System and method to estimate the location of a receiver in a multi-path environment

• US 20040008139A1
• Filed: 09/06/2002
• Published: 01/15/2004
• Est. Priority Date: 09/07/2001
• Status: Active Grant

• Current Assignee: CSR Technology Incorporated (Qualcomm, Inc.)
• Original Assignee: SIRF Technology Incorporated (Qualcomm, Inc.)
• Inventors: Casadei, Stefano, Stone, Jesse, Roy, Benjamin Van, Mann, Wallace
• Granted Patent: US 7,030,814 B2
• Time in Patent Office: Days
• US Class Current: 342/451
• CPC Class Codes: G01S 11/10 using Doppler effect
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: G01S 19/42 Determining position
• CPC Class Codes: G01S 19/50 whereby the position solution is constrained to lie upon a particular curve or surface, e.g. for locomotives on railway tracks
• CPC Class Codes: G01S 19/52 Determining velocity

Abstract

System and method to determine the location of a receiver in a multipath environment are provided. The received signal is correlated with the reference signals associated with the transmitting sources. Each correlation function is processed to derive various types of signal constraints, such as probability densities and uncertainty regions or intervals. In some embodiments, these constraints are for the code-phases and the Doppler frequencies. These signal constraints are transformed into constraints on the receiver variables and then fused together into a unified receiver constraint. A-priori constraints, such as constraints on the location of the receiver or the timestamp, may be incorporated into the unified receiver constraint. Some embodiments estimate a location based also on the estimated Doppler frequency. The constraints used by the invention are based on models of multipath effects and are geared towards mitigating these effects. In one of these models, a probability density for code-phase is obtained by convolving a gaussian distribution with an exponential distribution that describes the extra delay introduced by multipath. Another approach is based on identifying outliers in the set of code-phases. In other approaches, uncertainty region constraints and probability densities are combined. The present invention achieves faster and more sensitive signal acquisition and higher location accuracy in multipath environment, without compromising performance in other environments.

Claims

1. A method for determining location information of a receiver in a multipath environment, the method comprising the steps of:

receiving a signal containing a plurality of location-determining signals associated with a plurality of signal sources, wherein each of said signal sources is associated with a reference signal;

correlating said signal with said plurality of reference signal to yield a plurality of correlation functions;

generating a signal constraint from each correlation function;

transforming said signal constraints into receiver constraints;

fusing said receiver constraints to yield a unified receiver constraint; and

determining said location information based on said unified receiver constraint.

2. The method of claim 1, wherein one of said signal constraints comprises a code-phase probability density based on an estimated code-phase value.

3. The method of claim 2, wherein said code-phase probability density is further based on a multipath probability and an average multipath delay.

4. The method of claim 1, wherein said fusing comprises multiplying together a plurality of multipath probability densities to yield a unified probability density.

5. The method of claim 4, wherein said determining location information comprises performing a maximum likelihood calculation with said unified probability density.

6. The method of claim 5, wherein said determining location information further comprises calculating a plurality of initial search points and performing a search from said initial search points.

7. The method of claim 6, further comprising discarding initial search points not contained in an uncertainty region.

8. The method of claim 3, wherein said multipath probability and said average multipath delay are based on a plurality of auxiliary variables.

9. The method of the previous claim, wherein said plurality of auxiliary variables comprises a signal-to-noise-ratio.

10. The method of claim 1, wherein said generating a signal constraint further comprises summing a multipath-free density and multipath-affected density.

11. The method of the previous claim, wherein said multipath-affected density is a convolution of a gaussian density with an exponential density.

12. The method of claim 4, wherein said plurality of probability densities comprises a plurality of a-priori probability densities.

13. The method of claim 2, wherein said code-phase probability density is a gaussian density based on a plurality of auxiliary variables and said fusing comprises performing a least-square estimation method.

14. The method of claim 2, wherein said signal constraint further comprises a doppler probability density based on an estimated doppler frequency value.

15. The method of claim 1, wherein said receiver constraint comprises a system of equations in said receiver variables.

16. The method of claim 15, wherein said system of equations comprises equations based on an estimated code-phase value and equations based on an estimated frequency value.

17. The method of the previous claim, wherein a receiver velocity variable is set to zero.

18. The method of claim 1, wherein one of said signal constraints comprises an uncertainty interval.

19. The method of claim 18, wherein said uncertainty interval depends on a plurality of auxiliary variables.

20. The method of claim 18, wherein said uncertainty interval is a code-phase uncertainty interval and is extended on one side to account for multipath effects.

21. The method of claim 19, wherein said code-phase uncertainty interval extends to infinity on one side.

22. The method of claim 1, wherein one of said signal constraints comprises a probability density and an uncertainty interval.

23. The method of claim 22, wherein generating a signal constraint further comprises truncating said probability density to said uncertainty interval, yielding a truncated probability density.

