Frequency hopping (FH) spread spectrum is used in communications systems to provide protection against interference such as jamming. With fast FH, there are L ≥ 1 hops per data symbol transmitted. In the presence of severe interference, additional protection can be obtained by processing the LM values obtained from the demodulator. This processing is termed diversity combining. Many powerful and robust types of diversity combining have been developed to reduce the effects of a large jamming signal on some of the L hops. In this paper, a survey of combining methods is presented. Simulation performance results are given for severe noise and multitone jamming (SJR = 0.0 dB). It is found that bit error rates as high as 0.4 can be reduced to < 0.1 for L < 10 using any of several diversity combining methods.

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Conference Proceedings of the 1994 IEEE 3rd International Symposium on Spread Spectrum Techniques & Applications. Part 2 (of 2)
Gulliver, T.A., Felstead, E.B., Ezers, R.E., & Wight, J. S. (1994). Unified approach to time diversity combining for fast frequency hopped NCMFSK. In IEEE International Symposium on Spread Spectrum Techniques & Applications (pp. 303–308).