## 4 Case Study
Therefore, the information interruption rate affected by the communication distance was considered a fixed value. We combined the information interruption rate and bit error rate to obtain the curve of \(P_{Error\_1}\), \(P_{Error\_2}\) and \(P_{Error\_7}\) and \(P_{Error\_8}\) as shown in Figure 10. The communication distance of the channel is considered to be a fixed value but the health of the channel still produces random fluctuations over time. The health status of the uplink is slightly better than the health status of the downlink. Figure 7: Directed acrylic graph of a solar-powered UAV data-link system. Figure 8: Communication distance distribution curve of each link of solar-powered UAV data-link system. (**a**) Communication distance of UAV-Satellite links; (**b**) Communication distance of ground-satellite links. Figure 9: The health status probability of channel with changing communication distance. Figure 11 shows that in the UAV line-of-sight communication link, the health status of the child nodes are worse than that of the parent nodes. The health status of the uplink and downlink is basically the same. \(\alpha\)-chain G-RS uplink and downlink medium life are approximately 450 h. \(\alpha\)-chain UAV-RS uplink and downlink medium life are approximately 550 h. \(\alpha\)-NLOS uplink and downlink medium life are 350 h. Figure 12 shows that the health of the line-of-sight links are better than the health of non-line-of-sight links. Because of the redundancy of links, the telemetry link and telecontrol link did not reach the median life at 860 h. The telemetry link is redundant by 3 links and the telecontrol link is redundant by 2 links, so the health status of the telemetry link is slightly better than the health status of the remote link. Figure 13 shows that the health status of the UAV data-link system is worse than the health status of the telemetry link and the remote link. After 250 h, there is a significant difference. The UAV data-link system reaches the median life about 840 h.  
Figure 11: Health state probability prediction curve of Solar-powered UAV data-link intermediate node future 840 h.  
Figure 10: The health status probability of channel with constant communication distance. Figure 13 shows that although changes in the position of the solar-powered UAV during the mission changed the communication distance of each channel periodically, the health status of the entire solar-powered UAV data-link system tended to be stable. It can be seen from the data-link system health state prediction curve that both node 46 (telemetry link) and node 49 (telecontrol link) have an impact on the health status of the data-link system node 50 in the next 840 h but the latter is the main reason for the decline of system health status. The weak link is analyzed layer by layer using the prediction curve of the intermediate node: telecontrol \(\rightarrow\) non-line-of-sight link \(\rightarrow\)\(\beta\)-chain non-line-of-sight link \(\rightarrow\) UAV-RS uplink \(\rightarrow\) repeater satellite \(b\). At the same time, it can be seen from the DAG diagram of the solar-powered UAV data-link system that the repeater satellite b node in the \(\beta\) non-line-of-sight link is the parent node of the total of four nodes \(\beta\)-chain non-line-of-sight uplinks and downlinks. So, the repeater satellite \(b\) health status has a critical and direct impact on the health of the solar-powered UAV data-link.