Global positioning system receiver for monitoring the satellite transmissions and for reducing the effects of multipath error

• US 6,347,113 B1
• Filed: 11/09/1999
• Issued: 02/12/2002
• Est. Priority Date: 03/12/1999
• Status: Expired due to Term

• Current Assignee: Deere & Company
• Original Assignee: Navcom Technology, Inc. (Deere & Company)
• Inventors: Hatch, Ronald R.
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US09/437,108
• Time in Patent Office: 826 Days
• Field of Search: 375/147, 375/142, 375/145, 375/149, 375/150, 375/355, 375/346, 375/343, 342/357, 342/342
• US Class Current: 375/149
• CPC Class Codes: G01S 19/22 Multipath-related issues
• CPC Class Codes: G01S 19/30 code related G01S19/246 takes precedence
• CPC Class Codes: H04B 1/7085 using a code tracking loop, e.g. a delay-locked loop
• CPC Class Codes: H04B 1/709 Correlator structure

Abstract

A Global Positioning System receiver includes an intermediate frequency (IF) processor configured to downconvert broadcast signal to generate a first channel signal which is further downconverted to recover a PRN signal by an angle rotator. The receiver further includes a signal generator configured to generate N gated PRN signals. The N gated PRN signals are generated based on a local replica PRN signal time-divided by M intervals within a chip period of the local replica PRN signal. N and M are positive integers. A number of correlators is also provided. Each of which the correlators are configured to multiply a respective one of N gated PRN signals with the PRN signal to generate a number of correlation values. The correlation values are utilized to monitor distortions in the broadcast signal and/or to track the PRN signal with the local replica PRN signal. Further, methods of monitoring and/or tracking the PRN signal with the local replica PRN signal by utilizing the correlation values are also provided.

Claims

1. An apparatus for tracking an input signal, comprising:

a local signal generator configured to generate a local replica signal of the input signal;

a gated signal generator coupled to the local signal generator and configured to generate N gated signals, wherein the N gated signals are generated based on the local replica signal time-divided by M intervals within a chip period of the local replica signal, N and M are positive integers, and each of the gated signals has a time varying value within each chip period of the local replica signal;

a plurality of correlators configured to multiply the N gated signals with the input signal to generate a plurality of correlation values; and

a processor coupled to the local signal generator configured to adjust timing of the local replica signal based on the correlation values in order to accurately track the input signal with the local replica signal.

2. The apparatus according to claim 1 wherein each gated signal is associated with a respective one of the M intervals, and wherein each gated signal has a time varying value within the associated one of the M intervals and has a constant zero value in all other ones of the M intervals.

3. The apparatus according to claim 2 wherein a first gated signal among the N gated signals is associated with a first interval of the M intervals,

a second gated signal among the N gated signals is associated with a second interval of the M intervals,

the first and second intervals are located before and after a first transition point, respectively, and

the first transition point is a starting point of each chip period.

4. The apparatus according to claim 3 wherein

a first correlator among the plurality of correlators is configured to multiply the first gated signal with the input signal to generate a first correlation value among the N correlation values, and

a second correlator among the plurality of correlators is configured to multiply the second gated signal with the input signal to generate a second correlation value among the N correlation values.

5. The apparatus according to claim 4 wherein the processor is further configured to adjust timing of the local replica signal based on a sum of the first and second correlation values.

6. The apparatus according to claim 4 wherein the first and the second intervals are located closest to the first transition point among intervals located before and after the first transition point, respectively.

7. The apparatus according to claim 6 wherein

a third gated signal among the N gated signals is associated with a third interval of the M intervals, and

a fourth gated signal among the N gated signals is associated with a fourth interval of the M intervals,

the third and fourth intervals are second closest intervals to the first transition point among intervals located before and after the transition point, respectively,

a third correlator among the plurality of correlators is configured to multiply the third gated signal with the input signal to generate a third correlation value among the N correlation values, and

a fourth correlator among the plurality of correlators is configured to multiply the fourth gated signal with the input signal to generate a fourth correlation value among the N correlation values.

