Secrecy Rate Optimization for Irregular STAR-RIS-aided Communication Systems

• Fangmin Xu,
• Ruijie Wang,
• Haiyan Cao,

Vol. 20, No. 1, January 31, 2026
10.3837/tiis.2026.01.014, Download Paper (Free):

• STAR-RIS
• RHIs
• security rate
• irregular topology
• novel joint optimization

Abstract

This paper investigates the performance of the Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface (STAR-RIS) aided communication systems with irregular topology of STAR-RIS elements, with a focus on maximizing the system secrecy sum rate by jointly optimizing beamforming vector, phase shift and topology under the practical challenges of Residual Hardware Impairments (RHIs). To solve the non-convex optimization problem, we propose a novel alternating optimization framework, which decomposes the security rate optimization problem into three sub-problems: base station (BS) beamforming, STAR-RIS coefficient matrix optimization, and irregular topology selection. To solve these sub-problems, we adopt the Successive Convex Approximation (SCA) method and utilize Alternating Optimization (AO) for iterative improvement. For irregular topology optimization, a tabu search algorithm is implemented to select the optimal subset of active STAR-RIS elements while maintaining the sparsity constraints. The proposed approach is compared against conventional STAR-RIS and conventional Reconfigurable Intelligent Surface (RIS) schemes through simulations. By incorporating irregular topologies, STAR-RIS can effectively address practical deployment challenges, such as element malfunctions or path blockages, which may render certain elements inactive. The simulation results demonstrate that the proposed optimization framework for the irregular STAR-RIS topology significantly enhances the communication security of the system.

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