This paper focuses on multiple-access protocol design in a wireless network assisted by multiple reconfigurable intelligent surfaces (RISs). By extending the existing approaches in single-user or single-RIS cases, we present two benchmark schemes for this multi-user multi-RIS scenario. Inspecting their shortcomings, a simple but efficient method coined opportunistic multi-user reflection (OMUR) is proposed. The key idea is to opportunistically select the best user as the anchor for optimizing the RISs, and non-orthogonally transmitting all users' signals simultaneously. A simplified version of OMUR exploiting random phase shifts is also proposed to avoid the complexity of RIS channel estimation.

翻译：本文聚焦于多可重构智能表面（RISs）辅助无线网络中的多址接入协议设计。通过扩展现有单用户或单RIS情形下的方法，我们为多用户多RIS场景提出了两种基准方案。在分析其不足后，提出了一种简单而高效的方法——机会性多用户反射（OMUR）。其核心思想是机会性地选择最佳用户作为优化RIS的锚点，并同时以非正交方式传输所有用户的信号。为规避RIS信道估计的复杂度，还提出了利用随机相位偏移的OMUR简化版本。