Opportunistic Downlink Transmission With Limited Feedback

Opportunistic scheduling provides attractive sum-rate capacities in a multiuser network when the base-station has transmit-side channel state information (CSI), which is often estimated at the mobiles and provided to the base station via a feedback channel. This correspondence investigates opportunistic methods in the presence of limited feedback. For flat Rayleigh-fading channels, strategies with only one-bit feedback per user are demonstrated that capture the double-logarithmic capacity growth (with number of users) of full-CSI systems. Furthermore, for a given system configuration, it is shown that if the one-bit feedback is chosen judiciously, there is little to be gained by increasing the feedback rate. Our results provide optimal methods of calculating the one-bit feedback, as well as expressions for the sum-rate capacity in the one-bit feedback regime. It is shown that one may achieve proportional fairness of scheduling in this regime with no loss of throughput. For OFDM multiuser systems, the motivation for limited feedback is even more pronounced. An extension of the one-bit technique is presented for subchannel/user selection under both correlated and uncorrelated subchannel conditions, and optimal growth in capacity is demonstrated.