Patent ID: 7865307

Claim:
A method of determining if a real time clock (â€œRTCâ€) in a global positioning system (â€œUPSâ€) receiver system is accurate enough to be used on start up of the GPS receiver, the method comprising: transferring the time kept by the RTC clock to a GPS clock of the GPS receiver system; estimating the position of visible satellites, wherein the GPS clock is updated with signals from the RTC clock; based on the estimated position of the visible satellites, measuring a pseudo-noise (â€œPNâ€) code for each of the visible satellites; calculating an expected current full PN code phase for each of the visible satellites; computing the location of the GPS receiver using the expected current full PN code phases; comparing the computed location of the GPS receiver to a previously-computed location of the GPS receiver in units of time; determining whether the computed location of the GPS receiver has changed more than a predetermined threshold amount from the previously-computed location; and responsive to the determined amount exceeding the predetermined threshold amount, establishing a new GPS clock by acquiring the visible satellites using conventional methods.