# Design of Mega-Constellations for Global Uniform Coverage with Inter-Satellite Links
## 5 Conclusions  
In view of the major shortcomings of conventional constellation configurations with uneven coverage on a global scale, this paper proposes a mixed Walker constellation design scheme for the same orbital layer that takes collision avoidance into account and effectively improves global coverage performance. On the basis of this constellation configuration, an ISLs design scheme is presented to guarantee efficient and stable inter-satellite data transmission. The main contributions of this paper are concluded as follows:  
1. A model of a mega-constellation configuration with uniform global coverage has been developed, consisting of a mixture of Walker constellations with the same orbital altitude and different orbital inclinations. The simulation results show that the mixed  
Figure 10: Comparison of data transmission paths on any 3 groups of satellite nodes in the mixed Walker constellation proposed in the paper with 3, 4, and 5 ISLs on the satellite, respectively. **(a)** 3 ISLs per satellite; **(b)** 3 ISLs per satellite; **(c)** 3 ISLs per satellite; **(d)** 4 ISLs per satellite; **(e)** 4 ISLs per satellite; **(f)** 4 ISLs per satellite; **(g)** 5 ISLs per satellite; **(h)** 5 ISLs per satellite; **(i)** 5 ISLs per satellite; **(j)** Comparison of 3 ISL schemes for continuous communication; **(k)** Comparison of 3 ISL schemes for continuous communication; **(l)** Comparison of 3 ISL schemes for continuous communication.  
Walker constellation designed in this paper effectively compensates for the uneven distribution of the Walker constellation across the latitude zones and maintains a relatively balanced number of N Asset Coverage for all regions of the world. In addition, it has a higher number of N Asset Coverage than the Walker constellation of the same satellite magnitude in most parts of the world. It can be said that the mega-constellation designed in this paper has a superior global coverage performance.
2. During the design of the mega-constellations, we considered collision avoidance between satellites. This paper derives the minimum distance between any two satellites throughout their orbital period, based on space geometry and orbital dynamics theory. The collision-avoidance constraint is established at a safe distance. The orbital parameters of some satellites are adjusted so that the minimum distance between any two satellites in the mega-constellation is greater than the set safe distance.
3. Basis on the design of the mega-constellation configuration proposed in this paper, a scheme for the ISLs design is established according to the theory of the adjacency matrix in graph theory. This solution ensures that any two satellite nodes within the constellation can communicate in real-time. Moreover, the connection relationship of all satellite nodes is fixed. There is no need to switch links during data transmission, ensuring efficient and stable communication. Simulation results show that the communication distance between two satellite nodes decreases as the number of links on each satellite increases. Therefore, carrying as many ISLs on a satellite as conditions permit can improve the inter-satellite communication time efficiency.  
Conceptualization, L.J. and Y.Z.; data curation, L.J.; formal analysis, J.Y. and L.J.; funding acquisition, Y.Z.; investigation, L.J. and X.W.; methodology, L.J.; project administration, Y.Z.; supervision, Y.Z. and J.Y.; writing--original draft, L.J. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
The authors declare no conflict of interest.