Leveraging Hybrid UAV Relays in Adverse Weather for FSO Link Capacity Maximization

In the context of beyond the fifth-generation (B5G), free-space optics (FSO) is a vital technology for high data rate applications because of its low cost and licence-free high bandwidth. However, during adverse weather, the FSO link's capacity can be significantly impacted, and establishing parallel radio frequency (RF) backup links just for occasional utilization is both complex and costly. In this study, in order to improve the availability of FSO link in adverse weather conditions, we propose to use unmanned aerial vehicles (UAVs) as hybrid relays to intercept an FSO link. The UAVs construct an intermediate millimeter wave (MMW) link, while ensuring that the approach has no impact on the source and destination. The end-to-end system capacity is maximized by optimizing UAVs' location based on the negatively correlated FSO and MMW link length. The performance of the proposed model is compared to benchmark systems such as single FSO, fixed relay-assisted FSO, and fixed hybrid FSO/RF systems. The numerical results clearly demonstrate the proposed scheme's superiority. Finally, using weather statistics from the cities of Edinburgh and London in the United Kingdom, the performance of the proposed system and its counterparts in realistic scenarios is demonstrated, which illustrates that the proposed system may significantly improve link availability towards the carrier-class criterion.