A Comparative Study of BDS Triple-Frequency Ambiguity Fixing Approaches for RTK Positioning

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.

Improving the Stochastic Model of Ionospheric Delays for BDS Long-Range Real-Time Kinematic Positioning

“…All the timevarying parameters, such as coordinates of a kinematic station, tropospheric zenith delays, and ionospheric slant delays, will be eliminated after all related observations are contributed and prepared for the parameters of the next epoch. The details of the sequential processing can be found in the study by Ge et al [33] and Zhu et al [34].…”

“…The data of each baseline are divided into one-hour sessions and processed independently using the above-mentioned processing schemas. For each one-hour session, triple frequency data are processed in kinematic mode and integer ambiguity fixing is carried out using the strategy presented by Zhu et al [34]. The FAFT, the estimated station coordinates and ionospheric delays are also derived and analyzed for each schema and baseline.…”