# Performance Assessment of Multi-GNSS PPP Ambiguity Resolution with LEO-Augmentation
## 1 Introduction
Compared with the ordinary GNSS medium-Earth orbit (MEO) satellite, the LEO constellation has the following advantages: First, the LEO satellite has a lower orbital height, being 20 times closer to Earth than the MEO satellite, in addition to a shorter signal transmission path, and a smaller degree of power loss. Therefore, the signal power received on the ground is stronger, and the anti-interference and anti-deception performance is better. For example, the signal power of the Iridium satellite is 1000 times that of GPS [21]. Therefore, even in highly shielded environments (such as indoors, in forests, under bridges, and inside anyons), users can still receive continuous LEO navigation signals. Second, the LEO satellite moves faster than the ground station, and the continuous observation duration is only 10-20 min. The Doppler frequency shift phenomenon is evident, which is favorable for the carrier phase cycle slip detection [22]. At the same time, the fast motion of LEO satellites provides rapid geometric changes in a short period of time, which can accelerate the initialization of PPP, thus shortening the convergence time of precise point positioning. To prove the contribution of LEO to PPP, many researchers have conducted numerous LEO-enhanced precision point positioning experiments based on simulated observations. [PERSON] et al. [23] tested the performance of LEO-enhanced GPS PPP and compared it with that of GPS or GPS/GLONASS combination schemes. The results showed that the convergence time of the LEO-enhanced GPS and GPS/GLONASS combined scheme was reduced by 51.31% and 3.93%, respectively, compared with the GPS-only scheme, indicating that the contribution of the LEO satellite to the convergence speed of the PPP was greater than that of a MEO satellite. [PERSON] et al. [24] found that LEO-enhanced GNSSs(GPS/BDS/Galileo) could reduce the convergence time of PPP to 5 min. [PERSON] et al. [25] studied the performance of LEO-enhanced GNSSs (GPS/GLONASS/BDS/Galileo) under LEO constellations with different satellite numbers (60, 96, 192, 288), orbital heights (1000 km, 600 km), and orbital types (polar orbit, sun-synchronous orbit), and proposed a LEO constellation scheme consisting of 192 satellites with an orbital altitude of 1000 km, which could significantly shorten the convergence time of GRCE PPP by more than 70%. [PERSON] et al. [26] analyzed the performance of PPP ambiguity resolution with LEO-augmented multi-GNSS (GPS/GLONASS/BDS/Galileo), and the results showed that with the enhancement of 60, 192, and 288 LEO constellations, the TTFF of GREC PPP-AR was shortened from 7.1 min to 4.8 min, 1.1 min, and 0.7 min, respectively, and the positioning accuracy was improved by approximately 60%, 80%, and 90%, respectively. The performance of the three-frequency LEO-enhanced PPP-AR was better than that of dual-frequency. [PERSON] et al. [27] found that in harsh environments, the float solution and fixed solution performance of triple-frequency uncombined BDS/GPS/LEO PPP were improved to different degrees compared with that of only BDS, which they ascertained through six sets of shielding experiments using different elevation and azimuth angles. The above studies show that the LEO constellation can significantly improve the performance of PPP and PPP-AR; however, few studies have examined the contribution of the LEO float solution to PPP-AR. As mentioned above, the fast motion of LEO satellites provides rapid geometric changes in a short time, which can accelerate the initialization of PPP, and the fast convergence of ambiguity parameters is conducive to the rapid success of ambiguity fixing. Therefore, this study focused on the performance of the LEO float solution to enhance PPP-AR. The remainder of this article is structured as follows: The two LEO constellations we designed and the LEO observation simulation on the Multi-GNSS Experiment (MGEX) stations are introduced in Section 2. Because GNSSs (GPS/GLONASS/BDS-3/Galileo) were fully operational, the GNSS data are real observation data from MGEX stations.