On DPSK demodulation of DS/CDMA signals

Second-order multipath channel estimation procedures for direct-sequence code-division-multiple-access (DS/CDMA) communications induce phase ambiguity that necessitates differential phase-shift-keying (DPSK) modulation and detection. The maximum likelihood (ML) single-symbol multiuser DPSK/CDMA detector is derived with direct generalization to multiple-symbol (block) multiuser DPSK/CDMA detection. Exponential complexity requirements limit the use of the ML rule to theoretical lower-bound bit error rate benchmarking. Linear filter DPSK demodulators are viewed as a practical alternative. Phase-ambiguous RAKE filtering and MVDR filtering (for active interference suppression) followed by filter-output differential detection are considered. Short-data-record adaptive alternatives to costly and slow adaptive MVDR implementations are sought in the context of auxiliary-vector (AV) filtering. Numerical and simulation studies illustrate the developments.