Enhancement of a Tightly Coupled GPS/INS System for High Precision Attitude Determination of Land Vehicles

J. Wendel, T. Obert, G.F. Trommer

Abstract:	Attitude determination systems are used by the automobile industry for the development and optimization of vehicle suspension systems. Most systems currently used are based on mechanical gyroscopes, where a rapidly spinning mass provides a well defined direction in inertial space. These systems offer an accurate attitude solution for test drives lasting several minutes. This paper describes the enhancement of an attitude determination system based on a tightly coupled GPS/INS system. In this system, the required attitude information is calculated by a strapdown algorithm. Long-term stability is achieved by estimating the errors of the strapdown state by means of a Kalman filter. The necessary aiding information is provided by a single frequency stand-alone GPS receiver. Whereas in our previous design, pseudorange and delta-range measurements were used, the focus is now on using carrier phase measurements. The aim of this is to achieve an increased velocity accuracy, which is essential for an increased attitude accuracy. Usually, the integer ambiguities need to be resolved in order to be able to use carrier phase measurements. This is only possible with differential GPS, where a base station transmits corrections to cancel out atmospheric errors. In order to avoid the need for an integer ambiguity search algorithm and a base station, in this design time-differenced carrier phase measurements are used. While with this type of measurement the position accuracy can not be improved, a very accurate velocity can be achieved improving in consequence the attitude accuracy, which is the main design goal for an attitude determination system. Two methods to process the time-differenced carrier phase measurements in a Kalman filter are adressed. The verification of the system performance was done with an experimental GPS/INS system by hardware-in-the-loop tests. The results obtained with these hardware-in-the-loop tests were confirmed in a test drive.
Published in:	Proceedings of the 59th Annual Meeting of The Institute of Navigation and CIGTF 22nd Guidance Test Symposium (2003) June 23 - 25, 2003 Hyatt Regency Hotel Albuquerque, NM
Pages:	200 - 208
Cite this article:	Wendel, J., Obert, T., Trommer, G.F., "Enhancement of a Tightly Coupled GPS/INS System for High Precision Attitude Determination of Land Vehicles," Proceedings of the 59th Annual Meeting of The Institute of Navigation and CIGTF 22nd Guidance Test Symposium (2003), Albuquerque, NM, June 2003, pp. 200-208.
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