As an emerging wireless communication technology, reconfigurable intelligent surface (RIS) has become a basic choice for providing signal coverage services in scenarios with dense obstacles or long tunnels through multi-hop configurations. Conventional works of literature mainly focus on alternating optimization or single-beam calculation in RIS phase configuration, which is limited in considering energy efficiency, and often suffers from inaccurate channel state information (CSI), poor convergence, and high computational complexity. This paper addresses the design and optimization challenges for successive RIS-assisted multi-hop systems. Specifically, we establish a general model for multi-hop communication based on the relationship between the input and output electric fields within each RIS. Meanwhile, we derive the half-power beamwidth of the RIS-reflected beams, considering the beam direction. Leveraging these models and derivations, we propose deployment optimization and beam optimization strategies for multi-hop systems, which feature high aperture efficiency and significant gains in signal power. Simulation and prototype experiment results validate the effectiveness and superiority of the proposed systems and methods.

翻译：作为一种新兴的无线通信技术，可重构智能表面（RIS）已成为在密集障碍物或长隧道场景中通过多跳配置提供信号覆盖服务的基础选择。现有文献主要关注RIS相位配置中的交替优化或单波束计算，在能量效率考量上存在局限，且常受限于不准确的信道状态信息（CSI）、较差的收敛性及较高的计算复杂度。本文针对RIS辅助的级联多跳系统，探讨其设计与优化挑战。具体而言，我们基于各RIS内部输入与输出电场的关系，建立了多跳通信的通用模型。同时，结合波束方向推导了RIS反射波束的半功率波束宽度。利用这些模型与推导，我们提出了适用于多跳系统的部署优化与波束优化策略，该策略具有高孔径效率及显著信号功率增益的特点。仿真与原型实验结果验证了所提系统与方法的有效性和优越性。