Cascade optimization design of inter-satellite link enhanced with adaptability in future GNSS satellite networks

Inter-satellite communication and inter-satellite ranging are the foundation of autonomous navigation for satellite navigation systems. Due to cost limitations, it has been proposed in recent years to equip each satellite with one spot beam antenna, which points to different satellites according to a polling mechanism, resulting in an intermittently connected satellite network. This poses the problem of how to design the inter-satellite link (ISL) contact plan, which determines the evolution of network topology and has important effects on system performance. We propose a new framework for the ISL contact plan design in satellite navigation systems. Considering contact plan design as a multi-parameter and multi-objective optimization problem, the cascade optimization design (COD) is proposed as a method simple to implement and optimize the parameters of the contact plan. COD considers network load and geometry of satellites and has a good adaptability. In the proposed framework, both communication and measurement requirements are taken into account while the contact sequence and the slot length are optimized in two steps. Simulation results show that COD guarantees zero packet drops and achieves the least average delay with a selected network load. When the packet arrival rate is 0.45 packets/s, the packet drop ratio of COD is zero, while that of the traditional simulated annealing design (SAD) is 2.58%. The delay of COD is 22.97 s, which is only two-fifth of the SAD value of 58.77 s. At the same time, using COD the average autonomous navigation weighted dilution of precision decreases from 1.4408 to 0.9671. COD also has strong robustness and performance regardless of the onboard buffer size.