Symbol error rate performance of M-ary NCFSK with S + N selection combining in Rician fading

In this paper, we consider the performance of M-ary orthogonal noncoherent frequency shift keying (NCFSK) with two signal-plus-noise (S + N) selection combining (SC) models in slow, flat Rician fading channels. We assume the fading branches are independent but not necessarily identically distributed. The probability of error for each model is derived as a single integral with finite integration limits. Extensive Monte Carlo simulation results are presented to assess the validity of our analytical expressions. Our results indicate that, unlike previously published results, the performance of S + N SC is not always superior to that of classical SC in fading and is dependent on the value of the signal-to-noise ratio, the modulation order, the multipath intensity profile and the fading parameter. The performances of S + N SC schemes are also compared to the performances of equal gain combining and square-law combining receivers.