Reconfigurable Intelligent Surfaces aided Wireless Communication: Key Technologies and Challenges

Reconfigurable Intelligent Surface (RIS) has emerged as a key enabling technology to smartly reconfigure radio propagation environment for beyond the fifth generation or the sixth generation(B5G/6G) wireless communications, by adjusting the phase shifts and amplitudes of a large number of passive reflecting elements to control the signal reflection in real time. However, different from the traditional wireless base station or relay, RIS has the new feature of typically limited signaling processing capability and cannot perform active transmitting/receiving in general. So before introducing RIS into 3GPP standardization, the deployment scenario and the performance gain coming from RIS need to be studied and evaluated firstly, then the key technologies of RIS aided wireless communication including channel modeling of RIS, channel estimation and passive beamforming design need to be identified and studied, furthermore the new and unique challenges including RIS hardware imperfections for RIS deployment need to be analyzed and solved. In this paper, we provide a comprehensive survey on the key technologies research in RIS aided wireless communication system mainly in specification and implementation perspectives, and discuss some practical design and deployment problems to motivate future research and implementation of RIS.