Principles, Applications, and Challenges of Reconfigurable Intelligent Surface-Enabled Backscatter Communication: A Comprehensive Survey and Outlook

Backscatter communication (BackCom) networks are expected to provide ultra-low-power transmission and massive connectivity in future wireless communication systems. Nevertheless, the double-fading effect significantly reduces signal intensity and is a primary problem of modern BackCom systems. Reconfigurable Intelligent Surface (RIS) can artificially modify the wireless environment through numerous controllable reflecting elements. With the help of RIS, the desired signals in the BackCom procedure can be captured and reflected in the specified direction, which is able to alleviate the double-fading problem. Specifically, RIS can be a backscatter device to send information instead of a collaborator to enhance transmission, yielding the RIS-BackCom mechanism. However, a comprehensive review of this technique still needs to be made available, dramatically limiting its development. This paper presents the fundamental principles and functions of legacy BackCom systems, the RIS technique, and RIS-BackCom networks. Then, we discuss the system-level performance with different modulation and channel estimation approaches. Further, we introduce symbiotic radio (SR) networks developed from the RIS-BackCom technique. After that, we provide a survey on diverse optimization issues existing in the applications of RIS-BackCom networks. Finally, we envision emerging use scenarios, potential challenges, and possible solutions in future wireless communication networks.