Inertial Aiding of Phase-Tracking Loops for Automotive GPS Attitude Determination

Santiago Alban and Arne Dietrich

Abstract:	The increasing demand for navigation aids and sophisticated control systems in modern cars has led to a growing number of GPS applications in the automobile industry, including attitude determination. Attitude determination is a fundamental necessity for many vehicle stability control systems, calibration of inertial sensors, and for inertial navigation as a backup to standard GPS. Despite the accuracy and cost advantages of GPS over other methods of attitude determination, only a few commercial products have emerged with this capability. These systems are currently used only on a research basis, as they are prohibitively expensive for automobile consumer applications and perform poorly in most urban environments. The robustness shortcoming of GPS attitude determination in urban environments stems from the vulnerability of integrated carrier-phase measurements to multipath noise and frequent cycle slips. When these two problems occur simultaneously, the integrity of GPS attitude determination is compromised, and may be lost entirely. For this reason, integration with inertial sensors is a critical aspect of an automotive attitude system based on GPS, and can be implemented with numerous techniques of varying complexity and robustness benefits. The method that is presented in this paper involves using inertial measurements to aid tracking in a phase-lock loop using a technique designated as Doppler aiding, which can be considered one of the more straightforward variants of ultra-tight coupling. Ultra-tight coupling is arguably the most complex form of GPS/INS integration, but is also one that yields the most benefits in terms of system robustness. The performance improvements that are emphasized from Doppler aiding include better suppression of phase noise, higher phase-tracking bandwidth, and reduced probability of cycle slips. In addition, the novel capability of achieving open-loop phase-tracking without a cycle slip during short channel outages (less than 1sec) is presented. Each of these performance improvements is explained and quanti- fied, and the impact of using inexpensive components such as a TCXO and automotive-grade inertial sensors is considered. Results from simulation and post-processed real data are shown, which demonstrate these concepts and validate the feasibility of implementing Doppler-aiding with inexpensive GPS and inertial components. The implications of these results pertain not only to attitude determination, but also to other carrier-phase applications like precise positioning, for which demand exists for development of modern automobile control systems.
Published in:	Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004) June 7 - 9, 2004 Dayton Marriott Hotel Dayton, OH
Pages:	166 - 179
Cite this article:	Alban, Santiago, Dietrich, Arne, "Inertial Aiding of Phase-Tracking Loops for Automotive GPS Attitude Determination," Proceedings of the 60th Annual Meeting of The Institute of Navigation (2004), Dayton, OH, June 2004, pp. 166-179.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In