Phase-mismatched STAR-RIS with FAS-assisted RSMA Users

2025-03-12

AI Summary

This paper addresses the two-user communication scenario with a STAR-RIS in the absence of a direct link. We jointly model a phase-impaired STAR-RIS and a position-reconfigurable planar fluid antenna system (FAS), and propose a robust transmission scheme based on rate-splitting multiple access (RSMA). Our key contribution is the novel insight that FAS exploits spatial diversity to effectively mitigate the impact of STAR-RIS phase errors. We further derive, for the first time, that the equivalent channel gain follows a Student’s *t*-distribution, enabling closed-form analytical expressions for outage probability and ergodic capacity. Compared with conventional antenna systems (TAS), the proposed scheme significantly reduces outage probability and enhances ergodic capacity. Moreover, it quantifies the performance degradation induced by phase errors, thereby validating its effectiveness and practicality in 6G non-ideal RIS environments.

Technology Category

• Intelligent Robots: Multi-Robot Systems
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Multiagent Systems: Agent Communication

Application Category

• Search and Retrieval-Augmented AI: Retrieval-Augmented Generation (RAG) and multi-modal RAG
• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments

Abstract

This paper considers communication between a base station (BS) to two users, each from one side of a simultaneously transmitting-reflecting reconfigurable intelligent surface (STAR-RIS) in the absence of a direct link. Rate-splitting multiple access (RSMA) strategy is employed and the STAR-RIS is subjected to phase errors. The users are equipped with a planar fluid antenna system (FAS) with position reconfigurability for spatial diversity. First, we derive the distribution of the equivalent channel gain at the FAS-equipped users, characterized by a t-distribution. We then obtain analytical expressions for the outage probability (OP) and average capacity (AC), with the latter obtained via a heuristic approach. Our findings highlight the potential of FAS to mitigate phase imperfections in STAR-RIS-assisted communications, significantly enhancing system performance compared to traditional antenna systems (TAS). Also, we quantify the impact of practical phase errors on system efficiency, emphasizing the importance of robust strategies for next-generation wireless networks.

Problem

• Mitigate phase errors in STAR-RIS-assisted communications.
• Enhance system performance using fluid antenna systems.
• Quantify impact of phase errors on wireless efficiency.

Innovation

• STAR-RIS with phase errors and FAS-assisted RSMA
• FAS mitigates phase imperfections in STAR-RIS communications
• Analytical expressions for outage probability and average capacity