# Integrity Monitoring of PPP-RTK Positioning: Part II: LEO Augmentation
## 5 Conclusions  
In recent years, the continuously increasing number of LEO satellites has motivated investigations of LEO-augmented GNSS positioning. While the PPP method has become a hot spot in this regard, PPP-RTK positioning and its IM procedure have been less discussed. Based on the IM procedure proposed for the PPP-RTK positioning in the first part of this series of papers, this contribution discusses the influences of LEO augmentation on the PPP-RTK horizontal positioning and its HPLs. A dual-frequency L1/L5 scenario is simulated for networks of different sizes around Beijing with the planned CentiSpace LEO constellation augmenting the GPS, Galileo and BDS constellations. The study distinguishes between different scenarios with quiet and active multipath ionospheric environments, evaluates the formal standard deviations of the positional solutions in both the ambiguity-float and -fixed cases, and compares their HPLs without and with the augmentation of the LEO satellites. The influences of the LEO augmentation are not only reflected in the increased satellite numbers (especially at low elevation angles) and reduced HDOPs, but also in the improvement in the PPP-RTK positioning precision and HPLs. For the ambiguity-float solutions, LEO augmentation was found to be able to significantly shorten the convergence time of the formal horizontal precision. Under single-constellation scenarios and with a low precision of the ionospheric interpolation caused by, e.g., large network size or/and active ionospheric activities, the convergence time of the formal horizontal precision to 0.02 m has been reduced from more than 15 min to within 3 min. Similarly, the ambiguity-float HPLs are also significantly improved by adding the LEO constellation. The improvements in the HPLs have reached more than 60% after 5 to 30 min from commencement of processing. At 5 min, the HPLs are brought down from sub-meter to about 0.2 m for the tested scenario with simple multipath condition and high precision of the ionospheric interpolation, and from about 2.5 m to 1 m for the tested scenario with complicated multipath condition and low precision of the ionospheric interpolation. With the PAR enabled, the LEO augmentation is found able to accelerate the ambiguity resolution, especially for single-constellation scenarios and for low precision of the ionospheric interpolation. After reaching the FAR, the ambiguity-fixed formal horizontal precision is generally reduced to within 1 cm with LEO augmentation for all constellation combinations tested in the study. The improvements in the ambiguity-fixed HPLs are mostly within 10% to 60%. Figure 16: Improvements of the PAR-enabled HPLs by adding the LEO augmentation for (**a**) Network 1 under quiet multipath and ionospheric conditions (Category A); (**b**) Network 3 under active multipath and ionospheric conditions (Category D). Note that the y-scales are different in the two sub-figures. It needs to be mentioned that the results discussed in this contribution mainly rely on the changed measurement geometry after adding the tested LEO constellation, i.e., with the increased satellite numbers and their rapid geometry change. The influences of the LEO augmentation are illustrated with formal results based on the proposed IM model and the tested overbounding parameters. Different ionosphere interpolation strategies, IM procedures and overbounding parameters could lead to differences in the model and the formal results, and mis-modeled effects could lead to differences in the empirical results. In summary, this contribution intends to deliver the following qualitative findings under the given LEO constellation for L1/L5 GNSS-based PPP-RTK positioning:  
* The convergence time of the ambiguity-float formal horizontal precision could be significantly reduced when augmenting GNSS by LEO measurements. * The ambiguity-float HPLs can be significantly reduced in the first half hour with the LEO augmentation. * The LEO augmentation accelerates the ambiguity resolution at the user side.