Differential frequency hopping (DFH) is believed to have great potential in increasing the data rate of shortwave communication. Recent studies show that DFH suffers from an inherent serious drawback that its frequency transition matrix may be intercepted by any third-party receiver. This would heavily damage the anti-jamming performance of DFH. The root of this drawback is that differential frequency hopping sequence is not PN sequence but Markov chain. The invariant correlation between successive hops makes interception possible by statistically analyzing the intercepted DFH sequence. In this paper, we put forward a novel method named FH-DFH to deal with this problem. The basic idea of our method is to eliminate correlation between successive frequency hops by combining DFH with conventional FH technique. Analytical and simulation results show that DFH system using our method exhibits better anti-interception performance than not only normal DFH system but also oTVG-DFH system.
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