This thesis deals with the cellular communication in UAS (Unmanned Aerial Systems), with focus on the connectivity stack, the traffic model, and the feasibility of using UAVs (Unmanned Aerial Vehicles) in BVLOS (Beyond Visual Line-of-Sight) applications. The study is conducted by collecting over-the-air measurements, and with the use of hardware-in-the-loop emulators. The different scenarios used to test the system allow to distinguish and understand the different environmental conditions imposed on the UAVs (Unmanned Aerial Vehicles). From the statistical analysis of the collected data, conclusions are drawn about the performance of the system in the different scenarios, and about the quality of the traffic model.