A Robust Ratio-Threshold Technique to Mitigate Tone and Partial Band Jamming in Coded MFSK Systems

It is well known [Refs 1, 2] that a tone or partial-band noise jammer can so choose his jamming strategy as to cause the bit error rate of a frequency-hopped MFSK transmission system, to be an inverse linear function of Eb/No = (W/R)/(J/S), where W is the total available bandwidth available to the communicator, R is the bit rate and J/S is the jammer-to-signal power margin. This situation can be greatly improved by the use of coding, but with hard decisions, performance is still significantly worse than in additive Gaussian noise, unless sufficient time diversity (hops/bit) are employed to thwart such jammers - but at a cost in performance due to coherence loss. This paper investigates use of a simple robust technique which generates a "quality" bit based on the ratio of the maximum filter output to the second largest filter output. This improves coded system performance by as much as 6 dB for a tone jammer and makes lower redundancy (time diversity) more desirable. Performance is determined for both tone and partial band noise jamming and the two are shown to be almost equal and only slightly worse than for full-band Gaussian noise in a coded system.