Statistical analysis of asynchronous QPSK cochannel interference

The closed form expression of the probability density function of the disturbance due to a quaternary PSK (QPSK) cochannel interferer is obtained. Then the bit error rate performance of QPSK in the presence of multiple cochannel interferers and additive white Gaussian noise (AWGN) is analyzed. In particular, a closed form expression is given to evaluate the bit error probability of QPSK with multiple cochannel interference. It is shown that in order to determine the minimum signal-to-interference ratio required to obtain a fixed bit error probability, care must be given to the number of active interferers: in fact, strong differences are found when varying the number of interfering cochannel signals, using the same signal-to-total interference ratio. The comparison with respect to the Gaussian approximation is also discussed.