Efficient deployment of aerial relays in FSO-based backhaul networks

Using network flying platforms (NFPs) as aerial relays has been emerging as a promising solution for mobile backhaul frameworks in fifth generation and beyond wireless networks. Moreover, free space optics (FSO) technology has become the alternative to radio frequency technology for backhaul links due to its advantages of a high data rate, long transmission range, and negligible interference. In an FSO-based NFP relay backhaul network, due to the fragility of FSO links, how to deploy NFPs to satisfy network traffic demands is a challenging problem. Moreover, the establishment of non-essential FSO links leads to the extra deployment of NFPs due to the limited number of transceivers carried by each NFP, which makes the NFP deployment problem more complex. To solve these issues, we jointly consider the deployment of NFPs and the formation of network topology, the targets of which are to minimize the number of deployed NFPs and network congestion. The problem is formulated as mixed-integer nonlinear programming, which is hard to solve directly, and we linearize it based on transmission range simplification. A heuristic algorithm is proposed to solve the problem for large-scale network scenarios. Simulation results show that the joint optimization scheme of NFP deployment and network topology formation surpasses the single optimization scheme, and the proposed heuristic algorithm can solve the joint optimization problem efficiently in differently scaled networks.