UAV-BASED Dynamic FSO Access Networks: Technological Comparison, Design Considerations, and Future Directions

Despite the high data rates and security levels offered by free space optical (FSO) communication, its applications have been traditionally limited to point-to-point configurations due to the technology's narrow beamwidth and line-of-sight requirement. However, this research explores the potential of expanding FSO communication into more complex network topologies by utilizing it in dynamic access points (APs). These APs are notable for their capabilities in achieving high transmission rates and near-perfect physical layer security. Specifically, this article presents a novel approach to designing unmanned aerial vehicle (UAV)-based APs that uti-lize laser link technology. The approach integrates advanced technologies such as modulating ret-roreflectors (MRR), intelligent reflecting surfaces (IRS), and UAVs. We first examine various FSO AP topologies based on IRS, discussing the underlying technologies, their applications, and the challenges they face. A key issue identified is the high sensitivity of FSO-IRS AP networks to alignment errors, mainly due to beam clipping caused by the smaller dimensions of the IRS. To mitigate this challenge, we propose an alternative topology using MRR, which can establish a resilient FSO AP system. This MRR-based system shows robustness against UAV oscillations up to several hundred milliradians and has the potential to provide secure communication networks at the physical layer, outperforming existing radio, millimeter-wave, and terahertz technologies.