Reconfigurable intelligent surface (RIS), one of the key enablers for the sixth-generation (6G) mobile communication networks, is considered by designers to smartly reconfigure the wireless propagation environment in a controllable and programmable manner. Specifically, an RIS consists of a large number of low-cost and passive reflective elements (REs) without radio frequency chains. The system gain of RIS wireless systems can be achieved by adjusting the phase shifts and amplitudes of the REs so that the desired signals can be added constructively at the receiver. However, an RIS typically has limited signal processing capability and cannot perform active transmitting/receiving in general, which leads to new challenges in the physical layer design of RIS wireless systems. In this paper, we provide an overview of the RIS-aided wireless systems, including the reflection principle, channel estimation, and system design. In particular, two types of emerging RIS systems are considered: RIS-aided wireless communications (RAWC) and RIS-based information transmission (RBIT), where the RIS plays the role of the reflector and the transmitter, respectively. We also envision the potential applications of RIS in 6G networks.

可重构智能表面 (RIS) 是第六代 (6G) 移动通信网络的关键推动因素之一，设计人员认为它可以以可控和可编程的方式智能地重新配置无线传播环境。具体来说，RIS 由大量低成本和无源反射元件 (RE) 组成，没有射频链。RIS 无线系统的系统增益可以通过调整 RE 的相移和幅度来实现，以便可以在接收器处建设性地添加所需信号。然而，RIS通常具有有限的信号处理能力，并且一般不能进行主动发送/接收，这给RIS无线系统的物理层设计带来了新的挑战。在本文中，我们概述了 RIS 辅助无线系统，包括反射原理、信道估计和系统设计。特别地，考虑了两种新兴的 RIS 系统：RIS 辅助无线通信 (RAWC) 和基于 RIS 的信息传输 (RBIT)，其中 RIS 分别扮演反射器和发射器的角色。我们还设想了 RIS 在 6G 网络中的潜在应用。