Ultra-rapid products, which do not require any external connection unlike real-time services, are an important alternative for real-time global navigation satellite system (GNSS) applications. Especially, the inclusion of newly-emerged satellite systems in ultra-rapid products opens up considerable opportunities to improve the positioning performance. In this regard, this study concentrates on the employment of the most recent ultra-rapid products besides traditional ones for real-time single-frequency multi-GNSS positioning using code and carrier phase measurements. In the study, experimental tests were conducted for the ionosphere-free code-carrier combination to evaluate the performance of single-receiver single-frequency positioning. The results reveal that single-frequency positioning is able to provide sub-meter level positioning accuracy with ultra-rapid products despite its performance alters depending on the applied product. Also, the performance of single-frequency positioning which based on code-carrier combination is not influenced significantly from the possible decline in the precision of ultra-rapid products over time due to the convergence of phase ambiguities. On the other hand, the results demonstrate that the accuracy of pseudorange positioning can significantly be improved with the integration of multi-constellation and the improvement ratio can reach 30% compared with the GPS-only solutions. Furthermore, the convergence time of GPS-only solution can be decreased by a ratio of 37% on average with multi-GNSS combinations. Finally, the results show that for the multi-constellation analyses, the solutions which utilize the ultra-rapid product of Wuhan University provide the best performance in terms of positioning accuracy and convergence time.
Considering the remarkable progress of the Galileo constellation in recent years, the main objective of this study is to evaluate the performance of dual-and single-frequency Galileo-based precise point positioning (PPP), and its contribution to GPS and Galileo integration with different precise products generated by four analysis centers (ACs) within the context of the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). For this purpose, the daily observation dataset collected at ten IGS stations over one month was processed in both static and kinematic modes for Galileo-only, GPS-only, and GPS/Galileo PPP scenarios. For dual-frequency PPP, the results demonstrate that while the Galileo-only solutions are highly comparable with GPS-only PPP for the static mode, the mean 3D positioning errors for Galileo-only processes are approximately 1-cm higher than those obtained from GPS-only solutions for all agencies. The analysis to evaluate the influence of Galileo satellites with highly eccentric orbits, namely E14 and E18, on dual-frequency Galileo-only PPP performance indicates that including or excluding these satellites has no significant effect on the results. For single-frequency PPP, which is dependent on the GRAPHIC combination, Galileo-only PPP performs significantly better, approximately 40%, than GPS-only solutions in the static mode, whereas kinematic Galileo-only and GPS-only PPP solutions are quite similar for all agencies except for WHU. In addition, the RMS of observation residuals for Galileo in single-frequency PPP was noticeably lower than that for GPS, demonstrating that the observation quality of Galileo code measurements is better than those of GPS. Among the ACs, Galileo-based PPP solutions applying CODE products produced slightly better results than those obtained for GFZ and CNES/CLS in general, whereas processes using WHU products resulted in a worse performance, both in terms of positioning accuracy and of convergence time. The integration of Galileo with GPS was shown to enhance PPP performance significantly in both static and kinematic modes.
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