Direct Data Modulation via Passive RIS: Concept and Implementation of RIS-Backscatter Communications

Reconfigurable intelligent surface (RIS) has recently garnered attention for its ability to intelligently manipulate the wireless environment. However, the absence of radio frequency (RF) chains has traditionally limited the RIS's ability to transmit information. This article presents a practical approach where the RIS is utilized as the primary information generator, enabling direct information transmission without the need for RF chains. Our proposed method uses the adaptive RIS-backscatter scheme to modulate incident unmodulated electromagnetic (EM) waves. Notably, our main contributions lie in the development of the algorithm itself, followed by comprehensive validations through simulations and experiments, establishing the feasibility of our approach. This work presents a step forward in the field of RIS-based symbiotic radio (SR), enhancing the applicability of conventional RIS structures in practical wireless communication scenarios.