A Study on Optimum Weights for Multi-channel Transmit Diversity

In this paper, we study multi-channel transmit diversity, with multiple transmit antennas and single receive antenna, for DS-CDMA. A transit diversity we consider is to transmit the weighted and time-delayed versions of the same signal from multiple antennas. At the receiver, Rake reception is performed using a single receive antenna. The optimum antenna weights for maximizing the received SNR, thus minimizing the average bit error rate, is theoretically derived to show the optimum weight is to transmit from one antenna that have the maximum channel gain. This transmit diversity is equivalent to selection combining (SC) receive diversity. The combined effect of transmit diversity and transmit power control (TPC) is also theoretically analyzed. The BER performance with SC transmit diversity in a frequency non-selective Rayleigh fading environment is evaluated by computer simulations.