Phase-combining diversity using adaptive decision-aided branch-weight estimation for reception of faded M-ary DPSK signals

A practical adaptive phase-combining (PC) diversity-reception scheme based on approximate maximum-likelihood (ML) decision is proposed for M-ary differentially encoded phase-shift keying (MDPSK) with differential phase detection (DPD). The approximate ML decision chooses the data symbol that minimizes the weighted sum of the squared phase errors of L DPD detector ouptuts, where L is the number of diversity branches. The branch weights are adaptively estimated, based on feeding back past data decisions, from each branch DPD detector output-phase sequence. Adaptive PC diversity utilizes L DPD detector output-phase sequences only and requires no measurement function of the received signal instantaneous powers of the diversity branches. The average bit-error rate (BER) performance in the presence of additive white Gaussian noise (AWGN), Doppler spread, and multipath channel delay spread is evaluated by computer simulations for 4DPSK signal transmission in Rayleigh fading channels.