Differentially coherent diversity combining techniques for DPSK over fast Rayleigh fading channels

Performance of differential phase-shift keying (DPSK) is considered for fad ing channels with nonnegligible time-variation, as well as signal or noise correlation between diversity branches. A differentially coherent maximum-r atio combiner is derived, showing optimal weight dependence on the fading s tatistics. Bit error rate (BER) is evaluated analytically for Rayleigh fadi ng, and comparison is made between the optimal and the equal-gain different ially coherent combiner, The optimal combiner provides improvement in all s ituations, and reduces the error probability floor. Performance improvement is higher for higher Doppler spreads, with the exact amount depending on d iversity correlation. For low diversity correlation, equal-gain combining p erformance stays close to optimal.