## 4 Performance Evaluation
### Performance Results in the Real Scenario
As explained above, when the number of UAVs is smaller than 240, EAMUD-P achieves the highest ratio of the event link communication time, then EAUD-D/EAMUD-D and EAUD-P follow, but USP suffers the lowest one in Figure 13. Figure 14 illustrates histograms of the ratio of the event link communication time with respect to the number of UAVs. When the number of UAVs is  
Figure 12: Histograms of the average ratio of the event link communication time with respect to UAV dispatch energy threshold. small, as shown in Figure 14a, EAUD-D has two peaks on the 0 and 0.95-1.0 ranges but most events with EAUD-P suffer from lower ratios of the event link communication time, which spans on the 0.05-0.30 range. Hence, EAUD-D achieves higher average ratios of the event link communication time than EAUD-P does, which is shown in Figure 13. Similarly, EAMD-D also has two peaks on the 0 and 0.95-1.0 ranges as EAUD-D. However, most events with EAMD-P achieve higher ratios of the event link communication time in the 0.65-0.90 range, which means that EAMUD-P is the best one among these five schemes to recover from the communication link failure in the disaster when the UAV resource is scarce. When the number of UAV grows larger than 240, the average ratio of the event link communication time of each scheme approaches 1 for all schemes, as shown in Figure 13, which can be justified by histograms of the ratio of the event link communication time, as shown in Figure 14b. Figure 15 exhibits the relation between the average ratio of the event link communication time and the event percentage. As the event percentage grows, all events and their corresponding sub-events in the event queue of GCS increase accordingly. Hence, the probability for dispatching a UAV to serve a sub-event is getting lower under a fixed number of UAVs, which, in turn, degrades the average ratio of the event link communication time of each scheme. As mentioned above, because EAMUD-P executes the EBD algorithm to check whether the communication link failure of an event can be recovered by overlapping  
Figure 14: Histograms of the average ratio of the event link communication time with respect to the number of UAVs. Figure 13: The average ratio of the event link communication time vs the number of UAVs. communication durations of UAVs already dispatched for all sibling sub-events and that of the UAV dispatched for current sub-event, its average ratio of the event communication time is highest among these five schemes. Figure 16 illustrates histograms of the average ratio of the event link communication time with respect to the event percentage. As the event percentage grows from 30% to 60%, EAUD-D and EAMUD-D suffer from higher peaks on the 0-0.20 range, which means more events are unable to resume their link communication. Both of them have similar histograms in Figure 16a,b such that they have almost the same average ratio of the event link communication time, as shown in Figure 15. However, major events with EAUD-P span on the 0.05-0.40 range, but those with EAMUD-P distribute over the 0.65-0.95 range. These two histograms explain why the average ratio of the event link communication time of EAMUD-P is much higher than that of EAUD-P. In summary, these three simulation parameters have different influences on these two metrics. The average ratio of event link communication time of every scheme is proportional to the number of UAVs but it is inversely proportional to the event percentage when other simulation parameters are fixed. On the other hand, only three schemes achieve higher values for the average ratio of event link communication time with the larger UAV dispatch energy threshold. As mentioned above, these performance behaviors can be justified by histograms of the average ratio of the event link communication time with respect to these  
Figure 16: Histograms of the average ratio of the event link communication time with respect to the event percentage. Figure 10:0 The average ratio of the event link communication time vs the event percentage. three parameters.