LPI performance of an adaptive frequency-hopping system in an HF interference environment

Frequency-hopping is considered to be an effective method for combating active jamming in military radio systems. To further improve the performance, so-called adaptive frequency-hopping (AFH), which uses an adaptively selected pool of the "best" hopping-frequencies for the communication, has been proposed. In this paper, we examine the low probability of intercept (LPI) performance of such an AFH system on an interference-limited HF channel. The LPI property is evaluated with respect to two different hostile detectors; the radiometer and a sub-optimum matched filter detector. It is found that the matched filter detector is a much more serious threat against the AFH system, due to its ability to suppress the strong interfering HF signals in the detection process. Furthermore, the LPI performance proves to be very dependent on whether the interceptor can estimate the pool of hopping-frequencies used by the AFH system or not. If the interceptor cannot perform such an estimation, the AFH signal has a high chance of remaining undetected in the dense HF interference environment.