Bridging GPS Gaps in Urban Canyons: Can ZUPT Really Help?

Dorota A. Grejner-Brzezinska, Charles K. Toth and Yudan Yi

Abstract:	Land based mobile mapping systems (MMS) often operate in urban environments where frequent losses of GPS lock may occur. In such cases, the navigation of the vehicle is performed by an inertial navigation system (INS). However, INS errors grow exponentially with time, thus the duration of the free navigation mode should be controlled, and if necessary, supported by the static INS calibration in so-called Zero Velocity Update (ZUPT) mode. Consequently, if the system’s navigation is furnished by a free-navigation mode, periodic ZUPTs should be automatically requested by the system's controls, depending on the level of positioning error growth. Similarly, when less than four satellites are observed in a tight GPS/INS integration mode, the position error drift is not controlled in all directions. Thus, extended periods of poor observability might also require periodic static calibration. The ZUPT mode utilizes the zero velocity condition for a stationary INS, allowing an improved calibration of velocity error sources, such as alignment and the IMU sensor errors, leading to the lower positioning error rate as compared to the unaided, free navigation mode. A high-accuracy, tightly integrated GPS/INS system (double difference L1/L2 phase data, Litton LN-100 INS) presented in this paper, supports a fully digital imaging component designed for real-time mapping of highway central and edge lines. The primary focus of this paper is the observability analysis of the static INS calibration algorithm and the speed and reliability of the on-the-fly (OTF) ambiguity resolution, supported by the free INS navigation mode, and the free INS navigation mode combined with periodic ZUPTs. An analysis of positioning errors after ZUPT versus unaided and GPS/INS results, used as a benchmark solution, is presented.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	3139 - 3148
Cite this article:	Grejner-Brzezinska, Dorota A., Toth, Charles K., Yi, Yudan, "Bridging GPS Gaps in Urban Canyons: Can ZUPT Really Help?," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 3139-3148.
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