Hybrid Reconfigurable-Intelligent-Surface-Assisted Reflective Spatial Modulation for Backscatter Communication

Reconfigurable intelligent surface (RIS) is a promising technology that can modify wireless propagation environment, enabling cost-effective spectral and energy efficient communications. Moreover, due to its controllable reflection coefficients, an RIS can function as a backscatter device while enhancing the communication link. However, the application potential of conventional passive RIS is limited by the multiplicative fading effect. In this article, an active-passive hybrid RIS-assisted reflective spatial modulation (HRIS-RSM) scheme is proposed for backscatter communication, where the backscatter information is embedded into the modulated signal from the transmitter and jointly conveyed by the number of active reflecting elements (REs) groups on the RIS and the receive antenna indices at the receiver. Subsequently, maximum likelihood (ML) and greedy detections are formulated for the HRIS-RSM scheme. The theoretical bit error probabilities for the transmitter information, backscatter information, and overall information in the proposed HRIS-RSM scheme are derived under both ML and greedy detections. Simulation results validate the theoretical derivations and evaluate the performance of the proposed HRIS-RSM scheme, demonstrating its superior bit error rate performance compared to reference schemes.