RECEIVER FOR RECOVERY AND TRACKING OF SIGNALS MODULATED WITH P-CODE FOR GLOBAL POSITIONING SYSTEM RECYCLE FOR RESTORING AND TRACKING C-

摘要

A method and apparatus for improving signal processing speed and processing accuracy from global positioning system (GPS) receivers (50, 52) by ensuring access to a GPS carrier signal that has been modulated with an encrypted P-code sequence. In one disclosed embodiment of the present invention, the GPS L1 and L2 signals are correlated with a locally generated P-code signal to improve signal-to-noise ratio performance and thus facilitate the resolution of carrier cycle ambiguity, Correlated 66 to obtain a signal having a frequency component. In another embodiment, the received GPS signal is converted to the direct digital form 114 and then digitally correlated with the in-phase and quadrature components of the locally generated P-code signal. Signals from the correlation results are combined 124 and 126 at time intervals corresponding to previously determined encryption periods to provide in-phase (I) and quadrature samples (Q) 130,132.