Weighted Secrecy Sum Rate Optimization for Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface-Assisted Multiple-Input Single-Output Systems

Abstract

The study investigates the effectiveness of a novel Simultaneously Transmitting and Reflecting Reconfigurable Intelligent Surface (STAR-RIS) technology in enhancing the physical layer security of Multiple-Input Single-Output (MISO) systems. To address the complexity of the security challenge, we examine two distinct phase shift strategies, namely, the coupled phase scheme and the independent phase scheme. The coupled paradigm focuses on optimizing weighted sum secrecy rate (WSSR) through a customized Block Coordinate Descent (BCD) approach integrated with path tracking, aiming to achieve a balanced security enhancement. Furthermore, for the independent phase shift paradigm, an optimization algorithm based on the Concave–Convex Procedure (CCCP) is explored to provide a flexible security solution. The numerical results validate the superior performance of STAR-RIS, confirming its potential as a robust security enhancer for MISO systems.