Fig. 1. Constellation system period handling model

Fig. 2. Flow chart of improved algorithm based on MOSA

Fig. 3. Convergence properties of improved algorithm based on MOSA in FSA state. (a) Convergence property of network delay at n=3; (b) convergence property of PDOP at n=3; (c) convergence property of network delay at n=4; (d) convergence property of PDOP at n=4

Fig. 4. Comparison of performance between three kinds of topology structures. (a) Network average delay; (b) network maximum delay; (c) average PDOP; (d) maximum PDOP

Fig. 5. Comparison of optimized topology performance for multi-layer satellite. (a) Comparison of delay when links are interrupted; (b) comparison of PDOP when links are interrupted; (c)comparison of delay when satellites are interrupted; (d) comparison of PDOP when satellites are interrupted

Fig. 6. Topology structures optimized by algorithm. (a) Optimized topology at the 4th FSA state; (b) optimized topology at the 5th FSA state

Fig. 7. Number of exchanged links in constellation system period. (a) Comparison of exchanged links number; (b) comparison of links utilization