Differential detection via the Viterbi algorithm for offset modulation and MSK-type signals

The differentially coherent reception of two families of constant-envelope signals, the linear offset quaternary phase shift keying and the binary partial response continuous phase modulation with index 0.5, is addressed. When the conventional (PSK-type) differentially coherent detector is used, a large performance degradation, compared with that of coherent receiver, is observed. The reason for this is the presence of an inherent intersymbol interference (ISI) in the signal and also noise enhancement and correlation introduced by the receiver filter. A differential detection strategy which compensates for ISI and avoids noise enhancement is presented. A phase estimate that takes into account the presence of the inherent ISI is derived. This phase estimate is then used in the decision metric of a coherent receiver. The resulting decision rule can be implemented using the Viterbi algorithm. Simple Viterbi receivers with good performance are obtained. Simulation results are given