# Trajectories and Resource Management of Flying Base Stations for C-V2X
## 5 Numerical Results  
We present in this section results with different key performance indicators (KPIs). At first, we study the final sum throughput of the network with and without the support of the aerial component through a single metric to quantify the efficiency of the UAV. Then, we compare the actual percentage of vehicles served directly from the terrestrial network versus the one from the aerial network  
We have chosen to test the system under the application requirements of 25 and 50 Mb/s of data rate, in compliance with the already discussed extended sensing. The first metric of performance assessment of the system is the throughput gain. The gain, \(G\), is computed as  
\[G=\frac{S_{\text{UAV}}}{S_{\text{TBS}}} \tag{11}\]  
\[S_{\text{UAV}}=\sum_{j=1}^{U_{\text{UAV}}}T_{j} \tag{12}\]\[S_{\text{TBS}}=\sum_{v=1}^{U_{\text{TBS}}}T_{v} \tag{13}\]  
where \(S_{\text{UAV}}\) and \(S_{\text{TBS}}\) represent the ST gained only by the UAV and only by the terrestrial network, respectively, while \(U_{\text{UAV}}\) and \(U_{\text{TBS}}\) are the total number of users served only by the UAV or only by the TBSs, respectively. Figure 2 shows the gain \(G\) in percentage while increasing the percentage of active vehicles \(P_{v}\). A number of curves were introduced having different bandwidth values, which means a RR pool was changing in size. The bandwidth dedicated to the vehicular service is of 5, 10, 15 or 20 MHz. Figure 1(a),b refer to 25 Mb/s and 50 Mb/s, respectively. Figure 2: Obtained gain for different bands while varying the number of active vehicles, \(N_{v}\cdot P_{v}\), in the network. In each curve of Figure 2a,b, the gain \(G\) had a decreasing trend while increasing the number of active vehicles in the scenario. This can be easily explained by the fact that the TBSs were using a higher number of RRs as the traffic demand increased: due to the common resource pool, the UAV had a lower number of RRs still left available. This network response to an increased offered traffic, stayed the same as the bandwidth (i.e., RR pool capacity) reserved for vehicular applications increases. A larger system bandwidth allowed the UAV to maintain an interesting \(G\) value close to 10% with a higher number of active vehicles. Moreover, the values of the gain \(G\) in Figure 2a differ from the corresponding ones in Figure 2b. In the former plot, the values of \(G\) for the 10% of active vehicles range from a 20% to almost 120%, whereas half of such values can be observed in the latter. This can be explained in terms of availability of resources, too. In Figure 2b the application demand from vehicles is doubled w.r.t. Figure 2a, requiring then double the number of resources from TBSs and the UAV to serve each vehicle. This means that, not only the TBSs employ more resources subtracting them from the UAV pool, but also a lower number of vehicles will be served (see also Figure 3). Furthermore, note that, when considering the transitory in which a few of the travelling vehicles are equipped with C-V2X devices, these results are relevant. In fact, a single UAV was capable of providing up to 100% gain with the proposed approach, even with reuse factor of one. When a larger number of vehicles is equipped with C-V2X services, the probability that two vehicles are close enough to each other and can share useful nearby information with the short range dedicated communication in the 5.9 GHz band increases. For this reason, it is still acceptable that the gain in network throughput offered by the drone remains at 5% to 2% (i.e., in absolute numbers, it is in the order of hundreds of Mb/s). For the second set, Figure 3 shows the number of vehicles served by the entire network while increasing the number of active users. Two plots are shown when the traffic demand has 25 Mb/s (Figure 3a) and 50 Mb/s (Figure 3b) throughput requirement. Different curves for three different bandwidth sizes of 5, 10 and 20 MHz are shown. For each dedicated band, two curves differentiate the network behaviour with or without the presence of one UAV.