Full-Duplex Spoofing Relays for Wireless Surveillance with Inter-Relay Interference Suppression

In this work, we study a scenario where a distant central monitor covertly wiretaps the communication between a pair of suspicious users via several single-antenna full-duplex spoofing relays and a cooperative jammer for wireless surveillance. Under an adaptive transmission policy where the data rate of the suspicious users is determined based on the channel condition at the receiver, the spoofing relays intercept and forward manipulated information to control the data rate of the suspicious users for effective eavesdropping. We first propose an inter-relay interference suppression method to eliminate undesirable signals at the spoofing relays. Then, we provide a joint optimization technique for relay weights and jamming power to maximize the eavesdropping rate by a two-layer semi-definite relaxation approach. Simulation results show that the proposed solution outperforms other practical baseline schemes.