Variable rate noncoherent MFSK modulation over Nakagami fading channels

We propose a new adaptive scheme for power limited systems. For such systems, we offer a variable-rate and fixed-power non-coherent M-ary frequency shift keying (NC-MFSK) modulation scheme and analyze its performance over Nakagami fading channels. We recently addressed the system performance from the average link spectral efficiency, the average bit error rate (BER), and the probability of outage perspectives assuming that perfect channel estimates are available at the transmitter within a permissible delay. In this paper, we study the system performance in the case of outdated estimates. It is shown that only the average BER gets affected by outdated estimates. Our analysis shows that the system is insensitive to normalized delays f_dτ up to 10^-2 where f_d is the Doppler frequency and τ is the time delay. We then propose an adaptive switching thresholds system to better mitigate the effect of the delay.