Chiharu Yamazaki

Experiment and Simulation Results of Adaptive Antenna Array System at Base and Mobile Stations in Mobile Environment

In a time division duplex (TDD) based adaptive antenna array (AAA) and space division multiple access (SDMA) systems, array weights determined from the up-link signals can be applied to the down-link signal transmission because of the channel reciprocity. However, under time-varying fading conditions, for example that created by a rapidly moving mobile station (MS), the channel change between the array weight determination time in the up-link and the down-link signal transmission degrades the accuracy of the array weight. Thus, the spectral efficiency of the system degrades in the down-link. In this paper, we introduce a prototype of an MS with a 2-element antenna array and present the down-link mobility performance results of computer simulations and field experiments in a field trial system of i-Burst, which is a TDD based wireless broadband system employing the AAA/SDMA techniques at the base station. Both results show that adaptive antenna processing at an MS is effective in improving the down-link mobility performance of TDD-AAA/SDMA systems.

Experimental Performance Results of Adaptive Antenna Array System at Base and Mobile Stations in Mobile Environment

In a TDD based AAA/SDMA system, the array weights determined from up-link signals are applied to the downlink transmission because of the channel reciprocity. However, under fast fading conditions, for example due to fast moving MS, the array weights are no longer optimum for the downlink signal transmission and hence the spectral efficiency of the system degrades. In this paper, we present the downlink performance of MS with two antenna elements moving at speeds of ~5, 20 and 40 kmph in the field trial system of i-Burst, which is a wireless broadband system employing AAA and SDMA techniques. The field experiment results show that adaptive antenna processing at MS is effective in improving the mobility performance of TDD-AAA/SDMA system

Experimental Results on Mobility Improvement Effects of Adaptive Antenna Arrays Applied to Mobile Stations in SDMA System

Space division multiple access (SDMA) technology attained increasing interest due to its ability to increase system capacity, and thereby to improve frequency usage efficiency. Especially in the Time Division Duplex (TDD) system, the SDMA system is simple due to the reciprocity of TDD channel. However in a fast fading environment, performance of the downlink transmission degrades significantly, since the adaptive control can not track fast changing channels due to the time difference between receive and transmit time slot. iBurst is a TDD broad band wireless communication system, which uses SDMA technology with its 12-element antenna array on the base station side to increase frequency usage efficiency. In this paper, a 2- element Adaptive Antenna Array was introduced into an iBurst mobile station and the field experiments were carried out. The field experiment results show that the performance degradation in fast fading channels is recovered and the mobility is enhanced.