Performance Evaluation of Ratio Threshold For Frequency Hopped MFSK Communication in Partial-Band Tone Jamming Plus Background Noise

An investigation of the performance of Viterbi´s ratio threshold receiver in partial-band tone jamming plus additive background noise is presented. The frequency-hop system considered, employs M-ary Frequency Shift Key (MFSK) modulation and error correction coding. The goal of this work is to determine the sensitivity of Ratio Threshold performance to the added noise. First, it is found that for tone-jammed channels, the performance depends on the choice of metric, with integer metrics requiring as much as 1.0 dB more Eb/NJ over maximum likelihood metrics. Using integer metrics, the performance for partial-band tone jamming is compared in the absence and presence of background noise. It is found that the effectiveness of Ratio Threshold over hard decision decoding is somewhat reduced for small additive background noise levels. For example, at a background ES/No = 11.0 dB, Ro = 1/2, and M=4, the Ratio Threshold improvement is reduced by 1.6 dB. Also, slightly anomalous behavior was discovered when adding small amounts of background noise in the hard decision partial-band tone jammed system.