Jammer-Assisted Legitimate Eavesdropping in Wireless Powered Suspicious Communication Networks

To enhance public safety, it is necessary to legitimately eavesdrop communication between suspicious users, such as terrorists and criminals. In this paper, we investigate legitimate eavesdropping in a wireless-powered suspicious communication network (WPSCN) with a wireless-powered suspicious transmitter and a suspicious receiver, who is legitimately eavesdropped by a legitimate monitor with the help from a wireless-powered friendly jammer. The “harvest-then-transmit” protocol is adopted by the suspicious communication to coordinate wireless energy transfer and information transfer. Both the suspicious receiver and the legitimate monitor can act as power sources for the suspicious transmitter and the jammer. The legitimate monitor can control the suspicious communication rate by broadcasting power signals, while the jammer can harvest energy and then interfere with the suspicious communication in collaboration with the legitimate monitor. Four different metrics are adopted to evaluate the eavesdropping performance based on different application requirements, and they are the successful eavesdropping probability, the average eavesdropping rate, the relative eavesdropping rate, and the eavesdropping energy efficiency. For each performance metric, we derive the optimal transmit power of the monitor for energy transfer and the optimal jamming transmit power of the jammer to maximize the performance metric under the peak transmit power constraint at the monitor and the energy causality constraint at the jammer. Some important insights are derived from these optimal power control policies. The simulations are conducted to verify the proposed optimal power control for legitimate eavesdropping in the WPSCN. It is shown that the proposed optimal power control policies greatly outperform other benchmark schemes.