Codeword optimization for uplink CDMA dispersive channels

We present the application of greedy interference avoidance methods to codeword optimization in the uplink of a code division multiple access (CDMA) system in which the channel between a given user and the base station receiver is assumed known and stable for the duration of the transmission. Repeated application of greedy interference avoidance monotonically increases sum capacity and yields an optimal codeword ensemble that satisfies a simultaneous water-filling distribution. However, algorithms for codeword optimization based on the greedy interference avoidance procedure are in general different from water-filling schemes. We illustrate the algorithms with examples and look at properties of optimal codeword ensembles.