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

TL;DR

This paper compares reconfigurable intelligent surfaces (RISs) with relays, highlighting their differences, similarities, and potential spectral efficiency benefits in high-frequency wireless networks, while discussing open research challenges.

Contribution

It provides a detailed comparison between RISs and relays, including numerical analysis of spectral efficiency gains and identifies key open issues for future research.

Findings

RISs can significantly improve spectral efficiency at large sizes

RISs operate similarly to relays but have distinct configuration properties

Numerical results demonstrate spectral efficiency gains with large RISs

Abstract

Reconfigurable intelligent surfaces (RISs) have the potential of realizing the emerging concept of smart radio environments by leveraging the unique properties of meta-surfaces. 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. This paper 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.