Precise point positioning with LEO augmentation: results from two experimental satellites

Using LEO satellites for positioning and navigation has been a research hotspot in the GNSS community in recent years. As the LEO satellites are much closer to earth and move much faster relative to earth than GNSS, precise point positioning (PPP) convergence time can be substantially improved. Various simulation studies on LEO augmentation have been carried out, but its performance with real LEO observations in a real-world environment is rarely reported. The CENTISPACETM system, which is developed by Beijing Future Navigation Tech Co., Ltd., has launched four experimental satellites in the last two years, providing a good opportunity for studying LEO augmentation. We collect real LEO navigation observations from two CENTISPACETM satellites using a regional network. Before conducting LEO-augmented PPP, orbit determination and time synchronization (ODTS) for the experimental LEO satellites are first investigated, and a data-processing framework is established using the space-borne GNSS observations from LEO satellites and the LEO augmentation observations from ground stations. The LEO-augmented PPP algorithm is then derived, with a focus on the LEO relativistic effect. With these bases, we analyze the LEO-augmented PPP performance with different GNSS systems (including GPS, BDS, and Galileo) combined with LEO satellites. The static PPP tests using one (G/C/E), two (GC/GE/CE), and three (GCE) GNSS systems show that the average convergence time is significantly reduced with the participation of the two LEO satellites, from 32.7, 17.9, and 14.2 min to 16.7, 8.9, and 5.7 min, respectively. This indicates that adding only two LEO satellites improves the convergence times of static PPP with one, two, and three GNSS systems by 48.9%, 50.2%, and 59.8%, respectively. For PPP precision evaluation, the GNSS-only 3D positioning errors are 6.1, 4.6, and 4.6 cm with one, two, and three systems, respectively. They are reduced to 5.2, 3.9, and 3.8 cm by adding two LEO satellites, respectively. The corresponding improvements are 13.9%, 16.4%, and 18.8%, respectively. The above study not only validates the customized processing framework and strategy for LEO augmentation processing but also demonstrates the great potential of LEO augmentation. With more LEO satellites to be deployed in the future, much larger improvements can be achieved.