Feedback Schemes for FDD WCDMA Systems in Multipath Environments

Transmit diversity techniques provide attractive solutions for increasing downlink capacity in 3G systems within low-mobility environments. Open-loop and closed-loop transmit diversity modes with two transmit antennas have already been included into 3GPP WCDMA Release 4, and at the moment schemes exploiting a larger number of transmit antennas are being developed. This paper analyzes the performance of the 3GPP WCDMA closed–loop modes in multipath Rayleigh fading channels. We use signal-to-noise ratio (SNR) gain as a performance measure, which corresponds to the gain in expected SNR when feedback information from the receiver is applied in the transmitter.