Isamu Yoshii

Dynamic cell-size control according to geographical mobile distribution in a DS/CDMA cellular system

This paper proposes and investigates a dynamic cell size controlling scheme based on macro-diversity transmission for DS/CDMA. According to the time-variance of geographical mobile distribution, the transmission power of several base-stations is adaptively controlled considering the measured signal-to-interference power ratios of the received signals from mobile stations in order to minimize the calculated outage probabilities of the whole cells in the service area. Computer simulation shows the performance improvement.

An adaptive array antenna using combined DFT and LMS algorithms

Both classes of adaptive algorithm based on temporal update, e.g. LMS and spatial spectral estimation, e.g. DFT have advantages and disadvantages relatively. In order to compensate for their problems while maintaining advantages, this paper proposes and investigates an adaptive array antenna using a combined DFT and LMS algorithm. The proposed combined algorithm can improve the convergence speed of the weight coefficients in the temporal updating algorithm and the accuracy of the weight coefficients in the spatial spectral estimation algorithm.

Space and time signal processing based on adaptive antenna array for CDMA

An adaptive antenna array or a smart antenna can form a desired antenna pattern and adaptively control it if an appropriate set of antenna weights is provided and updated in software. We have studied an adaptive array antenna considering as an adaptive filter in the space and time domains for radio communications, so that the communication theory can be generalized into both the space and time domains. This paper focuses on space and time signal processing for CDMA and introduces a series of our research results in this area, such as appropriate structures and updating algorithms of an adaptive array antenna for CDMA, space and time interference canceller and optimum multiuser receiver for CDMA, and joint optimization between transmitting and receiving array antennas etc. Such space and time signal processing promises significant improvement of performance in a CDMA mobile communication system and other spread spectrum systems such as a spread spectrum vehicular communication and ranging system.

Transmitting array antenna beamforming based on linear goal programming for forward link of DS-CDMA

This paper investigates improvement of the radiation pattern design of the transmitting array antenna beamforming and transmission power control (TPC) for the forward link of DS-CDMA/FDD system. Optimum transmission beamforming and power can be derived with the information of the propagation channel of the forward link in order to improve user capacity. It is assumed that a channel is static, all mobile stations (MSs) report measured channel characteristics to a base station (BS) and that controls received SIRs of all MSs by using this information. Then, the optimum control of transmitting beam pattern based on linear goal programming is proposed to improve user capacity.

Adaptive directional receiver with different antenna spacing for CDMA

Pieter van Rooyen and Kohno proposed a combination receiver of adaptive arrays and MRC diversity, named a double spatial and temporal filter (DSTF) receiver. Each of the diversity branches consist of an array antenna. Each of the branches are separated spatially and independent. This assumption differs from the plane waves model. This paper discusses a method of combining an array antenna and a diversity antenna in plane waves model.

Bearing estimation for wideband signals in a multipath channel

In mobile communications there are problems due to multipath fading. An adaptive array antenna has been studied as a countermeasure to compensate for signal distortion due to fading because an array antenna can reduce multipath interference by using antenna directivity in the space domain. This paper proposes and investigates a method of estimating the direction of arrival (DOA) of wideband signals such as spread spectrum signals, in a multipath channel. The DOA estimation method can reduce the effect of signal distortion by creating a spatial spectrum which satisfies the sampling theory in the temporal domain. The DOA estimate calculated from this spatial spectrum is robust against signal distortion due to multipath. Computer simulations were used to evaluate the proposed method. In comparison with conventional the MUSIC algorithm, the proposed method showed superior performance in a multipath channel.