Study on Optimal Broadcast Ephemeris Parameters for GEO/IGSO Navigation Satellites

Area of Science:

• Satellite Navigation Systems
• Geodesy and Geophysics
• Orbital Mechanics

Background:

• Current broadcast ephemeris parameters for geosynchronous (GEO) and inclined geosynchronous (IGSO) navigation satellites (NSs) often rely on Global Positioning System (GPS)-type parameters, despite the growing number of these satellites.
• This can lead to suboptimal fit accuracy for positioning services utilizing GEO and IGSO NSs.

Purpose of the Study:

• To analyze orbital characteristics and propose optimal broadcast ephemeris parameter sets for GEO and IGSO NSs.
• To enhance the fit accuracy and user range error (URE) performance of navigation systems employing these satellites.

Main Methods:

• Adoption of nonsingular elements and orbital plane rotation to address singularity issues in GEO satellite orbits.
• Augmentation of the standard 16 GPS LNAV parameters with one to four correction parameters from a set of 28.
• Least-squares curve fitting and accuracy comparison using data from four BeiDou GEO and six BeiDou IGSO satellites.

Main Results:

• Optimal ephemeris parameter sets were determined, showing dependency on orbit type.
• Proposed parameters achieved URE accuracies within 2.4 cm for IGSO and 3.8 cm for GEO NSs.
• Accuracy improvements of up to 34.5% were observed compared to conventional parameter sets.

Conclusions:

• The developed optimal ephemeris parameter sets significantly improve positioning accuracy for GEO and IGSO satellites.
• Common parameter sets for both IGSO and GEO orbits were identified, promoting compatibility and uniformity.
• The study provides detailed insights into the effects of fitting intervals, parameter count, bit allocation, and orbit types on fit accuracy.