Faculty Profiles - YAMAZATO Takaya

Adaptive array antennas for the base station of a multi processing gain CDMA system Reviewed

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

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E82-A ( 12 ) page： 2687 - 2695 1999

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

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.

A scheme for throughput improvement in voice/data CDMA packet communications Reviewed

Abbas Sandouk, Takaya Yamazato, Masaaki Katayama, Akira Ogawa

IEEE Vehicular Technology Conference Vol. 50 ( 1 ) page： 362 - 366 1999

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

In this paper, voice and data users with different bit rales are integrated in multi-code CDMA slotted ALOHA (MC-CDMA S-ALOHA) system. Performance measurement is obtained in the respect of throughput for data and outage probability for voice. Moreover, we consider the Modified Channel Load Sensing Protocol (MCLSP) as a traffic control to improve the throughput of data. We show that the MC-CDMA technique is an effective one to obtain a good throughput for data at an acceptable voice outage probability. We also show that the throughput of data can be improved with MCLSP. © 1999 IEEE.

DOI： 10.1109/VETECF.1999.797157

An integrated voice/data CDMA packet communications with multi-code CDMA scheme Reviewed

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

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E82-A ( 10 ) page： 2105 - 2113 1999

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

In this paper, we consider an integrated voice and data system over CDMA Slotted-ALOHA (CDMA S-ALOHA). We investigate its performance when multi-code CDMA (MC-CDMA) is applied as a multi-rate scheme to support users which require transmission with different bit rates. Two different classes of data users are transmitted together with voice. Performance measurement is obtained in respect of throughput for data and outage probability for voice. Moreover, we consider the Modified Channel Load Sensing Protocol (MCLSP) as a traffic control to improve the throughput of data. As a result, we show that the MC-CDMA technique is an effective one to obtain good throughput for data users at an acceptable voice outage probability. Furthermore, we show that with MCLSP, the throughput of data can be improved to reach a constant value even at a high offered load of data users.

Chip-by-chip turbo coding for DS/SS systems Reviewed

Zheng C.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E82-A ( 12 ) page： 2751 - 2756 1999

Code acquisition of a DS/SS signal with transmit and receive antenna diversity Reviewed

Ikai Y.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E82-A ( 12 ) page： 2728 - 2733 1999

Performance of a LEOS communication system with overlaid and overlapped cell arrangement Reviewed

Ono K, Katayama M, Yamazato T, Ogawa A

MOBILE AND PERSONAL SATELLITE COMMUNICATIONS 3 page： 131 - 145 1999

Service fairness in CDMA cellular packet systems with site diversity reception Reviewed

Mori K.

IEICE Transactions on Communications Vol. E82-B ( 12 ) page： 1964 - 1972 1999

Performance of a LEOS communication system with overlaid and overlapped cell arrangement Reviewed

K Ono, M Katayama, T Yamazato, A Ogawa

MOBILE AND PERSONAL SATELLITE COMMUNICATIONS 3 page： 131 - 145 1999

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPRINGER-VERLAG LONDON LTD

The performance of a Low Earth-Orbital Satellite communication System with large overlap of neighboring cells and the layered cell structure is discussed. The rejection of a newly arrived call (call blocking) and the forced termination of a call which requests handover(call dropping) are used as the performance measures and simple one-dimensional model is introduced in order to analyze the performance. As the result, performance improvement by overlapping, overlaying, and the combination of them are shown. In addition, it is found that there are optimum parameters or combinations of them, which makes the performances best.

Throughput improvement of a dual-class multi-code CDMA ALOHA system with modified channel load sensing protocol Reviewed

Sandouk A.

IEEE International Conference on Communications Vol. 2 page： 1079 - 1083 1999

Transmitter precoding with multiple transmit/receive antennas for high data rate communication in bandwidth-limited channels Reviewed

Koichiro Ban, Masaaki Katayama, Takaya Yamazato, Akira Ogawa

IEEE Vehicular Technology Conference Vol. 50 ( 3 ) page： 1946 - 1950 1999

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

We develop a new concept of a multichannel transmission scheme utilizing multiple transmit/receive antennas in narrow-band communication systems. We study the problem to design a pre-filter at the transmitter, a post-filter at the receiver, and a signal mapping operation before pre-filtering. With this new concept, we could expect extremely high data rate and high efficiency communication systems. © 1999 IEEE.

