Spreading code adaptation for DS-CDMA with multipath

We examine joint transmitter and receiver adaptation in a peer-to-peer Direct Sequence (DS)-Code Division Multiple Access (CDMA) system with multipath. The multipath channel is modeled as frequency-selective, slow fading, and each user adapts independently to minimize the Mean Squared Error (MSE) at the receiver. Transmitter adaptation serves to pre-equalize the channel, and to avoid multiple-access interference from other users. A class of adaptive algorithms are presented which jointly optimize the transmitter and receiver with limited side information. We compare the performance with that obtained when transmitters and receivers are jointly adapted to minimize the sum MSE over all users, which would be appropriate for the reverse link of a cellular system. Numerical results which illustrate convergence properties are shown for both Least Squares and matched filter (Rake) receivers.