Decision feedback-based demodulation and adaptive equalization for doubly differential PSK

We extended the decision feedback-based demodulation and equalization techniques for differential phase shift keying (DPSK) to the demodulation and equalization of doubly differential PSK (DDPSK). The decision feedback demodulator for DDPSK comprises two consecutive differential detectors which are based on some reference signals obtained from previously detected and received data. The proposed equalizer is a hybrid of this decision feedback demodulator and a linear feedback equalizer. By modifying the equalizer output based on the decision feedback demodulation before feeding back into its feedback part, the proposed equalizer can act like an equalizer with decision feedback structure. Computer simulation results demonstrate that the performances of the decision feedback demodulation and the equalizer are comparable to those of the coherent receiver and the decision feedback equalizer (DFE) with coherent detection, respectively.