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 solve 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.

翻译：本文提出了一种适用于超越对角可重构智能表面辅助超可靠低时延通信系统的速率分裂多址接入通用优化框架。该框架能够求解一大类优化问题，其中目标函数和/或约束条件为用户的速率和/或能量效率的线性函数。利用该框架，我们证明了当系统过载时（即每小区用户数超过基站天线数），速率分裂多址接入与可重构智能表面可互为有益工具。此外，我们揭示了数据包长度越短和/或可靠性约束越严格时，速率分裂多址接入的增益越显著。进一步地，我们验证了速率分裂多址接入的增益随每小区用户数增加而增大，随基站天线数增加而减小。最后，我们证明了可重构智能表面（无论是常规对角型还是超越对角型）能显著提升系统性能，且超越对角可重构智能表面优于常规可重构智能表面。