Digital front-end for wireless communication system

• US 7,190,748 B2
• Filed: 05/10/2002
• Issued: 03/13/2007
• Est. Priority Date: 08/17/2001
• Status: Active Grant

• Current Assignee: DSP Group Incorporated (Synaptics Incorporated)
• Original Assignee: DSP Group Incorporated (Synaptics Incorporated)
• Inventors: Moon, Jaekyun, Kim, Younggyun
• Primary Examiner(s): VO, DON NGUYEN
• Application Number:
  US10/144,445
• Publication Number:
  US 20030072397A1
• Time in Patent Office: 1,768 Days
• Field of Search: 375/232, 375/260, 375/267, 375/345, 375/347, 375/350, 330/134, 330/289
• US Class Current: 375/345
• CPC Class Codes: H04B 7/0848 Joint weighting
• CPC Class Codes: H04B 7/0854 using error minimizing algorithms, e.g. minimum mean squared error [MMSE], "cross-correlation" or matrix inversion
• CPC Class Codes: H04B 7/0857 using maximum ratio combining techniques, e.g. signal-to- interference ratio [SIR], received signal strenght indication [RSS]
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 27/2657 Carrier synchronisation
• CPC Class Codes: H04L 27/2662 Symbol synchronisation
• CPC Class Codes: H04L 27/2675 Pilot or known symbols
• CPC Class Codes: H04W 28/18 Negotiating wireless communication parameters
• CPC Class Codes: H04W 56/00 Synchronisation arrangements
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]

Abstract

A digital front-end for a wireless communication system incorporates gain control, signal detection, frame synchronization and carrier frequency offset (CFO) estimation and correction features configured for use with multiple receive antennas. The digital front-end may be applied to a wireless communication system in which transmitted signals carry a repeated signal pattern, such as orthogonal frequency division multiplexing (OFDM) systems. An example of a repeated signal pattern is the preamble of a signal transmitted according to the IEEE 802.11a wireless local area network (WLAN) standard. The signal detection, frame synchronization, and CFO estimation techniques make use of signals received from multiple antenna paths to provide enhanced performance. The gain control feature may be configured to adjust the gain in steps. The frame synchronization technique may operate as a function of gain control, handling the input signal differently before and after gain adjustment.

Claims

1. A method comprising:

receiving observations of a wireless signal via multiple antennas;

measuring power levels of the observations by averaging a number of absolute squared samples of each of the observations;

identifying a largest power level among the measured power levels;

selecting an amplifier gain based on the largest measured power level; and

applying the amplifier gain to each of the observations.

2. The method of claim 1, further comprising:

determining whether the largest power level exceeds a threshold; and

decreasing the amplifier gain in a series of fixed increments until the largest power level does not exceed the threshold.

3. The method of claim 2, further comprising, upon determining that the largest power level does not exceed the threshold, adjusting the amplifier gain so that the largest power level is substantially equal to a reference power level.

4. The method of claim 2, further comprising:

measuring the largest power level upon elapse of a delay period following each of the incremental decreases in the amplifier gain; and

repeating the determination of whether the largest power level exceeds the threshold following each of the measurements.

5. The method of claim 4, wherein the threshold, the fixed increments, and the delay period are programmable.

6. The method of claim 2, wherein the threshold and the fixed increments are programmable.

7. The method of claim 1, further comprising:

detecting the wireless signal; and

measuring power levels of the observations only after elapse of a time delay following detection of the wireless signal.

8. The method of claim 1, further comprising quantizing each of the observations to the nearest power of 2 value.

9. The method of claim 1, wherein the wireless signal is transmitted according to the IEEE 802.11a standard.

10. The method of claim 1, further comprising filtering the observations.

11. The method of claim 1, further comprising filtering each of the observations with a filter transfer function of 1−

D².

12. The method of claim 1, further comprising filtering each of the observations with a filter transfer function of 1−

D.

13. The method of claim 1, further comprising filtering each of the observations with a filter transfer function of 1+D.

14. A method comprising:

receiving observations of a wireless signal via multiple antennas;

measuring power levels of the observations;

generating a correlation of the observations;

indicating a signal detection based on the correlation and a delayed version of the measured power levels;

identifying a largest power level among the measured power levels;

selecting an amplifier gain based on the largest measured power level; and

applying the amplifier gain to each of the observations.

