Variable-rate variable-power non-coherent M-FSK scheme for power limited systems

In response to the ongoing demand for low power applications, the two first authors have recently proposed in F.F. Digham and M.-S. Alouini (2004) a discrete-modulation and fixed-power non-coherent M-ary frequency shift keying scheme. In this paper, we propose an extension of that work by studying a discrete-modulation and continuous-power (DMCP) scheme for further power saving over Nakagami fading channels. The modulation level and power assignment are selected in order to minimize the average transmitted power while meeting average spectral efficiency and bit error rate constraints. We further investigate the problem with an additional peak power constraint. In this case, the modulation switching thresholds are shifted to higher values yielding reduction in both the achievable average spectral efficiency and the average transmitted power. However, the power loading function can be re-shaped to maintain the same average power of transmission for the cases on no-peak and with-peak power constraints. This reshaping is designed so as to involve constant power portions which can be of interest from a practical stand point.