# Design of Mega-Constellations for Global Uniform Coverage with Inter-Satellite Links
## 4 Simulation and Results
### Simulation Studies and Results on ISLs Scheme Design  
In order to verify the effectiveness of the mega ISLs design method introduced in this paper, simulations are carried out to validate it. The results are shown in Figure 10. In  
Figure 9: Global coverage performance of mixed Walker constellation vs. Walker constellation. (**a**) Distribution of N Asset Coverage around the globe for a Walker constellation with 5625 satellites; (**b**) Distribution of N Asset Coverage around the globe for a mixed Walker constellation with 5686 satellites; (**c**) Comparison of the distribution density of N Asset Coverage around the globe for the two mega-constellations.  
particular, Figure 10a-c represent a space diagram with three ISLs per satellite, for a total of 17,056 ISLs in the constellation. The subplots in the second and third rows of Figure 10 represent the loading of four and five ISLs per satellite for a total of 22,742 and 28,430 ISLs, respectively, in the constellation. To fully prove that the ISLs design can guarantee efficient data transmission between any two satellite nodes, three sets of satellites are arbitrarily selected for simulation analysis. The subgraphs in each column of Figure 10 enjoy the same set of source and target satellite nodes.  
There is at least one ISL on each satellite in the constellation. It ensures that information can be passed between any two satellite nodes, which also means that the global connectivity requirements of the ISLs design are met. In addition, in terms of the information transmission path between the two satellites, this ISL design solution ensures that the two satellites can communicate with each other in a shorter path. Comparing the graphs vertically, it can be visualized that as the number of links established on each satellite increases, the pathfinding selectivity on each satellite node increases as well as the communication distance between the two satellites decreases. For example, in Figure 10b, when 3 links are built per satellite, the data transmission path between the two satellite nodes is very tortuous, but when the number of links is increased to 4 in Figure 10e, the communication path between the two satellite nodes is optimized to a greater extent.  
Subplots in Figure 10j-1 simulate the data transmission path distance variation for three sets of satellite nodes, respectively, with 600 s of continuous communication. Each subplot compares the case of three, four, and five links built on the satellite accordingly. The outcomes show that the ISLs design presented in this paper can provide continuous and stable communication between satellites. As the number of satellite links increases, the communication distance between the two satellites decreases, especially when the number of links increases from three to four, which can bring about a significant reduction in communication distance. However, when the number of onboard links increases from four to five, the reduction in communication distance is significantly reduced. Therefore, the number of links established on the satellite can be determined by weighing various factors such as technical complexity, construction costs, and quality of communication services. Based on the above analysis, the ISLs design based on the mixed Walker constellation proposed in this paper can achieve global connectivity as well as stable and efficient inter-satellite data transmission.  
Figure 10: _Cont._