Performance of a low-latency repeater jammer implemented on an SDR

Frequency-hopping spread-spectrum (FHSS) radio systems change their radio frequency (RF) rapidly to decrease their susceptibility to jamming. Time-correlated jammers have the ability to jam FHSS systems much more efficiently than conventional jammers if they react quickly enough to the frequency changes of the target system. We implemented a low-latency repeater jammer on a USRP N321 software-defined radio (SDR) and studied the reaction time and jamming effectiveness of the repeater jammer. The fastest reaction time we achieved was 1.48 μs. However, the reaction time will depend on the required complexity of the jammer. The repeater jammer samples incoming radio signals and then retransmits the same signal with a frequency shift. The frequency shift applied by the jammer is changed periodically. To gauge the jamming effectiveness of the repeater jammer, we tested it against several frequency shift keying (FSK) systems. Against an FHSS system with 10 kHz hopping rate, the repeater jammer performed more efficiently than a wideband noise jammer in the absence of propagation delay. Against a static frequency target system, the performance of the repeater jammer was similar to a narrowband noise jammer that focusses all its power in the active channel.