Epoch-by-Epoch Positioning and Navigation

Paul J. de Jonge, Yehuda Bock and Michael Bevis

Abstract:	Geodetics, Inc. has developed a new class of instantaneous, real-time GPS positioning algorithms based on dual frequency phase and pseudorange data, which we call Epoch-by-EpochÆË positioning. The main advantage of this approach over traditional real-time methods is that integer-cycle phase ambiguities are independently estimated for each and every observation epoch, allowing precise positions (1-2 cm horizontal and 5-10 cm vertical) to be estimated given only a single epoch of data from two or more receivers, in either baseline or network mode. Our algorithms are extremely efficient – a single epoch on a single baseline can be processed in several milliseconds. There is no need for the initialization period associated with conventional RTK algorithms. More importantly there is no need for reinitialization immediately following loss-of-lock problems such as occur when a mobile GPS receiver passes under a bridge or other obstruction. Accordingly, our approach minimizes the amount of time a receiver spends in a non-productive prepositioning mode of operations. Epoch-by-EpochÆË positioning has other advantages, including a significantly extended range relative to conventional RTK, and a better framework for quality control. The Epoch-by-EpochÆË approach can also be applied to the autonomous real-time determination of precise attitude and heading (about 0.05 degrees) of a moving platform instrumented with 2-3 receivers and a rigid multiple-antenna structure. A combination of this autonomous navigational capability with precise instantaneous (relative) positioning is ideal for many applications such as automated airborne landing systems, harbor navigation, automated highways, machine control, and GPS/INS integration. Epoch-by-EpochÆË positioning also provides a useful architecture for static positioning, since relatively rare but highly discordant solutions (i.e. solution ‘outliers’ associated with extreme levels of measurement noise) can be recognized and excluded from any position averaging. When single epoch solutions are averaged by a median filter, the scatter of the averaged solutions is inversely proportional to the logarithm of averaging time.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	337 - 342
Cite this article:	de Jonge, Paul J., Bock, Yehuda, Bevis, Michael, "Epoch-by-Epoch Positioning and Navigation," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 337-342.
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