8. The apparatus according to claim 7 wherein the processor is further configured to adjust timing of the local replica signal based on a sum of the first and second correlation values subtracted by a sum of the third and fourth correlation values.

9. The apparatus according to claim 7 wherein N is equal to M.

10. The apparatus according to claim 9 wherein the processor is further configured to adjust timing of the local replica signal based on a sum of the N correlation values.

11. The apparatus according to claim 7 wherein a fifth gated signal among the N gated signals is associated with a fifth interval of the M intervals,

a sixth gated signal among the N gated signals is associated with a sixth interval of the M intervals,

a seventh gated signal among the N gated signals is associated with a seventh interval of the M intervals,

an eighth gated signal among the N gated signals is associated with an eighth interval of the M intervals,

the fourth and the fifth intervals are located closest to a second transition point among intervals located before and after the second transition point, respectively,

the third and fourth intervals are second closest intervals to the second transition point among M intervals located before and after the second transition point, respectively, and

the second transition point is a starting point of a previous chip period that occurs one chip period before a current chip period.

12. The apparatus according to claim 11 wherein

a fifth correlator among the plurality of correlators is configured to multiply the fifth gated signal with the input signal to generate a fifth correlation value among the N correlation values,

a sixth correlator among the plurality of correlators is configured to multiply the sixth gated input signal with the input signal to generate a sixth correlation value among the N correlation values,

a seventh correlator among the plurality of correlators is configured to multiply the seventh gated signal with the input signal to generate a seventh correlation value among the N correlation values, and

an eighth correlator among the plurality of correlators is configured to multiply the eighth gated signal with the input signal to generate an eighth correlation value among the N correlation values.

13. The apparatus according to claim 12 wherein the processor is further configured to adjust timing of the local replica signal based on a sum of the fifth and sixth correlation values subtracted by a sum of the seventh and eighth correlation values.

14. An apparatus for processing at least one satellite-based navigation broadcast signal that includes a carrier frequency signal modulated by a Pseudo Random Code (PRN) signal, comprising:

an intermediate frequency (IF) processor configured to downconvert the broadcast signal to generate a first channel signal;

an angle rotator configured to further downconvert the first channel signal, to thereby recover the PRN signal from the broadcast signal;

a signal generator configured to generate N gated PRN signals, wherein the N gated PRN signals are generated based on a local replica PRN signal time-divided by M intervals within a chip period of the local replica PRN signal, N and M are positive integers, and each of the gated signals has a time varying value within each chin period of the local replica signal; and

a first plurality of correlators each of which is configured to multiply a respective one of N gated PRN signals with a first phase signal of the PRN signal to generate a first plurality correlation values.

15. The apparatus according to claim 14 further comprising:

a first processor configured to adjust timing of the local replica PRN signal based on the first plurality of correlation values in order to accurately track the PRN signal with the local replica PRN signal.

16. The apparatus according to claim 15 further comprising:

a C/A code generator coupled to the processor and the first signal generator, wherein the PRN signal is a C/A code signal of the broadcast signal and the C/A code generator is configured to generate the local replica PRN signal.

17. The apparatus according to claim 15 further comprising:

a P code generator coupled to the processor and the first signal generator, wherein the PRN signal is a P code signal of the broadcast signal and the P code generator is configured to generate the local replica PRN signal.

23. The apparatus according to claim 15 wherein M is equal to one of the values of ten (10) and forty (40).

24. The apparatus according to claim 15 wherein the chip period is equally divided into M equal intervals.

25. The apparatus according to claim 15 wherein each N gated PRN signal is associated with one of the M intervals, and

wherein each N gated PRN signal has a time varying value within the associated one of the M intervals and has a constant zero value in all other ones of the M intervals.

26. The apparatus according to claim 25 wherein each N gated PRN signal has the time varying value within the associated one of the M intervals only when the local replica PRN signal changes its value at a first transition point, wherein the first transition point is a starting point of each chip period.

27. The apparatus according to claim 25 wherein each N gated PRN signal has the time varying value within the associated one of the M intervals only when the local replica PRN signal does not change its value at a first transition point, wherein the first transition point is a starting point of each chip period.

