LoS Coverage Analysis for UAV-Based THz Communication Networks: Toward 3-D Visualization of Wireless Networks

Terahertz (THz) links require a line-of-sight (LoS) connection, which is hard to be obtained in most scenarios. For THz communications, analyses based on LoS probability are not accurate, and a real LoS model should be considered to determine the LoS status of the link in a real 3-D environment. Considering unmanned aerial vehicle (UAV)-based THz networks, LoS coverage is analyzed in this work, where nodes are accurately determined to be in LoS or not. Specifically, by modeling an environment with 3-D blocks, our target is to locate a set of UAVs equipped with directional THz links to provide LoS connectivity for the distributed users among the 3-D obstacles. To this end, we first characterize and model the environment with 3-D blocks. Then, we propose a user-friendly algorithm based on 3-D spatial vectors, which determines the LoS status of nodes in the target area. In addition, using 3-D modeling, several metaheuristic algorithms are proposed for UAVs' positioning under 3-D blocks in order to maximize the LoS coverage percentage. In the second part of this article, for a UAV-based THz communication network, a geometrical-analysis-based algorithm is proposed, which jointly clusters the distributed nodes and locates the set of UAVs to maximize average network capacity while ensuring the LoS state of distributed nodes among 3-D obstacles. Moreover, we also propose a suboptimal hybrid k-means-geometrical-based algorithm with a low computational complexity that can be used for networks where the topology continuously changes, and thus, users' clustering and UAVs' positioning need to be regularly updated. Finally, by providing various 3-D simulations, we evaluate the effect of various system parameters, such as the number and heights of UAVs, as well as the density and height of 3-D obstacles on the LoS coverage.