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

• US 6,650,285 B2
• Filed: 12/23/2002
• Issued: 11/18/2003
• Est. Priority Date: 08/24/2000
• Status: Active Grant

• Current Assignee: Fast Location.Net, LLC
• Original Assignee: Fast Location.Net, LLC
• Inventors: Jandrell, Louis H. M.
• Primary Examiner(s): Camby, Richard M.
• Application Number:
  US10/328,078
• Publication Number:
  US 20030128158A1
• Time in Patent Office: 330 Days
• Field of Search: 342/357.12, 342/357.05, 342/357.02, 342/357.07, 342/358, 701/214, 701/208, 701/209, 701/213, 701/211, 701/212, 701/207, 375/148, 375/150, 375/200, 375/208, 375/343, 380/49
• US Class Current: 342/357.64
• CPC Class Codes: G01S 19/17 Emergency applications
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: G01S 19/29 carrier including Doppler, related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/34 Power consumption

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.

Claims

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.

2. The method of claim 1, wherein the analysis is by Fourier transform.

3. The method of claim 1, wherein the analysis is by Fast Fourier Transform.

4. The method of claim 1, further comprising decimating the squared signals before analysis.

5. The method of claim 4, wherein the decimation comprises filtering each squared signal through a low-pass filter to produce a plurality of narrow-band samples, each narrow-band sample comprising a plurality of sinusoidal components.

6. The method of claim 1, further comprising concatenating the squared signals before analysis to produce a concatenated signal.

7. The method of claim 1, further comprising auto-correlating the squared signal before analysis to produce an auto-correlated signal.

8. The method of claim 7, wherein the auto-correlation comprises emphasizing sinusoidal carriers and concentrating noise-energy in a zero time-shift component.

9. The method of claim 8, further comprising removing the zero time-shift component from the auto-correlated signal.

10. 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.

11. The method of claim 10, wherein the analysis is by Fourier transform.

12. The method of claim 10, wherein the analysis is by Fast Fourier Transform.

13. The method of claim 10, further comprising decimating the squared signals before analysis.

14. The method of claim 13, wherein the decimation comprises filtering each squared signal through a low-pass filter to produce a plurality of narrow-band samples, each narrow-band sample comprising a plurality of sinusoidal components.

15. The method of claim 10, further comprising concatenating the squared signals to produce a concatenated signal.

16. The method of claim 10, further comprising auto-correlating the squared signal before analysis to produce an auto-correlated signal.

17. The method of claim 16, wherein the auto-correlation comprises emphasizing sinusoidal carriers and concentrating noise-energy in a zero time-shift component.

18. The method of claim 17, further comprising removing the zero time-shift component from the auto-correlated signal.

19. The method of claim 10, further comprising transmitting the satellite identifier and the pseudoranging pulse.

20. The method of claim 10, further comprising compensating each signal for a plurality of frequency offsets to produce a plurality of compensated signals.

21. The method of claim 10, further comprising retrieving ephemeris data associated with particular satellites;

and

calculating a location based on a plurality of pseudoranges and ephemeris data.

22. The method of claim 10, further comprising compensating the compensated signal for time compression to produce a time-shifted signal.

23. The method of claim 10, further comprising selecting a candidate satellite identifier signal from a list of known satellite identifier signals;

multiplying the compensated signal by the candidate satellite identifier signal to produce a multiplied sample;

calculating an inverse Fourier transform of the multiplied sample to produce a candidate time series;

identifying a pseudoranging pulse component of the candidate time series; and

associating the pseudoranging pulse with the satellite identifier signal and an associated particular satellite.

24. The method of claim 10, further comprising additively stacking each of a plurality of compensated signals to produce a plurality of stacked signals.

25. 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.

