# Design and Evaluation of Dynamic Topology for Mega Constellation Networks
## 4 Modeling System Approach
### Simulation Parameter Settings  
It is assumed that there are 10,000 pairs of ground stations obeying the global traffic model that are randomly distributed among the nodes in each time slice, and each call covers the 4 critical parameters of the latitude and longitude location of the sender and  
Figure 4: General flow of the simulation.  
receiver, respectively. Regarding the specific distribution of calls, the two ground stations obey a global service volume distribution model between them.
* The distribution of calls in the continuous time from sending to receiving shows a negative exponential distribution.
* The time of arrival of calls at the receiving end obeys an independent Poisson distribution with the parameter \(\lambda\).
* The density of call service requests is adjusted by changing the value of the parameter \(\lambda\).  
The first deployment phase of the joint simulation targeting the [PERSON] constellation is primarily configured, as shown in Table 2. The entire simulation cycle is set to 5742 s with a step size of approximately 87 s, allowing for the subdivision of 1 cycle into 66 equally spaced time slots of identical length.  
The shortest call distance path of the interplanetary link is obtained by the Dijkstra algorithm. At the beginning of each time slice, 10,000 pairs of city pairs obeying the service volume distribution model are randomly selected to send communication calls from the ground station.  
The performance indicators such as call distance, total time delay, and the number of hops of packet forwarding are compared under different topologies to analyze the advantages and disadvantages of different topological configurations comprehensively. Among them, the 3D visualized physical topology constructed in the selected 1584 simulations is shown in Figure 5.  
Manhattan network (MHD) defines a mesh connection distinguished by high stability, low latency, and strong resistance to damage. Among the static topologies discussed in Section 2.1, the mesh topology is most commonly utilized in the static structure of LEO satellite constellations. For instance, the OneWeb constellation's fixed topology adopts a mesh configuration, making MHD more representative.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Satellite Parameters** & **Value** \\ \hline Models & walker1584 \\ Track height & 550 km \\ Number of track planes & 66 \\ Number of satellites in orbit & 24 \\ Track inclination & 53\({}^{\circ}\) \\ Operating cycle & 95.7 min \\ Timepiece size & 87 s \\ Number of channels per satellite & 300 \\ Minimum elevation angle of the ground station to access the satellite & 40\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: Parameters of the Walker constellation of 1584 satellites.  
Figure 5: 3D simulation view.  
In summary, the MHD is selected as the static benchmark topology, and the distance-based strategy and the longest visible time strategy as the dynamic benchmark topology, which are compared with the static topology and the two dynamic topologies designed in this paper to derive the topology with the best network performance and to verify the superior version. Table 3 shows the topologies used for the simulation validation and briefly describes them.