Systems, methods, and apparatus for frequency control

• US 20070066268A1
• Filed: 05/08/2006
• Published: 03/22/2007
• Est. Priority Date: 05/10/2005
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Simic, Emilija, Patrick, Christopher, Challa, Raghu, Rowitch, Douglas
• Granted Patent: US 8,139,685 B2
• Time in Patent Office: Days
• US Class Current: 455/318
• CPC Class Codes: G01S 19/235 Calibration of receiver components
• CPC Class Codes: H04B 1/26 for superheterodyne receivers multiple frequency-changing H03D7/16

Abstract

A receiver according to one embodiment includes a frequency control unit configured to receive a stream of samples including a plurality of received instances of a transmitted signal. The frequency control unit is configured to output a first correction signal (e.g. indicating a rotation) that is based on more than one of the received instances and a second correction signal (e.g. to control an oscillator) that is also based on more than one of the received instances. In some embodiments, a controlled oscillator is used to receive and/or transmit another signal, such as a signal received from a GPS space vehicle. In other embodiments, the received instances are from a GPS signal. In further embodiments, a fixed-frequency oscillator is used, and the second correction signal is used to receive and/or transmit another signal, such as a GPS signal.

Claims

1. A receiver comprising:

an oscillator configured to output a frequency reference having a frequency based on an oscillator control signal;

a first downconverter configured to receive a first local oscillator (LO) signal based on the frequency reference and to produce, according to the first LO signal, a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

a frequency control unit configured to calculate the oscillator control signal based on the first complex digital signal; and

a second downconverter configured to receive a second LO signal based on the frequency reference and to produce, according to the second LO signal, a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency.

2. The receiver according to claim 1, wherein the first complex digital signal includes a plurality of received instances of a transmitted signal, and

wherein the frequency control unit is configured to calculate a plurality of frequency errors, each based on a different one of the received instances of a transmitted signal, and to calculate the oscillator control signal based on the plurality of frequency errors.

3. The receiver according to claim 2, wherein the frequency control unit includes a plurality of fingers, each configured to decode symbols of a different one of the received instances and to calculate a corresponding one of the plurality of frequency errors, and

wherein each of the plurality of fingers is configured to calculate the frequency error based on at least one decoded symbol of the received instance.

4. The receiver according to claim 3, wherein each of the plurality of fingers is configured to rotate a value of the first complex digital signal by an angle based on the frequency error.

5. The receiver according to claim 4, wherein one of the plurality of fingers is configured to apply a first rotation angle to a value of the first complex digital signal, and

wherein another of the plurality of fingers is configured to apply a second rotation angle to the value of the first complex digital signal, wherein the second rotation angle is different than the first rotation angle.

6. The receiver according to claim 3, wherein each of at least two of the plurality of fingers is configured to adjust a code phase of the respective received instance according to a time correction derived from the received instance.

7. The receiver according to claim 1, wherein the frequency control unit comprises a first loop including a first gain and accumulate stage configured to calculate a rotation signal, and

wherein the frequency control unit is configured to rotate a value of the first complex digital signal by an angle indicated by the rotation signal, and

wherein the receiver comprises a second loop including a second gain and accumulate stage configured to calculate the oscillator control signal.

8. The receiver according to claim 7, wherein the second gain and accumulate stage is configured to calculate the oscillator control signal based on the rotation signal.

9. The receiver according to claim 7, wherein the first loop includes a plurality of first gain and accumulate stages, each configured to calculate a different one of a plurality of rotation signals, and

wherein the second gain and accumulate stage is configured to calculate the oscillator control signal based on the plurality of rotation signals.

10. The receiver according to claim 7, wherein the rotation signal indicates a Doppler error in the first RF signal, and wherein the oscillator control signal indicates a variation of the frequency of the frequency reference over time.

11. The receiver according to claim 7, wherein a response of the second loop is overdamped across an expected range of strengths of the plurality of received instances of a transmitted signal.

12. The receiver according to claim 7, wherein a ratio of a bandwidth of the first loop to a bandwidth of the second loop is substantially constant across an expected range of strengths of the plurality of received instances of a transmitted signal.

