A UAV-Based Mixed RF/FSO System with RIS-Aided Reflection Modulation Multiple Access

Reconfigurable Intelligent Surfaces (RISs) have recently gained an increasing attention due to their ability by significantly enhancing the communication quality. In this work, we employ RIS together with Index Modulation (IM) to propose a novel multiple access scheme named as Reflection Modulation Multiple Access (RMMA). The idea of RMMA is to split the RIS into subsurfaces and allow each user to select one subsurface to reflect its uplink signal using the IM concept. The proposed scheme is adopted in a dual-hop Unmanned Aerial Vehicle (UAV)based system in which the first hop operates via the radio frequency (RF) band, while the second hop operates via the free space optical (FSO). Channel fading of users-RIS, RIS-UAV and UAV-base station links are modeled as Rician, Air-to-Air (A2A) and Gamma-Gamma models, respectively. Results indicate that the proposed scheme can significantly improve the error rate performance as compared to conventional scheme.