A mechanism for attributing users to a plurality of sub bands in a time slot t in a multiple access communications system, said method comprising assigning a combination of users to a sub band on a Proportional Fairness basis, that is to say whichever combination of users maximizes a Proportional Fairness performance metric for that channel, where the performance metric is weighted by a weighting factor reflecting the difference for that user between a target throughput and a projected throughput.