Reconfigurable intelligent surfaces (RISs) or intelligent reflecting surfaces (IRSs) are regarded as one of the most promising and revolutionizing techniques for enhancing the spectrum and/ or energy efficiency of wireless systems. These devices are capable of reconfiguring the wireless propagation environment by carefully tuning the phase shifts of a large number of low-cost passive reflecting elements. In this article, we aim to answer four fundmental questions: 1) Why do we need RISs? 2) What is an RIS? 3) What are RIS's applications? 4) What are the relevant challenges and future research directions? In response, eight promising research directions are pointed out.

中文翻译：

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6G系统可重构智能表面：原理、应用和研究方向


可重构智能表面（RIS）或智能反射表面（IRS）被认为是增强无线系统频谱和/或能源效率最有前途和革命性的技术之一。这些设备能够通过仔细调整大量低成本无源反射元件的相移来重新配置无线传播环境。在本文中，我们旨在回答四个基本问题：1）为什么我们需要 RIS？ 2) 什么是RIS？ 3）RIS的应用是什么？ 4）相关挑战和未来研究方向是什么？对此，指出了八个有前景的研究方向。