GPS Position Can Be Computed without the Navigation Data

Niilo Sirola and Jari Syrjärinne

Abstract:	This paper presents an algorithm for computing a GPS receiver's position and the current time from C/A-code phase measurements to at least six satellites and a set of valid satellite ephemerides. Reference position and reference time are not necessary. The process uses a cost function having numerous local minima in addition to the global minimum. An exhaustive search over the 5- dimensional time-position-bias search space will reliably find the global minimizer, and thus solve the approximate position and time. Introducing a reference time within one minute from the true time resulted in worst-case computation time of a few seconds. If the current pseudorange correction parameters are available, the accuracy of this method is comparable to that of the conventional pseudo-range methods. As a conclusion, an accurate GPS position can be solved in a reasonable time even without the navigation data or precise system time.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	2741 - 2744
Cite this article:	Sirola, Niilo, Syrjärinne, Jari, "GPS Position Can Be Computed without the Navigation Data," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 2741-2744.
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