Multi-user demodulation and iterative decoding for frequency-hopped networks

Demodulation and decoding for frequency hop spread spectrum multiple access (FH/SSMA) systems has been traditionally conducted by conventional single user (non-collaborative) demodulation and error-correcting or erasure-correcting decoding techniques. In this paper, we study the demodulation and decoding aspects of collaborative multi-user reception for FH/SSMA and propose methods which improve the capacity of the system. Since hits from one or two other signals are the most likely events in FH/SSMA, the joint demodulation of two or of three received signals is performed based on likelihood ratio tests. Iterative decoding is used after the demodulation. Results are derived for both synchronous and asynchronous frequency hop systems. MFSK modulation with noncoherent demodulation and Reed-Solomon codes with hard-decisions minimum distance decoding are used. The performance of the proposed multi-user detector in AWGN and flat Rayleigh fading channels is evaluated. Scenarios when all simultaneous FH/SS signals or only a subset of them are collaboratively demodulated and decoded are simulated.