Adaptive BLAST-type decision-feedback equalizers for DS-CDMA systems

In this paper, a new adaptive equalization scheme for time-varying and frequency selective channels in direct sequence code division multiple access (DS-CDMA) systems is proposed. It consists of a number of serially connected stages and detects users in an ordered manner, applying a decision feedback equalizer (DFE) at each stage. V-BLAST detection ordering is implemented, that is, the stronger signal is extracted first so that the weaker users can be more easily detected. Both the equalizer filters and the order in which the users are extracted are updated in a recursive least squares (RLS) manner, efficiently realized through time- and order-update recursions. Two variants of this equalization scheme are considered, with and without knowledge of the spreading sequences. Their bit error rate (BER) performance is evaluated via simulations, in a severe near-far environment, and their superiority over existing techniques is demonstrated.