13. The receiver according to claim 7, wherein a bandwidth of the second loop is substantially constant across an expected range of strengths of the plurality of received instances of a transmitted signal

14. The receiver according to claim 7, wherein the frequency control unit is configured to calculate the oscillator control signal to be independent of the rotation signal.

15. The receiver according to claim 7, wherein the second loop includes a rotator configured to reverse said rotation of the value of the first complex digital signal.

16. The receiver according to claim 7, wherein the second gain and accumulate stage is selectably configured to operate in one of (A) a mode of enabling changes to the state of the oscillator control signal and (B) a mode of disabling changes to the state of the oscillator control signal, and

wherein selection between the operating modes of the second gain and accumulate stage is based on an average value of the rotation signal over time.

17. The receiver according to claim 7, wherein the second gain and accumulate stage is configured to calculate the oscillator control signal according to a gain factor, and

wherein the second gain and accumulate stage is configured to select the gain factor, according to an average value of the rotation signal over time, from among a plurality of different gain factors.

18. The receiver according to claim 7, wherein the second gain and accumulate stage is configured to limit, based on a magnitude of the rotation signal, a rate of change of the oscillator control signal.

19. The receiver according to claim 1, said second downconverter comprising:

a mixer configured to produce, according to the second LO signal, a downconverted signal based on the second RF signal; and

a digitizer configured to produce the second complex digital signal based on the downconverted signal.

20. The receiver according to claim 19, said receiver comprising a clock synthesizer configured to produce a sampling clock signal according to the frequency reference,

wherein said digitizer is configured to sample the downconverted signal according to the sampling clock signal.

21. The receiver according to claim 20, wherein said frequency control unit is configured to produce a timing adjustment signal based on the first complex digital signal, and

wherein said clock synthesizer is configured to produce the sampling clock signal according to the timing adjustment signal.

22. The receiver according to claim 1, said receiver comprising a plurality of first downconverters, each configured to receive a first LO signal based on the frequency reference and to produce, according to the first LO signal, a first complex digital signal based on a different received instance of the first RF signal,

wherein the frequency control unit is configured to calculate the oscillator control signal based on the first complex digital signals.

23. The receiver according to claim 1, said receiver comprising a plurality of second downconverters, each configured to receive a second LO signal based on the frequency reference and to produce, according to the second LO signal, a second complex digital signal based on a different received instance of the second RF signal.

24. The receiver according to claim 1, wherein the first RF signal comprises a signal received from a transmitter of a positioning satellite system.

25. The receiver according to claim 1, wherein the second RF signal comprises a signal received from a transmitter of a positioning satellite system.

26. A receiver comprising:

an oscillator configured to output a frequency reference having a frequency based on an oscillator control signal;

a first downconverter configured to receive a first local oscillator (LO) signal based on the frequency reference and to produce, according to the first LO signal, a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

a frequency control unit configured to calculate the oscillator control signal based on the first complex digital signal;

a second downconverter configured to receive a second LO signal based on the frequency reference and to produce, according to the second LO signal, a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency; and

a processing unit configured to produce a baseband digital signal based on the second complex digital signal and to calculate a physical position of the receiver based on the baseband digital signal.

27. A method of signal processing, said method comprising:

generating a frequency reference having a frequency based on an oscillator control signal;

according to a first local oscillator (LO) signal based on the frequency reference, producing a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

based on the first complex digital signal, calculating the oscillator control signal; and

according to a second LO signal based on the frequency reference, producing a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency.

28. A data storage medium having machine-readable instructions describing the method of signal processing according to claim 27.

29. A receiver comprising:

a first downconverter configured to output a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

a second downconverter configured to output a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency;

a frequency control unit configured to calculate a frequency correction signal based on the first complex digital signal; and

a processing unit configured to produce, according to the frequency correction signal, a baseband digital signal based on the second complex digital signal, wherein the baseband digital signal includes a stream of information symbols carried by the second RF signal.

