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The Effectiveness of Random MFSK (Multiple Frequency-Shift-Keying) Frequency-Hopping ECCM Radios against Worst-Case Partial-Band Noise Jamming

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Final rept. 1 Jul 1985-31 Jul 1986

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The system analyzed for bit error rate BER performance is frequency-hopped FH multiple frequency-shift-keying MFSK wherein the M symbol frequency assignments are independently and randomly chosen on each hop, and the information transmission is repeated L times L-hop diversity for a soft symbol decision. This FHRMFSK system is intended to counter systematic follow-on jamming. The reported analysis is of the systems BER in worst-case partial-band noise jamming WCPBNJ. To be effective, the receiver must employ nonlinear combining of the L hops several hop weighting schemes are evaluated with different assumptions about available real-time information on relative powers of signal, noise, and jamming. These include adaptive gain control, clipping, hard-decision, and self-normalizing nonparametric schemes. It is shown that a simple, self-normalizing receiver, using no jamming state information or measurements, can perform nearly as well as one using a priori values of received noise-plus-jamming powers for adaptive gain control. It is also demonstrated that a hard-decision receiver majority logic decoding of the L repetitions achieves an ECCM effect and is viable if the SNR is high. Although the BER varies with jammer power in much the same way as for conventional FHMFSK given the parameters M, L, and the unjammed SNR, including a diversity gain for high SNR, FHRMFSK in general is more vulnerable to WCPBNJ for M greater than 2. Therefore, it is concluded that implementation of effective diversity schemes is feasible, and that for a binary system the additional complexity of random hopping can be assessed to the additional protection gained against follow-on jamming.

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  • Radio Communications

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