M-ary CPM receivers for frequency domain processing and differential phase detector

This paper proposes an M-ary continuous phase modulation (CPM) receiver adopting both frequency domain processing and differential phase detection. The proposed CPM receiver recovers multi-level M-ary information data by equalizing correlated CPM phase signals in the frequency domain instead of by decoding the signals through conventional maximum-likelihood sequence estimation, e.g. Viterbi algorithms in the time domain. For frequency domain processing or frequency domain phase equalization, cyclic-prefix assisted transmission and differential phase detection are used in the transmitter and receiver, respectively. The proposed combination of differential phase detection and frequency domain phase equalization eliminates the complexity overhead of conventional CPM receivers using decomposition-based correlators and maximum-likelihood sequence estimators with marginal performance degradation. In terms of CPM modulation parameters such as modulation index and phase constraint length, the computational complexity of the proposed receiver increases logarithmically whereas the complexity of the Viterbi algorithm grows exponentially. In addition, the differential phase detector with frequency domain phase equalizer replaces a bank of correlators and filters of conventional decomposition-based CPM receivers. The numerical simulation results show that the proposed CPM receiver can achieve a bit error performance comparable to that of Viterbi algorithm-based decoders with decomposition-based correlators.