Performance Analysis and Architectures for INS-Aided GPS Tracking Loops

S. Alban, D.M. Akos, S.M. Rock

Abstract:	GPS and inertial sensors have complementary characteristics, which have been exploited in the design of integrated GPS-inertial navigation and guidance systems. Traditionally, most hybrid GPS-inertial systems have been mechanized by combining the information from GPS and an Inertial Navigation System using either loose integration (i.e., integration at the position, velocity and/or attitude level) or tight integration (integration at the pseudorange, Doppler, or carrier phase level). Such integration schemes provide users with limited immunity against momentary GPS outages and also allow detection of certain classes of GPS signal failures. A third scheme of integration can be used, in which the inertial sensors are used to aid the GPS phase frequency and code tracking loops directly. In this paper, this level of coupling is referred to as ultra-tight integration, and it offers potential improvements to GPS performance, such as higher phase-tracking bandwidth, and more resistance to radio frequency interference or multipath noise. In this paper we propose a simple architecture for GPS-inertial systems with ultra-tight integration and present the results of some trade studies and simulations quantifying the performance of such systems. Performances of the ultra-tight GPS-inertial system are evaluated using a simulation tool developed specifically for this study. The metrics used for the evaluation are allowable reduction in the carrier tracking loop-filter bandwidth for improved signal-to-noise ratio, and robustness against carrier-phase cycle-slips. The sensitivity of these metrics to inertial sensor quality and GPS receiver clock noise is discussed and quantified. These studies show that an ultra-tightly coupled system using low cost/performance inertial sensors and a typical temperature-compensated crystal oscillator can function with a carrier tracking loop-filter bandwidth as low as 3Hz. This structure shows a 14dB improvement in phasenoise suppression when compared to a traditional 15Hz loop filter, and comparable carrier-phase tracking bandwidth to that of the inertial sensors (>30Hz).
Published in:	Proceedings of the 2003 National Technical Meeting of The Institute of Navigation January 22 - 24, 2003 Disneyland Paradise Pier Hotel Anaheim, CA
Pages:	611 - 622
Cite this article:	Alban, S., Akos, D.M., Rock, S.M., "Performance Analysis and Architectures for INS-Aided GPS Tracking Loops," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 611-622.
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