Successive blind recursive constant modulus detectors for DS/CDMA signals with BPSK modulation

A successive detection technique using a multi-stage finite impulse response filter, controlled by the constant modulus algorithm (CMA), and a signal canceller (SC) to enable the blind detection of DS-CDMA signals is presented. This CMA/SC multi-stage system shows robustness of detection of different users in dense environments, it is easily implemented by simple gradient algorithms, and it requires lower computational effort than other reported algorithms. In addition, it does not require a knowledge of the spreading codes of the different users. A drawback of this multi-stage CMA/SC system is the relatively slow convergence of the CMA algorithm, which may not be suitable for some applications. This paper describes in detail a recursive constant-modulus filter/signal canceller (RCMA/SC) for the blind detection of DS/CDMA signals over an additive white Gaussian noise (AWGN) channel. The RCMA is derived by analogy to the recursive least squares algorithm (RLS) as a fast version of the CMA. The convergence properties of the algorithm are analyzed and compared with the conventional CMA. Simulation examples, for both the CMA and the RCMA, are given, to demonstrate the robustness of the proposed algorithm and its superiority from the point of view of fast convergence.