PERFORMANCE OF COHERENT QPSK COMMUNICATIONS OVER FREQUENCY-SELECTIVE FADING CHANNELS FOR BROAD-BAND PCS

The fading caused by multipath and the effect of delay spread affect b roadband wireless personal communications channels by introducing inte rsymbol interference, which appear when the root-mean-squared (rms) de lay spread is significant in comparison to the duration of the transmi tted symbols. This results, in the absence of equalizing, in an irredu cible error probability. In this paper, we show that it is easy to obt ain, for given power-delay profile models, the variance of the interfe rence components at the output of a QPSK receiver. Using Gaussian appr oximations, a general form for a ''fading factor'' is defined. This ap proach is applied, in the particular cases of exponential and Maxwell power-delay profiles, to analyze the performance of coherent QPSK modu lation over frequency-selective fading channels.