Diversity combining and SNR estimation for turbo-coded Frequency-Hopped Spread-Spectrum in partial-band interference and fading channels

In this paper we study diversity combining for turbo-coded frequency hopped spread-spectrum (FH/SS) communication systems in the presence of fading and partial band interference. For a fixed channel to information bit rate we compare different diversity order and code rate combinations for coherent binary phase shift keying (CBPSK) and non-coherent binary frequency shift keying (NCBFSK). We find that it is always better to use a low-rate code and no repetition for both CBPSK and NCBFSK. We apply a well-known approximation to the LLR for NCBFSK and find that it results in very similar performance to the exact LLR. We also propose a simple method for signal-to-noise ratio (SNR) estimation in NCBFSK without training symbols that offers performance near that of the case of exact knowledge of the SNR even for small hop sizes. In the case of CBPSK we propose an iterative method for estimating the SNR, also without training symbols, that offers performance near that of the case of perfect knowledge of the SNR when there is no interference, but otherwise requires large hop sizes to accurately estimate the SNR.