A reconfigurable intelligent surface (RIS) is a planar structure that is engineered to dynamically control the electromagnetic waves. In wireless communications, RISs have recently emerged as a promising technology for realizing programmable and reconfigurable wireless propagation environments through nearly passive signal transformations. With the aid of RISs, a wireless environment becomes part of the network design parameters that are subject to optimization. In this tutorial paper, we focus our attention on communication models for RISs. First, we review the communication models that are most often employed in wireless communications and networks for analyzing and optimizing RISs, and elaborate on their advantages and limitations. Then, we concentrate on models for RISs that are based on inhomogeneous sheets of surface impedance, and offer a step-by-step tutorial on formulating electromagnetically-consistent analytical models for optimizing the surface impedance. The differences between local and global designs are discussed and analytically formulated in terms of surface power efficiency and reradiated power flux through the Poynting vector. Finally, with the aid of numerical results, we discuss how approximate global designs can be realized by using locally passive RISs with zero electrical resistance (i.e., inhomogeneous reactance boundaries with no local power amplification), even for large angles of reflection and at high power efficiency.
翻译:重新配置的智能表面(RIS)是设计用于动态控制电磁波的平板结构。在无线通信中,RIS最近成为通过近乎被动的信号转换实现可编程和可校准无线传播环境的有希望的技术。在RIS的帮助下,无线环境成为网络设计参数的一部分,可以优化。在这个指导性文件中,我们把注意力集中在RIS的通信模型上。首先,我们审查最经常用于无线通信和网络分析和优化IRS的通信模型,并阐述其优点和局限性。然后,我们集中研究基于不相容的地表阻力表阻力表的RIS模型,并提供逐步的辅导,以制定电磁一致的分析模型,以优化地表阻力。我们讨论和全球设计之间的差别,并分析地表电能效率和通过Poynation矢量的再辐照变能力。最后,在数字结果的帮助下,我们讨论了如何利用高水平的电源反射力实现全球设计,甚至以高水平反射力反射法。