This letter studies the proactive eavesdropping in a suspicious decode-and-forward relay system, where the suspicious communication is divided into transmitter-to-relay (ST-SR) phase and relay-to-destination (SR-SD) phase with partial channel selection over $N \ge 2$ orthogonal channels, and the monitor (E) can only jam/overhear the E-SR/SR-E link over $M \le N$ sub-channels for practicality. Under this framework, with strict proof we first theoretically present the impact of jamming power and number of jamming channels selected by E on its eavesdropping success probability (ESP), and then reveal a fundamental trade-off: given jamming power (number of jamming channels), jamming with more channels (power) reduces the suspicious rate for E to overhear more clearly, but degrades the preconditions for successful eavesdropping. Results verify our obtained conclusions and show that the proposed jamming-assisted eavesdropping scheme with simple search method achieves pretty good performance compared with some intuitive schemes.

中文翻译：

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多通道译码转发中继系统通过干扰主动窃听

这封信研究了可疑解码转发中继系统中的主动窃听，其中可疑通信分为发射机到中继 (ST-SR) 阶段和中继到目的地 (SR-SD) 阶段，部分信道选择结束 $N \ge 2$ 正交信道，监视器 (E) 只能干扰/偷听 E-SR/SR-E 链路 $M \le N$ 实用的子频道。在此框架下，通过严格的证明，我们首先从理论上提出了 E 选择的干扰功率和干扰信道数量对其窃听成功概率（ESP）的影响，然后揭示了一个基本的权衡：给定干扰功率（干扰信道数量） )，使用更多信道（功率）进行干扰会降低 E 更清晰地偷听的可疑率，但会降低成功窃听的先决条件。结果验证了我们获得的结论，并表明与一些直观的方案相比，所提出的具有简单搜索方法的干扰辅助窃听方案取得了相当好的性能。