15. The method of claim 14, further comprising measuring the power levels by averaging absolute squared samples of the observations for multiple antennas during a time period.

16. The method of claim 14, further comprising:

multiplying an observation sample from each of the antennas with the complex conjugate of a delayed observation sample from the respective antenna;

calculating an average of the multiplication products over all of the antennas during a time period; and

calculating the correlation by generating the absolute value of the calculated average.

17. The method of claim 16, wherein generating the absolute value of the calculated average includes summing the absolute values of real and imaginary components of each of the multiplication products.

18. The method of claim 14, further comprising indicating the signal detection when the correlation is larger than a threshold value.

19. The method of claim 14, further comprising indicating the signal detection when the correlation is larger than the delayed version of one of the measured power levels multiplied by a threshold factor.

20. The method of claim 14, further comprising indicating the signal detection when the correlation is larger than both a threshold value and the delayed version of one of the measured power levels multiplied by a threshold factor.

21. The method of claim 20, wherein the threshold value and the threshold factor are programmable.

22. The method of claim 14, further comprising quantizing each of the observations to the nearest power of 2 value before measuring the power levels and calculating the correlation.

23. The method of claim 14, further comprising filtering each of the observations before measuring the power levels and calculating the correlation.

24. The method of claim 23, further comprising filtering each of the observations with a filter transfer function of 1−

D².

25. The method of claim 23, further comprising filtering each of the observations with a filter transfer function of 1−

D.

26. The method of claim 23, further comprising filtering each of the observations with a filter transfer function of 1+D.

27. A method comprising:

receiving observations of a wireless signal via multiple antennas;

calculating an absolute squared value of an inner product between a unit vector of observation samples from the antennas and a time delayed unit vector of observation samples from the antennas;

identifying a largest absolute squared inner product value among the calculated absolute squared inner product values;

measuring power levels of the observations;

identifying a largest power level among the measured power levels;

selecting an amplifier gain based on the largest measured power level; and

applying the amplifier gain to each of the observations.

28. The method of claim 27, further comprising adjusting the gain of the observation samples, and fixing the gain at a constant value of the observation samples upon satisfaction of a criterion.

29. The method of claim 28, further comprising:

converting each component of an observation sample to a sign magnitude value having a sign that is the same as the sign of the observation sample but a magnitude that is a fixed magnitude value while the gain varies;

using the sign magnitude value as a vector element for the inner product calculation while the gain is adjusted; and

using the observation sample as a vector element for the inner product calculation after the gain has been fixed at the constant value.

30. The method of claim 29, wherein the fixed magnitude value is programmable.

31. The method of claim 27, further comprising identifying the largest absolute squared inner product value when the largest absolute squared inner product value is larger than a threshold.

32. The method of claim 31, wherein the threshold is programmable.

33. The method of claim 27, further comprising:

comparing a current absolute squared inner product value with the largest absolute squared inner product value;

storing the larger of the compared absolute squared inner product values; and

identifying the stored absolute squared inner product value as the largest absolute squared inner product value if a previously identified absolute squared inner product value was identified more than a time period previously.

34. The methods of claim 33, wherein the time period is programmable.

35. The method of claim 27, further comprising quantizing the observation samples to the nearest power of 2 value before using the observation samples in one of the vectors.

36. A method comprising:

receiving observations of a wireless signal via multiple antennas;

generating a correlation of the observations for each of the antennas;

averaging the correlations over all of the antennas;

estimating a carrier frequency offset based on the angle of the averaged correlations;

measuring power levels of the observations;

identifying a largest power level among the measured power levels;

selecting an amplifier gain based on the largest measured power level; and

applying the amplifier gain to each of the observations.

37. The method of claim 36, further comprising generating the correlation by multiplying a current observation sample and the complex conjugate of a delayed version of the observation sample.

38. The method of claim 36, further comprising correcting the carrier frequency offset for subsequent observation samples based on the estimated carrier frequency offset.

39. The method of claim 36, wherein the wireless signal is transmitted according to the IEEE 802.11a standard, and wherein the wireless signal includes a short preamble and a long preamble, the method further comprising:

estimating the carrier frequency offset using the short preamble; and

correcting the carrier frequency offset from the long preamble.

40. The method of claim 39, further comprising:

re-estimating the carrier frequency offset using the corrected long preamble; and

correcting the carrier frequency offset in the wireless signal following the end of the long preamble based on the re-estimated carrier frequency offset.

