The research on Reconfigurable Intelligent Surfaces (RISs) has dominantly been focused on physical-layer aspects and analyses of the achievable adaptation of the propagation environment. Compared to that, the questions related to link/MAC protocol and system-level integration of RISs have received much less attention. This paper addresses the problem of designing and analyzing control/signaling procedures, which are necessary for the integration of RISs as a new type of network element within the overall wireless infrastructure. We build a general model for designing control channels along two dimensions: i) allocated bandwidth (in-band and out-of band) and ii) rate selection (multiplexing or diversity). Specifically, the second dimension results in two transmission schemes, one based on channel estimation and the subsequent adapted RIS configuration, while the other is based on sweeping through predefined RIS phase profiles. The paper analyzes the performance of the control channel in multiple communication setups, obtained as combinations of the aforementioned dimensions. While necessarily simplified, our analysis reveals the basic trade-offs in designing control channels and the associated communication algorithms. Perhaps the main value of this work is to serve as a framework for subsequent design and analysis of various system-level aspects related to the RIS technology.

翻译：可重构智能表面（RIS）的研究主要集中于物理层层面及传播环境可实现的适应性分析。相比之下，与RIS的链路/MAC协议及系统级集成相关的问题受到的关注要少得多。本文针对RIS作为一种新型网络元素集成到无线基础设施中所需的控制/信令程序的设计与分析问题展开研究。我们构建了一个通用模型，用于沿两个维度设计控制信道：i）分配带宽（带内与带外）和ii）速率选择（复用或分集）。具体而言，第二个维度产生了两种传输方案：一种基于信道估计及后续的自适应RIS配置，另一种则基于对预定义RIS相位剖面的扫描。本文分析了多个通信场景下控制信道的性能，这些场景由上述维度的组合得到。尽管分析进行了必要的简化，但它揭示了设计控制信道及相关通信算法时的基本权衡。本研究的主要价值或许在于为后续RIS技术相关系统级方面的设计与分析提供一个框架。