Instantaneous RTK Positioning Based on User Velocity Measurements

Nobuaki Kubo, Sam Pullen

Abstract:	Instantaneous Real Time Kinematic (RTK) techniques are one means to achieve real-time high-accuracy positioning. Single-epoch fixing is essential for RTK technology to be used in a vehicle because "nuisance" cycle slips during multiple-epoch fixing are not a problem. However, GPS satellite signals can be momentarily shaded or blocked in urban areas. Generally, in such cases, integer ambiguity values are lost and must be re-determined. However, it is often very difficult to find correct ambiguities in urban areas in a single epoch. The object of this paper is to improve the performance of instantaneous RTK positioning. In this paper, user velocity from Doppler frequency measurements is used to help resolve integer ambiguities. Both conventional widelane and LAMBDA methods with Doppler frequency measurements are evaluated. In urban areas, pseudorange measurements can deteriorate easily due to strong multipath, despite the use of advanced multipathmitigation techniques. On the other hand, Doppler frequency measurements do not deteriorate as much as pseudo-range, because the absolute multipath error of Doppler frequency measurement is only several centimeters (compared to several tens of centimeters). The proposed algorithm for single-epoch RTK positioning using raw data from GPS receivers is simple. After obtaining carrier phase, pseudo-range, and Doppler frequency measurements, ambiguity resolution is conducted. These algorithms have been tested by both static and moving users subjected to several different multipath conditions. Single-epoch ambiguity fixing performance was improved compared to conventional ambiguity resolution without velocity information.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	1406 - 1417
Cite this article:	Kubo, Nobuaki, Pullen, Sam, "Instantaneous RTK Positioning Based on User Velocity Measurements," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 1406-1417.
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