Reconfigurable Intelligent Surfaces for Wireless Communications: Principles, Challenges, and Opportunities

• Published in: IEEE transactions on cognitive communications and networking Vol. 6; no. 3; pp. 990 - 1002
• Main Authors: ElMossallamy, Mohamed A., Zhang, Hongliang, Song, Lingyang, Seddik, Karim G., Han, Zhu, Li, Geoffrey Ye
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.09.2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Beyond 5G; Electromagnetic radiation; intelligent reflecting surfaces; large intelligent surfaces; Millimeter wave propagation; Millimeter wave technology; MIMO (control systems); MIMO communication; Multiplexing; New technology; Optimization; passive beamforming; Principles; Reconfigurable intelligent surfaces; smart reflect-arrays; Surface waves; Wave propagation; Wireless communication; Wireless communications; Wireless networks
• ISSN: 2332-7731; 2332-7731
• DOI: 10.1109/TCCN.2020.2992604

Recently there has been a flurry of research on the use of reconfigurable intelligent surfaces (RIS) in wireless networks to create smart radio environments. In a smart radio environment, surfaces are capable of manipulating the propagation of incident electromagnetic waves in a programmable manner to actively alter the channel realization, which turns the wireless channel into a controllable system block that can be optimized to improve overall system performance. In this article, we provide a tutorial overview of reconfigurable intelligent surfaces (RIS) for wireless communications. We describe the working principles of reconfigurable intelligent surfaces (RIS) and elaborate on different candidate implementations using metasurfaces and reflectarrays. We discuss the channel models suitable for both implementations and examine the feasibility of obtaining accurate channel estimates. Furthermore, we discuss the aspects that differentiate RIS optimization from precoding for traditional MIMO arrays highlighting both the arising challenges and the potential opportunities associated with this emerging technology. Finally, we present numerical results to illustrate the power of an RIS in shaping the key properties of a MIMO channel.