Abstract
The real-time precise point positioning (RT PPP) technique has attracted increasing attention due to its high-accuracy and real-time performance. However, a considerable initialization time, normally a few hours, is required in order to achieve the proper convergence of the real-valued ambiguities and other estimate parameters. The RT PPP convergence time may be reduced by combining quad-constellation global navigation satellite system (GNSS), or by using RT ionospheric products to constrain the ionosphere delay. But to improve the performance of convergence and achieve the best positioning solutions in the whole data processing, proper and precise variances of the observations and ionospheric constraints are important, since they involve the processing of measurements of different types and with different accuracy. To address this issue, a weighting approach is proposed by a combination of the weight factors searching algorithm and a moving-window average filter. In this approach, the variances of ionospheric constraints are adjusted dynamically according to the principle that the sum of the quadratic forms of weighted residuals is the minimum, and the filter is applied to combine all epoch-by-epoch weight factors within a time window. To evaluate the proposed approach, datasets from 31 Multi-GNSS Experiment (MGEX) stations during the period of DOY (day of year) 023-054 in 2018 are analyzed with different positioning modes and different data processing methods. Experimental results show that the new weighting approach can significantly improve the convergence performance, and that the maximum improvement rate reaches 35.9% in comparison to the traditional method of priori variance in the static dual-frequency positioning mode. In terms of the RMS (Root Mean Square) statistics of positioning errors calculated by the new method after filter convergence, the same accuracy level as that of RT PPP without constraints can be achieved.
Highlights
With the rapid development of Global Navigation Satellite System (GNSS), real-time precise point positioning (RT PPP) with integer ambiguities resolution is possible thanks to the real-time precise orbits, clocks, and code/phase biases products of satellites, provided freely by the Center National d’Etudes Spatiales (CNES) [1]. These real-time products in the CLK93/CLK92 stream have been broadcasted by the CNES real-time analysis center since 14/09/2014 [2]
The results indicate that this new method can significantly reduce convergence time and improve reliability of positioning solutions in
In order to s s eliminate the uncalibrated code delyas (UCD) and uncalibrated phase delyas (UPD) of satellite, the code biases b Pi and phase biases b Li from CNES caster are applied to the raw observable model, the reparameterization of (1) can be written as [6]: sys,s sys,s
Summary
With the rapid development of Global Navigation Satellite System (GNSS), real-time precise point positioning (RT PPP) with integer ambiguities resolution is possible thanks to the real-time precise orbits, clocks, and code/phase biases products of satellites, provided freely by the Center National d’Etudes Spatiales (CNES) [1]. A priori variances are mainly used to determine the weights of observation and ionospheric constraint in the whole process of data processing This method may not be precise, especially when the accuracy of ionospheric products is uncertain, and it will lead to unreliable positioning results. In order to s s eliminate the UCD and UPD of satellite, the code biases b Pi and phase biases b Li from CNES caster are applied to the raw observable model, the reparameterization of (1) can be written as [6]: sys,s sys,s. The estimated parameter vector in the ionospheric delay constraint PPP can be expressed as:
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