24. The method of claim 22, wherein said generating a signal constraint further comprises calculating a distance between an estimated code-phase value and said uncertainty interval and calculating a multipath probability by comparing said distance with a code-phase variance value.

25. The method of claim 22, wherein said generating a signal constraint further comprises calculating an integral of said probability density inside said uncertainty interval.

26. The method of claim 18, wherein said uncertainty interval accounts for multipath effects and is utilized for searching said location-determining signals.

27. The method of claim 1, wherein said signal constraint comprises a collection of probability densities.

28. The method of the previous claim, wherein said collection of probability densities is parameterized by a multipath probability.

29. The method of claim 27, wherein said collection of probability densities is parameterized by a multipath delay parameter.

30. The method of claim 1, further comprising selecting a probability density from a collection of probability densities.

31. The method of the previous claim, wherein each density in said collection of probability densities is associated with a set of non-outlier signal sources.

33. The method of claim 30, wherein said selecting a probability density is based on a chi-square statistical test.

35. The method of claim 12, wherein said a-priority probability densities comprise an a-priori probability density based on a round-trip delay information.

36. The method of claim 12, wherein said a-priority probability densities comprise an a-priori probability density based on a base-station sector information.

37. The method of claim 12, wherein said a-priority probability densities comprise an a-priori probability density based on an altitude information.

55. The method of claim 2, wherein said determining location information comprises calculating the mean value of said unified receiver constraint.

56. The method of claim 2, wherein said determining location information comprises calculating the mean value of said unified receiver constraint by means of a random sampling method.

32. The method of previous claim, wherein said selecting a probability density is based on a chi-square statistical test.

34. A method for determining velocity information of a receiver in a multipath environment, the method comprising the steps of:

receiving a signal containing a plurality of location-determining signals associated with a plurality of signal sources, wherein each of said signal sources is associated with a reference signal;

correlating said signal with said plurality of reference signal to yield a plurality of correlation functions;

generating a signal constraint from each correlation function;

transforming said signal constraints into receiver constraints;

fusing a plurality of receiver constraints to yield a unified receiver constraint; and

determining said velocity information based on said unified receiver constraint.

38. A location determining system for a multipath environment comprising:

a plurality of signal sources associated with a plurality of reference signals;

a receiver, receiving a signal containing a plurality of location-determining signals transmitted by said signal;

means for correlating said signal with said plurality of reference signal to yield a plurality of correlation functions;

means for generating a signal constraint from each correlation function;

means for transforming said signal constraints into receiver constraints;

means for fusing said receiver constraints to yield a unified receiver constraint; and

means for determining said location information based on said unified receiver constraint.

39. The system of claim 38, wherein one of said signal constraints comprises a code-phase probability density based on an estimated code-phase value.

40. The system of the claim 38, comprising means for performing a maximum likelihood calculation with said probability density.

41. The system of claim 40, wherein said means for performing a maximum likelihood calculation further comprises means for calculating a plurality of initial search points and means for performing a search from said initial search points.

42. The system of claim 38, wherein said signal constraint comprises a multipath-free density and a multipath-affected density.

43. The method of claim 39, wherein said signal constraint further comprises a doppler probability density based on an estimated doppler frequency value.

44. The system of claim 38, wherein said receiver constraint comprises a system of equations in said receiver variables, and wherein said system of equations comprises equations based on an estimated code-phase value and equations based on an estimated frequency value.

45. The system of claim 38, wherein said signal constraint comprises a code-phase uncertainty interval extended on one side to account for multipath effects.

46. The system of claim 38, wherein one of said signal constraints comprises a probability density and an uncertainty interval.

47. The system of claim 38, comprising means for searching said location-determining signals based on a code-phase uncertainty that accounts for multipath effects.

48. The system of claim 38, further comprising means for selecting a probability density from a collection of probability densities.

49. The system of claim 38, further comprising means for performing a chi-square statistical test and means for selecting a probability density based on said chi-square statistical test.

50. The system of claim 38, comprising means for providing a plurality of a-priori probability densities.

51. The system of claim 50, wherein said a-priority probability densities comprise an a-priori probability density based on a round-trip delay information.

52. The system of claim 50, wherein said a-priority probability densities comprise an a-priori probability density based on a base-station sector information.

53. The system of claim 50, wherein said a-priority probability densities comprise an a-priori probability density based on an altitude information.

54. A velocity determining system for a multipath environment comprising:

a plurality of signal sources associated with a plurality of reference signals;

a receiver, receiving a signal containing a plurality of location-determining signals transmitted by said signal;

means for correlating said signal with said plurality of reference signal to yield a plurality of correlation functions;

means for generating a signal constraint from each correlation function;

means for transforming said signal constraints into receiver constraints;

means for fusing said receiver constraints to yield a unified receiver constraint; and

means for determining said velocity information based on said unified receiver constraint.