Some Issues Still in the Way to Ultimate Precision

Oscar Colombo

Abstract: There are several reasons why the precision of satellite positioning achieved at present is less than its ultimate potential, particularly in point positioning and long-baseline differential solutions. This short panel presentation will summarize three of the main limiting issues, mentioning some of the efforts made so far to reduce them, at least in some especial applications, and some possible future developments that might help users and providers of precise positioning services deal with them better. The three issues chosen are, in order of importance: (1) the carrier-phase multipath; (2) the often inconveniently long convergence time of long-range differential and of point-positioning solutions, even when fixing ambiguities in a reliable way; (3) the mismodeling of spacecraft orientation during eclipse maneuvers. In the case of kinematic positioning, the ultimate precision is given by the products of the carrier phase measurement STD times the PDOP, VDOP and HDOP; these products give the ideal 3D, vertical and horizontal precision, respectively. Those are theoretical limits that assume that the only thing to be estimated is the instantaneous position of the receiver, because everything else is already known perfectly, and that the only source of error is the data noise. In the case of static positioning, the limit is the kinematic one divided by the square root of the number of epochs with data. If those limits were achieved in everyday results, then the usual precision of instantaneous kinematic positioning in 3-D would be at the 1 cm level, given the good PDOP available, in principle, thanks to the high number of satellites in service; for static positioning it would be at the millimeter level, in considerably less than one hour. At present, such excellent results are not the norm in either kinematic or static positioning, be it in real time or in post-processing, because of several negative factors, including the three to be discussed, that have yet to be overcome in enough practical applications if we are to move closer to achieving them.
Published in: Proceedings of the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2016)
September 12 - 16, 2016
Oregon Convention Center
Portland, Oregon
Pages: 593 - 607
Cite this article: Colombo, Oscar, "Some Issues Still in the Way to Ultimate Precision," Proceedings of the 29th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2016), Portland, Oregon, September 2016, pp. 593-607.
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