Reconfigurable Intelligent Surfaces vs. Relaying: Differences, Similarities, and Performance Comparison

TLDR

Reconfigurable intelligent surfaces (RISs) enable smart radio environments by using metamaterials and large antenna arrays, and can function similarly to relays in wireless networks. This article explores RIS applications at millimeter‑wave and sub‑millimeter‑wave frequencies, compares RISs acting as anomalous reflectors with relays, and highlights key open issues for their deployment in wireless communications. Numerical results demonstrate that RISs achieve spectral‑efficiency gains when their size is sufficiently large relative to the wavelength.

Abstract

Reconfigurable intelligent surfaces (RISs) have the potential of realizing the emerging concept of smart radio environments by leveraging the unique properties of metamaterials and large arrays of inexpensive antennas. In this article, we discuss the potential applications of RISs in wireless networks that operate at high-frequency bands, e.g., millimeter wave (30-100 GHz) and sub-millimeter wave (greater than 100 GHz) frequencies. When used in wireless networks, RISs may operate in a manner similar to relays. The present paper, therefore, elaborates on the key differences and similarities between RISs that are configured to operate as anomalous reflectors and relays. In particular, we illustrate numerical results that highlight the spectral efficiency gains of RISs when their size is sufficiently large as compared with the wavelength of the radio waves. In addition, we discuss key open issues that need to be addressed for unlocking the potential benefits of RISs for application to wireless communications and networks.