LEO Constellations as a Decentralized GNSS Network: Optimizing PNT Corrections in Space
Abstract
With the rapid expansion of low Earth orbit (LEO) constellations, thousands of satellites are now in operation, many equipped with onboard GNSS receivers capable of continuous orbit determination and time synchronization. This development is creating an unprecedented spaceborne GNSS network, offering new opportunities for network-driven precise LEO orbit and clock estimation. Yet, current onboard GNSS processing is largely standalone and often insufficient for high-precision applications, while centralized fusion is challenging due to computational bottlenecks and the lack of in-orbit infrastructure. In this work, we report a decentralized GNSS network over large-scale LEO constellations, where each satellite processes its own measurements while exchanging compact information with neighboring nodes to enable precise orbit and time determination. We model the moving constellation as a dynamic graph and tailor a momentum-accelerated gradient tracking (GT) method to ensure steady convergence despite topology changes. Numerical simulations with constellations containing hundreds of satellites show that the proposed method matches the accuracy of an ideal centralized benchmark, while substantially reducing communication burdens. Ultimately, this framework supports the development of autonomous and self-organizing space systems, enabling high-precision navigation with reduced dependence on continuous ground contact.
Summary
The paper addresses the challenge of achieving high-precision, real-time orbit and clock determination for LEO satellites using onboard GNSS receivers. Current standalone GNSS processing on LEO satellites offers limited accuracy, while centralized fusion of GNSS data from the entire constellation is computationally expensive and faces communication bottlenecks. The authors propose a decentralized GNSS network approach where each satellite processes its own GNSS measurements and exchanges information with neighboring satellites. This approach models the LEO constellation as a dynamic graph and employs a momentum-accelerated gradient tracking (GT) method to ensure convergence despite the changing topology. The methodology involves modeling the inter-satellite communication topology as a time-varying graph. They then tailor a momentum-accelerated gradient tracking (GT) algorithm to this setting, which improves convergence rates and reduces communication overhead. Numerical simulations with constellations of hundreds of satellites demonstrate that the proposed decentralized method achieves accuracy comparable to an ideal centralized benchmark while significantly reducing the communication burden. This framework facilitates the development of autonomous and self-organizing space systems, reducing reliance on continuous ground contact for high-precision navigation.
Key Insights
- •The paper introduces a novel decentralized GNSS network architecture for LEO constellations, enabling cooperative onboard orbit and clock determination.
- •They model the inter-satellite communication topology as a time-varying graph and develop a momentum-accelerated gradient tracking (GT) algorithm tailored to this dynamic environment.
- •Simulations show that the decentralized approach achieves orbit determination errors of 0.12m with float ambiguities and 0.06m with integer-fixed ambiguities, comparable to centralized processing but with reduced communication.
- •Time synchronization accuracy of 0.21 ns (float) and 0.11 ns (fixed) are achieved via the decentralized approach, indicating significant improvement over standalone processing (7.95 ns).
- •The momentum-accelerated GT algorithm significantly improves convergence rates compared to vanilla GT due to the synergy between momentum and multi-round consensus, enabling the use of larger step sizes and momentum parameters.
- •The paper provides a rigorous estimability analysis using S-system theory to characterize identifiable parameter combinations in the spaceborne GNSS network.
- •The approach supports scalable and network-driven GNSS processing, addressing the challenges of centralized processing and limited communication resources in LEO constellations.
Practical Implications
- •The research has direct applications in LEO-based communication systems, formation flying missions, PNT services, satellite altimetry, and spaceborne sensing, all of which require real-time, precise orbit and clock determination.
- •Satellite operators and mission planners can benefit from this decentralized approach by reducing reliance on ground stations for orbit and clock corrections, leading to more autonomous and resilient LEO operations.
- •Practitioners can implement the proposed momentum-accelerated GT algorithm on onboard processors to achieve high-precision navigation without the need for continuous, high-bandwidth communication with ground stations.
- •Future research directions include investigating the robustness of the decentralized approach to node failures, exploring different communication topologies, and developing efficient quantization and compression techniques to further reduce communication overhead.
- •The framework can be extended to incorporate other sensor data, such as inter-satellite ranging measurements, to further improve the accuracy and reliability of the orbit and clock determination process.