Postdetection diversity receiver for DAPSK signals on the Rayleigh- and Rician-fading channel

In this paper, the optimum decision boundaries for (N, M) differential ampl itude phase-shift keying on the Rayleigh-fading channel are analyzed. A new postdetection maximal ratio combining (MRC) and weighted maximal ratio com bining (WMRC diversity receivers are proposed. In the Rayleigh-fading chann el, assuming a high signal-to-noise ratio and a small normalized Doppler fr equency, the analytical optimum decision boundaries are obtained. In additi on, it is shown that an outer optimum decision boundary is the inverse of t he inner optimum decision boundary. In the proposed MRC receiver, the decis ion at each branch is made based on the minimum distance criterion. The per formance of the MRC receiver is analyzed, in terms of the union bound for b it error probability. The proposed WMRC receiver assigns weighting factors to the decision variable at each branch, based on the optimum decision boun daries. The performance of the WMRC is investigated through computer simula tion and compared with those of MRC and equal gain combining (EGC). From th e results, the performances of MRC and WMRC are found to be better than tho se of the EGC receiver on both the Rayleigh- and Rician-fading channels. It is also found that the performance improvement of WMRC over MRC is more pr onounced as the number of diversity branches increases.