Low Complexity Turbo Decoders for Noncoherent FH/SS over Partial Band Jammed Channel

In this study, turbo codes were investigated in a slow frequency-hopped binary frequency shift keying spread spectrum (FH/BFSK-SS) system with partial band jamming and full-band thermal noise. A soft decision decoding metric which includes automatic gain control (AGC) is proposed for turbo code decoding with a non-coherent square law receiver of FH/BFSK. The study focused on the performance comparison of various reduced complexity turbo decoding algorithms using the above-mentioned soft decision decoding metric. These low complexity turbo decoding algorithms included Log-MAP, Max-Log-MAP and SOVA. From the simulation results, Log-MAP performed the best, but with the highest complexity. While, although SOVA performed the worst, it had the lowest complexity. Max-Log-MAP performed about 0.1dB worse than Log-MAP. The performance degradation was about 0.4dB between the SOVA and Log-MAP algorithms. Keyword: FH, SS, turbo code, AGC