Reconfigurable Intelligent Surfaces: Three Myths and Two Critical Questions
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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 desired receiver. Despite the massive attention RIS is currently receiving from the communication community, we have witnessed how several misconceptions are spreading, as epitomized by following (fictional) abstract: "While current wireless technologies treat the propagation channels as uncontrollable and given by nature, RIS constitutes a paradigm shift by enabling control of the channels. An RIS behaves as a mirror with the key difference that the reflection angle can be controlled, thus the path-loss is identical to that of a line-of-sight path having the same total length. The RIS achieves array gains both in reception and reflection, which makes RIS more spectrally efficient than using conventional active antenna arrays that only benefit from one array gain." Most of these statements are incorrect. In this article, we first review the fundamentals of RIS and then debunk three specific myths. To inspire further research, we conclude by identifying two critical questions that must be answered for RIS to become a successful technology.
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