Abstract
Compared with the traditional ionospheric-free linear combination precise point positioning (PPP) model, the un-differenced and uncombined (UDUC) PPP model using original observations can keep all the information of the observations and be easily extended to any number of frequencies. However, the current studies about the multi-frequency UDUC-PPP ambiguity resolution (AR) were mainly based on the triple-frequency BeiDou navigation satellite system (BDS) observations or simulated data. Limited by many factors, for example the accuracy of BDS precise orbit and clock products, the advantages of triple-frequency signals to UDUC-PPP AR were not fully exploited. As Galileo constellations have been upgraded by increasing the number of 19 useable satellites, it makes using Galileo satellites to further study the triple-frequency UDUC-PPP ambiguity resolution (AR) possible. In this contribution, we proposed the method of multi-frequency step-by-step ambiguity resolution based on the UDUC-PPP model and gave the reason why the performance of PPP AR can be improved using triple-frequency observations. We used triple-frequency Galileo observations on day of year (DOY) 201, 2018 provided by 166 Multi-GNSS Experiment (MGEX) stations to estimate original uncalibrated phase delays (UPD) on each frequency and to conduct both dual- and triple-frequency UDUC-PPP AR. The performance of UDUC-PPP AR based on post-processing mode was assessed in terms of the time-to-first-fix (TTFF) as well as positioning accuracy with 2-h observations. It was found that triple-frequency observations were helpful to reduce TTFF and improve the positioning accuracy. The current statistic results showed that triple-frequency PPP-AR reduced the averaged TTFF by 19.6% and also improved the positioning accuracy by 40.9%, 31.2% and 23.6% in the east, north and up directions respectively, compared with dual-frequency PPP-AR. With an increasing number of Galileo satellites, it is expected that the robustness and accuracy of the triple-frequency UCUD-PPP AR can be improved further.
Highlights
The precise point positioning (PPP) technique has drawn a lot of attention from the Global Navigation Satellite Systems (GNSS) community due to its flexible operation, permitting centimeterto millimeter-level positioning accuracy with a single receiver and unlimited coverage, which has been widely used for engineering applications and scientific research for many years [1]
We start with the estimating and discussing the characteristics of the Galileo uncalibrated phase delays (UPD), which is the prerequisite in precise point positioning with integer ambiguity resolution
We compare the performance of the dual- and triple-frequency float un-differenced and uncombined (UDUC)-PPP
Summary
The precise point positioning (PPP) technique has drawn a lot of attention from the Global Navigation Satellite Systems (GNSS) community due to its flexible operation, permitting centimeterto millimeter-level positioning accuracy with a single receiver and unlimited coverage, which has been widely used for engineering applications and scientific research for many years [1]. The basic idea of the TCAR/CIR method is that AR starts with the easy-to-fix extra-wide-lane (EWL) combination and steps to the shorter wavelength wide-lane (WL) and narrow-lane (NL) combinations sequentially, in which the WL combination is used to bridge the longest wavelength EWL and the shortest wavelength NL [10]. This method was further extended and modified by lots of follow-up studies e.g., References [11] or [12], [13] or [14] and [15]. Their simulated results suggested that the correctness rate of NL AR achieved 99% within 65 s, compared with only 64% within 150 s in the traditional dual-frequency PPP-AR
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