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 6,498,585 B2
• Filed: 11/19/2001
• Issued: 12/24/2002
• 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:
  US09/989,906
• Publication Number:
  US 20020111739A1
• Time in Patent Office: 400 Days
• Field of Search: 375/148, 375/150, 375/200, 375/208, 375/343, 380/49, 342/357.12, 342/357.02, 342/357.05, 342/358, 342/357.07, 701/208, 701/209, 701/210, 701/213, 701/211, 701/212, 701/207, 701/214
• 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 determining the received frequency of a signal transmitted at a known frequency, comprising:

digitizing the received signal to produce a digitized signal;

squaring the digitized signal to produce a squared signal;

analyzing the squared signal for spectral components; and

scaling the spectral components to identify a frequency of the received signal.

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. The method of claim 1, wherein the received signals are Global Positioning System (GPS) signals.

11. A system for determining the frequency of a received signal, comprising:

a means for digitizing the received 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; and

a means for scaling the spectral components to identify a frequency of the received signal.

12. The system of claim 11, wherein the analysis is by Fourier transform.

13. The system of claim 11, wherein the analysis is by Fast Fourier Transform.

14. The system of claim 11, further comprising a means for decimating the squared signals before analysis.

15. The system of claim 14, 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.

16. The system of claim 11, further comprising a means for concatenating the squared signals before analysis to produce a concatenated signal.

17. The system of claim 11, further comprising a means for auto-correlating the squared signal before analysis to produce an auto-correlated signal.

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

19. The system of claim 17, further comprising a means for removing the zero time-shift component from the auto-correlated signal.

20. The system of claim 11, wherein the received signals are Global Positioning System (GPS) signals.

21. The system of claim 11, further comprising a wireless device configured to house the digitizing, squaring, analyzing, and scaling means.

22. The system of claim 11, further comprising an attachment coupled to a wireless device, the attachment configured to house the digitizing, squaring, analyzing, and scaling means.

23. A system, comprising:

logic embedded on a computer readable medium; and

the logic operable to digitize a received signal to produce a digitized signal, square the digitized signal to produce a squared signal, analyze the squared signal for spectral components, and scale the spectral components to identify a frequency of the received signal.

24. The system of claim 23, wherein the analysis is by Fourier transform.

25. The system of claim 23, wherein the analysis is by Fast Fourier Transform.

26. The system of claim 23, the logic further operable to decimate the squared signals before analysis.

27. The system of claim 26, 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.

28. The system of claim 23, the logic further operable to concatenate the squared signals before analysis to produce a concatenated signal.

29. The system of claim 23, the logic further operable to auto-correlate the squared signal before analysis to produce an auto-correlated signal.

30. The system of claim 29, wherein the auto-correlation comprises emphasizing sinusoidal carriers and concentrating noise-energy in a zero time-shift component.

31. The system of claim 30, the logic further operable to remove the zero time-shift component from the auto-correlated signal.

32. The system of claim 23, wherein the received signals are Global Positioning System (GPS) signals.