Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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DS/SS/GMSK with differential detection over multipath Rayleigh fading channels Reviewed

Wakaki I, Ishiguro T, Yamazato T, Katayama M, Ogawa A

IEEE ISSSTA '96 - IEEE FOURTH INTERNATIONAL SYMPOSIUM ON SPREAD SPECTRUM TECHNIQUES & APPLICATIONS, PROCEEDINGS, VOLS 1-3 page： 399 - 403 1996

Performance degradation due to the access timing delay on CDMA unslotted ALOHA with channel load sensing Reviewed

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

ICUPC '96 - 1996 5TH IEEE INTERNATIONAL CONFERENCE ON UNIVERSAL PERSONAL COMMUNICATIONS RECORD, VOLS 1 AND 2 page： 111 - 114 1996

Performance evaluation of CDMA ALOHA systems with modified channel load sensing protocol Reviewed

H Okada, M Saito, T Sato, T Yamazato, M Katayama, A Ogawa

IEEE GLOBECOM 1996 - CONFERENCE RECORD, VOLS 1-3 page： 1291 - 1295 1996

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

The one of the problems that arise in the satellite packet communication system is the existence of a long access timing delay. In this paper, we clarify the effect of this access timing delay on the performance of CDMA ALOHA systems and then propose a new access control protocol, called Modified Channel Load Sensing Protocol (MCLSP), for the CDMA ALOHA systems. As a result, we found that by employing MCLSP, a significant improvement in the throughput performance was obtained even in the presence of a long access timing delay.

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Performance of bit-by-bit interleaved trellis coded 16DAPSK on Rayleigh fading channel Reviewed

T Yamazato, H Nakagawa, M Katayama, A Ogawa

ICUPC '96 - 1996 5TH IEEE INTERNATIONAL CONFERENCE ON UNIVERSAL PERSONAL COMMUNICATIONS RECORD, VOLS 1 AND 2 page： 543 - 547 1996

Throughput improvement of CDMA slotted aloha system by modified channel load sensing protocol Reviewed

M Saito, H Okada, T Sato, T Yamazato, R Katayama, A Ogawa

PIMRC'96 - THE SEVENTH IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, PROCEEDINGS, VOLS 1-3 page： 103 - 107 1996

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

In this paper, we present throughput performance of CDMA Slotted ALOHA system with Modified Channel Load Sensing Protocol (MCLSP). In MCLSP, hub station continuously senses channel load for a certain number of slot, and computes the probability with which each user station should transmit its packet, then broadcasts the computed value. As the access control is based on this probability, we can apply it to slotted system. We show that MCLSP can achieve significant improvement in throughput performance of CDMA Slotted ALOHA system even in large offered load.
One of the issues in such protocol is the access timing delay, which is the sum of process time and propagation time for the packet access control. We also show the effect of the access timing delay on the throughput performance.

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The receiver with an adaptive array antenna and satellite diversity for low earth-orbital multiple satellite communication systems Reviewed

H Sumino, M Katayama, T Yamazato, A Ogawa

MOBILE AND PERSONAL SATELLITE COMMUNICATIONS 2 page： 180 - 194 1996

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

In a user terminal of low earth orbit (LEO) satellite communication systems, there are some technical issues, such as tracking of the connecting satellite, reduction of the interference from other satellites, and hand-off between satellites. As an answer to these issues, this paper proposes a new receiver structure using a set of adaptive array antennas. Combining the outputs of these adaptive array antennas, the receiver realizes satellite diversity. We also show a down-link signal design which employs Code Division Multiplex scheme for this proposed receiver structure. The performance of the system with the receiver and the down-link signals is evaluated by computational simulation.

