Abstract
With the rapid development of emerging 5G and beyond (B5G), Unmanned Aerial Vehicles (UAVs) are increasingly important to improve theperformance of dense cellular networks. As a conventional metric, coverage probability has been widely studied in communication systems due to theincreasing density of users and complexity of the heterogeneous environment. In recent years, stochastic geometry has attracted more attention as a mathematical tool for modeling mobile network systems. In this paper, an analytical approach to the coverage probability analysis of UAV-assisted cellularnetworks with imperfect beam alignment has been proposed. An assumption was considered that all users are distributed according to Poisson ClusterProcess (PCP) around base stations, in particular, Thomas Cluster Process (TCP). Using this model, the impact of beam alignment errors on the coverageprobability was investigated. Initially, the Probability Density Function (PDF) of directional antenna gain between the user and its serving base stationwas obtained. Then, association probability with each tier was achieved. A tractable expression was derived for coverage probability in both Line-of-Sight (LoS) and Non-Line-of-Sight (NLoS) condition links. Numerical results demonstrated that at low UAVs altitude, beam alignment errors significantlydegrade coverage performance. Moreover, for a small cluster size, alignment errors do not necessarily affect the coverage performance.