Phase multi-path mitigation

• US 7,453,925 B2
• Filed: 10/18/2004
• Issued: 11/18/2008
• Est. Priority Date: 10/18/2004
• Status: Active Grant

• Current Assignee: Deere & Company
• Original Assignee: Navcom Technology, Inc. (Deere & Company)
• Inventors: Knight, Eugene Jerry, Keegan, Richard Gerald
• Primary Examiner(s): Liu; Shuwang
• Assistant Examiner(s): Perez; James M
• Application Number:
  US10/968,632
• Publication Number:
  US 20060083293A1
• Time in Patent Office: 1,492 Days
• Field of Search: 367/38, 367/43, 375/130, 375/140, 375147-153, 375/316, 375/322, 375/324, 375/328, 375/377, 375148-149, 375/354, 375/371, 342/357.06
• US Class Current: 375/148
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence

Abstract

A system and method for mitigating a multi-path-induced error in a global navigation satellite system (GNSS) is described. In one embodiment of the method, a composite signal is received. The composite signal includes a band-limited direct-path signal and at least one band-limited multi-path signal that are each modulated with periodic phase reversals. The composite signal is measured as a function of time during a time interval having at least one of the periodic phase reversals. A phase error φ_ε between the composite signal and the direct-path signal due to the multi-path signal is determined using the measured composite signal as a function of time and a pre-determined filter characteristic corresponding to a filter used to band limit the direct-path signal and the multi-path signal. The phase error φ_ε in a navigation computation is corrected.

Claims

1. A method of mitigating the effect of a multi-path-induced error in a global navigation satellite system (GNSS), comprising:

receiving a composite signal, including a band-limited direct-path signal and at least one band-limited multi-path signal, wherein the direct-path signal and the multi-path signal are modulated with periodic phase reversals;

measuring the composite signal as a function of time during a time interval having at least one of the periodic phase reversals;

determining a phase error φ

_ε

between the composite signal and the direct-path signal due to the multi-path signal in accordance with the measured composite signal as a function of time and a pre-determined filter characteristic of one or more filters in the GNSS that are used to band limit the direct-path signal and the multi-path signal;

wherein the determining is responsive to phase errors corresponding to time delays of the multi-path signal relative to the direct-path signal that are shorter than a filter step response time of the one or more filters used to band limit the direct-path signal and the multi-path signal; and

correcting for the phase error φ

_ε

.

2. The method of claim 1, further comprising determining a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal, and correcting an error in a pseudo-range corresponding to the time error Δ

t.

3. The method of claim 1, wherein measuring the composite signal further comprises measuring in-phase I and quadrature Q components of the composite signal.

4. The method of claim 1, wherein the direct-path signal and the multi-path signal include a Global Positioning System L-band carrier signal.

5. The method of claim 1, wherein the direct-path signal and the multi-path signal are encoded using a spread-spectrum pseudo-random-noise code.

6. The method of claim 1, wherein the global navigation satellite system (GNSS) is selected from the group consisting of a Global Positioning System (GPS), a Global Orbiting Navigation Satellite System (GLONASS), a GALILEO positioning system, a European Geostationary Navigation Overlay System (EGNOS), a Wide Area Augmentation System (WAAS), a Multifunctional Transport Satellite-Based Augmentation System (MSAS) and a Quasi-Zenith Satellite System (QZSS).

7. The method of claim 1, wherein the filter step response time of the one or more filters is less than or equal to 200 ns.

8. The method of claim 1, wherein the filter step response time of the one or more filters is less than or equal to 1 μ

s.

9. The method of claim 1, wherein the filter step response time of the one or more filters is between 40 ns and 200 ns.

10. The method of claim 1, further comprising mitigating a multi-path-induced error using a technique selected from the group consisting of a double-delta correction, a strobed correlator and a pulse-aperture correlator.

