The search for physical layer technologies that can play a key role in beyond 5G systems has started. One option is reconfigurable intelligent surfaces (RISs), which can collect wireless signals from a transmitter and passively beamform them toward 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 path loss 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?

中文翻译：

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可重构智能表面：三个误区和两个关键问题

已经开始寻找可以在 5G 系统之外发挥关键作用的物理层技术。一种选择是可重构智能表面 (RIS)，它可以收集来自发射器的无线信号，并将它们被动地波束形成到接收器。该技术具有令人兴奋的前景，并在通信社区中迅速受到关注，但在当前的炒作中，我们目睹了一些神话和夸大其词在文献中的传播。在本文中，我们中立地看待 RIS 技术。我们首先回顾基础知识，然后解释容易被误解的特定功能。特别是，我们揭穿了三个神话：1）当前的网络技术只能控制发射器和接收器，而不能控制两者之间的环境；2) 获得比传统波束成形更好的渐近阵列增益；3) 路径损耗与异常反射镜相同。为了激发进一步的研究，我们最后确定了 RIS 成为一项成功技术必须回答的两个关键问题：1) 什么是 RIS 令人信服的用例？2）我们如何实时估计信道并控制RIS？