28. The apparatus according to claim 25 wherein a first gated PRN signal among the N gated PRN signals is associated with a first interval of the M intervals, and

a second gated PRN signal among the N gated PRN signals is associated with a second interval of the M intervals,

wherein the first and second intervals are located before and after a first transition point, respectively, and the first transition point is a starting point of each chip period.

29. The apparatus according to claim 28 wherein

a first correlator among the first set of N correlators is configured to multiply the first gated PRN signal with the PRN signal to generate a first correlation value among the first plurality of correlation values, and

a second correlator among the first set of N correlators is configured to multiply the second gated PRN signal with the PRN signal to generate a second correlation value among the first plurality of correlation values.

30. The apparatus according to claim 29 wherein the processor is further configured to adjust timing of the local replica PRN signal based on a sum of the first and second correlation values.

31. The apparatus according to claim 29 wherein the first and the second intervals are located closest to the first transition point among intervals located before and after the transition point, respectively.

32. The apparatus according to claim 31 wherein

a third gated PRN signal among the N gated PRN signals is associated with a third interval of the M intervals, and

a fourth gated PRN signal among the N gated PRN signals is associated with a fourth interval of the M intervals,

the third and fourth intervals are second closest intervals to the second transition point among intervals located before and after the transition point, respectively,

a third correlator among the first set of N correlators is configured to multiply the third gated PRN signal with the PRN signal to generate a third correlation value among the first plurality of correlation values, and

a fourth correlator among the first set of N correlators is configured to multiply the fourth gated PRN signal with the PRN signal to generate a fourth correlation value among the first plurality of correlation values.

33. The apparatus according to claim 32 wherein the processor is further configured to adjust timing of the local replica PRN signal based on a sum of the first and second correlation values subtracted by a sum of the third and fourth correlation values.

34. The apparatus according to claim 25 wherein N is equal to M.

35. The apparatus according to claim 34 wherein the processor is further configured to adjust timing of the local replica PRN signal based on a sum of the first plurality of correlation values.

36. The apparatus according to claim 25 wherein a fifth gated PRN signal among the N gated PRN signals is associated with a fifth interval of the M intervals,

a sixth gated PRN signal among the N gated PRN signals is associated with a sixth interval of the M intervals,

a seventh gated PRN signal among the N gated PRN signals is associated with a seventh interval of the M intervals,

an eighth gated PRN signal among the N gated PRN signals is associated with an eighth interval of the M intervals,

the fourth and the fifth intervals are located closest to a second transition point among M intervals located before and after the second transition point, respectively,

the third and fourth intervals are second closest intervals to the second transition point among M intervals located before and after the second transition point, respectively, and

the second transition point is a starting point of a previous chip period that occurs one chip period before a current chip period.

37. The apparatus according to claim 36 wherein

a fifth correlator among the N correlators is configured to multiply the fifth gated PRN signal with the PRN signal to generate a fifth correlation value among the first plurality of correlation values,

a sixth correlator among the N correlators is configured to multiply the sixth gated PRN signal with the PRN signal to generate a sixth correlation value among the first plurality of correlation values,

a seventh correlator among the N correlators is configured to multiply the seventh N gated PRN signal with the PRN signal to generate a seventh correlation value among the first plurality of correlation values, and

an eighth correlator among the N correlators is configured to multiply the eighth gated PRN signal with the PRN signal to generate an eighth correlation value among the first plurality of correlation values.

38. The apparatus according to claim 37 wherein the processor is further configured to adjust timing of the local replica PRN signal based on a sum of the fifth and sixth correlation values subtracted by a sum of the seventh and eighth correlation values.

39. The apparatus according to claim 25 further including a second plurality correlators each of which is configured to multiply the N gated PRN signals with a second phase signal of the PRN signal to generate a second plurality of correlation values.

