# On the Performance of a UAV-Aided Wireless Network Based on NB-IoT
## 5 Results and Discussion
the node is scheduled an uplink resource on the NPUSCH (for example, if the UAB has flown away too fast), it will not be able to successfully transmit its packet. This effect becomes relevant when discussing latency, because the value of \(v\) creates a trade-off between low application delays and successful transmissions. At first glance, it is also evident that the TSP trajectory is able to serve a higher number of nodes for every UAB speed, making more robust what first proposed in [1]. In fact, this trajectory ensures the UAB gets in close vicinity with each cluster and each node, while minimizing the distance travelled. On the opposite, the circular trajectory decreases the percentage of successful transmissions of 50% with respect to TSP and Paparazzi ones, on average. The coverage extension and the time spent over each node, does not allow in this case a sufficient service. The analysis on the other metrics would allow us to finally assess and discuss the final trajectory-dependent performance. Figure 6 represents the access rate, \(R_{\text{acc}}\), again while varying the UAB speed for different trajectories. By looking at increasing speeds and for the same trajectory, we have the value of \(R_{\text{acc}}\) dropping for each trajectory at 25 m/s, as it was for the service in Figure 5. With the UAB driving faster, the occasions to attempt channel access decrease. From Equation (8), we observe this metric evaluates together the number of overall attempts tried by nodes and, from these, the ones which are successful. This might explain why the Paparazzi and circular trajectories have higher access rates; these can be achieved if the total number of attempts is small (the denominator) with respect to other trajectories. If a lower number of nodes try to access at the same time to the channel (maybe for connectivity issues) the probability of successful transmission increases (see Equation (1)). Figure 5: Percentage of served IoT nodes for different UAB speeds and trajectories with \(h=200\) m.  
Figure 6: Access rate of IoT nodes for different UAB speeds and trajectories with \(h=200\) m.  
Then, another figure of merit is the latency with which packets are transmitted (on average), \(\Delta\tau_{\text{avg}}\), in Figure 7. As expected, the latency decreases with increasing speed for each trajectory; the NB-IoT nodes which can successfully transmit their packet are served faster because the UAB will reach them with a smaller delay. Furthermore, if we focus on the latency of the different trajectories, we notice the TSP path performs better, just followed by the circular one. In fact, the distances covered by these two trajectories are fairly smaller with respect to the other. On the contrary, for its characteristic of scanning the entire service area, the Paparazzi trajectory employs much larger delays than the other two. Furthermore, we are interested in the network throughput, \(T_{\text{net}}\), that can be achieved. Numerical results are presented in Figure 8. As formulated in Equation (11), these results will also depend on the ones of Figures 5 and 7 because of the dependence on service completion and latency in Equation (6). Interestingly, we can see three different trends with varying UAB speeds, \(v\), for the three different trajectories: (i) The TSP has a maximum, (ii) the circular does not change significantly, while (iii) the Paparazzi shows an improvement with increasing velocities. The maximum shown by the network throughput in the TSP trajectory corresponds exactly to the service-latency trade-off with UAB speed mentioned before. However, because of the low total service offered, the circular trajectory is hardly showing any maxima. Similarly, the maximum cannot be appreciated for the Paparazzi path, but the network throughput appears to be increasing with increasing speed. In fact, we observed that, at lower UAB speeds as 10 to 15 m/s, the average latency is so large (almost one or a half hour) that the maximum cannot occur for the chosen UAB speed range.