41. The method of claim 40, further comprising adding an offset value to the correction of the carrier frequency offset following the end of the long preamble.

42. The method of claim 40, further comprising:

adjusting the amplifier gain applied to each of the observations at the beginning of the short preamble; and

estimating the carrier frequency offset using the short preamble after the amplifier gain adjustment.

43. A wireless receiver comprising:

multiple antennas that receive observations of a wireless signal;

a gain control unit that measures power levels of the observations by averaging a number of absolute squared samples of each of the observations, identifies a largest power level among the measured power levels, and selects an amplifier gain based on the largest measured power level; and

an amplifier that applies the amplifier gain to each of the observations.

44. The receiver of claim 43, wherein the gain control unit determines whether the largest power level exceeds a threshold, and decreases the amplifier gain in a series of fixed increments until the largest power level does not exceed the threshold.

45. The receiver of claim 44, further comprising, upon determining that the largest power level does not exceed the threshold, adjusting the amplifier gain so that the largest power level is substantially equal to a reference power level.

46. The receiver of claim 44, wherein the gain control unit measures the largest power level upon elapse of a delay period following each of the incremental decreases in the amplifier gain, and repeats the determination of whether the largest power level exceeds the threshold following each of the measurements.

47. The receiver of claim 46, wherein the threshold, the fixed increments, and the delay period are programmable.

48. The receiver of claim 44, wherein the threshold and the fixed increments are programmable.

49. The receiver of claim 43, further comprising a signal detection unit that detects the wireless signal, wherein the gain control unit measures power levels of the observations only after elapse of a time delay following detection of the wireless signal.

50. The receiver of claim 43, wherein the gain control unit quantizes each of the observations to the nearest power of 2 value.

51. The receiver of claim 43, wherein the wireless signal is transmitted according to the IEEE 802.11a standard.

52. The receiver of claim 43, further comprising a filter that filters the observations.

53. The receiver of claim 43, further comprising a filter that filters the observations with a filter transfer function of 1−

D².

54. The receiver of claim 43, further comprising a filter that filters the observations with a filter transfer function of 1−

D.

55. The receiver of claim 43, further comprising a filter that filters the observations with a filter transfer function of 1+D.

56. A receiver comprising:

multiple antennas that receive observations of a wireless signal;

a gain control unit that measures power levels of the observations, identifies a largest power level among the measured power levels, and selects an amplifier gain based on the largest measured power level;

a signal detection unit that generates a correlation of the observations, and indicates a signal detection based on the correlation and a delayed version of the measured power level; and

an amplifier that applies the amplifier gain to each of the observations.

57. The receiver of claim 56, further comprising a power control unit that measures the power level by averaging absolute squared samples of the observations for multiple antennas during a time period.

58. The receiver of claim 56, wherein the signal detection unit multiplies an observation sample from each of the antennas with the complex conjugate of a delayed observation sample from the respective antenna, calculates an average of the multiplication products over all of the antennas during a time period, and calculates the correlation by generating the absolute value of the calculated average.

59. The receiver of claim 58, wherein the signal detection unit generates the absolute value of the calculated average by summing the absolute values of real and imaginary components of each of the multiplication products.

60. The receiver of claim 58, wherein the signal detection unit indicates the signal detection when the correlation is larger than a threshold value.

61. The receiver of claim 56, wherein the signal detection unit indicates the signal detection when the correlation is larger than the delayed version of the measured power level multiplied by a threshold factor.

62. The receiver of claim 56, wherein the signal detection unit indicates the signal detection when the correlation is larger than both a threshold value and the delayed version of the measured power level multiplied by a threshold factor.

63. The receiver of claim 62, wherein the threshold value and the threshold factor are programmable.

64. The receiver of claim 56, further comprising a quantizer that quantizes each of the observations to the nearest power of 2 value before the power level is measured and the correlation is calculated.

65. The receiver of claim 56, further comprising a filter that filters each of the observations before the power level is measured and the correlation is calculated.

66. The receiver of claim 65, wherein the filter has a filter transfer function of 1−

D².

67. The receiver of claim 65, wherein the filter has a filter transfer function of 1−

D.

