Wireless Physical-Layer Surveillance via Proactive Eavesdropping and Alternate Jamming

In this paper, we develop a wireless physical-layer surveillance scheme where two devices (M 1 and M 2 ) work cooperatively to eavesdrop on and intervene in a suspicious transmission link from a source (S) to a destination (D). Unlike existing approaches which rely on the use of a multi-antenna fullduplex radio as the monitor, in our scheme, M 1 and M 2 are both single-antenna nodes operating in half-duplex mode. Within any odd time slot, M 1 sends a jamming signal to deteriorate the signal reception at D and M 2 eavesdrops on the transmission from S. During the next (even) slot, M 1 overhears the signal sent from S, and M 2 forwards its received signal during the previous slot to realize jamming. In this manner, the jamming signal received at M 1 can be perfectly removed after self-interference cancellation, and the signals from S during the two consecutive slots are jointly decoded with high reliability, thus enabling successful surveillance. On the other hand, the detection performance at D is heavily degraded due to the injection of the jamming signal, thereby preventing information leakage from S to D.