Beamforming Dual-loop Optimization Algorithm for RIS-assisted UAV Communication Systems

• Published in: Zhengzhou Daxue Xuebao. Gongxue Ban = Journal of Zhengzhou University. Engineering Science Vol. 46; no. 2; p. 67
• Main Authors: Guo, Xinying, Liu, Longfei, Zhu, Chunhua
• Format: Journal Article
• Language: Chinese; English
• Published: Zhengzhou Zhengzhou University 01.01.2025
• Subjects: Algorithms; Beamforming; Communications systems; Complexity; Convergence; Convex analysis; Convexity; Design optimization; Manifolds; Optimization algorithms; Phase shift; Relay; Urban environments
• ISSN: 1671-6833
• DOI: 10.13705/j.issn.1671-6833.2025.02.005

In order to enhance the spectrum efficiency of the RIS-UAV relay communication system formed by integrating UAV and RIS in complex urban environments, research was conducted to explore the optimization of maximizing system downlink sum rate of RIS-UAV relay communication system with fixed trajectory, and a multi-variable non-convex optimization problem of joint active and passive beamforming was constructed. To address this, a lowcomplexity AO dual-loop algorithm based on FP and manifold optimization was designed. Firstly, it was simplified by using the FP algorithm. Secondly, followed by the design of the base station′s active beamforming by using standard convex optimization algorithms, and the design of the RIS′s passive beamforming by using manifold optimization algorithms. Finally, the alternating iterative optimization through the dual internal and external loops continues until convergence is achieved. Simulation results demonstrated that the proposed algorithm had better convergence and lower complexity compared to classical schemes. Moreover, at a maximum transmission power of 20 dBm, the sum rate achieved approximately 6 dB gain over the random phase scheme. Additionally, when the RIS employed 3 bit discrete phase shift, the system′s sum rate performance was nearly equivalent to that with continuous phase shift.