40. The apparatus according to claim 39 wherein

a third gated PRN signal among the N gated PRN signals is associated with a third interval of the M intervals,

a fourth gated PRN signal among the N gated PRN signals is associated with a fourth interval of the M intervals,

the third and fourth intervals are second closest intervals to a first transition point among M intervals located before and after the fourth transition point, respectively, wherein the first transition point is a starting point of each chip period,

a third correlator among the first plurality of correlators is configured to multiply the third N gated PRN signal with the first phase signal of the PRN signal to generate a third correlation value among the first plurality of correlation values,

a fourth correlator among the first plurality of correlators is configured to multiply the fourth N gated PRN signal with the first phase signal of the PRN signal to generate a fourth correlation value among the first plurality of correlation values,

a first correlator among the second plurality of correlators is configured to multiply the third N gated PRN signal with the second phase signal of the PRN signal to generate a first correlation value among the second plurality of correlation values, and

a second correlator among the second plurality of correlators is configured to multiply the fourth N gated PRN signal with the second phase signal of the PRN signal to generate a second correlation value among the second plurality of correlation values.

41. The apparatus according to claim 40 further comprising:

a second transition-product-memory means coupled to the processor configured to receive the third and fourth correlation values among the first plurality of correlation values and, first and second correlation values from the second plurality of correlation values only when the local replica PRN signal changes its value at the first transition point and configured to store the received values as a first, second, third and fourth stored values respectively.

42. The apparatus according to claim 41 further comprising:

a carrier lock loop coupled to the angle rotator and configured to recover the carrier frequency signal based on, in part, the fourth stored value subtracted by the third stored value which is then divided by a result of the first stored value subtracted by the second stored value.

43. The apparatus according to claim 25 wherein the M is an even integer number, and a first half and a second half of the M intervals are located before and after a first transition point, respectively, and the first transition point is a starting point of each chip period.

44. The apparatus according to claim 43 wherein a pair of the N gated PRN signals associated with a pair among the M intervals equidistanced from the first transition point are added before being multiplied by a respective correlator among the first plurality of correlators.

45. The apparatus according to claim 14 further comprising:

a second processor configured to monitor for distortions in the broadcast signal based on a relationship among the first plurality of correlation values.

46. The apparatus according to claim 14 wherein the relationship among the first plurality of correlation values is an average value thereof.

18. An apparatus for processing at least one satellite-based navigation broadcast signal that includes a carrier frequency signal modulated by a Pseudo Random Code (PRN) signal, comprising:

an intermediate frequency (IF) processor configured to downconvert the broadcast signal to generate a first channel signal;

an angle rotator configured to further downconvert the first channel signal, to thereby recover the PRN signal from the broadcast signal;

a signal generator configured to generate N gated PRN signals, wherein the N gated PRN signals are generated based on a local replica PRN signal time-divided by M intervals within a chip period of the local replica PRN signal, and N and M are positive integers;

a first plurality of correlators each of which is configured to multiply a respective one of N gated PRN signals with a first phase signal of the PRN signal to generate a first plurality correlation values;

a first processor configured to adjust timing of the local replica PRN signal based on the first plurality of correlation values in order to accurately track the PRN signal with the local replica PRN signal; and

a memory device coupled to the N correlators and the processor, wherein the memory device includes;

a first transition-product-memory means configured to receive the first plurality of correlation values only when the local replica PRN signal changes its value at a first transition point and configured to store the received values,

wherein the first transition point is a starting point of each chip period.

19. The apparatus according to claim 18 wherein the processor is further configured to adjust timing of the local replica PRN signal based on the first plurality of correlation values stored in the first transition-product-memory means.

20. The apparatus according to claim 18 wherein the memory device comprises:

a product-memory means configured to receive the first plurality of correlation values only when the local replica PRN signal does not change its value at the first transition point and configured to store the received values.

21. The apparatus according to claim 20 wherein the processor is further configured to adjust timing of the local replica PRN signal based on the first plurality of correlation values stored in the product-memory means added to corresponding values stored in the first transition-product-memory means.

22. The apparatus according to claim 20 wherein the processor is further configured to adjust timing of the local replica PRN signal based on the first plurality of correlated values stored in the product-memory means subtracted by corresponding values stored in the first transition-product-memory means.

