Enhancing Millimeter Wave Link Capacity in Adverse Weather Using Hybrid UAV Relays

In the context of sixth generation (6G) and beyond, millimeter wave (MMW) is a vital technology for high data-rate applications in the realm of radio frequency (RF) communications due to its high bandwidth and low interference. However, adverse weather conditions, particularly rain, can significantly impact the MMW link capacity. In this study, we propose to exploit unmanned aerial vehicles (UAVs) as hybrid relays to improve the availability of MMW links in adverse weather conditions. The UAV relays exploit an intermediate free-space optical (FSO) relay link without impacting the RF source and destination nodes. We maximize the end-to-end channel capacity by optimizing the UAVs' locations based on the negatively correlated MMW and FSO link coverage lengths. We compare the proposed model's performance with benchmark systems, including a single MMW link, a static location relay-aided MMW system, and static hybrid FSO-RF systems. The numerical results clearly demonstrate the proposed scheme's superiority, including better performance when tested on realistic rainy channel conditions based on measured weather information in the United Kingdom.