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The performance of CDMA system using pi/4-shift QPSK and pi/2-shift BPSK with the nonlinearity of HPA Reviewed

K Kashyap, T Wada, M Katayama, T Yamazato, A Ogawa

PIMRC'96 - THE SEVENTH IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, PROCEEDINGS, VOLS 1-3 page： 492 - 496 1996

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

In this paper, we evaluate the bit-error rate performance of Direct-Sequence Spread Spectrum (DS/SS) system using pi/4-shift QPSK and pi/2-shift BPSK and observe the effect of the nonlinearity of High Power Amplifier (HPA) of transmitters which occurs when the HPA is operated near its saturation region. Hard limiter is chosen as the example of nonlinear amplifier and the numerical results are reported by using coherent as well as differential detection at the receiving end. With the employment of either pi/4-shift QPSK or pi/2-shift BPSK, the DS/SS signal is not much influenced by the nonlinearity of the HPA as the two modulation schemes have the advantage of nearly constant envelope.

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The DS/CDMA system using transmission diversity for indoor wireless communications Reviewed

K Ban, M Katayama, T Yamazato, A Ogawa

PIMRC'96 - THE SEVENTH IEEE INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR AND MOBILE RADIO COMMUNICATIONS, PROCEEDINGS, VOLS 1-3 page： 808 - 812 1996

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

In multi-path fading channels, direct-sequence spread spectrum (DS/SS) technique is often employed because of the capability to resolve signals from different paths and realize path diversity at the receiver. This advantage of DS/SS, however, is only when the time difference of propagation delay between paths is greater than a chip duration. In indoor communications, the delay spread is often very small and the above condition on the delay and chip duration is no longer satisfied, and this performance improvement by the path diversity with conventional DS/SS systems cannot be expected. In this paper we propose a new diversity technique for indoor wireless communication systems where delay spread is smaller than a chip duration. In this system, the transmitter sends signals at the same time from multiple antennas with intentional time delays, which allow a receiver to distinguish and combine the signals from different antennas.

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Throughput performance improvement of spread-slotted Aloha in mobile satellite communications Reviewed

A Jamalipour, M Katayama, T Yamazato, A Ogawa

1996 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS - CONVERGING TECHNOLOGIES FOR TOMORROW'S APPLICATIONS, VOLS. 1-3 page： 1740 - 1744 1996

A modified power control scheme for remedying the effects of traffic nonuniformity in LEO satellite communications systems Reviewed

Abbas Jamalipour, Masaaki Katayama, Takaya Yamazato, Akira Ogawa

International Journal of Wireless Information Networks Vol. 3 ( 1 ) page： 29 - 39 1996

Language：English Publishing type：Research paper (scientific journal) Publisher：Kluwer Academic/Plenum Publishers

It has been shown in our previous studies that the geographical traffic nonuniformity considerably affects the performance of the low earth orbit satellite communications systems. In this paper, a new scheme for improving the throughput characteristics of these systems at nonuniform traffic distribution is proposed. In this method, some parts of the users under the satellite which is flying over the area with high traffic load are assigned to its neighbor satellites with lower transmitting power levels. It is shown that the method equalizes the traffic loads of the satellites to some degree and, hence, can improve the throughput characteristics of the system. © 1996 Plenum Publishing Corporation.

DOI： 10.1007/BF02106660

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A spread-spectrum system with dual processing gains designed for cyclic noise in power line communications Reviewed

H Niwa, M Katayama, T Yamazato, A Ogawa, N Isaka

IEEE ISSSTA '96 - IEEE FOURTH INTERNATIONAL SYMPOSIUM ON SPREAD SPECTRUM TECHNIQUES & APPLICATIONS, PROCEEDINGS, VOLS 1-3 page： 816 - 820 1996

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

Many electric appliances using power lines for their power supply often tend to emit larger noise to the lines when the absolute instantaneous voltage of the power-supplying AC is higher. Thus, total noise on the lines has positive relation to the AC voltage. In this paper, We first model the noise to be cyclic stationary Gaussian with the instantaneous power (variance) proportional to the n-th power of the absolute instantaneous voltage of the AC. Considering this statistical feature of the noise, we also propose a power-line communication system and show its performance. The proposed system employs two processing gains: the smaller ope for the period with lower AC voltage and the larger for the rest period.

