Performance of Space-Time Diversity in CDMA Over Frequency-Selective Fading Channels

Asynchronous direct-sequence code-division multiple-access (DS - CDMA) using space-time spreading system is investigated over frequency-selective fast-fading channels. The underlaying transmit diversity scheme, previously introduced in the literature, is based on two transmit and one receive antenna. It was shown that when employed in flat fast-fading channels, the received signal quality can be improved by utilizing the spatial and temporal diversities at the receiver side. Here, the bit-error-rate (BER) performance of the underlying system is investigated for an uplink transmission where a decorrelator detector is used at the base station receiver. In particular, we derive a closed form expression for the probability of error over frequency-selective fast-fading channels. The analytical BER is derived as a function of both the number of multipath and users. The BER results show that the space-time spreading scheme exploits both the temporal and spatial diversity in a time-varying multipath channel. The results also show the accuracy of the derived expression when compared with simulation results for different number of users.