30. The receiver according to claim 29, said receiver comprising an oscillator configured to output a frequency reference,

wherein said second downconverter includes a mixer configured to mix the second RF signal with a local oscillator (LO) signal based on the frequency reference, and

wherein the frequency control unit is configured to calculate the frequency correction signal based on a frequency error of the frequency reference.

31. The receiver according to claim 30, wherein said frequency control unit is configured to calculate a oscillator control signal based on the first complex digital signal, and

wherein said oscillator is configured to vary, according to the oscillator control signal, a frequency of the frequency reference.

32. The receiver according to claim 30, wherein said mixer is configured to produce, according to the local oscillator signal, a downconverted signal based on the second RF signal,

said second downconverter comprising a digitizer configured to produce the second complex digital signal based on the downconverted signal.

33. The receiver according to claim 32, said receiver comprising a clock synthesizer configured to produce a sampling clock signal according to the frequency reference,

wherein said digitizer is configured to sample the downconverted signal according to the sampling clock signal.

34. The receiver according to claim 33, wherein said frequency control unit is configured to produce a timing adjustment signal based on the first complex digital signal, and

wherein said clock synthesizer is configured to produce the sampling clock signal according to the timing adjustment signal.

35. The receiver according to claim 31, said receiver comprising a plurality of first downconverters, each configured to receive another LO signal based on the frequency reference and to produce, according to the other LO signal, a first complex digital signal based on a different received instance of the first RF signal,

wherein the frequency control unit is configured to calculate the oscillator control signal based on the first complex digital signals.

36. The receiver according to claim 31, said receiver comprising a plurality of second downconverters, each configured to receive the LO signal and to produce, according to the LO signal, a second complex digital signal based on a different received instance of the second RF signal.

37. The receiver according to claim 36, said receiver comprising a plurality of processing units, each configured to produce, according to the frequency correction signal, a baseband digital signal based on a corresponding one of the second complex digital signals.

38. The receiver according to claim 29, wherein the processing unit is configured to rotate a value of the second complex digital signal by an angle indicated by the frequency correction signal.

39. The receiver according to claim 29, said receiver comprising an oscillator configured to output a frequency reference,

wherein the processing unit is configured to rotate a value of the second complex digital signal according to a Doppler error of the second RF signal, and

wherein the frequency control unit is configured to calculate the frequency correction signal according to a time-varying frequency error of the frequency reference.

40. The receiver according to claim 29, wherein the first complex digital signal includes a plurality of received instances of a transmitted signal, and

wherein the frequency control unit is configured to calculate a plurality of frequency errors, each based on a different one of the received instances of a transmitted signal, and to calculate the frequency correction signal based on the plurality of frequency errors.

41. The receiver according to claim 40, wherein the frequency control unit includes a plurality of fingers, each configured to decode symbols of a different one of the received instances and to calculate a corresponding one of the plurality of frequency errors, and

wherein each of the plurality of fingers is configured to calculate the frequency error based on at least one decoded symbol of the received instance.

42. The receiver according to claim 41, wherein each of the plurality of fingers is configured to rotate a value of the first complex digital signal by an angle based on the frequency error.

43. The receiver according to claim 42, wherein one of the plurality of fingers is configured to apply a first rotation angle to a value of the first complex digital signal, and

wherein another of the plurality of fingers is configured to apply a second rotation angle to the value of the first complex digital signal, wherein the second rotation angle is different than the first rotation angle.

44. The receiver according to claim 41, wherein each of at least two of the plurality of fingers is configured to adjust a code phase of the respective received instance according to a time correction derived from the received instance.

45. The receiver according to claim 29, wherein the frequency control unit comprises a first loop including a first gain and accumulate stage configured to calculate a rotation signal, and

wherein the frequency control unit is configured to rotate a value of the first complex digital signal by an angle indicated by the rotation signal, and

wherein the receiver comprises a second loop including a second gain and accumulate stage configured to calculate the frequency correction signal.

46. The receiver according to claim 45, wherein the second gain and accumulate stage is configured to calculate the frequency correction signal based on the rotation signal.

