Performance of multiuser diversity in the presence of feedback errors

We compare the performance of three physical layer scheduling algorithms: round robin; transmit time selection diversity (TTSD); maximum SNR. With TTSD, downlink transmission is suspended if the instantaneously received SNR in the mobile station falls below a given threshold, which requires only one feedback bit per user; this considerably decreases the overhead of the feedback signaling when compared with a maximum SNR scheduler. In the case of FDD systems, TTSD and maximum SNR schedulers require a fast feedback channel from mobile to base station, like the one in the FDD WCDMA system. It is shown that, while the maximum SNR scheduler outperforms the other two schedulers when the feedback signaling is error-free, TTSD is better in the case of feedback bit errors. Furthermore, while orthogonal space-time coding does not improve the performance with channel aware schedulers when compared to single antenna transmission, it is shown that space-time coding makes the system more robust and gives gain in the case of feedback errors.