11. The method of claim 1, further comprising determining an amplitude of the direct-path signal, an amplitude of the multi-path signal, a phase difference φ

_m between the direct-path signal and the multi-path signal, and a time delay δ

of the multi-path signal relative to the direct-path signal in accordance with a filter step response, a measured amplitude of the composite signal and the measured composite signal as a function of time.

12. The method of claim 1, further comprising determining a phase difference φ

_m between the direct-path signal and the multi-path signal in accordance with a filter step response, a measured amplitude of the composite signal and the measured composite signal as a function of time.

13. The method of claim 1, wherein a first procedure determines a first set of parameters including a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal, and a phase φ

_3rd equal to 180°

minus the sum of the phase error φ

_ε

and a phase difference φ

_m between the direct-path signal and the multi-path signal.

14. The method of claim 13, wherein the first set of parameters are determined using a least-squares fitting process.

15. The method of claim 13, wherein a second procedure determines a second set of parameters including an amplitude of the direct-path signal, an amplitude of the multi-path signal, and the phase error φ

_ε

, from which the phase difference φ

_m can be determined using the phase φ

_3rd.

16. The method of claim 15, wherein the second set of parameters are determined from a least-squares fitting process.

17. A device that mitigates the effect of a multi-path-induced error in a global navigation satellite system (GNSS), comprising:

a receiver that receives a composite signal, including a band-limited direct-path signal and at least one band-limited multi-path signal, wherein the direct-path signal and the multi-path signal are modulated with periodic phase reversals;

a measurement mechanism that samples the composite signal as a function of time during a time interval having at least one of the periodic phase reversals;

a processor;

a memory including at least one program module that is executed by the processor, the at least one program module containing instructions for determining a phase error φ

^ε

between the composite signal and the direct-path signal due to the multi-path signal in accordance with the measured composite signal as a function of time and a pre-determined filter characteristic of one or more filters in the GNSS that are used to band limit the direct-path signal and the multi-path signal;

wherein the determining is responsive to phase errors corresponding to time delays of the multi-path signal relative to the direct-path signal that are shorter than a filter step response time of the one or more filters used to band limit the direct-path signal and the multi-path signal; and

wherein the device is configured to correct for the phase error φ

_ε

.

18. The device of claim 17, wherein the measurement mechanism samples the composite signal while the device is synchronized with a carrier signal and a code signal.

19. The device of claim 17, the at least one program module further containing instructions for determining a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal, and correcting an error in a pseudo-range corresponding to the time error Δ

t.

20. The device of claim 17, wherein the measurement mechanism measures in-phase I and quadrature Q components of the composite signal.

21. The device of claim 17, wherein the direct-path signal and the multi-path signal include a Global Positioning System L-band carrier signal.

22. The device of claim 17, wherein the code comprises a spread-spectrum pseudo-random-noise code.

23. The device of claim 17, wherein the global navigation satellite system (GNSS) is selected from the group consisting of a Global Positioning System (GPS), a Global Orbiting Navigation Satellite System (GLONASS), a GALILEO positioning system, a European Geostationary Navigation Overlay System (EGNOS), a Wide Area Augmentation System (WAAS), a Multifunctional Transport Satellite-Based Augmentation System (MSAS) and a Quasi-Zenith Satellite System (QZSS).

24. The device of claim 19, wherein the filter step response time of the one or more filters is less than or equal to 200 ns.

25. The device of claim 19, wherein the filter step response time of the one or more filters r is less than or equal to 1 μ

s.

26. The device of claim 19, wherein the filter step response time of the one or more filters is between 40 and 200 ns.

27. The device of claim 17, the at least one program module further containing instructions for mitigating a multi-path-induced error using a technique selected from the group consisting of a double-delta correction, a strobed correlator and a pulse-aperture correlator.

28. The device of claim 17, the at least one program module further containing instructions for determining an amplitude of the direct-path signal, an amplitude of the multi-path signal, a phase difference φ

_m between the direct-path signal and the multi-path signal, and a time delay δ

of the multi-path signal relative to the direct-path signal in accordance with a filter step response of the one or more filters, a measured amplitude of the composite signal and the measured composite signal as a function of time.

