空中IRS辅助的MISO系统安全鲁棒资源分配算法
Secure and Robust Resource Allocation Algorithm for Aerial IRS Assisted MISO Systems
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摘要: 空中智能反射面(Aerial Intelligent Reflecting Surface, AIRS)结合了空中平台与智能反射面(Intelligent Reflecting Surface, IRS)的优势,能被灵活地部署在各种无线网络拓扑中以提高通信系统的性能指标。针对无线传输易受到障碍物阻挡和用户窃听而导致传输质量差和安全性能低的问题,本文提出了一种AIRS辅助的多输入单输出(Multiple-Input Single-Output, MISO)通信系统安全鲁棒资源分配算法。考虑到窃听信道的不确定性,以最大化系统的最坏情况总保密速率为目标,在满足基站最大发射功率约束、AIRS相移约束、AIRS部署位置约束以及合法用户最小保密速率约束的条件下,建立了一个联合设计基站主动波束成形、多个AIRS被动波束成形以及多个AIRS部署位置的多变量资源分配问题。然而,优化变量之间的高度耦合导致所建立的问题是复杂非凸的。为了求解上述非凸问题,首先利用块坐标下降(Block Coordinate Descent, BCD)方法将原问题分解为三个子问题,然后应用变量松弛、罚函数以及连续凸近似(Successive Convex Approximation, SCA)等方法来处理这些非凸子问题,最后提出一种交替迭代算法对原优化问题进行迭代求解。仿真结果表明,所提出的资源分配算法相较于其他基准算法能够更为显著地提高通信系统的最坏情况总保密速率并且具有良好的鲁棒性。这一结果不仅验证了AIRS在实现安全无线通信方面的巨大潜力,同时也突显出合理设计AIRS部署位置及其被动波束成形的重要性。Abstract: Aerial intelligent reflecting surface (AIRS) combines the advantages of aerial platforms and intelligent reflecting surface, which can be flexibly deployed in various wireless network topologies to improve system performance. Motivated by the remarkable advantages of AIRS, to address the challenge of poor transmission quality and low-security performance in wireless transmission caused by obstacle blocking and eavesdropping, this study proposes a secure and robust resource allocation algorithm for AIRS-assisted multiple-input single-output communication systems. Considering the impact of the imperfect channel state information of eavesdropping channels, a multivariable robust resource allocation problem was formulated for jointly designing the active beamforming of the base station, passive beamforming of multiple AIRSs, and deployment locations of multiple AIRSs to maximize the worst-case sum secrecy rate of communication systems while satisfying the maximum transmission power constraint of the base station, phase shift constraints of the AIRS, deployment location constraints of the AIRS, and minimum secrecy rate constraints of legitimate users. However, the formulated resource allocation problem was naturally non-convex because of the high degree of coupling and non-linear relationship between these optimization variables, making the aforementioned problem impossible to solve directly. To address the abovementioned sophisticated non-convex problem, first, the block coordinate descent method was used to decompose the original problem into three manageable subproblems, including active beamforming design, passive beamforming design, and deployment location design. Then, these non-convex subproblems were transformed into convex optimization problems by applying variable relaxation, penalty functions, and successive convex approximation methods. Finally, an overall algorithm was proposed to solve the original optimization problem. The algorithm gradually converges to a suboptimal solution of the original problem by solving each subproblem in alternating iterations. Simulation results show that the proposed resource allocation algorithm can effectively improve the worst-case sum secrecy rate of the communication system and has better robustness than other benchmark algorithms. These results validate the significant potential of AIRS in enabling secure wireless communications and emphasize the importance of designing deployment locations and passive beamforming for AIRS.