Trellis-coded differentially coherent (TCDC) MPSK with carrier-phase-noise

The authors consider trellis-coded M-ary phase shift keying (MPSK) when used with differentially coherent demodulation over a carrier-phase-noise dominated channel. A tight upper-bound to the probability of error is introduced. This bound shows the presence of an irreducible probability of error. When compared to coherently demodulated trellis-coded MPSK, the irreducible probability of error of the differentially coherent scheme is much lower. This improved robustness to carrier-phase-noise is obtained at the expense of signal-to-noise-ratio (SNR), coding gain. Numerical results for two Ungerboeck codes with differentially coherent MPSK demodulation show poor SNR coding gain. A modification of Ungerboeck codes which makes them more suitable for use with differentially coherent demodulation is shown to increase the SNR gain while maintaining good robustness to carrier-phase-noise