New Tools for Network RTK Integrity Monitoring

X. Chen, H. Landau, U. Vollath

Abstract:	Over the last few years Network RTK has been proven to be an efficient technology for high accuracy positioning. The principle of Network RTK is that a significant portion of ionospheric, tropospheric and ephemeris errors are estimated over a region and this information is provided to rovers in the field. Among spatially correlated errors, ionosphere is most difficult to model and contributes the largest error for network RTK users in terms of reliability and availability. The ionospheric index I95, which was proposed by Wanninger (2002), is a good measure to predict the linear ionospheric effect for single baseline RTK users. However, in Network RTK this effect is actually modeled in the network server and taken out by the software, since the model in the server is at least linear (if not more complex). Therefore Network RTK requires different measures to describe potential residual errors in the generated data stream transmitted to the user. The authors propose to use two different ionospheric linearity indicators (IRIM and IRIU) to predict Network RTK performance. Similar indicators can be used for the non-dispersive part too. This paper proposes two indicators of ionospheric linearity: • Ionospheric Residual Integrity Monitoring (IRIM): Omitting one reference station from interpolation and then comparing the interpolation results at that station with the real measurements. Compute a weighted RMS over all satellites. This can also be considered as integrity monitoring for residual interpolation and ambiguity resolution in the network. • Ionospheric Residual Interpolation Uncertainty (IRIU): With sufficient surrounding reference stations, an interpolation method such as Weighted Linear Interpolation Method (WLIM) produces standard deviation of interpolation. The standard deviation represents the ionospheric linearity over the interpolation region for the field user. Two network scenarios are presented in this paper. One is in Japan, with a very high ionospheric gradient (maximum 40 ppm for low elevation satellites), another one is in Bavaria, Germany, with medium ionospheric gradients but very disturbed around local noon. Test results show that both ionospheric linearity indicators highly correlate with the differential ionospheric residuals "seen" by a real rover in the field. In conclusion, ionospheric linearity indicators (IRIM and IRIU) are very useful tools to predict the rover performance. Such measures can improve the RTK reliability and productivity of rovers working in a networking system.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1355 - 1360
Cite this article:	Chen, X., Landau, H., Vollath, U., "New Tools for Network RTK Integrity Monitoring," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1355-1360.
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