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.

中文翻译：

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多链路无线系统主动窃听的能量效率


在本文中，我们研究了无线通信系统的合法监视，其中包括多个可疑环节。我们提出了窃听能源效率（EEE）的新目标来评估窃听性能。我们的总体目标是在窃听所有可疑链路的同时最大化 EEE，这可以通过在考虑许多实际限制（例如可疑发射器的传输策略、功率预算）的情况下干扰或协助可疑接收器处的每个可疑链路来实现合法监听器（LM）的数量，以及整个系统的窃听率。公式化的问题导致了一个具有挑战性的混合整数非线性规划（MINLP）问题。针对这一问题，我们利用窃听的特殊性，提出了一种新颖的窃听方案，通过一系列变换将复杂的MINLP问题转化为凹优化问题，并用拉格朗日乘子法求解。考虑到当 LM 的能力不足以窃听所有可疑链接时，我们提出的窃听方案不可行，我们提出了一种启发式算法来获得 EEE 和窃听率之间的权衡。数值结果表明，我们提出的窃听方案优于主动干扰方案和平均功率窃听方案。