68. The receiver of claim 65, wherein the filter has a filter transfer function of 1+D.

69. A receiver comprising:

multiple antennas that receive observations of a wireless signal;

a frame synchronization unit that calculates an absolute squared value of an inner product between a unit vector of observation samples from the antennas and a time delayed unit vector of observation samples from the antennas, and identifies a largest absolute squared inner product value among the calculated absolute squared inner product values;

a gain control unit that measures power levels of the observations, identifies a largest power level among the measured power levels, and selects an amplifier gain based on the largest measured power level; and

an amplifier that applies the amplifier gain to each of the observations.

70. The receiver of claim 69, wherein the gain control unit fixes the gain at a constant value of the observation samples upon satisfaction of a criterion.

71. The receiver of claim 70, wherein the frame synchronization unit converts each component of an observation sample to a sign magnitude value having a sign that is the same as the sign of the observation sample but a magnitude that is a fixed magnitude value while the gain varies, uses the sign magnitude value as a vector element for the inner product calculation while the gain is adjusted, and uses the observation sample as a vector element for the inner product calculation after the gain has been fixed at the constant value.

72. The receiver of claim 71, wherein the fixed magnitude value is programmable.

73. The receiver of claim 69, wherein the frame synchronization unit identifies the largest absolute squared inner product value when the largest absolute squared inner product value is larger than a threshold.

74. The receiver of claim 73, wherein the threshold is programmable.

75. The receiver of claim 69, wherein the frame synchronization unit compares a current absolute squared inner product value with the largest absolute squared inner product value, stores the larger of the compared absolute squared inner product values, and identifies the stored absolute squared inner product value as the largest absolute squared inner product value if a previously identified absolute squared inner product value was identified more than a time period previously.

76. The receiver of claim 75, wherein the time period is programmable.

77. The receiver of claim 69, further comprising a quantizer that quantizes the observation samples to the nearest power of 2 value before the observation samples are used in one of the vectors.

78. A receiver comprising:

multiple antennas that receive observations of a wireless signal;

a carrier frequency offset estimation unit that generates a correlation of the observations for each of the antennas, averages the correlations over all of the antennas, and estimates a carrier frequency offset based on the angle of the averaged correlations;

a gain control unit that measures power levels of the observations, identifies a largest power level among the measured power levels, and selects an amplifier gain based on the largest measured power level; and

an amplifier that applies the amplifier gain to each of the observations.

79. The receiver of claim 78, wherein the carrier frequency offset estimation unit generates the correlation by multiplying a current observation sample and the complex conjugate of a delayed version of the observation sample.

80. The receiver of claim 78, further comprising a carrier frequency offset correction unit that corrects the carrier frequency offset for subsequent observation samples based on the estimated carrier frequency offset.

81. The receiver of claim 78, wherein the wireless signal is transmitted according to the IEEE 802.11a standard, and wherein the wireless signal includes a short preamble and a long preamble, and the carrier frequency offset estimation unit estimates the carrier frequency offset using the short preamble, the receiver further comprising a carrier frequency offset correction unit that corrects the carrier frequency offset from the long preamble.

82. The receiver of claim 81, wherein the carrier frequency offset estimation unit re-estimates the carrier frequency offset using the corrected long preamble, and the carrier frequency offset correction unit corrects the carrier frequency offset in the wireless signal following the end of the long preamble based on the re-estimated carrier frequency offset.

83. The receiver of claim 82, further comprising adding an offset value to the correction of the carrier frequency offset following the end of the long preamble.

84. The receiver of claim 82, wherein the gain control unit adjusts the amplifier gain applied to each of the observations at the beginning of the short preamble, wherein the carrier frequency offset estimation unit estimates the carrier frequency offset using the short preamble after the amplifier gain adjustment.

85. A wireless receiver comprising:

multiple antennas that receive observations of a wireless signal;

a gain control unit that measures power levels of the observations, identifies a largest power level among the measured power levels, selects an amplifier gain based on the largest measured power level, and adjusts the amplifier gain to a fixed value so that the largest power level does not exceed a threshold;

an amplifier that applies the adjusted amplifier gain to each of the observations; and

a frame synchronization unit that calculates an absolute squared value of an inner product between a unit vector of observation samples from the antennas and a time delayed unit vector of observation samples from the antennas, and identifies a largest absolute squared inner product value among the calculated absolute squared inner product values,

wherein the frame synchronization unit converts each component of an observation sample to a sign magnitude value having a sign that is the same as the sign of the observation sample but a magnitude that is a fixed magnitude value while the gain is adjusted, uses the sign magnitude value as a vector element for the inner product calculation while the gain is adjusted, and uses the observation sample as a vector element for the inner product calculation after the gain has been adjusted to the fixed value.

