EM-based sequential detection for mixed mode Ricean/Rayleigh fading channels with unresolved delays

This paper considers a sub-optimal sequential non-coherent pilot-aided receiver based on the expectation-maximization (EM) algorithm for unresolved mixed mode Ricean/Rayleigh channels. The proposed detection technique iteratively finds the maximum likelihood (ML) estimate using symbol-by-symbol maximizations. It is shown that the EM-based scheme that uses a decorrelation matrix, yields diversity-like gains in the case of BPSK or 4QAM DS-CDMA signaling for various spreading gains even if the multipath is unresolved and the channel is highly correlated and only known statistically. Comparison with minimum mean square error (MMSE) schemes that assume instantaneous knowledge of the channel, showed the superiority of the EM-based structure over one single-sided tapped delay line MMSE (KS-MMSE) scheme and its very close performance to a double-sided tapped delay line MMSE approach (KD-MMSE) although the EM-based structure does not know the channel.