# Initial Assessment of the LEO Based Navigation Signal Augmentation System from Luojia-1A Satellite
## 1 Introduction
Generally, the information augmentation helps to improve positioning performance of current navigation signals in terms of precision or integrity. The signal augmentation extends the performance of current navigation constellation, in terms of availability, robustness, convergence, etc. The navigation signals augmentation from LEO platform is expected to avoid the limitation of current GNSS systems and enhance the positioning and navigation performance. The early research exploring the benefit of LEO satellite to improve RTK performance is found in [PERSON]'s patent published in 1995 [19]. After that, there are a few pieces of research investigating the benefit of combining the Iridium constellation and current GNSS in terms of increasing visible satellites, reducing the positioning dilution of precision (PDOP) [20; 21]. The integrity benefit from a dense LEO constellation also attracted research interests [22; 23]. With fast-moving LEO platforms, the convergence time can be greatly reduced. [PERSON] et al. reported that combining GPS/BDS/Iridium constellations can reduce the PPP convergence time from about 30 min to about 5 min [24]. [PERSON] et al. explored the benefit of LEO constellation on Arctic aviation applications [25], which is also considered as a key technology for the marine navigation [26]. They also analyzed the error sources for LEO navigation signals and attempted to model them [27]. A few researchers even investigated the optimal design of broadcast ephemeris for LEO navigation satellites [28; 29; 30]. [PERSON] systematically investigated certain challenging issues of LEO navigation receiver implementation [31]. In recent years, there have been a few ambitious commercial broadband LEO constellation proposals that can potentially serve as promising navigation sources. In such cases, the performance of the satellite positioning can be further improved [27]. Another benefit of LEO signal augmentation is that it is capable of transmitting stronger signals, which can even penetrate the building wall. With the orbit height reduced from 20,200 km to 650 km, the free space loss of the signal strength for 1.5 GHz signal may reduce up to 30 dB. The Iridium constellation announced their Satelles Time and Location (STL) service in 2016, which has successfully demonstrated the potential of indoor positioning applications and time synchronization applications with LEO navigation systems [32]. With recognizing the importance of LEO navigation augmentation system, the commercial aerospace industries also present great interests in developing LEO navigation augmentation systems as their value-added services. Researchers from Wuhan University are developing their space-based real-time information service system, which integrates the PNT service, remote sensing service, and communication service into a single satellite platform, which is named the 'PNTRC' concept [33; 34]. The scientific experimental satellite Luojia-1A was successfully launched on 2 June 2018, carrying the integrated payload of night light photogrammetry and LEO navigation augmentation systems. They collected first-hand real LEO-based navigation augmentation signals from the Luojia-1A satellite for data analysis. In this research, the initial performance of LEO-based navigation augmentation systems from the Luojia-1A satellite is assessed.