Abstract
Concerning the triple-frequency ambiguity resolution, in principle there are three different realizations. The first one is to fix all the ambiguities of the original frequencies together. However, it is also believed that fixing the combined integer ambiguities with longer wavelength, such as extra-wide-lane (EWL), wide-lane (WL), should be advantageous. Also, it is demonstrated that fixing sequentially EWL, WL and one type of original ambiguities provides better results, as the previously fixed ambiguities increase parameters’ precision for later fixings. In this paper, we undertake a comparative study of the three fixing approaches by means of experimental validation. In order to realize the three fixing approaches from the same information in terms of adjustment, we developed a processing strategy to provide fully consistent normal equations. We first generate the normal equation with the original undifferentiated carrier phase ambiguities, then map it into that with the combined and double-differenced ambiguities required by the individual approach for fixing. Four baselines of 258 m, 22 km, 47 km and 53 km are selected and processed in both static and kinematic mode using the three ambiguity-fixing approaches. Indicators including time of first fixed solution (TFFS), the correct fixing rate, positioning accuracy and RATIO are used to evaluate and investigate results. We also made a preliminary theoretical explanation of the results by looking into the decorrelation procedure of the ambiguity searching algorithm and the intermediate results. As conclusions, integrated searching of original ambiguities or combined ambiguities has almost the same fixing performance, whereas the sequential fixing of EWL, WL and B1 ambiguities overperforms the integrated searching. By the way, the third-frequency data can shorten the TFFS significantly but can hardly improve the positioning.
Highlights
Along with the development of real-time kinematic (RTK) positioning, the distance between users and the reference station is always a challenge in order to enlarge its service coverage
For the above four baselines, Scheme 1 (S1) and Scheme 2 (S2) are equivalent in the ambiguity convergence measured by the fixing index RATIO in this experiment, and Scheme 3 (S3) performs usually better than S1 and S2, regardless of global navigation satellite system (GNSS) systems, data types and the positioning modes, especially for medium-range baselines
In the comparative study of the three triple-frequency ambiguity resolution schemes, medium-range RTK is realized by applying adapted temporal constraint to ionospheric slant delay parameters and tropospheric zenith delay parameters
Summary
Along with the development of real-time kinematic (RTK) positioning, the distance between users and the reference station is always a challenge in order to enlarge its service coverage. Thereafter, on the one hand, a number of studies worked on providing possible accurate ionospheric and tropospheric delay information and imposing proper constraints on them to retain the strength of the solution and reduced observation residuals and demonstrated their efficiency via the resulting ambiguity fixing performance [6,7,8]. [12,22] has studied the contribution of the third-frequency of GPS and Galileo on long-range RTK ambiguity resolution, the results of a cascading fixing scheme in the sequence of EWL, WL and L1/E5 ambiguities are very promising only simulated observations were available and employed. Galileo and all GPS Block IIF and III satellites are transmitting signals at third or even more frequencies In this contribution, the comparative study on the above-mentioned three fixing schemes is carried out based on the BDS triple-frequency data. Afterwards, data processing strategy is presented, and results are compared and analyzed before conclusions are drawn
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