Performance of coded slow frequency hopping M-ary FSK with clamped average energy metric in follow-on and partial band jamming

The performance of a coded slow frequency hopping non-coherent M-ary FSK is studied. During each frequency hop N_s bits are transmitted. The credibility of the received bits is evaluated by a clamped average energy metric-algorithm. The algorithm uses signal history of length W_L=N_FRHOP(N_s-b), where N_FRHOP is the number of frequency hops included in signal history and b is the number of bits in a frequency hop excluded from the signal history, to estimate the average received energy. The estimate of the average energy is obtained by filtering the samples in the signal history with an averaging filter. This average energy is used as a baseline when setting the damping thresholds which are used in limiting the acceptable signal coordinates. The intelligence of the receiver is enhanced with a few decision rules based on the thresholds. The calculated credibility measures of the bits are fed to the decoder which performs soft decision decoding. The channel is considered as an AWGN-channel with partial band or follow-on jamming. The coding scheme chosen is the optimal binary convolutional (7,1/3)-code. Although binary coding and hence bit interleaving is not optimal for an M-ary channel, in practical implementations it is widely used. Bit interleaving is used to provide the decoder random error statistics. The estimation of the average received energy is formulated in a way that the effects of the follow-on jamming are greatly reduced. Clamped average energy metric gives good performance in follow-on jamming thus suggesting good performance in overlay systems