Low-rank Wiener filtering for asynchronous DS-CDMA systems with adaptive antenna arrays

In this paper, a novel space-time adaptive near-far robust array receiver for asynchronous DS-CDMA systems is developed without the need for prior synchronization. There are the same basic requirements that are needed by the conventional receiver of an asynchronous DS-CDMA system. To implement in real-time systems a computationally efficient version of the proposed receiver is developed that is based on the concept of the multistage Wiener filter (MWF) of Goldstein and Reed. This multistage technique results in a self-synchronizing detection criterion that requires no inversion or eigendecomposition of a covariance matrix. As a consequence this receiver achieves a complexity that is only a linear function of the size of antenna array (J), the rank of the MWF (M), the system processing gain (N), and the number of samples in a chip interval (S), i.e., O(JMNS). The complexity of the equivalent receiver based on the minimum mean-squared error (MMSE) criterion is a function of O(( JNS)³). Moreover, this multistage scheme has a rapid adaptive convergence under limited observation-data support. Simulations are conducted to evaluate the convergence behavior of the proposed receiver with the different amount of sample support and the various rank of the MWF. The performance advantage of the proposed detector over other DS-CDMA receivers is investigated.