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.