Reconfigurable intelligent surface (RIS), as a revolutionary technique, appears to ameliorate undesirable propagation environment in a controllable manner, which has the potential to substantially boost security of private information in the future smart radio environment. Much recent attention has been directed to the RIS-enhanced secure communication, among which the terrestrial network scenarios are generally concerned, while the exploration of aerial-ground communication integrated with RIS remains an open issue. Furthermore, in the available research, the ideal assumption of line-of-sight channel for aerial-ground link cannot be exploited in complex urban environment. Inspired by this, we provide in this paper the secrecy rate maximization problem under a complex urban scenario, where the drone’s high mobility and RIS’s tunable capability are utilized to against the potential eavesdropper. Although the established problem is intractable to tackle, we devise an iterative algorithm combining alternating optimization and successive convex approximation method as the solution, which jointly optimizes the phase shifts, the drone’s trajectory along with transmit power for the single-user scenario. The proposed designs are also extended to the multi-user multi-eavesdropper system. Eventually, extensive simulation experiments indicate the remarkable benefits brought by our proposed scheme on secrecy performance and the necessity of optimizing phase shifts.

中文翻译：

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可重构智能地面增强型安全空地通信

可重构智能表面（RIS）作为一种革命性的技术，似乎以可控的方式改善不良传播环境，有可能在未来的智能无线电环境中大大提高私人信息的安全性。近来，RIS 增强的安全通信备受关注，其中普遍关注地面网络场景，而与 RIS 集成的空地通信的探索仍然是一个悬而未决的问题。此外，在现有的研究中，在复杂的城市环境中无法利用理想的空地链路视距信道假设。受此启发，我们在本文中提供了复杂城市场景下的保密率最大化问题，无人机的高机动性和 RIS 的可调能力被用来对抗潜在的窃听者。尽管已建立的问题难以解决，但我们设计了一种将交替优化和逐次凸逼近方法相结合的迭代算法作为解决方案，联合优化了单用户场景的相移、无人机轨迹以及发射功率。所提出的设计也扩展到多用户多窃听系统。最终，大量的模拟实验表明我们提出的方案在保密性能和优化相移的必要性方面带来了显着的好处。我们设计了一种将交替优化和逐次凸逼近方法相结合的迭代算法作为解决方案，该算法联合优化了单用户场景的相移、无人机轨迹以及发射功率。所提出的设计也扩展到多用户多窃听系统。最终，大量的模拟实验表明我们提出的方案在保密性能和优化相移的必要性方面带来了显着的好处。我们设计了一种将交替优化和逐次凸逼近方法相结合的迭代算法作为解决方案，该算法联合优化了单用户场景的相移、无人机轨迹以及发射功率。所提出的设计也扩展到多用户多窃听系统。最终，大量的模拟实验表明我们提出的方案在保密性能和优化相移的必要性方面带来了显着的好处。