Energy Efficiency of Proactive Eavesdropping for Multiple Links Wireless System

In this paper, we investigate the legitimate surveillance of wireless communication system, which includes multiple suspicious links. We propose a novel objective of eavesdropping energy efficiency (EEE) to value the performance of eavesdropping. Our general objective is to maximize EEE while all the suspicious links are eavesdropped, which can be accomplished through either jamming or assisting each suspicious link at a suspicious receiver under the consideration of many practical limitations, such as transmission strategy of a suspicious transmitter, power budget of legitimate monitor (LM), and eavesdropping ratio of a whole system. The formulated problem leads to a challenging mixed-integer nonlinear programming (MINLP) problem. To solve this problem, we propose a novel eavesdropping scheme by the special characteristic of eavesdropping, and the complex MINLP problem can be transformed to a concave optimization problem by a series of transformations, which can be solved by the Lagrange multiplier method. Considering the infeasibility of our proposed eavesdropping scheme when the power of LM is insufficient to eavesdrop all the suspicious links, we propose a heuristic algorithm to obtain a tradeoff between EEE and eavesdropping ratio. Numerical results show that our proposed eavesdropping schemes outperform the proactive jamming scheme and the average-power eavesdropping scheme.