Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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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.

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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

Performance analysis of an integrated voice and data CDMA system Reviewed

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

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS Vol. 83 ( 4 ) page： 61 - 70 2000

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

This research is an analysis of the mixed system of data packets and CDMA voice signals transmitted by the channel load sensing protocol. The voice signal is a medium requiring instantaneous action to complete the transmission within a certain time whereas the data packet is a medium requiring high reliability but allows temporal delay. The blocking probability and Erlang capacity are derived for the voice signal while the throughput is derived for the data packet. The characteristics in the system using CDMA strongly depend on the number of simultaneously transmitting stations. In particular, in the present system, due to the mixture of different media, the effect of traffic on each medium needs to be considered. In regard to this point, this paper analyzes the effect of traffic on each medium from the relationship of the required quality of the media and the number of simultaneously transmitting stations. Then the optimization of the system with two kinds of media is considered. Further, the system capacity is derived as a guideline for the system optimization. The data offered load is derived to make maximally efficient use of the channel. (C) 2000 Scripta Technica.

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Performance analysis of an integrated voice and data CDMA system Reviewed

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

ELECTRONICS AND COMMUNICATIONS IN JAPAN PART II-ELECTRONICS Vol. 83 ( 4 ) page： 61 - 70 2000

OFDM systems with Multiple Trellis Coded Modulation Reviewed

M Harada, T Yamazato, M Katayama, A Ogawa

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

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

In an attempt to improve the performance under frequency selective fading environment, we propose in this paper an Orthogonal-Frequency-Division-Multiple-Access (OFDM) system in which MTCM (Multiple Trellis Coded Modulation) is applied to a set of multiple subcarriers. The code is designed to enlarge the summation of the Euclidean distance and the product distance. We also propose a scheme for assigning the symbols to subcarriers adaptively based on the channel state information (CSI) fed back from the reception receive end, and evaluate the performance applying these two codes and the proposed scheme under a multipath Rayleigh fading environment.

DOI： 10.1109/PIMRC.2000.881535

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Throughput evaluation in CDMA/shared-TDD packet systems in a cellular environment Reviewed

K Mori, T Kobayashi, T Yamazato, A Ogawa

WCNC: 2000 IEEE WIRELESS COMMUNICATIONS AND NETWORKING CONFERENCE, VOLS 1-3 page： 321 - 326 2000

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

This paper examines the inter-cell interference between uplinks and downlinks when a shared-TDD scheme is applied to CDMA packet communication systems in cellular environments. The CDMA/shared-TDD cellular packet systems experience two additional types of interference: one is the interference between base stations and the other is between mobile stations. The effect of these interferences on the throughput performance Is evaluated. Computer simulation demonstrated that interference between base stations rarely degrades uplink throughput, but interference between mobile stations substantially degrades downlink throughput.

DOI： 10.1109/WCNC.2000.904650

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Transmission power control for downlinks in CDMA/shared-TDD cellular packet systems Reviewed

K Mori, T Kobayashi, T Yamazato, A Ogawa

PIMRC 2000: 11TH IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, VOLS 1 AND 2, PROCEEDINGS page： 1520 - 1524 2000

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

This paper proposes a transmission power control scheme for downlinks in CDMA/shared-TDD cellular packet systems that experience inter-cell interference between uplinks and downlinks. The proposed scheme increases the downlink transmission power for re-transmission packets and thus improves the signal-to-interference ratio for the packets. Simulation results show that the proposed scheme improves downlink throughput without sacrificing the uplink throughput.

DOI： 10.1109/PIMRC.2000.881672

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Adaptive Array Antennas for the Base Station of a Multi Processing Gain CDMA System Reviewed

MORIMOTO Akihito, KATAYAMA Masaaki, YAMAZATO Takaya, OGAWA Akira

IEICE Trans. Fundamentals Vol. 82 ( 12 ) page： 2687 - 2696 1999.12

Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

This paper discusses the employment of adaptive array antennas at the base station of a Multi Processing Gain (MPG) CDMA system. It is shown that the adaptive array antenna with the weight control scheme based on the signal before despreading procedure does not increase but even decreases the performance than that with an omni-directional antenna, and the cause of this serious performance degradation is revealed. Then it is shown that the performance with the weight control scheme based on the signal after despreading procedure is always better than that with an omni-directional antenna. Furthermore, the possibilities of performance improvement by the combination of adaptive array antenna and interference cancellation techniques are mentioned.

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Papers - YAMAZATO Takaya