29. The device of claim 17, the at least one program module further containing instructions for determining a phase difference φ

_m between the direct-path signal and the multi-path signal in accordance with a filter step response, a measured amplitude of the composite signal and the measured composite signal as a function of time.

30. The device of claim 17, the at least one program module further containing instructions for a first procedure that determines a first set of parameters including a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal, and a phase φ

_3rd equal to 180 °

minus the sum of the phase error φ

_ε

and the phase difference φ

_m between the direct-path signal and the multi-path signal.

31. The device of claim 30, wherein the first set of parameters are determined using a least-squares fitting process.

32. The device of claim 30, wherein the at least one program module further containing instructions for a second procedure that determines a second set of parameters including an amplitude of the direct-path signal, an amplitude of the multi-path signal and the phase error φ

_ε

, from which the phase difference φ

_m can be determined using the phase φ

_3rd.

33. The device of claim 32, wherein the second set of parameters are determined from a least-squares fitting process.

34. A device that mitigates the effect of a multi-path-induced error in a global navigation satellite system (GNSS), comprising:

a receiving means that receives a composite signal, including a band-limited direct-path signal and at least one band-limited multi-path signal, wherein the direct-path signal and the multi-path signal are modulated with periodic phase reversals;

a measurement means that samples the in-phase I and quadrature Q components of the composite signal as a function of time during a time interval having at least one of the periodic phase reversals;

a processor means;

a memory means including at least one program module that is executed by the processor, the at least one program module containing instructions for;

determining an amplitude of the direct-path signal;

determining an amplitude of the multi-path signal;

determining a phase difference φ

_m between the direct-path signal and the multi-path signal;

determining a time delay δ

of the multi-path signal relative to the direct-path signal; and

determining the phase error φ

_ε

between the composite signal and the direct-path signal due to the multi-path signal,

wherein the determining operations are in accordance with a pre-determined filter step response of one or more filters in the GNSS used to band limit the direct-path signal and the multi-path signal, a measured amplitude of the composite signal and the measured in-phase I and quadrature Q components of the composite signal as a function of time, wherein the determining is responsive to phase errors corresponding to time delays of the multi-path signal relative to the direct-path signal that are shorter than the filter step response time of the one or more filters, and wherein the device is configured to correct for the phase error φ

_ε

.

35. The device of claim 34, wherein the global navigation satellite system (GNSS) is selected from the group consisting of a Global Positioning System (GPS), a Global Orbiting Navigation Satellite System (GLONASS), a GALILEO positioning system, a European Geostationary Navigation Overlay System (EGNOS), a Wide Area Augmentation System (WAAS), a Multifunctional Transport Satellite-Based Augmentation System (MSAS) and a Quasi-Zenith Satellite System (QZSS).

36. A method of mitigating the effect of a multi-path-induced error in a global navigation satellite system (GNSS), comprising:

receiving a composite signal, including a band-limited direct-path signal and at least one band-limited multi-path signal, wherein the direct-path signal and the multi-path signal are modulated with periodic phase reversals;

measuring the composite signal as a function of time during a time interval having at least one of the periodic phase reversals;

determining a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal, in accordance with the measured composite signal as a function of time and a pre-determined filter characteristic of one or more filters in the GNSS used to band limit the direct-path signal and the multi-path signal;

wherein the determining is responsive to phase errors corresponding to time delays of the multi-path signal relative to the direct-path signal that are shorter than a filter step response time of the one or more filters used to band limit the direct-path signal and the multi-path signal; and

correcting for an error in a pseudo-range corresponding to the time error Δ

t.

37. The method of claim 36, wherein measuring the composite signal further comprises measuring in-phase I and quadrature Q components of the composite signal.

