Active RIS Assisted Index Modulation for Wireless Communication System

Index modulation and reconfigurable intelligent surfaces (RIS) have garnered significant attention in recent years due to their promising potential in advancing wireless communications. In this letter, we combine these two techniques and propose an amplification factor-indexed modulation (AFIM) scheme to improve the spectral efficiency in active RIS (A-RIS) aided systems, where the optimized amplification factor of A-RIS is modulated to transmit additional information bits. A closed-form expression for the average bit error probability of AFIM is derived. Furthermore, we extend AFIM to an A-RIS assisted hybrid index modulation (A-RIS-HIM) system, which incorporates reflecting modulation and receive spatial modulation. Besides, two low-complexity detectors based on greedy detection (GD) are proposed for the A-RIS-HIM system. Simulation results are provided to substantiate the effectiveness of the proposed scheme in terms of bit error rate.