Numerical method for efficiently computing the performance of continuous phase frequency shift keying (CPFSK) is presented. The receiver uses a phase diversity technique with a delay-and-multiply frequency discriminator to recover the phase of the optical signal. The moment generating function (MGF) of the discriminator is derived and used in the calculation of bit error rate (BER). The results of numerical integration show that the receiver output is far from Gaussian. Exact mean and variance are derived for the Gaussian approximation (GA). The effects of laser Linewidth, filter bandwidth, and shot noise correlation are all considered.
