摘要：

智能反射面(RIS)被认为是未来无线通信技术中具有潜力的技术之一。无人机(UAV)也因其独特优势在无线通信领域日益受到关注。然而, 随着通信环境的日益复杂化, 信息传输面临着日益严峻的窃听风险, RIS与UAV的结合则为未来无线通信领域开辟了新的解决路径与可能性。为此, 提出一种基于RIS-UAV的保密无线通信系统。该系统利用UAV的灵活性和RIS的动态调整能力, 有效抵御潜在窃听行为。从物理层安全角度出发, 该系统考虑了RIS的相移和UAV的飞行轨迹, 旨在最大化系统的平均保密速率。由于该问题本质上是非凸的, 因此所提解决方案将问题分解为2个子问题。首先, 通过系统的特殊结构推导出相移的闭式解; 其次, 通过一阶泰勒展开将UAV的飞行轨迹转化为凸问题, 并采用逐次凸逼近法进行迭代求解。仿真结果表明, 该系统在平均保密速率方面表现良好, 与基准方案相比, 该系统的平均保密速率提升了约12.5%, 与固定RIS和无RIS方案相比, 性能也得到显著提升。此外, 该方案在安全性、计算复杂度等方面也显示出明显优势, 计算复杂度为O(MN+KN^3.5)。

关键词: 智能反射面, 无人机, 轨迹优化, 无源波束形成, 物理层安全

Abstract:

Reconfigurable Intelligence Surface (RIS) is a promising technology for future wireless communication. Unmanned Aerial Vehicles (UAVs) are gaining increasing attention in the field of wireless communications because of their unique advantages. However, with the increasing complexity of communication environments, information transmission faces increasingly severe eavesdropping risks, and the integration of RIS with UAV opens new solutions and possibilities for the future of wireless communications. Motivated by this opportunity, this paper proposes a secure wireless communication system based on RIS-UAV. The system leverages the flexibility of UAVs and the dynamic adjustment capabilities of RIS to effectively counter potential eavesdropping behavior. From the perspective of physical layer security, the system considers the phase shift of RIS and flight trajectory of UAVs, aiming to maximize the average security rate of the system. Because the problem is inherently nonconvex, the solution decomposes it into two sub-problems. First, a closed-form solution of the phase shift is derived from the unique structure of the system. Subsequently, the UAV flight trajectory is converted into a convex optimization problem via first-order Taylor expansion, and the iterative convex approximation method is used for the iterative solution. In simulations, the average secrecy rate of the proposed system increases by approximately 12.5% compared with the benchmark scheme. This performance is a significant improvement compared with those of the fixed RIS and no-RIS schemes. Additionally, this system demonstrates unique advantages in terms of security and computational complexity, with a computational complexity of O(MN+KN^3.5).

Key words: Reconfigurable Intelligence Surface (RIS), Unmanned Aerial Vehicle (UAV), trajectory optimization, passive beamforming, physical layer security