# Experimental Study on LTE Mobile Network Performance Parameters for Controlled Drone Flights
## 4 Development of the Setup for Experimental Measurements  
In this research, 14 locations were chosen that represent various network configurations (urban/rural, dense/sparsely populated areas, wood-covered areas, and areas with good/poor network coverage on the ground). Yellow paths (in Figure 2) are locations where the flights took place covering multiple territories in Latvia, see Figure 2. In every location, the flight took place at altitudes (above take-off height) of 40 m, 60 m, 90 m, and 110 m. Each of the 14 locations had 8 flights (four different heights and two frequency modes), totaling 112 flights. The overall flight distance was approximately 700 km. The mobile network operates in different frequencies that have different propagation characteristics. As it is not feasible to test all frequencies, it was decided to focus on gathering two different flight modes, which were executed in all locations.  
* Automatic mode: where the measuring device switches to the most appropriate frequency decided by mobile network algorithms.
* Band 20 (800 MHz): this is the frequency band with the best areal coverage and is very widely used.  
This scientific article descriptively includes detailed information based on the flights made and measurements recorded and analyzed within route No. 1 (see Figure 2).  
To verify the proposed KPIs (see Table 4) of the network and satisfy the safety criteria for autonomic drone flights in the future, the testing of the network parameters was conducted at several altitudes on a specified trajectory near the towns of Lode and Piltene (see Figure 3, thick yellow line). Lode and Piltene are located northwest of the map (number 1 in Figure 2).  
The altitudes chosen were 40, 60, 90, and 110 m. Measurements were conducted using a OnePlus NORD BE2029 mobile phone with its original integrated antenna with the capability of operating on 2G, 3G, 4G, and 5G bands. The phone was attached to a DJI M30 drone to ensure the measurements at the set altitudes were possible. The dedicated software used was the Echo One mobile network analyzer made by Enhanced (Oulu, Finland) [48]. The image of the used setup is seen below (see Figure 4). The phone was in a waterproof case during the measurement. This was done for security reasons, e.g., deterioration of the weather would not damage the phone.  
Figure 2: Map of measurement locations in Latvia.  
Flights were operated by an observer and pilot with supporting technical staff on-premises that prepared the flight plans and monitored the data logging process. Coordinates of the flight were from 57\({}^{\circ}\)16'16.3'' N 21\({}^{\circ}\)42'05.3'' E to 57\({}^{\circ}\)16'51.9'' N 21\({}^{\circ}\)48'37.6'' E (see in Figure 3, thick yellow line). The flight distance measured was approximately 6.7 km, which the drone completed with an average speed of 15 m/s. The weather was cloudy without rain and 17 \({}^{\circ}\)C.  
When measurements were conducted, the mobile device had an automatic mode enabled, which ensured that the device switched between 2G, 3G, and 4G, depending on signal parameters. Based on data gathered during flights, a more accurate relation between signal KPIs (RSRP, RSRQ, and SINR) and network KPIs (latency, downlink, and uplink speed) could be determined. The UAV's control and data transfer need to set the criteria for network KPIs and from them, the related signal KPIs can be determined.  
Figure 4: DJI M30 and OnePlus NORD BE2029 mobile phone are prepared for measurements and ready to take off.  
Figure 3: The drone’s flight path (thick yellow line).