38. The method of claim 36, wherein the direct-path signal and the multi-path signal include a Global Positioning System L-band carrier signal.

39. The method of claim 36, wherein a first procedure determines a first set of parameters including the time error Δ

t and a phase φ

_3rd equal to 180 °

minus the sum of a phase error φ

_ε

between the composite signal and the direct-path signal due to the multi-path signal and a phase difference φ

_m between the direct-path signal and the multi-path signal.

40. The method of claim 39, wherein the first set of parameters are determined using a least-squares fitting process.

41. A device that mitigates the effect of a multi-path-induced error in a global navigation satellite system (GNSS), comprising:

a receiver that receives a composite signal, including a band-limited direct-path signal and at least one band-limited multi-path signal, wherein the direct-path signal and the multi-path signal are modulated with periodic phase reversals;

a measurement mechanism that samples the composite signal as a function of time during a time interval having at least one of the periodic phase reversals;

a processor;

memory including at least one program module that is executed by the processor, the at least one program module containing instructions for determining a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal, in accordance with the measured composite signal as a function of time and a pre-determined filter characteristic of one or more filters in the GNSS used to band limit the direct-path signal and the multi-path signal;

wherein the determining is responsive to phase errors corresponding to time delays of the multi-path signal relative to the direct-path signal that are

shorter than a filter step response time of the one or more filters used to band limit the direct-path signal and the multi-path signal; and

wherein the device is configured to correct for in an error corresponding to the time error Δ

t in a pseudo-range.

42. The device of claim 41, wherein the measurement mechanism samples the composite signal while the device is synchronized with a carrier signal and a code signal.

43. The device of claim 41, wherein the measurement mechanism measures in phase I and quadrature Q components of the composite signal.

44. The device of claim 41, wherein the direct-path signal and the multi-path signal include a Global Positioning System L-band carrier signal.

45. The device of claim 41, the at least one program module further containing instructions for a first procedure that determines a first set of parameters including the time error Δ

t and a phase φ

_3rd equal to 180°

minus the sum of the phase error φ

_ε

between the composite signal and the direct-path signal due to the multi-path signal and the phase difference φ

_m between the direct-path signal and the multi-path signal.

46. The device of claim 45, wherein the first set of parameters are determined using a least-squares fitting process.

47. A device that mitigates the effect of a multi-path-induced error in a global navigation satellite system (GNSS), comprising:

a receiving means that receives a composite signal, including a band-limited direct-path signal and at least one band-limited multi-path signal, wherein the direct-path signal and the multi-path signal are modulated with periodic phase reversals;

a measurement means that samples the in-phase I and quadrature Q components of the composite signal as a function of time during a time interval having at least one of the periodic phase reversals;

a processor means;

a memory means including at least one program module that is executed by the processor, the at least one program module containing instructions for;

determining a time error Δ

t, the time error Δ

t corresponding to a difference between an actual phase reversal time including the effect of the multi-path signal and a phase reversal time without the effect of the multi-path signal;

wherein the determining operation is in accordance with a pre-determined filter step response corresponding to one or more filters in the GNSS that are used to band limit the direct-path signal and the multi-path signal, a measured amplitude of the composite signal and the measured in-phase I and quadrature Q components of the composite signal as a function of time, wherein the determining is responsive to phase errors corresponding to time delays of the multi-path signal relative to the direct-path signal that are shorter than the filter step response time of the one or more filters, and wherein the device is configured to correct for an error corresponding to the time error Δ

t in a pseudo-range.

48. The device of claim 47, wherein the global navigation satellite system (GNSS) is selected from the group consisting of a Global Positioning System (GPS), a Global Orbiting Navigation Satellite System (GLONASS), a GALILEO positioning system, a European Geostationary Navigation Overlay System (EGNOS), a Wide Area Augmentation System (WAAS), a Multifunctional Transport Satellite-Based Augmentation System (MSAS) and a Quasi-Zenith Satellite System (QZSS).