86. The receiver of claim 85, wherein the gain control unit determines whether the largest power level exceeds a threshold, and decreases the amplifier gain in a series of fixed increments until the largest power level does not exceed the threshold and, upon determining that the largest power level does not exceed the threshold, adjusts the amplifier gain to the fixed value so that the largest power level is substantially equal to a reference power level.

87. A method comprising:

receiving observations of a wireless signal via multiple antennas;

measuring power levels of the observations;

identifying a largest power level among the measured power levels;

selecting an amplifier gain based on the largest measured power level;

adjusting the amplifier gain to a fixed value so that the largest power level does not exceed a threshold;

applying the adjusted amplifier gain to each of the observations; and

performing frame synchronization, wherein frame synchronization includes;

calculating an absolute squared value of an inner product between a unit vector of the observation samples from the antennas and a time delayed unit vector of the observation samples from the antennas,

identifying a largest absolute squared inner product value among the calculated absolute squared inner product values, converting each component of each of the observation samples to a sign magnitude value having a sign that is the same as the sign of the observation sample but a magnitude that is a fixed magnitude value while the gain is adjusted,

using the sign magnitude value as a vector element for the inner product calculation while the gain is adjusted, and

using the observation sample as a vector element for the inner product calculation after the gain has been adjusted to the fixed value.

88. The method of claim 87, further comprising:

determining whether the largest power level exceeds a threshold;

decreasing the amplifier gain in a series of fixed increments until the largest power level does not exceed the threshold; and

upon determining that the largest power level does not exceed the threshold, adjusting the amplifier gain to the fixed value so that the largest power level is substantially equal to a reference power level.

89. A wireless receiver comprising:

multiple antennas that receive observations of a wireless signal;

an amplifier that applies a gain to each of the observations;

a gain control unit that measures power levels of the observations, adjusts the amplifier gain during a preamble period of the wireless signal based on at least one of the measured power levels, and adjusts the gain to a fixed value when a largest one of the measured power levels is less than a threshold level; and

a frame synchronization unit that synchronizes a frame of the wireless signal, wherein the frame synchronization unit uses a sign of the observations and a reference magnitude before the amplifier gain is adjusted to the fixed value, and uses the sign of the observations a magnitude of the observations as an observation vector after the amplifier gain is adjusted to the fixed value.

90. The receiver of claim 89, wherein the frame synchronization unit calculates an absolute squared value of an inner product between a unit vector of observation samples from the antennas and a time delayed unit vector of observation samples from the antennas, identifies a largest absolute squared inner product value among the calculated absolute squared inner product values, converts each component of an observation sample to a sign magnitude value having a sign that is the same as the sign of the observation sample but a magnitude that is the reference magnitude value while the gain is adjusted, uses the sign magnitude value as a vector element for the inner product calculation while the gain is adjusted, and uses the observation sample as a vector element for the inner product calculation after the gain has been adjusted to the fixed value.

91. A method comprising:

receiving observations of a wireless signal via multiple antennas;

amplifying the observations with a gain;

measuring power levels of the observations;

adjusting the gain during a preamble period of the wireless signal based on at least one of the measured power levels;

adjusting the gain to a fixed value when a largest one of the measured power levels is less than a threshold level; and

synchronizing a frame of the wireless signal, wherein frame synchronization uses a sign of the observations and a reference magnitude before the amplifier gain is adjusted to the fixed value, and uses the sign of the observations and a magnitude of the observations as an observation vector after the amplifier gain is adjusted to the fixed value.

92. The method of claim 91, wherein synchronizing a frame comprises:

calculating an absolute squared value of an inner product between a unit vector of observation samples from the antennas and a time delayed unit vector of observation samples from the antennas;

identifying a largest absolute squared inner product value among the calculated absolute squared inner product values;

converting each component of an observation sample to a sign magnitude value having a sign that is the same as the sign of the observation sample but a magnitude that is the reference magnitude value while the gain is adjusted;

using the sign magnitude value as a vector element for the inner product calculation while the gain is adjusted; and

using the observation sample as a vector element for the inner product calculation after the gain has been adjusted to the fixed value.