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

A method for determining a location, comprising:

• 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.

A system for interpreting Global Positioning System (GPS) signals, comprising:

• 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.

A system for determining a location, comprising:

• 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.

A system, comprising:

• 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.

A method for determining the location of a wireless device, comprising:

• 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.