The Challenges of LEO Based Navigation Augmentation System – Lessons Learned from Luojia-1A Satellite

Abstract

The Low earth orbiter (LEO) based navigation signal transmitters have advantages in fast-changing geometry and low free space signal loss, which can be served as a complementary or extension of current MEO/GEO based GNSS. Broadcasting navigation signals from LEO can significantly reduce the convergence time for the long baseline RTK\precise point positioning (PPP) and improve the signal strength. Hence LEO based navigation is considered as one of the key technology of next-generation positioning, navigation and timing (PNT) systems. This study assessed the pseudorange and carrier phase measurements observed from Luojia-1A satellite with the geometry-free combination method and the zero-baseline method. The assessment results indicate that the pseudorange precision variation subject to elevation angle is caused by both signal strength variation and multipath effect. The pseudorange measurement precision reaches 0.7 m and 0.8 m respectively for the dual frequency pseudorange measurements and the carrier phase precision is 2.8 mm and 2.6 mm respectively. Based on the data collected from Luojia-1A satellite, the challenges of LEO navigation augmentation data processing were addressed. The most distinguishing features of LEO navigation signals are their large signal strength variation, large Doppler variation and large acceleration variation. All these features have adversary effect on LEO signal processing and data processing, which has not been revealed. These challenges still need to be seriously investigated to further improve the performance of the LEO based navigation augmentation system.