Reconfigurable Intelligent Surface-Based Symbiotic Radio for 6G: Design, Challenges, and Opportunities

Energy efficiency (EE) and spectrum efficiency (SE) are two key performance metrics in the sixth generation (6G) wireless communication networks due to the ultra-massive connectivity requirements in future Internet of Things scenarios such as smart cities and factories. Reconfigurable intelligent surface (RIS)-based symbiotic radio (SR) is a promising technology to simultaneously achieve high EE and SE. In this article, a comprehensive review of the RIS-based SR system is presented including the system architectures, operating principles, technical advantages, application scenarios and state-of-the-art transceiver design. Moreover, a star-QAM-aid-ed joint spatial modulation scheme is proposed to realize RIS-based SR and simulation results are provided to illustrate the performance of the proposed scheme. Finally, the critical design challenges for the implementation of RIS-based SR and some promising future research directions are discussed.