Operational Performance of RTK Positioning when Accounting for the Time Correlated Nature of GNSS Phase Errors

C. Miller, K. O'Keefe, Y. Gao

Abstract:	In order for Real-Time Kinematic (RTK) Global Positioning System (GPS) to provide a realistic positional accuracy estimate, the stochastic model must correctly describe the errors within the observables, including their temporal correlation. Temporal correlation is generally ignored by modern RTK manufacturers. Assuming correlated observations to be independent results in an over-optimistic state variance-covariance (VCV) matrix. This can lead to too much confidence being placed in GPS obtained positions, especially when combined in survey networks with terrestrial obtained positions. One method of accounting for the temporal correlation found in GPS errors is the time-differencing Kalman filter, published previously by Petovello et al (2009). This previously untested approach is implemented and evaluated using real RTK GPS data. Using traditional survey methods, a 3-dimensional survey testing network was created, and adjusted using least squares. Each of the 6 testing points within the network were characterized with different signal challenges to experience a variety of multi-path scenarios. The network was repeatedly surveyed using commercial RTK equipment and software, with baselines up to 10 km in length. The positions and accuracy of each point were determined using both commercial RTK software and the time-differencing Kalman filter. Using the state VCV matrix, error ellipses (95% confidence interval) are formed and analyzed in the local coordinate system. When temporal correlation is ignored, the error ellipses do not contain the absolute position as often as they should at the 95% confidence interval (CI). Using the state VCV matrix established with the timedifferencing Kalman filter, the error ellipses are more realistic and contain the absolute position 95% of the time. The time-differencing Kalman filter is not without its difficulties, as ambiguity resolution and filter tuning are shown to be difficult tasks.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1513 - 1524
Cite this article:	Miller, C., O'Keefe, K., Gao, Y., "Operational Performance of RTK Positioning when Accounting for the Time Correlated Nature of GNSS Phase Errors," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 1513-1524.
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