Opportunistic multi-antenna downlink transmission with finite-rate feedback

Multiple-antenna downlink transmission offers significant capacity improvement when the transmit-side channel state information (CSI) is available. The sum-rate capacity with infinite-rate feedback (full or partial CSI) scales linearly with the number of transmit antennas (multiplexing gain) and double logarithmically with the number of users (multiuser diversity gain). In this paper we present a new scheduling scheme which requires only finite-rate feedback and yet retains the optimal multiplexing and multiuser diversity gains achievable by dirty-paper coding and show that its sum-rate throughput scales like N_t log log KN_r where N_t and N_r are the number of transmit and receive antennas and K is the number of users. While our scheduling schemes is asymptotically optimal, it also exhibits a good performance for practical network sizes. We also show that by appropriate design of the feedback mechanism, we can refrain the aggregate amount of feedback from increasing with the number of users and for asymptotically large networks the total number of feedback bits is bounded by N_t log N_t. We also demonstrate that despite having an opportunistic user selection, fairness among the users is maintained and all are equality likely to be scheduled.