Dynamic power and sub-carrier assignment in a multi-user OFDM system

It is well known that independent time variations in channel fading across multiple users can be exploited by channel aware scheduling to obtain multiuser diversity gains. In a wideband orthogonal frequency division multiplexing (OFDM) system with frequency-selective fading it is possible to schedule different users in different subcarriers in a given scheduling interval and obtain additional multiuser diversity gain from frequency selectivity. In this paper we present the optimum algorithm for scheduling multiple users across subcarriers assuming each user's channel is known as in the case of a time-division duplexing (TDD) system. We present the optimal algorithm for bandwidth and power allocation across users that is used for scheduling. We also present a simple suboptimal algorithm with performance close to the optimum algorithm. We present several numerical results for both delay-tolerant and delay-sensitive packet data and show that 50-90% improvement in capacity can be achieved under idealized conditions.