# On the Performance of a UAV-Aided Wireless Network Based on NB-IoT
## 5 Results and Discussion
As expected, the TSP trajectory shows a relevantly higher throughput with respect to the other two, up to 16 kb/s. Moreover, because of a much larger average latency, the Paparazzi trajectory achieves an even lower throughput than the circular one (that had a much worse percentage of served nodes). Figure 7: Perceived latency of IoT nodes for different UAB speeds and trajectories with \(h=200\) m.  
As last performance metric, we study the impact of trajectories on the average energy consumption, \(E\), in Figure 9. For decreasing values of the UAB speed, \(v\), the energy consumed by NB-IoT nodes tend to decrease until few hundreds of m). Even if this appears to be a positive effect, we should consider the motivations behind this behaviour. To avoid cluttering, we now show the impact of two different UAB heights, \(h\), for the same trajectory. The TSP path is the trajectory chosen for its better results in terms of almost all metrics. In this case, the percentage of served NB-IoT nodes with varying UAB speed, \(v\), is plotted in Figure 10. The behaviour of the two curves with respect to speed is the same as already discussed in Figure 5. However, we can see a slight difference from before, that is a lesser sharp decrease of successful transmissions when the speed is 25 m/s. We observe that for lower speeds the system performs better at lower UAB heights, \(h\), while for higher speeds increasing heights improve the service. One might expect that, since for higher altitudes the transmitter-receiver distance increases on average, the curve with the larger UAB height would perform always worse than the other (as it happens for values of \(v\) lower than or equal to 20 m/s). However, this does not consider the NB-IoT  
Figure 5.0 Network throughput for different UAB speeds and trajectories with \(h=200\) m.  
Figure 5.1 Energy consumption of IoT nodes for different UAB speeds and trajectories with \(h=200\) m.  
signalling messages procedure and timing. In fact, for increasing values of \(h\), not only the transmitter-receiver distance gets higher, but also the coverage range of the UAB increases (given by the angle of incidence of the UAB with the ground, or elevation angle in [7,8]). Consequently, it increases the time interval during which, on average, the NB-IoT node remains in the coverage range of the UAB. As shown in Figure 10, this effect can be more appreciated with increasing values of speed. What has been discussed above is confirmed in Figure 11, showing the average energy consumption, \(E\), with varying UAB speeds and heights. Being an average, its value depends on the number of nodes able to reach the UAB connectivity and enter the RA (i.e., signalling) procedure. The curves' decreasing trend with speed is the same for the two \(h\) values, and was already discussed for the TSP in Figure 5.2 A higher altitude lets a larger number of nodes being in connectivity with the UAB, and try and start the RA procedure. This fact increases the overall energy consumption, regardless of successful transmission or not. With lower speeds, more nodes would be able to complete the signalling procedure, whether with higher speeds the energy consumed could be only for the transmission of NB-IoT Msg1 and/or Msg2. Our analysis on the energy consumption can be validated by Figure 5.3 It represents the access rate, \(R_{\text{acc}}\), for different UAB heights and speeds in the TSP trajectory. Here, the curves trend with respect the to speed, \(v\), is the same, as for Figure 11, and the curve with the higher height, \(h\), has a lower access rate. This means that we have a larger number of attempts that does not correspond to the same number of successful transmissions. In fact, also due to the average larger transmitter-receiver distances with a higher-height UAB, it gets more difficult for nodes to complete the RA procedure. Related to average latency, \(\Delta\tau_{\text{avg}}\), we observe a quite less significant impact.