## 3 System Description
### Unmanned Aerial Vehicle
#### 3.1.1 Hardware Components for the UAV  
Since the main objective of the UAV is using it for mobile network measurement flights, hardware components were adapted to create a functional drone with the sensing capabilities to perform that duty. The most prominent components used to build the UAV were as follows: \begin{table}
\begin{tabular}{c c} \hline \hline
**Requirement** & **Description** \\ \hline Functional Requirement 1 & The UAV must be able to perform yaw, pitch and roll manoeuvres \\ Non-functional Requirement 1 & The UAV must be able to have a mobile phone as the payload \\ Non-functional Requirement 2 & The UAV must be able to stand off the ground for at least one minute \\ Non-functional Requirement 3 & The UAV must use Galileo as the GNSS for positioning \\ Non-functional Requirement 4 & The UAV must be able to fly away tens of meters \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Requirements for the UAV. \begin{table}
\begin{tabular}{c c} \hline \hline
**Security Threat** & **Countermeasure** \\ \hline Base station monitoring & Credentials for base station access. \\ UAV command spoofing & Wi-Fi as the wireless protocol. Galileo as the GNSS. ArduPilot as the base station software. \\ Data tampering & Credentials for base station access. Wi-Fi as the wireless protocol. \\  & Galileo as the GNSS. ArduPilot as the base station software. \\ UAV hijacking & Wi-Fi as the wireless protocol. Galileo as the GNSS. ArduPilot as the base station software. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Security threats and their countermeasures. Raspberry Pi 3B+: this is the component used to run the operating system used by the open-source drone to govern the other components [27]. This provides an entry point to modify every setting possible for drone flights, which is maximized by using the ArduPilot program, as explained in the software section of this paper. As far as this proposal is concerned, its pinout is used combined with the Navio2 Autopilot for flight guidance and coordination. The Raspberry 3B+ makes use of a processor with a clock frequency of 1.4 GHz and 1 GB of SDRAM memory, which offers enough computational capabilities for the purpose described in this paper, and, since it can provide IEEE 802.11.b/g/n/ac and Bluetooth connectivity, it has the required wireless interfaces for connectivity and data transfer. 2. Navio2: this is a controller board used, as in every UAV, to manage the drone flight on a real-time basis, making the UAV more stable and keeping it afloat in a safer way. Depending on the requirements, it makes use of either Linux-based Application Performance Monitoring (APM) or a tailored middleware to work with the Robot Operating System (ROS). This controller has a high resolution MS5611 barometer and 14 Pulse Width Modulation (PWM) output ports for control. One of its most prominent features is that the GNSS module (uBlox M8N) can use Galileo as the GNSS of choice. Considering its high accuracy level, and the fact that there are fewer applications that make use of Galileo (as opposed to, for example, GNSS), Galileo was used for UAV positioning. 3. Other components required for UAV assembly (batteries, drone frame kit, motors and propellers) were also required. They are described as follows: 1. Frame F450 [28]: For the frame or \"skeleton\" of the UAV, a Frame F450 with landing gear was chosen. This frame makes it possible to assemble all the parts on it and ensure stability to the drone. Among its main characteristics are resistance, lightness and a comparatively small size, which enable mounting several components while keeping low battery consumption benefits due to weight or stability. 2. MaxPRO 2650 Batteries [29]: 11.1V and 2650 mAh batteries were used to power the UAV. They belong to the LiPo battery (Lithium polymer) family, which are the most used for drones since they allow fast discharges and can provide significant amounts of energy in a short time, in addition to being light and small compared to others. 3. Motors [30]: Set of four Emax 2213-935 KV motors.