairness in packet reception that depends on the location of the mobile stations in the uplink of CDMA cellular packet communication systems. This paper proposes an adaptive transmit permission probability control scheme that reduces this unfairness in CDMA cellular slotted-ALOHA systems with site diversity. The proposed scheme adaptively controls the transmit permission probability according to the offered load and the location of the mobile stations. Successful packet reception rate, fairness coefficient and throughput performance are evaluated in fading environments with imperfect power control. Computer simulation shows that adaptive transmit permission probability control improves fairness of service for all mobile stations and throughput performance across all channel loads compared with the conventional scheme.

Scopus

An initial code acquisition scheme for indoor packet DS/SS systems with macro/micro antenna diversity Reviewed

Ikai Y., Katayama M., Yamazato T., Ogawa A.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E83-A ( 11 ) page： 2070 - 2077 2000

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences

In this paper, we study macro/micro diversity techniques for code acquisition of a direct-sequence spreadspectrum signal in an indoor packet communication system. In the system discussed, the base station has several radio ports each with a cluster of antennas, and the terminal also has multiple antennas. The performance in the uplink of this system is analyzed under Lognormal shadowing and flat Rayleigh fading. The numerical results show great performance improvements by proposed diversity techniques. In addition, it is clarified that the mean acquisition time, which is often used as the measure of performance, is not suitable for packet radio systems as it underestimates the necessary preamble length for initial code acquisition.

Scopus

An OFDM system with reduced non-linear effect Reviewed

M Harada, T Yamazato, H Okada, M Katayama, A Ogawa

IEEE VEHICULAR TECHNOLOGY CONFERENCE, FALL 2000, VOLS 1-6, PROCEEDINGS page： 1794 - 1798 2000

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

In this paper, we discuss on the realization of reduced peak power transmission for the OFDM systems. Since the signals have large amplitude fluctuations in conventional OFDM systems, signets amplified by a non-linear amplifier Pre greatly distorted, resulting in severe performance degradation, In order to avoid this large amplitude fluctuation, we propose a scheme for reducing the nonlinear distortion by using the set of the signal point series which show low Penk-to-Mean-Envelope-Power-Ratio (PMEPR) value. In this system, one symbol is transmitted with multicarriers and the received signal is detected with maximum likelihood sequence (MLS) detection.

Web of Science

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An OFDM system with reduced non-linear effect Reviewed

Harada M, Yamazato T, Okada H, Katayama M, Ogawa A

IEEE VEHICULAR TECHNOLOGY CONFERENCE, FALL 2000, VOLS 1-6, PROCEEDINGS page： 1794 - 1798 2000

A study on reducing the nonlinear distortion in multicarrier systems Reviewed

Harada M., Yamazato T., Katayama M., Ogawa A.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E83-A ( 10 ) page： 1992 - 1995 2000

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences

In this paper, we discuss on the realization of reduced peak power transmission for the multicarrier systems. Since the signals have large amplitude fluctuations in conventional multicarrier systems, signals amplified by a nonlinear amplifier are greatly distorted, resulting in severe performance degradation. In order to avoid this large amplitude fluctuation, we propose a scheme for reducing the nonlinear distortion by using the set of the signal point series which show low peak to mean envelope power ratio (PMEPR) value. In this system, one symbol is transmitted with multicarriers and the received signal is detected with maximum likelihood sequence detection.

Scopus

Efficient channel parameter estimators for DS-CDMA systems in slow time-varying channels using a modified version of the SAGE algorithm Reviewed

YR Senhaji, T Yamazato, M Katayama, A Ogawa

GLOBECOM '00: IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, VOLS 1- 3 page： 1483 - 1487 2000

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

A modified version of the SAGE algorithm applied for joint estimation of delays, incidence azimuths and attenuation parameters characterizing the channel is presented. The modifications are based on using different observation intervals In optimizing the parameters and using time correlation in estimating delays, for the purpose of a further reduction in sAGE's computational weight, and Improving its accuracy in delay estimation. We show analytically that short observation intervals are sufficient for optimizing the delays and the azimuths, and verify through simulation the reliability of using time correlation.
Two other estimators are proposed combining the modified SAGE with a sequential estimation of the attenuation parameters suitable for slowly varying channels.

DOI： 10.1109/GLOCOM.2000.891887

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Efficient channel parameter estimators for DS-CDMA systems in slow time-varying channels using a modified version of the SAGE algorithm Reviewed

Senhaji YR, Yamazato T, Katayama M, Ogawa A

GLOBECOM '00: IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE, VOLS 1- 3 page： 1483 - 1487 2000

Effects of cell structure on quality of service of LEOS communication systems Reviewed

Ono K.

IEICE Transactions on Communications Vol. E83-B ( 4 ) page： 782 - 789 2000

Joint optimization of transmitter/receiver with multiple transmit/receive antennas in band-limited channels Reviewed

Ban K.

IEICE Transactions on Communications Vol. E83-B ( 8 ) page： 1697 - 1703 2000

OFDM systems with Multiple Trellis Coded Modulation Reviewed

Harada M, Yamazato T, Katayama M, Ogawa A

PIMRC 2000: 11TH IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1 AND 2, PROCEEDINGS page： 814 - 818 2000

Performance evaluation of modified HPSK for Wideband CDMA Reviewed

T Yamazato, A Fujiwara, M Katayama, A Ogawa

2000 IEEE SIXTH INTERNATIONAL SYMPOSIUM ON SPREAD SPECTRUM TECHNIQUES AND APPLICATIONS, PROCEEDINGS, VOL 1 AND 2 page： 751 - 755 2000

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

In mobile communications, power is a very important factor and non-linear amplification of power amplifier cannot be avoided due to their high power efficiency. HPSK modulation scheme has been proposed as the spreading technique for W-CDMA and cdma2000. HPSK is a complex spreading scheme that is designed to minimize the zero-crossing signal transition. However, there is a possibility that signal transition of HPSK go through zero.
In this paper, we propose a new modulation scheme for W-CDMA and cdma2000. The scheme is based on HPSK, but we modified the complex scrambling to avoid zero-crossing. We call it as modified HPSK (m-HPSK), It is shown that m-HPSK outperforms HPSK in the presence of non-linear amplification.

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Performance evaluation of modified HPSK for Wideband CDMA Reviewed

Yamazato T, Fujiwara A, Katayama M, Ogawa A

2000 IEEE SIXTH INTERNATIONAL SYMPOSIUM ON SPREAD SPECTRUM TECHNIQUES AND APPLICATIONS, PROCEEDINGS, VOL 1 AND 2 page： 751 - 755 2000

Performance Analysis of an Integrated Voice and Data CDMA System Reviewed

Sato T.

Electronics and Communications in Japan, Part II: Electronics (English translation of Denshi Tsushin Gakkai Ronbunshi) Vol. 83 ( 4 ) page： 61 - 70 2000

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Papers - YAMAZATO Takaya