Frequency hopping (FH) spread spectrum is a well known technique used in communications systems to provide protection against interference such as jamming. With fast FH (FFH) (one or more hops per transmitted data symbol), powerful and robust methods for diversity combining have been developed as an additional jamming countermeasure. These same techniques can be applied to reduce the effects of multiple access interference, and so can be considered for civilian CDMA applications. Although the performance of a FFH communications system can be degraded considerably by fading, few results exist which show the effects of fading on the diversity combining process. In this paper, both analytic and simulation results are presented for several diversity combining methods in a Rayleigh fading channel, which is often considered to be the worst case. The performance of these combining methods in fading is compared with that in AWGN and multitone interference to determine which methods are effective against these degradations.

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Journal European transactions on telecommunications and related technologies
Citation
Gulliver, T.Aaron, Ezers, Rolands E., Felstead, E.Barry, & Wight, J. S. (1995). Performance of diversity combining for fast frequency hopped NCMFSK in Rayleigh fading. European transactions on telecommunications and related technologies, 6(1), 53–62.