47. A method of tracking an input signal, comprising the steps of:

generating a local replica signal of the input signal;

generating N gated signals based on the local replica signal time-divided by M intervals within a chip period of the local replica signal, wherein N and M are positive integers, and each of the gated signals has a time varying value within each chip period of the local replica signal;

multiplying the N gated signals with the input signal to generate a plurality of correlation values; and

adjust timing of the local replica signal based on the correlation values in order to accurately track the input signal with the local replica signal.

48. The method according to claim 47 wherein each gated signal is associated with a respective one of the M intervals, and

wherein each gated signal has a time varying value within the associated one of the M intervals and has a constant zero value in all other ones of the M intervals.

49. The method according to claim 48 wherein a first gated signal among the N gated signals is associated with a first interval of the M intervals,

a second gated signal among the N gated signals is associated with a second interval of the M intervals,

the first and second intervals are located before and after a first transition point, respectively, and

the first transition point is a starting point of each chip period.

50. The method according to claim 49 wherein the multiplying step further comprises the steps of:

multiplying the first gated signal with the input signal to generate a first correlation value among the N correlation values, and

multiplying the second gated signal with the input signal to generate a second correlation value among the N correlation values.

51. The method according to claim 50 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica signal based on a sum of the first and second correlation values.

52. The method according to claim 50 wherein the first and the second intervals are located closest to the first transition point among intervals located before and after the first transition point, respectively.

53. The method according to claim 52 wherein

a third gated signal among the N gated signals is associated with a third interval of the M intervals, and

a fourth gated signal among the N gated signals is associated with a fourth interval of the M intervals,

the third and fourth intervals are second closest intervals to the first transition point among intervals located before and after the transition point, respectively, and

wherein the multiplying step further comprises the steps of:

multiplying the third gated signal with the input signal to generate a third correlation value among the N correlation values, and

multiplying the fourth gated signal with the input signal to generate a fourth correlation value among the N correlation values.

54. The method according to claim 53 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica signal based on a sum of the first and second correlation values subtracted by a sum of the third and fourth correlation values.

55. The method according to claim 48 wherein N is equal to M.

56. The method according to claim 55 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica signal based on a sum of the N correlation values.

57. The method according to claim 48 wherein a fifth gated signal among the N gated signals is associated with a fifth interval of the M intervals,

a sixth gated signal among the N gated signals is associated with a sixth interval of the M intervals,

a seventh gated signal among the N gated signals is associated with a seventh interval of the M intervals,

an eighth gated signal among the N gated signals is associated with an eighth interval of the M intervals,

the fourth and the fifth intervals are located closest to a second transition point among intervals located before and after the second transition point, respectively,

the third and fourth intervals are second closest intervals to the second transition point among M intervals located before and after the second transition point, respectively, and

the second transition point is a starting point of a previous chip period that occurs one chip period before a current chip period.

58. The method according to claim 57 wherein the multiplying step further comprises the steps of:

multiplying the fifth gated signal with the input signal to generate a fifth correlation value among the N correlation values,

multiplying the sixth gated input signal with the input signal to generate a sixth correlation value among the N correlation values,

multiplying the seventh gated signal with the input signal to generate a seventh correlation value among the N correlation values, and

multiplying the eighth gated signal with the input signal to generate an eighth correlation value among the N correlation values.

59. The method according to claim 58 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica signal based on a sum of the fifth and sixth correlation values subtracted by a sum of the seventh and eighth correlation values.

60. A method of processing at least one satellite-based navigation broadcast signal that includes a carrier frequency signal modulated by a Pseudo Random Code (PRN) signal, comprising the step of:

downconverting the broadcast signal, to thereby recover the PRN signal from the broadcast signal;

generating N gated PRN signals based on a local replica PRN signal time-divided by M intervals within a chip period of the local replica PRN signal, wherein N and M are positive integers, and each of the gated PRN signals has a time varying value within each chip period of the local replica PRN signal; and

multiplying the N gated PRN signals with a first phase signal of the PRN signal to generate a first plurality correlation values.

