Energy Efficiency of Proactive Cooperative Eavesdropping Over Multiple Suspicious Communication Links

This paper studies the wireless surveillance of multiple suspicious communication links. We propose a cooperative eavesdropping scheme, where a primary legitimate monitor and an assistant legitimate monitor cooperatively jam the suspicious links for an effective proactive eavesdropping. The objective is to maximize the eavesdropping energy efficiency (EEE) of our proposed cooperative eavesdropping scheme, by optimizing jamming power allocation and the cooperative strategy of legitimate monitors subject to several constraints, i.e., energy transfer constraint and eavesdropping load balancing constraint. Furthermore, the formulated problem is a difficult mixed integer nonlinear programming problem and, therefore, is non-convex and combinational. To solve the problem efficiently, a threshold-based policy of optimal jamming power allocation is proposed. Therefore, the original optimization problem is decoupled into two sub-problems: the selection of optimal eavesdropper under the given jammer and the whole EEE maximization over the selection of optimal jammer. Numerical results show that our proposed cooperative eavesdropping achieves higher EEE and eavesdropping rate than non-cooperative proactive eavesdropping.