A Survey of Reconfigurable Intelligent Surfaces: Towards 6G Wireless Communication Networks with Massive MIMO 2.0
Reconfigurable intelligent surfaces (RISs) tune wireless environments to increase spectrum and energy efficiencies. In view of much recent attention to the RIS concept as a promising technology for 6G wireless communications, we present a survey of RISs in this paper. Specifically, we categorize recent research studies of RISs as follows. For RIS-aided communications, the summary includes capacity/data rate analyses, power/spectral optimizations, channel estimation, deep learning-based design, and reliability analysis. Then we review RISs implementations as well as the use of RISs in secure communications, terminal-positioning, and other novel applications. We further identify future research directions for RISs, with an envision of the RIS technology playing a critical role in 6G communication networks similar to that of massive MIMO in 5G networks. As a timely summary of RISs, our work will be of interest to both researchers and practitioners working on RISs for 6G networks.
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