61. The method according to claim 60 further comprising the step of:

adjusting timing of the local replica PRN signal based on the first plurality of correlation values in order to accurately track the PRN signal with the local replica PRN signal.

62. The method according to claim 61 further comprising the step of:

generating a C/A code signal as the local replica PRN signal, wherein the PRN signal is a C/A code signal of the broadcast signal.

63. The method according to claim 61 further comprising the step of:

generating a P code signal as the local replica PRN signal, wherein the PRN signal is a P code signal of the broadcast signal.

69. The method according to claim 61 wherein M is equal to one of the values of ten (10) and forty (40).

70. The method according to claim 61 wherein the chip period is equally divided into M equal intervals.

71. The method according to claim 61 wherein each N gated PRN signal is associated with one of the M intervals, and

wherein each N gated PRN signal has a time varying value within the associated one of the M intervals and has a constant zero value in all other ones of the M intervals.

72. The apparatus according to claim 71 wherein each N gated PRN signal has the time varying value within the associated one of the M intervals only when the local replica PRN signal changes its value at a first transition point, wherein the first transition point is a starting point of each chip period.

73. The apparatus according to claim 71 wherein each N gated PRN signal has the time varying value within the associated one of the M intervals only when the local replica PRN signal does not change its value at a first transition point, wherein the first transition point is a starting point of each chip period.

74. The method according to claim 71 wherein a first gated PRN signal among the N gated PRN signals is associated with a first interval of the M intervals, and

a second gated PRN signal among the N gated PRN signals is associated with a second interval of the M intervals,

wherein the first and second intervals are located before and after a first transition point, respectively, and the first transition point is a starting point of each chip period.

75. The method according to claim 74 wherein the multiplying step further comprises the steps of:

multiplying the first gated PRN signal with the PRN signal to generate a first correlation value among the first plurality of correlation values, and

multiplying the second gated PRN signal with the PRN signal to generate a second correlation value among the first plurality of correlation values.

76. The method according to claim 75 wherein adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on a sum of the first and second correlation values.

77. The method according to claim 75 wherein the first and the second intervals are located closest to the first transition point among intervals located before and after the transition point, respectively.

78. The method according to claim 77 wherein

a third gated PRN signal among the N gated PRN signals is associated with a third interval of the M intervals, and

a fourth gated PRN signal among the N gated PRN signals is associated with a fourth interval of the M intervals,

the third and fourth intervals are second closest intervals to the second transition point among intervals located before and after the transition point, respectively, and

the step of multiplying the N gated PRN signals with the first phase signal of the PRN signal further comprises the steps of:

multiplying the third gated PRN signal with the PRN signal to generate a third correlation value among the first plurality of correlation values, and

multiplying the fourth gated PRN signal with the PRN signal to generate a fourth correlation value among the first plurality of correlation values.

79. The method according to claim 78 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on a sum of the first and second correlation values subtracted by a sum of the third and fourth correlation values.

80. The method according to claim 71 wherein N is equal to M.

81. The method according to claim 80 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on a sum of the first plurality of correlation values.

82. The method according to claim 71 wherein a fifth gated PRN signal among the N gated PRN signals is associated with a fifth interval of the M intervals,

a sixth gated PRN signal among the N gated PRN signals is associated with a sixth interval of the M intervals,

a seventh gated PRN signal among the N gated PRN signals is associated with a seventh interval of the M intervals,

an eighth gated PRN signal among the N gated PRN signals is associated with an eighth interval of the M intervals,

the fourth and the fifth intervals are located closest to a second transition point among M intervals located before and after the second transition point, respectively,

the third and fourth intervals are second closest intervals to the second transition point among M intervals located before and after the second transition point, respectively, and

the second transition point is a starting point of a previous chip period that occurs one chip period before a current chip period.

