Interference-plus-noise covariance matrix estimation for adaptive space-time processing of DS/CDMA signals

The presence of the desired signal during the estimation of the minimum-variance-distortionless-response (MVDR) or a auxiliary-vector (AV) filter under limited data records leads to significant signal-to-interference-plus-noise ratio (SINR) performance degradation. We quantify this observation in the context of DS/CDMA communications by deriving two new close approximations for the probability density functions (under both desired-signal-"present" and desired-signal-"absent" conditions) of the output SINR and bit-error-rate (BER) of the sample-matrix-inversion (SMI) MVDR receiver. To avoid such performance degradation we propose a DS/CDMA receiver that utilizes a simple pilot-assisted algorithm that estimates and then subtracts the desired signal component from the received signal prior to filter estimation. Then, to accommodate decision directed operation we develop two recursive algorithms for the on-line estimation of the MVDR and AV filter and we study their convergence properties. Finally, simulation studies illustrate the BER performance of the overall receiver structures.