# Mobile Network Performance and Technical Feasibility of LTE-Powered Unmanned Aerial Vehicle
## 4 Results
### Effect of Fly Height on Handover  
One of the major technological features of the UMTS Soft/Softer handover architecture was absent when the LTE system was developed. This is mainly due to the adjacent cell frequency reuse and orthogonality in LTE, and because the LTE system has a flat architecture [46]. Therefore an assumption was made that only hard handovers occur during the test. The UE's signal quality was analyzed to see what happened during the handoff from one eNodeB to another eNodeB along the route during the drive test.  
Figure 16 shows the \(RSRP\) and \(RSRQ\) levels for a scenario where the terrestrial UE moved throughout the path. It can be seen from the results that in three points ping-pong handovers occurred (red circles). The ping-pong HO happens when a UE is handed over from one cell to another but quickly handed back to the original cell. During the drive test, the UE was served by two dominant cells: cell 12 and cell 11. When the link is handed from cell 12 to cell 11, the \(RSRP\) level changed from \(-96\) dBm to \(-95\) dBm, and the \(RSRQ\) level changed from \(-12\) dB to \(-14\) dB.  
Figure 17 shows the \(RSRP\) and \(RSRQ\) results for the drone UE when flying at the height of 40 m. Along the path, the drone was served by three different cells; Cell 11, Cell 41, and Cell 42. During the handover from Cell 11 to Cell 41, the \(RSRP\) and \(RSRQ\) values changed from \(-78\) dBm to \(-84\) dBm and from \(-11\) dB to \(-9\) dB, respectively. Next, during the handover process from Cell 41 to Cell 42, the \(RSRP\) value changed from \(-81\) dBm to \(-84\) dBm, and the \(RSRQ\) value changed from \(-11\) dB to \(-10\) dB.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Elevation** & **0 m** & **40 m** & **80 m** & **170 m** \\ \hline Average Uplink & & & & \\ Throughput (kbps) & 6451 & 5245 & 5051 & 6737 \\ Average Downlink & & & & \\ Throughput (kbps) & & & & \\ Average delay (ms) & 25.4 & 24.73 & 23.44 & 36.63 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Average throughput and delay.  
Figure 15: Data rates at 0m (**a**), 40m (**b**), 80m(**c**), and 170m (**d**).  
Figure 18 shows the handover procedure at the height of 80 m. In this scenario, drone UE was served by two cells, which were Cell 1 and Cell 11. The \(RSRP\) value during the handover procedure from cell 11 to cell 1 changed from \(-79\) dBm to \(-77\) dBm and \(RSRQ\) changed from \(-13\) dB to \(-12\) dB.  
Figure 16: \(RSRP\) and \(RSRQ\) level during handover at 0 m (ground level).  
Figure 17: \(RSRP\) and \(RSRQ\) level during handover at 40 m.  
Based on Figure 19, three dominant cells were involved in serving the UE during the test: Cell 16, Cell 12, and Cell 11. When the link was handed from Cell 16 to Cell 12, the \(RSRP\) level did not change, remaining at \(-87\) dBm, and only the \(RSRQ\) level changed from \(-18\) dB to \(-17\) dB. Next, during the handover process from Cell 12 to Cell 11, the \(RSRP\) value changed from \(-87\) dBm to \(-84\) dBm, and the \(RSRQ\) value changed from \(-17\) dB to \(-15\) dB.  
Figure 19: \(RSRP\) and \(RSRQ\) level during handover at 170 m.  
Figure 18: \(RSRP\) and \(RSRQ\) level during handover at 80 m.  
Based on Figures 16-19, a conclusion can be deduced that, as the drone UE went to a higher altitude, the signal quality was slightly degraded. However, the handover still occurred in good condition because there was no glitch or loss of connection, such as a sudden drop signal during the handover.