Adaptive frequency hopping in HF environments

A frequency hopping scheme (1 bit per chip) is proposed and studied in some detail for channels in the HF-band. This band is subject to interference that varies with time and frequency, due to varying transmission and channel propagation conditions. To make efficient use of the available channel resource an adaptive frequency hopping algorithm has been implemented by means of a neural network to make use of the available channel information from the link quality analysis (LQA) in selecting the frequency slot in contrast to having a uniformly distrinuted selection process. The algorithm proposed combines the advantages of low probability of detection during transmission and reduced fading and interference disturbance when detecting transmitted signals. The disturbances not eliminated by the channel selection is further reduced by using block codes with first order soft decision decoding. The results on residual bit error rate and average signal to interference ratio are promising with an overall reduction in bit error rate of more than two orders of magnitude at moderate signal to noise and signal to interference ratios for a course channel model based upon the results by P. J. Laycock et al. (1988)