Preliminary Test Results of RTK-aided Conical Domain Model for SBAS Ionospheric Correction

Donguk Kim, Deokhwa Han, Changdon Kee

Abstract: A satellite-based augmentation system (SBAS) provides the vertical ionospheric correction to reduce ionospheric delay error, which is the biggest error source for GNSS users. It is a major issue of the SBAS for generating accurate and reliable ionospheric correction to improve the navigation performance of the single-frequency SBAS uses. In a standardized SBAS system, the ionosphere is assumed to be a thin-shell model and we estimate the vertical ionospheric delay of predefined grid points. While the thin-shell assumption has the advantage of being simple, it can cause significant errors for converting slant delay to vertical delay using obliquity factor, especially at low-elevation angle. Since the obliquity factor is defined as the function of only satellite’s elevation angle, the ionospheric delay has same value at the same elevation angle regardless of their azimuth angle unlike the actual environment. The conical domain model was proposed in order to mitigate the estimation error caused by the obliquity factor. Since the slant ionospheric delay of the regional reference stations are similar for a specific satellite, the ionospheric delay can be modeled as a plane function for each individual satellite considered as the vertex of the cone. The SBAS users can reduce their ionospheric delay using estimated planar fit parameters of each satellite. The conical domain model can mitigate the induced error of obliquity factor efficiently; nonetheless, there is still a limit to accuracy because this model uses only a limited number of pseudorange measurements. Unlike the grid-based model, which employs a lot of observations from all visible satellites, the conical-domain model that uses only observations of specific satellite for fitting a plane is particularly sensitive to pseudorange measurement quality. This paper proposed a new conical domain method using precise double-differenced carrier-phase measurements for estimating the ionospheric delay accurately. The double- differenced ionospheric delay can be obtained by the real-time kinematic (RTK) technique for determining the integer ambiguity of carrier-phase observations. This precise and relative values can be utilized as the additional measurements indicating the relative gradient between two satellite’s planes. Based on this property, we can construct a new conical-based planar fit model using both smoothed pseudorange and double-differenced carrier-phase measurements. We conducted the feasibility test to evaluate the performance of the proposed method using simulation data. Consequently, under the storm condition, the 95% user range error is enhanced about 24% through the proposed method with compare to the general conical domain method. Furthermore, the 95% HPE and VPE is significantly enhanced about 27% and 33%, respectively.
Published in: Proceedings of the ION 2019 Pacific PNT Meeting
April 8 - 11, 2019
Hilton Waikiki Beach
Honolulu, Hawaii
Pages: 1031 - 1044
Cite this article: Kim, Donguk, Han, Deokhwa, Kee, Changdon, "Preliminary Test Results of RTK-aided Conical Domain Model for SBAS Ionospheric Correction," Proceedings of the ION 2019 Pacific PNT Meeting, Honolulu, Hawaii, April 2019, pp. 1031-1044.
https://doi.org/10.33012/2019.16785
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