A Survey of Reconfigurable Intelligent Surfaces: Towards 6G Wireless Communication Networks with Massive MIMO 2.0
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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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