Throughput performance of an FHMA system with variable rate coding

We compare throughput bounds for a frequency-hopped multiple-access (FHMA) system employing variable rate as well as fixed rate coding (FRC). Nonfading as well as Rayleigh-fading channels are explored. The throughput bounds for the variable rate coding (VRC) schemes are based on the assumption that the number of active users in the system, m, is known at any time while the bounds for the FRC scheme assumes that the fixed code rate is optimized for the user population mean, /spl lambda/, where the population is assumed to be Poisson distributed. We present bounds for theoretical "perfect" codes which achieve the capacity as well as bounds for Reed-Solomon (RS) codes of practical block lengths. Finally, we show the dependence of a VRC scheme upon the accuracy of the estimates of m and present a general comparison of the gains of using VRC versus a realistic FRC scheme.