Error rate of S + N selection combining M-ary NCFSK in Nakagami fading

The performance of M-ary orthogonal noncoherent frequency-shift keying (NCFSK) with N branch signal-plus-noise (S + N) selection combining (SC) in Nakagami-m fading is studied. Both independent, identically distributed and independent, nonidentically distributed diversity branches are considered. Two S + N SC receiver structures are studied and their performances are analyzed. Tractable expressions are derived for the symbol error rate performance of these receiver structures in Nakagami-m fading with integer values of m. The performances of the S + N SC combiners are compared to those of classical SC and square-law combining (SLC). The effects of the modulation order, the fading parameter, the average decay factor and the number of diversity branches on the performance of S + N SC are examined and compared to the cases of classical SC and SLC. Monte Carlo simulation results are presented to test the validity of our analytical expressions.