## 2 Related Works
### Study of the State-of-the-Art  
It was described in [10] how a UAV can be used to obtain measurements related to Antennas Under Tests (referred to as AUT). The authors developed a methodology that, considering major parameters (distance from the antenna, its aperture, the operating wavelength, etc. ), made use of a UAV to take in situ far-field measurements. The work developed comprised of five different subsystems (Transmitting, Receiving, Positioning, Recording and Data-Processing subsystems) and a simulation framework used for three of the most frequent use cases (probe in an elevated range, probe mounted on a UAV and a misalignment error analysis). The reviewed paper proved that there was interest behind the idea of using UAVs for wireless network measurements, but it provided a simulated environment for some tailored use cases, instead of offering an actual prototype with mobile network data collected from a real environment. No comparative measurements or time usage information were provided, as opposed to our own paper. Another similar example was shown in [11], where an \"antijam and accurate antenna parameters' measurement framework\" named A3 PNet was put forward. It was cited how the measurement of the antenna down-tilt angle of mobile communication base stations was regarded as a critical task for academia and industry, and how UAVs could be used for that purpose. Measurement enhancement in an unfavourable environment (i.e., wind at certain altitude destabilizes the UAV used for antenna-related measurements) was the main topic of the reviewed paper, as (a) an Adaptive Feature Recovery Module (AFRM), (b) a Contour Modulation Strategy (CMS) and (c) an Antenna Down-tilt Measurement Module (ADMM) were introduced for the sole purpose of improving an antenna attitude and performance. In this context, UAVs were expected to be used as autonomously as possible with next to no human intervention. The work presented was remarkable in one sense, but it had a different purpose than the one presented in our paper (an inexpensive open-source tool to perform reliable mobile network measurements, making use of Galileo as the GNSS). It was described in [12] how it is desirable to have a visual measurement system that can be used for Autonomous Aerial Refuelling in UAVs. It was described how UAVs of relatively large sizes can fly in an autonomous manner when they are performing tasks, but, unlike manned aircrafts, they lack aerial refuelling capabilities that would enable them to perform longer missions. To deal with this challenge, a Virtual Reality-based simulation environment was built, where visual markers and a camera were set in the simulated receiver UAV and the tanker aircraft, respectively. By making use of marker detections and point matching capabilities, the authors of the reviewed paper made a pose estimation that enabled them to demonstrate their hypothesis. The V-Realm Builder platform in MATLAB was used to create the simulated environment. Tests were carried out in a hardware-in-loop system to understand the feasibility of the proposed system. Overall, this piece of research showed how UAVs could be used in application domains that were traditionally kept for other larger, more complex aircraft or devices, but the scope of this paper was significantly different from the solution put forward in our own research and development works. A similar orientation could be found in [13]. It was shown by the authors of this paper how a UAV could be employed to measure different kinds of parameters (temperature, humidity, thermal noise from the UAV, etc. ), to the point that a UAV could be used as a Mobile Measurement Platform (MMP). However, it must be considered how these measurements were not as accurate as expected, since they were obtained in an indirect manner. Nevertheless, an example of the possibilities that UAVs offer when used as MMPs, using a UAV as a support system for three-dimensional reconstruction of archaeological files, was described.