Transmit diversity using filtered feedback weights in the FDD/WCDMA system

The transmit diversity concept adopted for the FDD mode of the third generation WCDMA system in 3G standardization has an open-loop and a closed-loop mode. The open-loop mode applies space-time block coding and is provides full diversity for two transmit antennas. The closed-loop mode has two submodes, which both utilize downlink channel measurements and feedback signaling in controlling the phase and/or gain transmit weights in the two transmit antennas. In this paper we review the open- and closed-loop concepts and propose an enhancement to the feedback modes to further improve their performance. The enhanced feedback modes allow the base station to filter the feedback weights received from the terminal to improve beam resolution and system robustness