Noncoherent detection of continuous phase modulation using overlapped observations

Combined noncoherent detection and decoding using multiple-symbol overlapped observations (noncoherent coded modulation) [Raphaeli, 1994] was shown to achieve a performance very close to the performance of coherent coded PSK signals. The present authors successfully apply the technique to the detection of uncoded or coded CPM (continuous phase modulation). The results show that most CPM schemes require short observations to achieve almost the same power efficiency as coherent CPM using the Viterbi algorithm but without phase tracking. The required observation length is much shorter than the one used in the previously proposed methods for noncoherent detection that approach the coherent performance, and also the decoding complexity is much lower. A new trellis diagram for noncoherent CPM is suggested for simplifying the analysis and the decoder structure. The error performance for uncoded CPM is evaluated by using the union bound technique applied on the symbols-difference trellis diagram. A very efficient sub-optimal decoding algorithm with very small degradation is also used. In the paper both full and partial response CPM schemes with arbitrary mod index are considered. Simulation results for convolutionally encoded CPM are included.