ANALYSIS OF AN ANTIJAM FH ACQUISITION SCHEME

An easily implemented matched filter scheme for acquiring hopping code synchronization of incoming frequency-hopping (FH) signals is analyzed, and its performance is evaluated for two types of jamming: partial-band noise jamming and partial-band multitone jamming. The system is designed to reduce jammer-induced false alarms. The system's matched-filter output is compared to an adaptive threshold that is derived from a measurement of the number of acquisition channels being jammed. Example performance calculations are given for the frequency coverage of the jamming either fixed over the entire acquisition period or "hopped," that is, changed for each acquisition pulse in order to prevent the communicator from evading the jamming. The example calculations consider 8 frequencies in the acquisition pattern, chosen from 128 total hop frequencies in the system band. Also, we consider two variations of adaptive threshold. It is shown that the jammer's optimum strategy (the worst case) is to maximize the false-alarm probability without regard for the effect on detection probability, for both partial-band noise and multi-tone jamming. It is also shown by direct comparison with a conventional fixed-threshold scheme that a significantly lower probability of false acquisition results from using an adaptive matched-filter threshold, demonstrating that the matched-filter acquisition strategy studied here is superior to conventional non-adaptive threshold schemes.