GPS satellite signal tracking system for GPS receivers

For use with a GPS receiver arranged to start a search for recapturing a GPS satellite signal when reception of said satellite signal is lost for a predetermined period of time, a GPS satellite signal tracking system for a GPS receiver including the steps of:

• starting a narrow-band search for a satellite signal with the lost satellite signal receiving frequency in the center of a PLL search frequency;
• and
• successively varying the center frequency of the PLL search frequency along a Doppler shift curve of the satellite signal receiving frequency and repeating said narrow-band search at the thus varied center frequency until said satellite signal is recaptured.

For use with GPS receiver arranged to start a wide-band search for recapturing a satellite signal by varying of PLL search frequency widely across the entire width of the maximum variable range of a satellite signal receiving frequency when reception of a satellite signal is lost for a predetermined period of time, a GPS satellite signal tracking system for a GPS receiver including the steps of:

• initially conducting a narrow-band search for a satellite signal with the lost satellite signal receiving frequency in the center of said narrow-band search for a period of time given by dividing a PLL capture range by a Doppler shift rate of the satellite signal receiving frequency being caused by the movement of the GPS satellite within such a frequency shift range as defined by the Doppler shift rate and a Doppler shift being caused by a traveling speed of the GPS receiver;
• and thereafter
• starting a wide-band search for the satellite signal with an estimated satellite signal receiving frequency in the center after failing to recapture the satellite signal within said period of time, said estimated satellite signal receiving frequency being determined by recalculating the Doppler frequency of the GPS satellite at the time when said period of time has elasped from orbital information of the GPS satellite stored in the GPS receiver.

For use with a GPS receiver arranged to start a wide-band search repeatedly for recapturing a GPS satellite by varying a PLL search frequency widely across the entire width of the maximum frequency shift range of a satellite signal receiving frequency, a GPS satellite signal tracking system for a GPS receiver including the steps of:

• estimating a satellite signal receiving frequency at the time of commencing a wide-band search at least from the second time and thereafter by recalculating a Doppler frequency of the GPS satellite and an offset frequency of a built-in clock of the GPS receiver at the point of time at which the wide-band search is started;
• and
• performing the wide-band search with the estimated satellite signal receiving frequency in the center for a predetermined period of time.