Optimization of Rate-Splitting Multiple Access in Beyond Diagonal RIS-assisted URLLC Systems

TL;DR

This paper develops an optimization framework for rate splitting multiple access in RIS-assisted URLLC systems, demonstrating how RSMA and RIS enhance performance, especially under overload and strict reliability conditions.

Contribution

It introduces a general optimization framework for RSMA in beyond diagonal RIS-assisted URLLC systems, highlighting the mutual benefits and performance improvements over traditional methods.

Findings

RSMA and RIS are beneficial in overloaded systems.

Benefits of RSMA increase with shorter packets and stricter reliability.

BD-RIS outperforms regular RIS in system performance.

Abstract

This paper proposes a general optimization framework for rate splitting multiple access (RSMA) in beyond diagonal (BD) reconfigurable intelligent surface (RIS) assisted ultra-reliable low-latency communications (URLLC) systems. This framework can provide a suboptimal solution for a large family of optimization problems in which the objective and/or constraints are linear functions of the rates and/or energy efficiency (EE) of users. Using this framework, we show that RSMA and RIS can be mutually beneficial tools when the system is overloaded, i.e., when the number of users per cell is higher than the number of base station (BS) antennas. Additionally, we show that the benefits of RSMA increase when the packets are shorter and/or the reliability constraint is more stringent. Furthermore, we show that the RSMA benefits increase with the number of users per cell and decrease with the number of BS antennas. Finally, we show that RIS (either diagonal or BD) can highly improve the system performance, and BD-RIS outperforms regular RIS.