Patent ID: 6731701
Filing Date: 2004-05-04
Classification: G01S,H04B

Abstract:
A method of predicting navigation symbols for use in a global positioning tracking process, the navigation symbols being transmitted from a global positioning satellite in the form of a carrier signal modulated by a data-stream signal comprising the symbols, the navigation data symbols being conveyed in a sequence of one or more repeating frames, said data-stream signal having a first group of symbols which is repeated within the stream once every M number of frames at predetermined locations in the frames, M being equal to or greater than 1, said method comprising:(a) detecting the symbols of the first group within the frames of the data-stream signal; (b) storing in a memory a sequence of the detected symbol values of the first group over at least M frames; (c) providing the sequence stored in the memory to the global positioning tracking process; (d) subsequently monitoring the data-stream signal to detect a change in the symbol values of the first group, said subsequently monitoring comprising the steps of detecting the symbols of the first group within subsequently transmitted frames, comparing their values with the sequence of previously detected symbol values stored in memory to find differences, and counting the number of differences encountered since the start of a group of frames; and (e) repeating steps (a) and (b) when the number of differences exceeds a predetermined number.