An improved blind adaptive MMSE receiver for fast fading DS-CDMA channels

Blind adaptive minimum mean-squared errors (MMSE) receivers for multiuser d irect-sequence code-division multiple access (DS-CDMA) systems that assume knowledge of the steering vector, i.e., the cross-correlation between the d esired output and the Input signal, are known for their robustness against channel fading as they do not attempt to explicitly track the channel of th e user of interest. However, these receivers often have higher excess mean squared error and, hence, poorer performance than training-sequence based a daptive MMSE receivers. In this paper, an improved correlation matrix estim ation scheme for blind adaptive MMSE receivers is provided. The new scheme takes advantage of the fact that the desired linear receiver can be express ed as a function of the interference correlation matrix only, rather than t he total data correlation matrix. A theoretical analysis is performed for t he flat fading case which predicts that the new estimation scheme will resu lt in significant performance improvement. Blind adaptive MMSE receivers wi th the new estimation scheme appear to achieve performance comparable to th e training-sequence based adaptive MMSE receivers. Detailed computer simula tions for the fast multipath fading environment verify that the proposed sc heme yields strong performance gains over previous methods.