Noncoherent MLSE detection of M-DPSK for DS-CDMA wireless systems

This paper focuses on maximum-likelihood sequence estimation of noncoherent M-ary differential phase-shift keying (AT-DPSK) receivers for code division multiple-access (CDMA) systems, which make use of direct-sequence spread-spectrum modulations. A typical frequency-selective Rayleigh environment with multipath diversity at the receiver is considered. In this scenario, the optimum noncoherent decision metric, which requires an estimation of the channel tap weights envelope, is derived. Then, in order not to increase the receiver implementation complexity, a joint channel and data estimation strategy is proposed, which does not require the transmission of a known training sequence (blind estimation). In this case, the decision metric becomes a simple equal gain combining of multiple-symbol square-law detection decision metrics. For this suboptimum noncoherent detector, useful bounds on the bit error probability are provided through a theoretical analysis. Nonconstant and constant multipath intensity profiles are both considered for this purpose. Simulations are also carried out in order to verify the accuracy of the theoretical bounds.