Motivated to understand the increasingly severe threat of unmanned aerial vehicles (UAVs) to the confidentiality of terrestrial radio links, this paper analyzes the ergodic and E-outage secrecy capacities of the links in the presence of multiple cooperative aerial eavesdroppers flying autonomously in three-dimensional (3D) spaces and exploiting selection combining (SC) or maximal ratio combining (MRC). The “cut-off” density of the eavesdroppers under which the secrecy capacities vanish is identified. By decoupling the analysis of the random trajectories from the random channel fading, closed-form approximations with almost sure convergence to the secrecy capacities are devised. The analysis is extended to study the impact of the oscillator phase noises and finite memories of the aerial eavesdroppers on the secrecy performance of the ground link. Validated by simulations, the cut-off density only depends on the range of the link in the case of SC eavesdropping, while it depends on the flight region of the eavesdroppers in the case of MRC eavesdropping.

中文翻译：

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协同空中窃听下地面无线电链路的保密性能

为了了解无人驾驶飞机（UAV）对地面无线电链路的机密性的日益严重的威胁，本文分析了在存在多个以三维方式自主飞行的协作式空中窃听者的情况下，链路的遍历和电子中断保密能力（3D）空间并利用选择组合（SC）或最大比率组合（MRC）。确定了保密能力消失的窃听者的“临界”密度。通过将随机轨迹的分析与随机信道衰落解耦，可以设计出几乎可以肯定地收敛到保密容量的闭式近似。扩展分析以研究振荡器相位噪声和天线窃听器的有限记忆对接地链路保密性能的影响。