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This paper considers multiple beamforming in the transmitter and receiver in MIMO channels and discusses the weight control procedure. The first half of the paper describes the transmitter and receiver weight conditions for realizing large capacity, for the cases with and without interference signals from other users. The second half proposes a weight control method which can realize high capacity in a real environment. In the proposed system, the control signal is exchanged between the transmitter and the receiver and the transmitter and receiver weights are determined. Using the proposed method, a satisfactory transmission weight can be determined even if the transmitter does not know the propagation information. As a result of simulation, we see that the proposed method is less affected by the propagation path and can assure stable throughput. We also find that the proposed method can achieve high throughput even if a control error occurs. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 88(6): 55–70, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20145 [ABSTRACT FROM AUTHOR]

To obtain a matching over a wide frequency range, pyramid-type and wedge-type matching layers are used in front of the multilayered wave absorbers. In this paper, a transmission mode approximation is proposed in which the period of the wedges and the incident polarization direction are taken into account in the calculation of the characteristics of a wedge-type wave absorber. The degree of difference of the equivalent permittivity derived by the propagation mode approximation from the one by the conventional method (corresponding to the low-frequency limit) is presented by numerical calculations. It is also shown that there is a difference from the wave absorber characteristics derived by the conventional method even at a wavelength longer than the wedge period. The tendency of the reflection to increase at the higher frequency side is visually explained by replacing it with the taper shape. [ABSTRACT FROM AUTHOR]

To understand the propagation structure of the microcells with a tall and medium-height antenna in an urban area, the fundamental propagation parameters are found and the structural model of the propagation loss was constructed. The fundamental propagation parameters were obtained based on the multivariable analysis of the propagation data at 800 MHz measured m the Tokyo Metropolitan area. These parameters are the distance between the transmitter and receiver, the average building height between the transmitter and receiver, and the base-station height which have high correlation and regression coefficients with the propagation loss. The relationship of parameters obtained from the model is (20 - α) log(h) for the base-station height characteristics and (α - 20) log (H) for the building height characteristics if the distance characteristics are α log (d). The relationships of coefficients of the conventional estimation equation and the regression equation obtained by the measured data almost agreed with those of the model so that the validity of the model was confirmed. [ABSTRACT FROM AUTHOR]

A case exists in which cancellation of interference is not possible with an interference canceler which cancels the interference wave from ground radio stations mixing into the ground station for the satellite communication. It is found experimentally that this is caused by the difference in the frequency characteristics of the input signals to the two antennas by the multipath effects. Further, a method is proposed to discriminate whether the arriving interferences can be cancelled. Its effectiveness is confirmed experimentally. Whether or riot the interferences can be cancelled can be determined by the amount of variation of the received electric field intensity of the interferences. If there is a signal with a constant-shaped spectrum, the distortion of the shape can be used for discrimination. As a result, the condition and limit of applications of the interference canceler are found. [ABSTRACT FROM AUTHOR]

Satellite communication has the following problems. The propagation delay is larger than in the terrestrial channel. When the carrier frequency exceeds 10 GHz, the bit-error rate tends to increase due to the effect of rain and snow, which degrades the transmission efficiency. To cope with such problems, a highly efficient error control protocol has been proposed to prevent the degradation of the transmission efficiency. This paper describes a new large- capacity, highly efficient retransmission scheme for satellite communication (extended SREJ scheme), which was devised considering the compatibility to the terrestrial network. The method is based on the SREJ (selective reject) scheme, which is specified in the HDLC (high-level data link control) protocol, employed widely in terrestrial data transmission. To evaluate quantitatively REJ, SREJ and extended SREJ schemes, a satellite communication control equipment was developed. The result of the data transmission experiment is described in detail, indicating that the extended SREJ scheme is efficient. Then, through the discussion of practical usefulness, it is shown that the extended SREJ scheme has no problem from the viewpoint of the number of buffers in transmitting and receiving stations. Further- more, to realize the efficient processing as far as possible, even if the bit-error rate is higher than 1.0 × 10-4, the extended SREJ/REJ scheme is discussed by combining the proposed scheme with the REJ scheme. [ABSTRACT FROM AUTHOR]

The performances (throughput and transmission delay) of the Co-back-N ARQ scheme are affected greatly by the bit error rate of the link and the round-trip propagation delay. This paper discusses the transmission delay of the tandem Co-back-N scheme, in which the round-trip propagation delay can substantially be reduced. First, the generating function for the transmission delay distribution is derived, and then the result is applied to derive the average transmission delay. As a result, it is shown clearly that the performance of the tandem Co-back-N ARQ scheme is better than that of the standard Co-back-N ARQ scheme. [ABSTRACT FROM AUTHOR]

This paper presents an analysis method for the maximum throughput of the window controlled data link under the effect of the propagation delays. The data link is divided into two submodels, and each stochastic process is analyzed independently and the results are integrated. The Calculation by this method is simpler than that by the direct analysis, and highly, accurate evaluation can be made for comparatively general frame length distribution. It is shown that this approach provides very good approximation, especially for the throughput efficiency ranging from 0.7 to 1.0. The region satisfying certain thoughtput value is derived and effective way of selecting the value of window size is presented. [ABSTRACT FROM AUTHOR]