Utilizing Adaptive Antenna Arrays

PERFORMANCE IMPROVEMENTS IN WIRELESS CDMA COMMUNICATIONS UTILIZING ADAPTIVE ANTENNA ARRAYS by Weichen Ye This dissertation studies applications of adaptive antenna arrays and spacetime adaptive processing (STAP) in wireless code-division multiple-access (('D11 A) communications. The work addresses three aspects of the CDMA communications problems: (I) near-far resistance, (2) reverse link, (3) forward link. In each case, adaptive arrays are applied and their performance is investigated. The near-far effect is a well known problem which affects the reverse link of CDMA communication systems. The near-far resistance of STA P is analyzed for two processing methods: maximal ratio combining and optimum combining. It. is shown that while maximal ratio combining is not near-far resistant, optimum combining is near-far resistant when the number of cochannel interferences is less than the system dimensionality. The near-far effect can be mitigated by accurate power control at the mobile station. With practical limitations, the received signal power at a base station from a power-controlled user is a random variable clue to power control error. The statistical model of signal-to-interference ratio at the antenna array output of a base station is presented, and the outage probability of the ('DMA reverse link is analyzed while considering Rayleigh fading, voice activity and power control error. New analytical expressions are obtained and demonstrated by computer simulations. For the application of an adaptive antenna. array at the forward link, a receiver architecture is suggested for the mobile station that utilizes a small two-antenna array For interference suppression. Such a receiver works well only when the channel vector of the desired signal is known. The identifying spreading codes (as in IS-95A for example) are used to provide an adaptive channel vector estimate, and control t he beam steering weight, hence improve t he receiver performance. Numerical results are presented to illustrate the operation of the proposed receiver model and the improvement in performance and capacity. PERFORMANCE IMPROVEMENTS IN WIRELESS CDMA COMMUNICATIONS UTILIZING ADAPTIVE ANTENNA ARRAYS