Isolation of GPS Multipath and Receiver Tracking Errors

Michael S. Braasch

Abstract:	GPS receiver dynamic tracking error is an often misunderstood concept. Flight test results and field experiences at Ohio University have shown dynamics- induced errors which can be related directly to the receiver architecture. It is welI known that carrier- aiding of the code-tracking loop helps in maintaining code-lock during receiver dynamics. However, heavy carrier-aiding inhibits the monitoring of multipath which can be important in a weighted position solution. Since multipath is a major barrier to sub-centimeter accuracy in differential carrier-phase (kinematic GPS) applications, the ability to monitor the signal is crucial. Furthermore, to evaluate the effects of multipath in airborne receivers, it is necessary to isolate multipath from receiver tracking errors. With a receiver at a surveyed location, total pseudorange error can easily be computed. Isolation of specific error sources, however, is more complex. For dual-frequency receivers, the combination of multipath and receiver tracking error can be obtained through proper manipulation of pseudorange and integrated Doppler data (this is true for dynamic as well as static receivers). Separation of multipath and receiver tracking error can be difficult, though, particularly for a highly dynamic receiver platform. This results from the fact that the two error sources can be similar in magnitude and frequency. Historically, receiver dynamic tracking error often has been ignored or overlooked when analyzing multipath data. This paper describes a controlled experiment which allows for the isolation of multipath and receiver tracking errors. The theory behind the dynamic tracking error phenomenon will be described along with the isolation technique. Data collection and analysis results wilI be presented to confirm the viability of the technique.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	511 - 521
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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