Reconfigurable intelligent surfaces (RISs) have the potential of realizing the emerging concept of smart radio environments by leveraging the unique properties of metamaterials and large arrays of inexpensive antennas. 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. The present paper, therefore, 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 for application to wireless communications and networks.

中文翻译：

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可重新配置的智能表面与中继：差异，相似性和性能比较

通过利用超材料和大量廉价天线的独特特性，可重构智能表面（RIS）有潜力实现智能无线电环境的新兴概念。在本文中，我们讨论了RIS在高频段（例如毫米波（30–100 GHz）和亚毫米波（大于100 GHz））工作的无线网络中的潜在应用。当在无线网络中使用时，RIS可以类似于中继的方式进行操作。因此，本白皮书详细介绍了配置为用作异常反射器和中继器的RIS之间的关键区别和相似之处。尤其是，我们举例说明了数值结果，该数值结果突出了RIS的尺寸（与无线电波的波长相比）足够大时，其频谱效率的提高。此外，我们讨论了一些关键的开放问题，这些问题需要解决才能释放RIS在无线通信和网络中的潜在优势。