GPS Position Can Be Computed without the Navigation Data

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 5dimensional 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.