Multiple Reconfigurable Intelligent Surface-Based Index Modulation With Optimal Combination

This study proposes multiple reconfigurable intelligent surface (RIS)-based index modulation (IM), called MRB-IM, to improve channel capacity by activating one or more RISs within multiple RIS (MRIS). Generally, MRIS suffers from the secondary reflection that, in imperfect condition, can be considered as inter-RIS interference (IRI) within MRIS. On the other hand, the proposed MRB-IM has a larger capacity but less of an effect on IRI because it only happens between the active MRIS. The optimal combination algorithm is applied to select the best possible RIS combinations for the activation bits in IM. The simulation is done to support the analytical channel capacity based on mutual information and bit error rate. The results show that the proposed system offers higher capacity and a lower bit error rate compared to the conventional MRIS. The complexity of the system is mentioned as another benefit of MRB-IM.