Performance of coherent QPSK communications over frequency-selective fading channels for broadband PCS

The fading caused by multipath and the effect of delay spread affect broadband wireless personal communications channels by introducing intersymbol interference, which appear when the root-mean-squared (rms) delay spread is significant in comparison to the duration of the transmitted symbols. This results, in the absence of equalizing, in an irreducible error probability. In this paper, we show that it is easy to obtain, for given power-delay profile models, the variance of the interference components at the output of a QPSK receiver. Using Gaussian approximations, a general form for a “fading factor” is defined. This approach is applied, in the particular cases of exponential and Maxwell power-delay profiles, to analyze the performance of coherent QPSK modulation over frequency-selective fading channels.