A Comprehensive Review on Reconfigurable Intelligent Surface for 6G Communications: Overview, Deployment, Control Mechanism, Application, Challenges, and Opportunities

With the emergence of cellular networks, the wireless communication network system has evolved from the first generation to the sixth generation (6G), which will provide an integrated framework for a variety of utilities, applications, and technologies. One emerging technology for 6G communication network systems is reconfigurable intelligent surfaces (RIS), which is ideal for smooth and controllable wireless signal transmission. RIS is mainly a programmable structure that can regulate the propagation of electromagnetic waves by smartly tuning a large number of elements via an electronic controller. This study presents a complete overview of RIS, including its hardware architecture, key characteristics, control mechanism, carrier frequency, communication duplex mode, and working procedure. The study also elaborates on the RIS propagation scenarios, advantages of implementing RIS, deployment, and different types of communication by utilizing RIS. Finally, we conclude with a discussion of challenges and future research directions to overcome limitations to achieve the goal of RIS implementation and RIS-aided communication for 6G communication systems.