Influence of Fading on the Gaussian Approximation for BPSK and QPSK with Asynchronous Cochannel Interference

We investigate the performance of BPSK and QPSK with coherent detection and matched filtering in the presence of both time and phase asynchronous cochannel interfering signals. More precisely, we analyze the role played by different channel statistics on the distribution of the decision variable at the output of the matched filter. The results show that the Gaussian approximation is accurate not only in the (obvious) case of a large number of interferers, but also when the desired signal is subject to fading, whatever the number of interferers is. For example, when the desired signal is subject to Rayleigh fading, even in the presence of only one unfaded interferer the Kullback–Leibler distance between the exact distribution of the decision variable and that obtained with the Gaussian approximation on the interference is lower than 0.01 [nats] for all cases of practical interest.