Survey Quality Real-Time GPS: Solving the Time to Fix vs. Reliability Paradox

Shaowei Han and Rod Johnson

Abstract:	Carrier phase ambiguity resolution is the corner stone of modern real-time GPS surveying systems. Availability of fixed ambiguity solutions is the difference between waiting and working. Evaluation of the time to fix carrier phase ambiguities in a variety of real-world conditions is often a primary motivator when GPS system buying decisions are made, but solving the paradox of speed versus reliability continues to be one of the greatest challenges facing real-time GPS surveying. In an effort to translate GPS receiver technology to fast, reliable centimeter level solutions for surveyors, scientists and engineers are required to push the limits of real-time carrier phase performance. Operational constraints of real world environments, such as extended baseline length, signal multipath and organic obstructions require strong mathematical modeling and progressive stochastic modeling techniques. Advanced, adaptive stochastic modeling in addition to careful statistical modeling as implemented in the Ashtech® Instant-RTK™ technology and featured in the new Z-Xtreme™ GPS receiver demonstrates unprecedented success in solving the ambiguity resolution speed vs. reliability paradox. Tests on baselines shorter on 7km show the ambiguity can be successfully resolved over 92.78% of time at reliability level of 99.9% while 84.16% of them are resolved using single epoch of data. The test on a baseline at 10km show that 99.9% reliability can still be achieved with impressive time to fix. The positioning accuracy is easily achieved at the system specification of 0.010+1ppm horizontal and 0.020+2ppm vertical (standard error).
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:	1550 - 1557
Cite this article:	Han, Shaowei, Johnson, Rod, "Survey Quality Real-Time GPS: Solving the Time to Fix vs. Reliability Paradox," 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. 1550-1557.
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