Single-frequency precise point positioning enhanced with multi-GNSS observations and global ionosphere maps

Due to its low-cost, sub-meter-precision, and large number of possible users, precise point positioning with single-frequency receivers (SF-PPP) has attracted a great deal of interest in recent years. One crucial issue in SF-PPP is the handling of ionospheric delays, which cannot be eliminated by combining observations on different frequencies. For validation and evaluation purposes, four SF-PPP models, which are ionospheric-corrected, -free, -unconstrained, and -constrained, were realized with different ionosphere treatments in SF-PPP. To enhance real-time SF-PPP performance, the contribution of multi-Global Navigation Satellite System (GNSS) observations and (predicted) global ionosphere maps (GIMs) was investigated in this study. To demonstrate the performance of the four SF-PPP models, two sets of multi-GNSS observations, which came from 33 Multi-GNSS Experiment (MGEX) ground static and one airborne kinematic observation data, were utilized to perform SF-PPP in simulated kinematic and real kinematic mode, respectively. The results indicated that the ionospheric-corrected and -constrained SF-PPP models performed better than the ionospheric-free and -unconstrained SF-PPP models in positioning convergence, while the ionospheric-unconstrained SF-PPP model showed advantages over the other three SF-PPP models in positioning accuracy after convergence. The positioning accuracy derived from Global Positioning System (GPS) + GLONASS + BeiDou Navigation Satellite System + Galileo ionospheric-constrained (IC)SF-PPP solutions is 9.1, 7.2, and 17.0 cm in the east, north, and the up components, respectively, which is somewhat worse than that of the ionospheric-unconstrained (IU)SF-PPP solutions (7.3, 6.1, and 15.2 cm) due to the low accuracy of GIMs. Compared to the IUSF-PPP solutions, the positioning accuracy during the convergence period (e.g. 1 h) derived from ICSF-PPP solutions is improved by 85.3% from 116.3 to 17.1 cm in the east, by 71.6% from 67.6 to 19.2 cm in the north, and by 72.6% from 194.7 to 53.4 cm in the up, respectively. Overall, the ionospheric-constrained SF-PPP demonstrated good performance in both positioning convergence and accuracy. Enhanced by employing multi-GNSS observations and external ionospheric products (i.e. GIMs), the ionospheric-constrained SF-PPP can achieve the positioning accuracy of about 0.7-1.0 dm in the horizontal component and 0.15-0.25 dm in the vertical component after a certain convergence time, i.e. 1 h in this study.