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A new M-ary/SSMA scheme applicable in LEO satellite communication systems Reviewed

T Wada, T Yamazato, M Katayama, A Ogawa

IEEE GLOBECOM 1996 - CONFERENCE RECORD, VOLS 1-3 page： 384 - 389 1996

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

In this paper, we discuss a non-coherent reception of M-ary spread-spectrum multiple-access (M-ary/SSMA) signals in the presence of large Doppler frequency shift.
The Hadamard Codes (H-codes) is applied as orthogonal codes. The influence of Doppler frequency shift has a particular characteristic according to the property of H-codes. Making use of this property, we, first, propose an initial carrier frequency acquisition method which can estimate the value of large Doppler frequency shift. We, then, proposed a M-ary/SSMA scheme that is based on the simultaneous transmission of two distinctive H-codes.

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Adaptive transmit permission control on spreadslotted aloha packets applicable in leos systems Reviewed

Jamalipouri A., Katayamat M., Yamazato T., Ogawai A.

IEICE Transactions on Communications Vol. E79-B ( 3 ) page： 257 - 264 1996

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

A new transmit permission control scheme applicable in multi-cell communication systems is proposed. In this scheme, by prohibiting the transmissions from the users with relatively high propagation loss to their connecting hub stations, level of multiple access interference is decreased, and hence throughput characteristics are improved. Moreover, we continue our discussion to propose two adaptive forms of the transmit permission control scheme, in which the prohibition condition becomes more intelligent by considering the level of the offered traffic loads to hub stations. These methods are utilized in a slotted Aloha random transmission of the spread spectrum packets, and on the uplinks of a low earth orbit satellite communication system as an example of the multi-cell systems. It is shown that the adaptive schemes exhibits significantly improved characteristics at all offered traffic loads in these systems.

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Throughput performance of Spread Slotted ALOHA System with Modified Channel Load Sensing Protocol

M. Saito, H. Okada, T. Sato, T. Yamazato, M. Katayama and A. Ogawa

Technical Report of IEICE Vol. SAT95 ( 83 ) page： 67-72 1995.12

Throughput analysis of spread-slotted ALOHA in LEO satellite communication systems with nonuniform traffic distribution Reviewed

A Jamalipour, M Katayama, T Yamazato, A Ogawa

IEICE TRANSACTIONS ON COMMUNICATIONS Vol. E78B ( 12 ) page： 1657 - 1665 1995.12

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

An analytical framework to study the nonuniformity in geographical distribution of the traffic load in low earth orbit satellite communication systems is presented. The model is then used to evaluate the throughput performance of the system with direct-sequence packet spread-slotted ALOHA multiple-access technique. As the result, it is shown that nonuniformity in traffic makes the characteristics of the system significantly different from the results of uniform traffic case and that the performance of each user varies according to its location. Moreover, the interference reached from users of adjacent satellites is shown to be one of the main factors that limit the performance of system.

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A Study on M-ary Spread-Spectrum Scheme Using Pseudo Noise Sequences in the Presence of Carrier Frequency Offset

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

Symposium on Information Theory and Its Applications (SITA) Vol. SITA95 ( C-6-3 ) page： 597-600 1995.10

Adaptive Transmission Control Scheme for Spread-Slotted Aloha Mobile Satellite Communication Systems

Abbas Jamalipour, M. Katayama, T. Yamazato, A. Ogawa

Symposium on Information Theory and Its Applications (SITA) Vol. SITA95 ( C-8-4 ) page： 777-780 1995.10

Performance of Bit Interleaved Trellis Coded 16DAPSK in Land Mobile Radio Communicatinon

H. Nakagawa, T. Yamazato, M. Katayama, A. Ogawa

Symposium on Information Theory and Its Applications (SITA) Vol. SITA95 ( D-3-1 ) page： 297-300 1995.10

A Study of DS/SS/GMSK with Differential Detection

I. Wakaki, T. Ishiguro, T. Yamazato, M, Katayama and A. Ogawa

Technical Report of IEICE Vol. SST95 ( 85 ) page： 25-30 1995.10

Throughput Analysis of Spread Unslotted Aloha System in Rayleigh Channel

T. Yamazato, T. Sato, H. Okada, M. Katayama and A. Ogawa

1995 Society Conference of IEICE Vol. SB-4-2 page： - 1995.9

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Papers - YAMAZATO Takaya