Diversity receiver scheme and system performance evaluation for a CDMA system

Abstract

Performance of a code-division multiple-access (CDMA) system is studied. The frame-error rate (FER) and bit-error rate (BER) of the forward traffic channel are obtained by using a simulation system based on TIA/EIA/IS-95. A diversity receiver structure with an adaptive search engine is developed and analyzed. The adaptive rate of the search engine is optimized to achieve high diversity gain. The diversity gain factor is derived based on a cluster of wide-band tapped delay-line multipath fading models. The relationships between receiver diversity gain, multipath channel characteristics, and the number of distributed antennas are derived. The multipath channel characteristics have a major impact on the system performance. Simulation shows that when channel mean delay spread is less than the chip interval, a distributed antenna system is essential for improving the system capacity. When more users are served in the system, FER is more sensitive to the channel characteristics. Uncaptured energy acts as self-interference, which can increase the BER by an order of magnitude and reduce system capacities, FER could also be improved by reducing the resolution of the diversity receiver branches to one half of the chip interval. The system performance for the indoor and outdoor environments are evaluated by utilizing the proposed diversity receiver over typical personal communications services channel models specified by the Joint Technical Committee (JTC).