Reconfigurable Intelligent Surfaces for 6G Vision

Abstract

Reconfigurable Intelligent Surfaces (RIS), also known as intelligent reflecting surfaces, offer a transformative mechanism for shaping wireless environments—turning propagation spaces into programmable platforms. These capabilities align well with the emerging 6G vision, where networks demand unparalleled spectral efficiency, adaptability, and sustainability. RIS technology leverages planar arrays of low-power, tunable elements— like metasurfaces with diodes or varactors—to manipulate electromagnetic waves via controlled phase shifts, thereby enabling dynamic beam steering, focusing, and channel reconfiguration Digital LibraryPMC. Early literature explores RIS design paradigms, channel modeling, and performance analyses of hardware implementations. For example, numerous varactor- and PIN-diode-based RIS prototypes operating across sub-6 GHz to millimeter-wave bands demonstrated phase shifts of over 180°, beam steering up to tens of degrees, and power gains in the tens of dB range PMC+1. RISs have also been shown to enhance spectrum and energy efficiency by creating favorable propagation paths with minimal active transmission hardware ResearchGateDigital Library. RISs' low-cost, passive nature allows integration into existing infrastructure (e.g., walls, street lamps), enabling broad deployment with minimal energy consumption—making them ideal for 6G’s sustainability goals IEEE AccessETSI. However, challenges remain: accurate channel state information acquisition, beamforming optimization, control complexity, and deployment strategies require rigorous research and innovation arXivDigital LibraryResearchGate. This survey synthesizes RIS principles, hardware architectures, and use-case potentials, emphasizing how RIS could underpin the intelligent, programmable radio environments envisioned for 6G, while recognizing critical technological barriers that pre-2020 research has identified.