Back to results
US 6,725,157 B1Granted
Indoor GPS clock
AssigneeTrimble Navigation Limited
InventorYiming Yu
Life of this patent
Estimating the term…
Abstract
An indoor GPS clock using GPS signals lower that −143 dBm for issuing disciplined frequency and time standard signals. The indoor GPS clock includes a correlation machine using long integration periods for enabling the indoor GPS clock to operate with low signal levels; a carrier-less tracking loop for tracking the low level signals without carrier offset feedback, a clock bias loop for providing clock bias feedback; and a reference oscillator using the clock bias feedback for providing disciplined frequency and time signals having greater accuracy than is available in conventional GPS positioning receivers. The indoor GPS clock also includes a holdover driver providing compensation for predicted drift in clock bias error for disciplining the reference oscillator for several hours when the GPS signal is no longer being received.
Claims35
A method using a GPS signal for providing a frequency standard signal, comprising:
- acquiring said GPS signal using coherent acquisition integration periods having multiple GPS code epochs, said acquisition integration periods including at least forty said code epochs, wherein the step of acquiring includes:
- determining first and second correlation levels for first and second integration periods, respectively;
- stripping GPS data bit information from said first and second correlation levels for providing first and second data stripped correlation levels, respectively;
- linearly accumulating said first and second data stripped levels for providing an extended correlation acquisition level;
- and using said extended correlation level for acquiring said GPS signal;
- tracking said GPS signal, after said GPS signal has been acquired, using coherent tracking integration periods having multiple said GPS code epochs;
- and
- disciplining said frequency standard signal using said coherent tracking integration periods to track GPS frequency.
5 more elements
A method using a GPS signal for providing a frequency standard signal, comprising:
- acquiring said GPS signal using coherent acquisition integration periods having multiple GPS code epochs, wherein the step of acquiring includes:
- determining first and second correlation levels for first and second integration periods, respectively;
- squaring said first and second correlation levels for providing first and second squared correlations, respectively;
- summing said first and second squared correlations for providing an incoherent correlation sum;
- and using said incoherent correlation sum for acquiring said GPS signal;
- tracking said GPS signal, after said GPS signal has been acquired, using coherent tracking integration periods having multiple said GPS code epochs;
- and
- disciplining said frequency standard signal using said coherent tracking integration periods to track GPS frequency.
5 more elements
A method using a GPS signal for providing a frequency standard signal, comprising:
- acquiring said GPS signal using coherent acquisition integration periods having multiple GPS code epochs;
- generating local mixing samples having a frequency having no feedback correction for an actual carrier frequency of said GPS signal;
- adjusting said local mixing sample frequency according to said frequency standard signal and continuing computations of estimated Doppler shifts of said actual carrier frequency;
- multiplying samples of said GPS signal by said local mixing samples for forming intermediate signal samples;
- said intermediate signal samples used for carrier-less tracking of said GPS signal after said GPS signal has been acquired;
- and
- disciplining said frequency standard signal using said carrier-less tracking to track said carrier frequency of said GPS signal.
4 more elements
The method of claim wherein:
- said acquisition integration periods include at least forty said code epochs.
A GPS clock for providing a frequency standard signal, comprising:
- a long integration correlation machine for acquiring a GPS signal using coherent acquisition integration periods having multiple GPS code epochs, said coherent acquisition integration periods including at least forty GPS code epochs, wherein the correlation machine determines first and second correlation levels for first and second integration periods, respectively;
- and comprises a signal processor including a data stripper for stripping GPS data bit information from said first and second correlation levels for providing first and second data stripped correlation levels, respectively;
- and a summer for linearly accumulating said first and second data stripped correlation levels for providing an extended correlation level, said extended correlation level used for acquiring said GPS signal;
- a signal tracking loop including the correlation machine for tracking said GPS signal, after said GPS signal has been acquired, using coherent tracking integration periods having multiple said GPS code epochs;
- and
- a clock bias loop using said signal tracking loop for disciplining said frequency standard signal to track GPS frequency.
3 more elements
A GPS clock for providing a frequency standard signal, comprising:
- a long integration correlation machine for acquiring a GPS signal using coherent acquisition integration periods having multiple GPS code epochs, wherein the correlation machine determines first and second correlation levels for first and second integration periods, respectively;
- and comprises a signal processor including a squarer for squaring said first and second correlations for providing first and second squared correlations, respectively;
- and an incoherent summer for summing said first and second squared correlations for providing an incoherent correlation sum, said incoherent correlation sum used for acquiring said GPS signal;
- a signal tracking loop including the correlation machine for tracking said GPS signal, after said GPS signal has been acquired, using coherent tracking integration periods having multiple said GPS code epochs;
- and
- a clock bias loop including said signal tracking loop for disciplining said frequency standard signal to track GPS frequency.
3 more elements
A GPS clock for providing a frequency standard signal, comprising:
- a long integration correlation machine using coherent acquisition integration periods having multiple GPS code epochs for acquiring a GPS signal;
- a carrier-less tracking loop including a carrier numerically controlled oscillator (NCO) for generating local mixing samples having a frequency having no feedback correction for an actual carrier frequency of said GPS signal by adjusting said local mixing sample frequency according to said frequency standard signal and continuing computations of estimated Doppler shifts of said actual carrier frequency;
- wherein the correlation machine multiplies samples of said GPS signal by said local mixing samples for forming intermediate signal samples, said intermediate signal samples used for tracking of said GPS signal after said GPS signal has been acquired;
- and
- a clock bias loop using said carrier-less tracking loop for disciplining said frequency standard signal to track said actual carrier frequency of said GPS signal.
2 more elements
Dependencies are inferred from the claim text.