Initial Assessment of the LEO Based Navigation Signal Augmentation System from Luojia-1A Satellite

Abstract

A low Earth orbiter (LEO)-based navigation signal augmentation system is considered as a complementary of current global navigation satellite systems (GNSS), which can accelerate precise positioning convergence, strengthen the signal power, and improve signal quality. Wuhan University is dedicated to LEO-based navigation signal augmentation research and launched one scientific experimental satellite named Luojia-1A. The satellite is capable of broadcasting dual-frequency band ranging signals over China. The initial performance of the Luojia-1A satellite navigation augmentation system is assessed in this study. The ground tests indicate that the phase noise of the oscillator is sufficiently low to support the intended applications. The field ranging tests achieve 2.6 m and 0.013 m ranging precision for the pseudorange and carrier phase measurements, respectively. The in-orbit test shows that the internal precision of the ephemeris is approximate 0.1 m and the clock stability is 3 × 10−10. The pseudorange and carrier phase measurement noise evaluated from the geometry-free combination is about 3.3 m and 1.8 cm. Overall, the Luojia-1A navigation augmentation system is capable of providing useable LEO navigation augmentation signals with the empirical user equivalent ranging error (UERE) no worse than 3.6 m, which can be integrated with existing GNSS to improve the real-time navigation performance.

Advances in BeiDou Navigation Satellite System (BDS) and satellite navigation augmentation technologies

“…Signal augmentation technologies refer to the technology of signal extension which provides a signal source that is capable of transmitting ranging signals to expand and extend GNSS. Through signal augmentation technologies, users can obtain accurate and reliable locations in scenarios where GNSS cannot be used or does not work well (Ma 2018;Reid et al 2016;Wang et al 2018a). To overcome the vulnerability of the GNSS system from the perspective of availability, reliability, and anti-interference, some researchers both in China and abroad have proposed that LEO satellites broadcast a ranging signal to augment the performance of the satellite navigation system that is composed of Medium Earth Orbit (MEO) and High Earth Orbit (HEO) satellites.…”

“…There are many advantages of using LEO satellites for satellite navigation signal augmentation in addition to the increase in visibility and the improvement to accuracy (Wang et al 2018b), including the following: (1) Leo satellites move fast which helps to speed up the convergence of the accuracy positioning filter. Results show that the convergence time of precise point positioning is shortened from 30 to 1-2 min when using LEO; (2) As LEO satellites are at low altitude, the signal-in-space is stronger than that of the MEO or HEO satellites.…”

“…The Luojia-1A satellite has the main function of providing precise measurements of orbit and timing, storing GNSS onboard observations and downloading to the ground, and LEO augmentation experiments. The Luojia-1A satellite was used to carry out experiments investigating the navigation signal augmentation based on the LEO satellite platform in China for the first time (Wang et al 2018a).…”

“…9. Users can simultaneously receive a dual frequency signal from BDS, GPS, and Luojia-1A in order to achieve the hybrid satellite constellation positioning of the HEO, MEO, and LEO satellites, improving the performance in navigation and positioning (Wang et al 2018b). As the frequency of the augmentation signal from Luojia-1A is different from that of the existing GNSS signal, a modified receiver with specific receiving antenna is installed onto the equipment of a user to collect the signals from both GNSS and Luojia-1A.…”

A Practical Adaptive Clock Offset Prediction Model for the Beidou-2 System

“…The real-time POD capacity will improve the LEO satellites' performance, such as cutting the radio occultation data processing latency [10,11], reducing the dependency of the ground control point for the remote sensing satellite imagery data processing, and supporting the LEO navigation augmentation applications [12][13][14]. The Luojia-1A satellite has demonstrated the potential benefit of navigation signal augmentation from the LEO satellite [15,16].Supporting the real-time PPP by the predicted clocks attracts much attention in the GNSS communities. The international GNSS service (IGS) released its clock prediction product (known as the ultra-rapid products) to support the RTPPP applications.…”