Online 3D Placement for UAV-aided Free-space Optical Communication under Shadowing

Abstract

This paper studies 3-dimensional (3D) placement for an unmanned aerial vehicle (UAV) to build a free-space optical (FSO) communication links to relay the signals for two users that are shadowed by obstacles. The key challenge of FSO communication is the possible signal blockage due to obstacles. UAV can be adopted as a relay to build connection with two users, and it is essential to find a good relay position. Existing work is either based on heuristic methods or to optimize the UAV relay position on 2D, which cannot fully unleash the potential of UAV relay. In contrast, as note that the globally optimal relay position potentially lies on the equipotential surface, this paper develops UAV search strategies to build wireless relay communication channels for two ground users that are probably shadowed by obstacles. As the two users may have different transmission power, it may not be the best choice to search on the middle perpendicular plane. Based on this insight, this paper develops a strategy to search on a selected perpendicular plane to the ground and finds a sub-optimal UAV service position. The maximum length of search trajectory being linear to the geographical scale. Numerical experiments are conducted over a real-world urban topology and demonstrate that the performance of the proposed search is very close to the globally optimal one found by brute force search.