Communication Models for Reconfigurable Intelligent Surfaces: From Surface Electromagnetics to Wireless Networks Optimization

• Published in: Proceedings of the IEEE Vol. 110; no. 9; pp. 1164 - 1209
• Main Authors: Di Renzo, Marco, Danufane, Fadil H., Tretyakov, Sergei
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.09.2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE); Institute of Electrical and Electronics Engineers
• Subjects: Angle of reflection; Design optimization; Design parameters; Electromagnetic radiation; Electromagnetic scattering; Electromagnetics; Engineering Sciences; Impedance; Mathematical models; Metamaterials; Metasurfaces; modeling; Network design; optimization; Planar structures; Power efficiency; Reactance; Receivers; Reconfigurable intelligent surfaces; reconfigurable intelligent surfaces (RISs); Signal and Image processing; smart radio environments (SREs); Surface waves; Wireless communication; Wireless communications; Wireless networks
• ISSN: 0018-9219; 1558-2256
• DOI: 10.1109/JPROC.2022.3195536

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 article, 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.