Reconfigurable Intelligent Surfaces For Wireless Communications

Abstract

Reconfigurable Intelligent surface (RIS) is a programmable structure that can be used to control the propagation of electromagnetic waves by changing the electric and magnetic properties of the surface. RIS can customize the radio propagation environments by reconfiguring the phase and amplitude of the incident signals. RIS is a thin surface composed of N elements, each being a reconfigurable scatter: a small antenna receives and re-radiates without amplification, but with a configurable time-delay. RISs are made of passive or active metamaterials. The active metamaterial may be tunable metamaterial by changing the bias voltages of the varactor or PIN diodes, reconfigurable metamaterial using plasma, graphene, vanadium dioxide (VO2) materials and space-time-coding digital metamaterial with the aid of field programmable gate array (FPGA). RIS can be categorized into three types: 1. Reflector type: the RIS only reflects incident signals towards the users on the same side of the base station (BS). 2. Transmissive type: the incident signal will penetrate the RIS and be transmitted towards users on the opposite side of the BS. 3. Hybrid type: the incident signals will be spitted into two parts: one part is transmitted and the other is reflected. The RIS is mainly considered to be a beyond 5G technology operating at frequencies from tens of Gigahertz’s (GHz) to Terahertz’s (THz). At these frequency bands, the signal propagation is heavily attenuated and be blocked completely by the obstacles in the propagation environment. RIS can be made in different shapes, including but not limited to building facades, indoor walls and road bill boards, Typical applications of RIS, can be categorized into two types: 1, wireless communication, RIS can improve the spectrum efficiency, coverage extension and energy efficiency. 2. RF sensing, RIS has a wide range of applications in improving security, smart space, safety and the communication reliability of wireless networks. This talk will be focused on the different RIS types and presented the most recent research activities at FEE Antenna Research Group in Faculty of Electronic Engineering, Menoufia University, Egypt in this topic.