83. The method according to claim 82 wherein the multiplying step further comprises the steps of:

multiplying the fifth gated PRN signal with the PRN signal to generate a fifth correlation value among the first plurality of correlation values,

multiplying the sixth gated PRN signal with the PRN signal to generate a sixth correlation value among the first plurality of correlation values,

multiplying the seventh N gated PRN signal with the PRN signal to generate a seventh correlation value among the first plurality of correlation values, and

multiplying the eighth gated PRN signal with the PRN signal to generate an eighth correlation value among the first plurality of correlation values.

84. The method according to claim 83 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on a sum of the fifth and sixth correlation values subtracted by a sum of the seventh and eighth correlation values.

85. The method according to claim 71 further including the multiplying step further comprises the steps of:

multiplying the N gated PRN signals with a second phase signal of the PRN signal to generate a second plurality of correlation values.

86. The method according to claim 85 wherein

a third gated PRN signal among the N gated PRN signals is associated with a third interval of the M intervals,

a fourth gated PRN signal among the N gated PRN signals is associated with a fourth interval of the M intervals,

the third and fourth intervals are second closest intervals to a first transition point among M intervals located before and after the fourth transition point, respectively, wherein the first transition point is a starting point of each chip period, and

the step of multiplying the N gated PRN signals with the first phase signal of the PRN signal further comprising the steps of:

multiplying the third N gated PRN signal with the first phase signal of the PRN signal to generate a third correlation value among the first plurality of correlation values,

multiplying the fourth N gated PRN signal with the first phase signal of the PRN signal to generate a fourth correlation value among the first plurality of correlation values,

multiplying the third N gated PRN signal with the second phase signal of the PRN signal to generate a first correlation value among the second plurality of correlation values, and

multiplying the fourth N gated PRN signal with the second phase signal of the PRN signal to generate a second correlation value among the second plurality of correlation values.

87. The method according to claim 86 further comprising:

storing the third and fourth correlation values among the first plurality of correlation values and, first and second correlation values from the second plurality of correlation values only when the local replica PRN signal changes its value at the first transition point as a first, second, third and fourth stored values respectively.

88. The method according to claim 87 further comprising:

recovering the carrier frequency signal based on, in part, the fourth stored value subtracted by the third stored value which is then divided by a result of the first stored value subtracted by the second stored value.

89. The method according to claim 71 wherein the M is an even integer number, and a first half and a second half of the M intervals are located before and after a first transition point, respectively, and the first transition point is a starting point of each chip period.

90. The method according to claim 89 wherein a pair of the N gated PRN signals associated with a pair among the M intervals equidistanced from the first transition point are added before being multiplied by a respective correlator among the first plurality of correlators.

91. The method according to claim 60 further comprising:

monitoring for distortions in the broadcast signal based on a relationship among the first plurality of correlation values.

92. The method according to claim 60 wherein the relationship among the first plurality of correlation values is an average value thereof.

64. A method of processing at least one satellite-based navigation broadcast signal that includes a carrier frequency signal modulated by a Pseudo Random Code (PRN) signal, comprising the step of:

downconverting the broadcast signal, to thereby recover the PRN signal from the broadcast signal;

generating N gated PRN signals based on a local replica PRN signal time-divided by M intervals within a chip period of the local replica PRN signal, wherein N and M are positive integers;

multiplying the N gated PRN signals with a first phase signal of the PRN signal to generate a first plurality correlation values;

adjusting timing of the local replica PRN signal based on the first plurality of correlation values in order to accurately track the PRN signal with the local replica PRN signal; and

storing the first plurality of correlation values as first transition-product values only when the local replica PRN signal changes its value at a first transition point, wherein the first transition point is a starting point of each chip period.

65. The method according to claim 64 wherein adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on the first plurality of correlation values stored in the first transition-product-memory means.

66. The method according to claim 64 further comprising the step of:

storing the first plurality of correlation values as non-transition-product values only when the local replica PRN signal changes its value at the first transition point.

67. The method according to claim 66 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on the first transition-product values added to corresponding non-transition-product values.

68. The method according to claim 66 wherein the adjusting step further comprises the step of:

adjusting timing of the local replica PRN signal based on the first non-transition-product values subtracted by corresponding transition-product values.