Improving The Performance Of Precise Poınt Positioning With Multi-Gnss
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Precise Point Positioning (PPP) is the positioning technique which enables centimetre-level positioning accuracy with only one receiver in static mode. The main strength of PPP lies behind the employment of precise orbit and clock products acquired from a global network. Over the past ten years, PPP has been a popular topic within the Global Navigation Satellite Systems (GNSS) community and widely used in a range of GNSS applications, such as precise surveying, atmospheric monitoring and modelling, aerial triangulation, geohazard monitoring, etc. However, long initial time which is required to converge an optimal solution is still the main restriction of PPP. In recent years, the emergence of new navigation systems has offered the prospect of overcoming the limitation of PPP. The combination of multi-GNSS provides additional satellite resources for satellite navigation and positioning. Therefore, the combination of multi-GNSS makes it possible to improve the satellite geometry and to increase the number of visible satellites. Nevertheless, the combination of multi-GNSS entails new modelling approaches and more complex processing strategies. The principal objective of this study is to investigate the influence of multi-GNSS on PPP performance. For this purpose, the multi-GNSS approach containing both the functional and stochastic models were presented, and some improvements were introduced to optimize the implementation of the Kalman filter on PPP. Furthermore, a PPP software package, named PPPH, was developed to evaluate the performance of multi-GNSS. PPPH was designed to perform multi-GNSS PPP solution, which includes the observations from GPS, GLONASS, Galileo, and BeiDou. Further, PPPH enables to specify modelling and filtering options and also includes several tools to analyse the results. A comparison between PPPH and online PPP services was performed to validate PPPH's results. It was confirmed that PPPH provides centimetre-level positioning accuracy in static mode and convergence time is similar to the solutions obtained from online PPP services. The influence of multi-GNSS on PPP performance was investigated in terms of positioning accuracy and convergence time. The results showed that the GPS/GLONASS PPP and the multi-GNSS PPP improves the positioning accuracy at the rate of 16.2% and 21.6%, respectively in relative to GPS-only PPP. On the other hand, the GPS/GLONASS PPP and multi-GNSS PPP was reduced the convergence time obtained from GPS-only PPP by 28.1% and 33.2%, respectively.