In this work, we investigate the physical layer security of a jamming-based underlay cognitive satellite-terrestrial network consisting of a radio frequency link at the first hop and an optical feeder at the second hop. Particularly, one secondary user (SU) is transmitting data to an end-user optical ground station through the aid of a relay satellite, in the presence of an active eavesdropper at each hop. Moreover, another SU located in the first hop is acting as a friendly jammer and continuously broadcasting an artificial noise that cannot be decoded by the wiretapper so as to impinge positively on the system’s secrecy. Owing to the underlying strategy, the SUs are permanently adjusting their transmit powers in order to avoid causing harmful interference to primary users. The RF channels undergo shadowed-Rician and Rayleigh fading models, while the optical link is subject to Gamma-Gamma turbulence with pointing error. Closed-form and asymptotic expressions for the intercept probability (IP) are derived considering two different scenarios regardless of the channel’s conditions, namely (i) absence and (ii) presence of a friendly jammer. The effect of various key parameters on IP, e.g., sources’ transmit power, artificial noise, maximum tolerated interference power, and fading severity parameters are examined. Precisely, we aim to answer the following question: could a friendly jammer further enhance the security of such a system even in a low SNR regime? All the derived results are corroborated by Monte Carlo simulations and new insights into the considered system’s secrecy are gained.

中文翻译：

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基于干扰的底层认知星地网络的物理层安全


在这项工作中，我们研究了基于干扰的底层认知卫星地面网络的物理层安全性，该网络由第一跳的射频链路和第二跳的光馈线组成。特别是，在每一跳都存在主动窃听者的情况下，一个二级用户（SU）通过中继卫星的帮助将数据传输到最终用户光地面站。此外，位于第一跳的另一个SU充当友好干扰器，不断广播窃听者无法解码的人工噪声，从而对系统的保密性产生积极影响。根据基本策略，SU 会永久调整其发射功率，以避免对主要用户造成有害干扰。 RF 通道经历阴影莱斯和瑞利衰落模型，而光学链路则经历带有指向误差的 Gamma-Gamma 湍流。无论信道条件如何，都考虑两种不同的场景，即 (i) 不存在和 (ii) 存在友方干扰机，得出截获概率 (IP) 的闭合形式和渐近表达式。检查了各种关键参数对IP 的影响，例如源的发射功率、人工噪声、最大容忍干扰功率和衰落严重性参数。准确地说，我们的目标是回答以下问题：即使在低信噪比情况下，友方干扰机能否进一步增强此类系统的安全性？所有导出的结果均通过蒙特卡罗模拟得到证实，并且获得了对所考虑系统的保密性的新见解。