Simultaneously Transmitting and Reflecting (STAR)-RISs: A Coupled Phase-Shift Model

Abstract

A simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS) aided communication system is investigated, where an access point sends information to two users located on each side of the STAR-RIS. Different from current works assuming that the phase-shift coefficients for transmission and reflection can be independently adjusted, which is non-trivial to realize for purely passive STAR-RISs, a coupled transmission and reflection phase-shift model is considered. Based on this model, a power consumption minimization problem is formulated for both non-orthogonal multiple access (NOMA) and orthogonal multiple access (OMA). In particular, the amplitude and phase-shift coefficients for transmission and reflection are jointly optimized, subject to the rate constraints of the users. To solve this non-convex problem, an efficient element-wise alternating optimization algorithm is developed to find a high-quality suboptimal solution, whose complexity scales only linearly with the number of STAR elements. Finally, numerical results are provided for both NOMA and OMA to validate the effectiveness of the proposed algorithm by comparing its performance with that of STAR-RISs using the independent phase-shift model and conventional reflecting/transmitting-only RISs.

14 pages, 3 figures

References in corpus (3)

• STAR: Simultaneous Transmission And Reflection for 360° Coverage by Intelligent Surfaces
• Intelligent Reflecting Surface-Assisted Multiple Access with User Pairing: NOMA or OMA?
• Intelligent Omni-Surfaces for Full-Dimensional Wireless Communications: Principle, Technology, and Implementation

Cited by in corpus (9)

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• Safeguarding NOMA Networks via Reconfigurable Dual-Functional Surface under Imperfect CSI
• Simultaneously Transmitting and Reflecting Surfaces for Ubiquitous Next Generation Multiple Access in 6G and Beyond
• Spectral and Energy Efficiency Maximization of MISO STAR-RIS-assisted URLLC Systems
• Reconfigurable Intelligent Surfaces for 6G -- Applications, Challenges and Solutions
• Simultaneously Transmitting And Reflecting (STAR) RIS for 6G: Fundamentals, Recent Advances, and Future Directions
• STAR-RISs: A Correlated T&R Phase-Shift Model and Practical Phase-Shift Configuration Strategies
• Design Optimization of NOMA Aided Multi-STAR-RIS for Indoor Environments: A Convex Approximation Imitated Reinforcement Learning Approach