CMA-based adaptive 2-D RAKE receivers for QS DS-CDMA systems over frequency-selective channels

The problem of blind multiuser detection is considered for quasi-synchronous (QS) direct-sequence code-division-multiple-access (DS-CDMA) systems over frequency-selective channels. We show that the beamforming approach in the conventional 2-D RAKE receiver does not exploit the full potential of using multiple antennas. We propose a novel RAKE receiver structure which uses linear filtering in a joint spatio-temporal fashion. The filters are blindly adapted based on the constant modulus algorithm (CMA) which has been shown to converge to a decorrelator detector. In comparison with the 2-D RAKE receiver, it offers superior performance, computational simplicity and is more near-far resistant. Also unlike the 2-D RAKE receiver, it does not assume knowledge of all multipath delays.