A Study on Optimum Weights for Delay Transmit Diversity for DS-CDMA in a Frequency Non-selective Fading Channel

SUMMARY In this paper, we study DS-CDMA delay transmit diversity that transmits the weighted and time-delayed versions of the same signal from multiple antennas in a frequency non-selective fading environment. At a receiver, one receive antenna is used and the received delayed signals are coherently combined by Rake receiver. The set of optimum antenna weights for maximizing the received signal-to-noise power ratio (SNR) is theoretically derived to reveal that the optimum solution is to transmit only from the best antenna that has the maximum channel gain. The bit error rate (BER) performance improvement over conventional delay transmit diversity is theoretically analyzed and confirmed by computer simulations. The combined effect of transmit diversity and transmit power control (TPC) is also evaluated. Furthermore, the impact of fading decorrelation between the transmit and receive channels is also investigated for both the time division duplex (TDD) and frequency division duplex (FDD)