Abstract
Conventional ambiguity resolution (AR) strategy of directly fixing all raw frequency ambiguities for uncombined precise point positioning (PPP) generally requires a long initial time to ensure fixing reliability. The rich signals from multi-frequency GNSS can provide new opportunities for rapid PPP AR. In this paper, based on a unified multi-frequency uncombined PPP model, the raw frequency ambiguities are linearly transformed to the between-satellite-single-differenced extra-wide-lane (EWL), wide-lane (WL), and narrow-lane (NL) ambiguities, and a cascading ambiguity resolution (CAR) method of fixing EWL/WL/NL ambiguities sequentially is proposed. Meanwhile, a partial ambiguity fixing (PAF) strategy with ambiguity subset adaptively selected based on the successively increased elevations is also adopted in each step to improve the fixing rate. Further, experiments with globally distributed stations are carried out to verify the algorithm. With the constraints of EWL/WL AR, the precision of NL ambiguity and its variance-covariance matrix can be effectively optimized, so the time to first fix (TTFF) is significantly shortened, and the ratio value is also improved to varying degrees. As for BDS-only solution, the average TTFF is shortened from 23.7 min to 10.9 min, with an improvement over 50%; for GPS/BDS, GPS/Galileo, and GPS/Galileo/BDS combined solutions, the TTFF is shortened from 14.3 min, 9.4 min, and 6.7 min to 8.1 min, 2.6 min, and 1.8 min, which are, respectively, shortened by 43.4%, 72.3%, and 73.1%. In general, the proposed CAR strategy can shorten the TTFF of multi-GNSS multi-frequency PPP to about 2 min. The performance of EWL/WL/NL ambiguity-fixed solutions is also analyzed. The NL solution is generally at centimeter-level accuracy over the entire period; however, limited by the atmosphere errors during the convergence stage, the EWL/WL solutions can only obtain decimeter-level accuracy, and the difference between them and NL solution gradually decreases with the continuous improvement of atmosphere accuracy.
Highlights
Precise point positioning (PPP) technology can achieve unified high-precision positioning on a global scale, and it does not require the support of dense reference stations, which greatly improves the flexibility of Global Navigation Satellite System (GNSS) positioning and has been widely used in geodetic and geodynamic applications [1,2,3]
Data Description. e multi-constellation and multifrequency observation data of Global Positioning System (GPS), Galileo, and BeiDou Navigation Satellite System (BDS) from the International GNSS Service (IGS) Multi-GNSS Experiment (MGEX) network and Australian Regional GPS Network (ARGN), as well as the rapid precise satellite orbit and clock correction provided by GeoForschungsZentrum Potsdam (GFZ) are used to validate the PPP performance with the proposed method
We focus on fast Ambiguity resolution (AR) strategy of multi-GNSS and multi-frequency uncombined PPP
Summary
Precise point positioning (PPP) technology can achieve unified high-precision positioning on a global scale, and it does not require the support of dense reference stations, which greatly improves the flexibility of Global Navigation Satellite System (GNSS) positioning and has been widely used in geodetic and geodynamic applications [1,2,3]. Ambiguity resolution (AR) can shorten the convergence time to a certain extent and improve the positioning reliability at the same time [6]. A wide range of studies have been studied concerning reliable FCB estimation for integer ambiguityfixing [7,8,9]. In the real-time perspective, it still needs significant improvement since it cannot provide almost instantaneous positioning likewise the widely used real-time
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