Legitimate Surveillance of Suspicious Communications With QoS Guarantees for Unsuspicious Users

In this letter, legitimate surveillance of a pair of suspicious users (SUs) who shares the same spectrum with a pair of unsuspicious users (UUs), in the presence of a full-duplex monitor, is investigated. The monitor can proactively jam the suspicious communication for better eavesdropping performance. The problem of jamming transmit power optimization for maximizing the successful eavesdropping probability under the constraint that the quality of service (QoS) of the UUs is not affected, is investigated. After important properties of the problem are obtained, a high-complexity optimal algorithm and a low-complexity suboptimal algorithm are derived. The superiority of the proposed algorithms compared to the benchmark algorithm is verified by simulation results.