Reconfigurable Intelligent Surfaces: Three Myths and Two Critical Questions

TL;DR

This paper critically examines reconfigurable intelligent surfaces (RIS), debunking common myths and highlighting key questions to address for RIS to realize its potential in future wireless systems.

Contribution

It provides a neutral review of RIS fundamentals, clarifies misconceptions, and identifies critical research questions for practical deployment.

Findings

Debunks three common myths about RIS technology.

Highlights the importance of real-time channel estimation and control.

Emphasizes the need for convincing use cases for RIS.

Abstract

The search for physical-layer technologies that can play a key role in beyond-5G systems has started. One option is reconfigurable intelligent surfaces (RIS), which can collect wireless signals from a transmitter and passively beamform them towards the receiver. The technology has exciting prospects and is quickly gaining traction in the communication community, but in the current hype we have witnessed how several myths and overstatements are spreading in the literature. In this article, we take a neutral look at the RIS technology. We first review the fundamentals and then explain specific features that can be easily misinterpreted. In particular, we debunk three myths: 1) Current network technology can only control the transmitter and receiver, not the environment in between; 2) A better asymptotic array gain is achieved than with conventional beamforming; 3) The pathloss is the same as with anomalous mirrors. To inspire further research, we conclude by identifying two critical questions that must be answered for RIS to become a successful technology: 1) What is a convincing use case for RIS?; 2) How can we estimate channels and control an RIS in real time?