Method and apparatus for rapidly estimating the doppler-error and other receiver frequency errors of global positioning system satellite signals weakened by obstructions in the signal path
First Claim
1. A method for processing Global Positioning System (GPS) signals, comprising:
- receiving a GPS signal from one or more GPS satellites;
digitizing the GPS signal to produce a digitized signal;
squaring the digitized signal to produce a squared signal;
analyzing the squared signal for spectral components;
scaling the spectral components to identify a frequency of the received signal;
generating a frequency-offset compensator based on the identified frequency; and
applying the frequency-offset compensator to the GPS signal to extract a satellite identifier and a pseudorange pulse.
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Abstract
Frequency-offset components are extracted from a set of digitized samples of signals transmitted by a satellite. The samples are squared to produce squared samples and decimated. The squared samples are auto-correlated to produce an auto-correlate, and the auto-correlate is truncated. The truncated auto-correlate is transformed into the frequency domain to obtain double-frequency offset components. The scaled offset frequencies are used to compensate for Döppler-shift and receiver frequency errors and for Döppler induced time errors in digitized samples used to estimate pseudorange information.
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Citations
60 Claims
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1. A method for processing Global Positioning System (GPS) signals, comprising:
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receiving a GPS signal from one or more GPS satellites;
digitizing the GPS signal to produce a digitized signal;
squaring the digitized signal to produce a squared signal;
analyzing the squared signal for spectral components;
scaling the spectral components to identify a frequency of the received signal;
generating a frequency-offset compensator based on the identified frequency; and
applying the frequency-offset compensator to the GPS signal to extract a satellite identifier and a pseudorange pulse. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for determining a location, comprising:
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communicating with a reference network to calibrate the time of day;
receiving a GPS signal from one or more GPS satellites;
digitizing the GPS signal to produce a digitized signal;
squaring the digitized signal to produce a squared signal;
analyzing the squared signal for spectral components;
scaling the spectral components to identify a frequency of the received signal;
generating a frequency-offset compensator based on the identified frequency;
applying the frequency-offset compensator to the GPS signal to produce a compensated signal;
extracting a satellite identifier and a pseudoranging pulse from the compensated signal; and
calculating a location based on the satellite identifier, pseudoranging pulse, and the calibrated time of day. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. A system for interpreting Global Positioning System (GPS) signals, comprising:
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a means for receiving a GPS signal from one or more GPS satellites;
a means for digitizing the GPS signal to produce a digitized signal;
a means for squaring the digitized signal to produce a squared signal;
a means for analyzing the squared signal for spectral components;
a means for scaling the spectral components to identify a frequency of the received signal;
a means for generating a frequency-offset compensator based on the identified frequency; and
a means for applying the frequency-offset compensator to the GPS signal to extract a satellite identifier and a pseudorange pulse. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32, 33, 34, 35)
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36. A system for determining a location, comprising:
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a means for communicating with a reference network to calibrate the time of day;
a means for receiving a GPS signal from one or more GPS satellites;
a means for digitizing the GPS signal to produce a digitized signal;
a means for squaring the digitized signal to produce a squared signal;
a means for analyzing the squared signal for spectral components;
a means for scaling the spectral components to identify a frequency of the received signal;
a means for generating a frequency-offset compensator based on the identified frequency;
a means for applying the frequency-offset compensator to the GPS signal to produce a compensated signal;
a means for extracting a satellite identifier and a pseudoranging pulse from the compensated signal; and
a means for calculating a location based on the satellite identifier, pseudoranging pulse, and the calibrated time of day. - View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50)
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51. A system, comprising:
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logic embedded on a computer-readable medium; and
the logic operable to receive a GPS signal from one or more GPS satellites, digitize the GPS signal to produce a digitized signal, square the digitized signal to produce a squared signal, analyze the squared signal for spectral components, scale the spectral components to identify a frequency of the received signal, generate a frequency-offset compensator based on the identified frequency; and
apply the frequency-offset compensator to the GPS signal to extract a satellite identifier and a pseudorange pulse. - View Dependent Claims (52, 53, 54, 55, 56, 57, 58, 59)
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60. A method for determining the location of a wireless device, comprising:
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communicating with a reference network to calibrate a time of day;
receiving two or more GPS signals from a plurality of GPS satellites;
storing a signal including GPS signals from a plurality of satellites;
digitizing each GPS signal to produce a digitized signal;
squaring each digitized signal to produce a squared signal;
filtering each squared signal through a low-pass filter to produce a plurality of narrow-band samples, each narrow-band signal comprising a plurality of sinusoidal components;
concatenating the decimated signals to produce a concatenated signal;
auto-correlating the concatenated signal to emphasize sinusoidal carriers and concentrate noise-energy in a zero time-shift component to produce an auto-correlated signal;
removing the zero time-shift component from the auto-correlated signal;
calculating a first Fourier transform on the truncated auto-correlated signal to produce a first-transformed signal;
identifying a carrier wave significantly stronger than a noise floor in the first-transformed signal;
resealing the carrier wave frequencies to yield a frequency-offset compensator;
retrieving the GPS signals from storage;
applying the frequency-offset compensator to each retrieved GPS signal;
additively stacking the compensated GPS signals to produce a plurality of stacked signals;
calculating a second Fourier transform of the stacked GPS signals to produce a plurality of second-transformed signals;
calculating a time-compression compensator for each second-transformed signal;
applying the time-compression compensator to each second-transformed signal to produce compensated signals;
selecting a candidate signal from a list of known satellite broadcast signals;
multiplying the compensated signals by the candidate signal to produce a plurality of multiplied signals;
calculating an inverse Fourier transform of the multiplied signals;
additively stacking the inverse transforms of the multiplied signals to produce a plurality of stacked transforms;
identifying a plurality of pseudorange pulses within the stacked transforms;
associating each pseudorange pulse with a specific GPS satellite;
retrieving a pseudorange from each pseudorange pulse; and
calculating the location of the wireless device based on the pseudoranges, known GPS satellite information, and calibrated time of day.
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Specification