Performance of OTF Ambiguity Resolution Search Algorithms for Real Time Positioning Under Varying Conditions

David Walsh, Vidal Ashkenazi, Geraint Ffoulkes-Jones

Abstract:	Centimetre level differential positioning using on-the- fly (OTF) GPS carrier phase ambiguity resolution has been shown to be possible by a number of research centres. However, for many kinematic applications (eg Category III precision approach and landing for aircraft) the accuracy, continuity and integrity of the position solution are of paramount importance if the method is to be used in practice, either as a sole means positioning system or as part of an integrated system. A vital accuracy and continuity concern is the time it takes to resolve the integer carrier phase ambiguities. Until the ambiguities are resolved GPS will not provide centimetre level positioning. This can be significantly affected by many factors, eg number of satellites available and, particularly, unmodelled errors (eg multipath) which can vary significantly in a short space of time. Therefore, even though very fast ambiguity resolution may be possible, it is necessary to determine whether OTF ambiguity resolution can be carried out within performance limits and with the reliability required in realistic operating conditions. This paper describes a series of tests carried out to determine the performance of GPS ambiguity resolution for precise positioning, using a moving vehicle on land, under a variety of conditions. Two algorithms are described which search for the ambiguities with (i) the minimum sum of squares of residuals, or (ii) the minimum change of residuaI. Results are given for extensive tests using different frequencies, receiver separations, numbers of satellites, and, importantly, short periods of data with similar satellite geometry but different umnodelled errors. Particular emphasis is placed on the variation of the time taken to resolve the ambiguities, and hence the suitability of the method for critical precise positioning applications.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	313 - 321
Cite this article:	Walsh, David, Ashkenazi, Vidal, Ffoulkes-Jones, Geraint, "Performance of OTF Ambiguity Resolution Search Algorithms for Real Time Positioning Under Varying Conditions," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 313-321.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In