47. The receiver according to claim 45, wherein the first loop includes a plurality of first gain and accumulate stages, each configured to calculate a different one of a plurality of rotation signals, and

wherein the second gain and accumulate stage is configured to calculate the frequency correction signal based on the plurality of rotation signals.

48. The receiver according to claim 45, wherein the rotation signal indicates a Doppler error in the first RF signal, and wherein the frequency correction signal indicates a variation of the frequency of the frequency reference over time.

49. The receiver according to claim 45, wherein a response of the second loop is overdamped across an expected range of strengths of the plurality of received instances of a transmitted signal.

50. The receiver according to claim 45, wherein a ratio of a bandwidth of the first loop to a bandwidth of the second loop is substantially constant across an expected range of strengths of the plurality of received instances of a transmitted signal.

51. The receiver according to claim 45, wherein a bandwidth of the second loop is substantially constant across an expected range of strengths of the plurality of received instances of a transmitted signal.

52. The receiver according to claim 45, wherein the frequency control unit is configured to calculate the frequency correction signal to be independent of the rotation signal.

53. The receiver according to claim 45, wherein the second gain and accumulate stage is selectably configured to operate in one of (A) a mode of enabling changes to the state of the frequency correction signal and (B) a mode of disabling changes to the state of the frequency correction signal, and

wherein selection between the operating modes of the second gain and accumulate stage is based on an average value of the rotation signal over time.

54. The receiver according to claim 45, wherein the second gain and accumulate stage is configured to calculate the frequency correction signal according to a gain factor, and

wherein the second gain and accumulate stage is configured to select the gain factor, according to an average value of the rotation signal over time, from among a plurality of different gain factors.

55. The receiver according to claim 45, wherein the second gain and accumulate stage is configured to limit, based on a magnitude of the rotation signal, a rate of change of the frequency correction signal.

56. The receiver according to claim 29, wherein the first RF signal comprises a signal received from a transmitter of a positioning satellite system.

57. The receiver according to claim 29, wherein the second RF signal comprises a signal received from a transmitter of a positioning satellite system.

58. The receiver according to claim 29, said receiver comprising an upconverter configured to produce, according to a signal based on the frequency correction signal, a third RF signal based on a third complex digital signal different than the first and second complex digital signals.

59. A receiver comprising:

a first downconverter configured to output a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

a second downconverter configured to output a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency;

a frequency control unit configured to calculate a frequency correction signal based on the first complex digital signal; and

a processing unit configured to produce, according to the frequency correction signal, a baseband digital signal based on the second complex digital signal, wherein the baseband digital signal includes a stream of information symbols carried by the second RF signal,

wherein the processing unit is configured to calculate a physical position of the receiver based on the baseband digital signal.

60. A method of signal processing, said method comprising:

producing a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

producing a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency;

calculating a frequency correction signal based on the first complex digital signal; and

according to the frequency correction signal, producing a baseband digital signal based on the second complex digital signal, wherein the baseband digital signal includes digital information carried by the second RF signal.

61. A data storage medium having machine-readable instructions describing the method of signal processing according to claim 60.

62. A receiver comprising:

a first downconverter configured to produce a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

a processing unit configured to calculate a timing adjustment signal based on the first complex digital signal;

a clock synthesizer configured to produce a sampling clock signal according to the timing adjustment signal; and

a second downconverter configured to produce, according to the sampling clock signal, a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency.

63. The receiver according to claim 62, said receiver comprising an oscillator configured to output a frequency reference,

wherein said clock synthesizer is configured to produce the sampling clock signal based on the frequency reference, and

wherein the timing adjustment signal indicates a frequency error of the frequency reference.

64. The receiver according to claim 63, wherein said first downconverter is configured to mix the first RF signal with a local oscillator (LO) signal based on the frequency reference.

65. The receiver according to claim 63, said second downconverter including:

a mixer configured to produce, according to a second LO signal based on the frequency reference, a downconverted signal based on the second RF signal; and

a digitizer configured to produce the second complex digital signal based on the second RF signal, wherein the digitizer is configured to produce the second complex digital signal according to the sampling clock signal.