26. The system of claim 25, wherein the analysis is by Fourier transform.

27. The method of claim 25, wherein the analysis is by Fast Fourier Transform.

28. The system of claim 25, further comprising a means for decimating the squared signals before analysis.

29. The method of claim 28, wherein the means for decimation comprises a means for filtering each squared signal through a low-pass filter to produce a plurality of narrow-band samples, each narrow-band sample comprising a plurality of sinusoidal components.

30. The method of claim 25, further comprising a means for concatenating the squared signal before analysis to produce a concatenated signal.

31. The method of claim 25, further comprising a means for auto-correlating the squared signal before analysis to produce an auto-correlated signal.

32. The system of claim 31, wherein the means for auto-correlation comprises a means for emphasizing sinusoidal carriers and concentrating noise-energy in a zero time-shift component.

33. The system of claim 32, further comprising a means for removing the zero time-shift component from the auto-correlated signal.

34. The system of claim 25, further comprising a wireless device configured to house the digitizing, squaring, analyzing, and scaling means.

35. The system of claim 25, further comprising an attachment coupled to a wireless device, the attachment configured to house the digitizing, squaring, analyzing, and scaling means.

36. 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.

37. The system of claim 36, wherein the analysis is by Fourier transform.

38. The system of claim 36, wherein the analysis is by Fast Fourier Transform.

39. The system of claim 36, further comprising a means for decimating the squared signals before analysis.

40. The system of claim 39, wherein the means for decimation comprises a means for filtering each squared signal through a low-pass filter to produce a plurality of narrow-band samples, each narrow-band sample comprising a plurality of sinusoidal components.

41. The system of claim 36, further comprising a means for concatenating the squared signal before analysis to produce a concatenated signal.

42. The system of claim 36, further comprising a means for auto-correlating the squared signal before analysis to produce an auto-correlated signal.

43. The system of claim 42, wherein the means for auto-correlation comprises a means for emphasizing sinusoidal carriers and concentrating noise-energy in a zero time-shift component.

44. The system of claim 43, further comprising a means for removing the zero time-shift component from the auto-correlated signal.

45. The system of claim 36, further comprising a means for transmitting the satellite identifier and the pseudoranging pulse.

46. The system of claim 36, further comprising a means for compensating each signal for a plurality of frequency offsets to produce a plurality of compensated signals.

47. The system of claim 36, further comprising a means for retrieving ephemeris data associated with the particular satellites;

and

a means for calculating a location based on a plurality of pseudoranges and ephemeris data.

48. The system of claim 36, further comprising a means for compensating the compensated signal for time compression to produce a time-shifted signal.

49. The system of claim 36, further comprising a means for selecting a candidate satellite identifier signal from a list of known satellite identifier signals;

a means for multiplying the compensated signal by the candidate satellite identifier signal to produce a multiplied sample;

a means for calculating an inverse Fourier transform of the multiplied sample to produce a candidate time series;

a means for identifying a pseudoranging pulse component of the candidate time series; and

a means for associating the pseudoranging pulse with the satellite identifier signal and an associated particular satellite.

50. The system of claim 36, further comprising a means for additively stacking each of a plurality of compensated signals to produce a plurality of stacked signals.

51. 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.

52. The system of claim 51, wherein the analysis is by Fourier transform.

53. The system of claim 51, wherein the analysis is by Fast Fourier Transform.

54. The system of claim 51, the logic further operable to decimate the squared signals before analysis.

55. The system of claim 54, wherein the decimation comprises filtering each squared signal through a low-pass filter to produce a plurality of narrow-band samples, each narrow-band sample comprising a plurality of sinusoidal components.

56. The system of claim 51, the logic further operable to concatenate the squared signals to produce a concatenated signal.

57. The system of claim 51, the logic further operable to auto-correlate the squared signal to produce an auto-correlated signal.

58. The system of claim 57, wherein the auto-correlation comprises emphasizing sinusoidal carriers and concentrating noise-energy in a zero time-shift component.

59. The system of claim 58, the logic further operable to remove the zero time-shift component from the auto-correlated signal.

60. 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.