DOI： 10.1109/VETECF.1999.801737

Multimedia Packet Transmission using CDMA

T. Yamazato, M. Katayama and A. Ogawa

Technical Report of IEICE Vol. SST98 ( 42 ) page： 39339 1998.12

Hierarchical Transmission of Huffman Code Using Multi-Code/Multi-Rate DS/SS Modulation with appropriate Power Control Reviewed

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

IEICE Transaction on Communications Vol. E81-B ( 12 ) page： 2283-2289 1998.12

Hierarchical transmission of Huffman code using multi-code/multi-rate DS/SS modulation with appropriate power control Reviewed

Makido S, Yamazato T, Katayama M, Ogawa A

IEICE TRANSACTIONS ON COMMUNICATIONS Vol. E81B ( 12 ) page： 2283 - 2289 1998.12

Hierarchical transmission of Huffman code using multi-code/multi-rate DS/SS modulation with appropriate power control Reviewed

S Makido, T Yamazato, M Katayama, A Ogawa

IEICE TRANSACTIONS ON COMMUNICATIONS Vol. E81B ( 12 ) page： 2283 - 2289 1998.12

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

For transmission of video signals, it is important that the system allows a certain degree of flexibility in bit rate as well as quality, depending upon the requirements of media and channel conditions. In this paper, we discuss the hierarchical transmission of Huffman code using multi-code/multi-rate DS/SS system to realize flexible transmission. We first discuss and show that the structure of Huffman code tree directly expresses hierarchical structure, and that parallel transmission of Huffman code can achieve hierarchical transmission. By assigning different transmission data rate to the bits in each stratum, it is possible to transmit different amount of information from each stratum. Further, we show the quality of each of the stratum can easily controlled by an appropriate power distribution to each parallel transmission branch.

A Channel Control Scheme Considering Channel Response for Multi-carrier Transmission Reviewed

T. Shibata, N. Suzuki, M. Fujimoto, K. Nishikawa, T. Yamazato, A. Ogawa

IEICE Transaction on Communications Vol. J81-B-I ( 11 ) page： 700-708 1998.11

Initial acquisition of code timings and carrier frequencies of CDM down-link signals in multiple-LEO-satellite communication systems Reviewed

Ishizu M, Katayama M, Yamazato T, Ogawa A

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E81A ( 11 ) page： 2281 - 2290 1998.11

Initial acquisition of code timings and carrier frequencies of CDM down-link signals in multiple-LEO-satellite communication systems Reviewed

M Ishizu, M Katayama, T Yamazato, A Ogawa

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E81A ( 11 ) page： 2281 - 2290 1998.11

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

In this paper, we discuss the initial acquisition of the code division multiplexed DS/SS down-link signals at a user terminal of multiple LEO mobile satellite communication systems. In LEO systems, a receiver generally receives signals from plural satellites for soft hand-off and for satellite diversity as a countermeasure to shadowing. In this situation, the signal from each satellite becomes the interference to the signals from other satellites. In addition to this inter-satellite interference, we have to consider the intra-satellite interference from user channels to a pilot channel because of the loss of orthogonality of channels at initial acquisition stage especially under frequency offsets due to Doppler effect. Thus in this paper, we analytically evaluate the performance of an initial acquisition scheme, taking the intra/inter-satellite interference under Doppler shift into account.

New quasi-synchronous sequences for CDMA slotted ALOHA systems Reviewed

Saito M, Yamazato T, Katayama M, Ogawa A

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E81A ( 11 ) page： 2274 - 2280 1998.11

Performance evaluation of DS/CDMA communications systems modulated with pi/2-shift BPSK over multipath Rayleigh fading channels Reviewed

MMA Galib, T Yamazato, M Katayama, A Ogawa

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E81A ( 11 ) page： 2304 - 2310 1998.11

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

In mobile communications, power is a very important factor and nonlinear amplification of power amplifiers cannot be avoided due to their high power efficiency. This article presents the performance of pi/2-shift BPSK modulation scheme used in DS/SS/CDMA wireless communications over multipath Rayleigh fading channel and compares the performance with the performance of conventional BPSK and offset QPSK CDMA systems. The performance parameters: Out-of-Band power, average Bit Error Rate (BER) and Spectral Efficiency have been evaluated. In order to obtain improved performance on fading channels, a RAKE receiver has been employed. Finally it is shown that pi/2-shift BPSK outperforms conventional BPSK and offset QPSK in the presence of nonlinear amplification.