LEO-constellation-augmented multi-GNSS real-time PPP for rapid re-convergence in harsh environments

Abstract

GNSS signals are blocked in forests, urban canyons, and indoors. Precise positioning can hardly be guaranteed in these challenging environments. A low earth orbit (LEO) constellation serving as a navigation system can provide stronger signal power to ground receivers due to its shorter transmission path than GNSS. The fast motion of LEO satellites contributes to the fast change of spatial geometry, allowing for rapid convergence of precise point positioning (PPP), and is effective in detecting carrier phase cycle slips. This study comprehensively analyzed the LEO-constellation-augmented multi-GNSS for real-time PPP in various challenging environments, including the blocking of satellite signals, cycle slips, the two issues occurring simultaneously, and significant multipath effects. An improved cycle slip detection and fixing algorithm taking advantage of LEO satellites is proposed. The GPS, BDS, and a 96-satellite polar-orbiting LEO constellation are designed, and observations at a mid-latitude station are simulated. The results show that the inclusion of LEO satellites shortens the convergence time and significantly improves the cycle slip fixing performance of multi-GNSS PPP. Three to four visible LEO satellites can shorten the GPS/BDS/LEO (GCL, C is the designation used in RINEX for BDS) PPP convergence time to 4 min compared to 20 min for the GPS/BDS (GC) solutions. Additionally, the correct cycle slip fixing time shortens from 3.3 min for the GC solution to 0.8 min for the GCL solution. When LEO satellites are free of cycle slips, the GNSS integer cycle ambiguities can be instantaneously fixed, and PPP instantaneous re-convergence is obtained. When significant multipath effects are considered, the time for GNSS/LEO first correct fixing is 3 min longer. The PPP solutions are noisier because the relatively shorter continuous observation time of LEO satellites is not beneficial for the smooth of multipath errors. In the case of GNSS and LEO satellites under both signal shielding and cycle slips, the GNSS/LEO PPP re-convergence and cycle slip fixing both degrade when the cut-off elevation increases from 20° to 40°, since LEO satellites are almost out of sight at a cut-off elevation of 40°. It is concluded that the inclusion of LEO satellites considerably improves the GNSS PPP in terms of the (re-)convergence and cycle slip fixing performance.

Principle and performance of BDSBAS and PPP-B2b of BDS-3

“…On one hand, LEO satellites can broadcast satellite-based augmentation corrections; on the other hand, LEO satellites and BDS-3 satellites can form a hybrid constellation to broadcast normal navigation and positioning signals, which will significantly improve the geometric strength of the integrated constellation, and then improve the orbit precision of BDS-3 satellites and the measurement accuracy of satellite clock offset. The participation of LEO constellation in providing PPP-B2b service can effectively improve the convergence speed of PPP-B2b (Li et al, 2022). Assuming that 120 LEO satellites at an altitude of 975 km with an orbital inclination of 55° are evenly distributed on 12 orbital planes and participate in PPP service together with PPP-B2b, the required convergence time corresponding to the positioning accuracies of 10 and 100 cm are shown in Table 5.…”

A Novel Satellite PRN Code Assignment Method Based on Improved RLF Algorithm

“…Satelles company tested the STL’s service performance indoors in a high-rise building and found an indoor positioning accuracy of 20 m and a timing accuracy at the sub-microsecond level [ 11 , 12 ]. In addition, due to the lower orbit, navigation signals from the LEO satellite are stronger, which adds robustness to the navigation service [ 13 ]. For example, Iridium signals are 300 to 2400 times stronger than GNSS on the ground [ 14 ], and users have already employed LEO-based signals in environments with high GNSS interference [ 15 ].…”

Multi-GNSS positioning for landslide monitoring: a case study at the Recica landslide

“…With a modernization of legacy GPS and GLONASS systems, as well as with a finalization of the new European Galileo and Chinese BeiDou systems, about 120 navigation satellites for GNSS users around the world are available presently (Li et al, 2022). Higher number of satellites is expected to lead to a higher robustness of GNSS solutions and under some conditions also to a higher accuracy and precision of positioning.…”