Design and Performance Analysis of QRM-Aided RIS for Multiple Access Systems

Reconfigurable intelligent surface (RIS)-based re f lection modulation (RM) is recognized as an innovative concept for effectively transferring information with more spectral effi ciency. This paper investigates the performance enhancements enabled by the quadrature reflection modulation (QRM) into uplink multiple access (MA) transmission. Specifically, we pro pose a novel QRM indexing-aided RIS grouping design for the MA system, termed QRMMA, to boost the system's spectral efficiency and enhance the error performance. The main idea is to separate the RIS groups into two orthogonal subsets equally, then each subset is further divided into pairs, where each user should select a single subgroup from each pair based on its transmitted data. To evaluate the performance of the proposed system, we derive an approximate expression for the average bit error probability (ABEP) and ergodic capacity over Rician fading channels. Simulation results demonstrate that the proposed QRMMA system can achieve a significantly enhanced performance compared to its conventional counterparts while maintaining higher spectral efficiency.