This paper proposes a general optimization framework to improve the spectral and energy efficiency (EE) of ultra-reliable low-latency communication (URLLC) simultaneous-transfer-and-receive (STAR) reconfigurable intelligent surface (RIS)-assisted interference-limited systems with finite block length (FBL). This framework can solve a large variety of optimization problems in which the objective and/or constraints are linear functions of the rates and/or EE of users. Additionally, the framework can be applied to any interference-limited system with treating interference as noise as the decoding strategy at receivers. We consider a multi-cell broadcast channel as an example and show how this framework can be specialized to solve the minimum-weighted rate, weighted sum rate, global EE and weighted EE of the system. We make realistic assumptions regarding the (STAR-)RIS by considering three different feasibility sets for the components of either regular RIS or STAR-RIS. Our results show that RIS can substantially increase the spectral and EE of URLLC systems if the reflecting coefficients are properly optimized. Moreover, we consider three different transmission strategies for STAR-RIS as energy splitting (ES), mode switching (MS), and time switching (TS). We show that STAR-RIS can outperform a regular RIS when the regular RIS cannot cover all the users. Furthermore, it is shown that the ES scheme outperforms the MS and TS schemes.

翻译：本文提出了一种通用优化框架，用于提升有限块长（FBL）下超可靠低延迟通信（URLLC）同时发射与反射可重构智能表面（STAR-RIS）辅助干扰受限系统的频谱效率与能量效率（EE）。该框架可求解目标函数和/或约束条件为用户速率和/或能量效率线性函数的一类广泛优化问题。此外，该框架适用于采用"将干扰视为噪声"作为接收端解码策略的任何干扰受限系统。我们以多小区广播信道为例，展示了如何将该框架特化为求解系统的最小加权速率、加权和速率、全局能量效率及加权能量效率。针对（STAR-）RIS，我们考虑了三种不同组件的可行集——包括常规RIS或STAR-RIS——以符合实际场景。结果表明，若反射系数得到合理优化，RIS可显著提升URLLC系统的频谱效率与能量效率。同时，我们研究了STAR-RIS的三种传输策略：能量分裂（ES）、模式切换（MS）与时隙切换（TS）。分析显示，当常规RIS无法覆盖所有用户时，STAR-RIS性能优于常规RIS。此外，ES方案的性能优于MS与TS方案。