RIS-embedded UAVs communications for multi-hop fully-FSO backhaul links in 6G networks

In the upcoming 6G network, the use of reconfigurable intelligent surface (RIS) is expected to revolutionize wireless communications, providing high data rate, directivity, and extending coverage to skip-zones. This paper presents a detailed analysis on RIS for a fully free-space optical (FSO) ground-to-aerial-to-ground system, by means of single and multiple unmanned aerial vehicles (UAVs). Specifically, we introduce a network architecture suitable for FSO backhaul transmissions, connecting ground stations that are not in Line of Sight (LoS) through RIS-embedded UAVs. We present the derivations of outage probability and bit error rate (BER) in case of singleand two-RIS embedded UAVs FSO paths, and for single and multiple RIS number of elements. Numerical results assess the effectiveness of the proposed system, specifically in case of multiple UAVs and number of RIS elements.