OSCILLATOR FREQUENCY CORRECTION IN GPS SIGNAL ACQUISITION
First Claim
1. A method for correcting oscillator frequency error in GPS signal acquisition, comprising the steps of:
- receiving at least one broadcasted GPS signal;
estimating a plurality of Doppler offsets;
correlating the signal to produce a plurality of correlation results for each of the plurality of Doppler estimates;
calculating a magnitude separation of peak and null states of corresponding pairs of correlation results; and
searching the peak and null separation to find the Doppler estimate producing the largest magnitude separation in peak and null states, the found Doppler estimate defining a frequency error estimate for the at least one broadcasted GPS signal.
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Abstract
A method (50) for correcting oscillator frequency error in GPS signal acquisition includes a first step (52) of receiving at least one broadcasted GPS signal. A next step (54) includes estimating a plurality of Doppler offsets. A next step (56) includes correlating the signal to produce a Doppler modulation for each of the plurality of Doppler estimates. A next step (58) includes calculating a magnitude separation of peak and null states of each modulation. A next step (60) includes searching the peak and null separation to finding the Doppler estimate producing the largest magnitude separation in peak and null states. The found Doppler estimate defines a frequency error estimate for the at least one broadcasted GPS signal, which will be common across all satellites.
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Citations
20 Claims
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1. A method for correcting oscillator frequency error in GPS signal acquisition, comprising the steps of:
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receiving at least one broadcasted GPS signal;
estimating a plurality of Doppler offsets;
correlating the signal to produce a plurality of correlation results for each of the plurality of Doppler estimates;
calculating a magnitude separation of peak and null states of corresponding pairs of correlation results; and
searching the peak and null separation to find the Doppler estimate producing the largest magnitude separation in peak and null states, the found Doppler estimate defining a frequency error estimate for the at least one broadcasted GPS signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for correcting oscillator frequency error in GPS signal acquisition, comprising the steps of:
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receiving at least one broadcasted GPS signal;
constructing a code phase estimate from a signal envelope accumulation;
estimating a plurality of Doppler offsets and centering the plurality of Doppler estimates using the code phase estimate;
correlating the signal to produce correlation magnitudes that follow a sin(x)/x curve of a Doppler modulation for each of the plurality of Doppler estimates;
calculating a magnitude separation between the maximum and minimum correlations corresponding to the peak and null states of the curve; and
searching the separations to finding the Doppler estimate producing the largest magnitude separation, the found Doppler estimate defining a frequency error estimate for the at least one broadcasted GPS signal. - View Dependent Claims (16, 17, 18, 19)
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20. A method for correcting oscillator frequency error in GPS signal acquisition, comprising the steps of:
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receiving at least one broadcasted GPS signal;
constructing a code phase estimate from a signal envelope accumulation;
estimating a plurality of Doppler offsets and centering the plurality of Doppler estimates using the code phase estimate;
correlating the signal to produce correlation magnitudes of a Doppler error modulation for each of the plurality of Doppler estimates;
curve fitting the Doppler error modulation to a sin(Tƒ
/2)/(Tƒ
/2) curve, where T is the coherent integration interval, and ƒ
is the frequency error, using at least two correlation magnitudes; and
using the shift in Doppler value of the curve fit to estimate a Doppler error defining a frequency error for the at least one broadcasted GPS signal.
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Specification