66. The receiver according to claim 62, wherein the first complex digital signal includes a plurality of received instances of a transmitted signal, and

wherein the processing unit is configured to calculate a plurality of timing errors, each based on a different one of the received instances of a transmitted signal, and to calculate the timing adjustment signal based on the plurality of timing errors.

67. The receiver according to claim 66, wherein the processing unit includes a plurality of fingers, each configured to decode symbols of a different one of the received instances and to calculate a corresponding one of the plurality of timing errors, and

wherein each of the plurality of fingers is configured to calculate the timing error based on at least one decoded symbol of the received instance.

68. The receiver according to claim 67, wherein each of at least two of the plurality of fingers is configured to adjust a code phase of the respective received instance according to a time correction derived from the received instance.

69. The receiver according to claim 67, wherein each of the plurality of fingers is configured to decode symbols of a different one of the received instances and to calculate a corresponding frequency error, and

wherein each of the plurality of fingers is configured to calculate the frequency error based on at least one decoded symbol of the received instance, and

at least one of the plurality of fingers is configured to rotate a value of the first complex digital signal by an angle based on the corresponding frequency error.

70. The receiver according to claim 69, wherein one of the plurality of fingers is configured to apply a first rotation angle to a value of the first complex digital signal, and

wherein another of the plurality of fingers is configured to apply a second rotation angle to the value of the first complex digital signal, wherein the second rotation angle is different than the first rotation angle.

71. The receiver according to claim 69, wherein said receiver comprises a rotator configured to rotate the second complex digital signal by an angle based on at least one of the plurality of frequency errors.

72. The receiver according to claim 62, said receiver comprising:

an oscillator configured to produce a frequency reference having a frequency based on an oscillator control signal,

wherein the first downconverter is configured to receive a first local oscillator (LO) signal based on the frequency reference and to produce, according to the first LO signal, the first complex digital signal, and

wherein the processing unit is configured to calculate the oscillator control signal based on the first complex digital signal.

73. The receiver according to claim 62, said receiver comprising:

an oscillator configured to produce a frequency reference having a frequency based on an oscillator control signal; and

a plurality of first downconverters, each configured to receive a first local oscillator (LO) signal based on the frequency reference and to produce, according to the first LO signal, a first complex digital signal based on a different received instance of the first RF signal,

wherein the processing unit is configured to calculate the oscillator control signal based on a plurality of the first complex digital signals.

74. The receiver according to claim 62, said receiver comprising a plurality of first downconverters, each configured to produce a first complex digital signal based on a different received instance of the first RF signal,

wherein the processing unit is configured to calculate the timing adjustment signal based on a plurality of the first complex digital signals.

75. The receiver according to claim 62, said receiver comprising a plurality of second downconverters, each configured to produce, according to the sampling clock signal, a second complex digital signal based on a different received instance of the second RF signal.

76. The receiver according to claim 62, said receiver comprising an upconverter configured to produce, according to a frequency correction signal based on the first complex signal, a third RF signal based on a third complex digital signal different than the first and second complex digital signals.

77. The receiver according to claim 62, said receiver comprising:

a plurality of upconverters, each configured to produce, according to a signal based on the timing adjustment signal, a third RF signal based on a third complex digital signal; and

a plurality of antennas, each configured to transmit a signal based on a different one of the third RF signals.

78. The receiver according to claim 62, wherein the first RF signal comprises a signal received from a transmitter of a positioning satellite system.

79. The receiver according to claim 62, wherein the second RF signal comprises a signal received from a transmitter of a positioning satellite system.

80. A method of signal processing, said method comprising:

producing a first complex digital signal based on a first radio-frequency (RF) signal having a first carrier frequency;

calculating a timing adjustment signal based on the first complex digital signal;

producing a clock signal according to the timing adjustment signal; and

at least one among (A) producing, according to the clock signal, a second complex digital signal based on a second RF signal having a second carrier frequency different than the first carrier frequency and (B) producing, according to the clock signal, a third RF signal based on a third complex digital signal and having a third carrier frequency different than the first carrier frequency.

81. A data storage medium having machine-readable instructions describing the method of signal processing according to claim 80.