A common framework for blind multistage multiuser receivers of DS-CDMA in frequency-selective fading channels
The multistage (MS) Wiener filter proposed in J.S. Goldstein et al. (1998) is extended to blind maximum likelihood (ML) multiuser detection for direct-sequence (DS) code-division multiple access (CDMA) systems. This multistage ML detector is shown to share the same structure with the MS minimum-mean squared error (MMSE), minimum output energy (MOE) and best linear unbiased estimator (BLUE) filter banks (FBs) derived in S.-H. Wu et al. (2002) and S.-H. Wu et al. (2003), each with a distinctive output scaling matrix. Based on this result, a common framework is proposed for the implementation and analysis of coherent maximum ratio combining (MRC) and non-coherent differential equal gain combining (EGC) of these receivers. A generic bit error rate (BER) formula is provided for receivers constructed within this common framework. The BER floors for EGC receivers are analyzed and compared to those of the MRC schemes presented in S.-H. Wu et al. (2003). Based on simulation results, the heterogeneous EGC BLUE-ML receiver exhibits the best performance due to the fact that BLUE-FB is essentially the ML channel estimator and ML-FB is the ML symbol detector for the linear Gaussian system models of DS-CDMA systems.