Optimal feedback weighting for soft-decision cancellers

• US 20060227909A1
• Filed: 09/23/2005
• Published: 10/12/2006
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: III Holdings 1, LLC
• Inventors: Thomas, John K., McCloud, Michael L., Nagarajan, Vijay
• Granted Patent: US 8,761,321 B2
• Time in Patent Office: Days
• US Class Current: 375/346
• CPC Class Codes: H03D 1/04 Modifications of demodulators to reduce interference by undesired signals
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation

Abstract

A receiver produces optimal weights for cancelling multipath interference. An SINR measurement module generates SINR measurements corresponding to soft symbol estimates produced by a baseband receiver from a received multipath signal. Each soft symbol estimate is replaced with either a hard estimate or a weighted soft estimate based on how each corresponding SINR measurement compares to a predetermined threshold. The received multipath signal and estimated interference signals generated from the hard symbol estimates and/or the weighted soft symbol estimates are combined to produce interference cancelled signals that may be combined via maximum ratio combining to produce an interference-cancelled MRC signal.

Claims

1. A receiver, comprising:

an SINR measurement module configured for producing a plurality of SINR measurements corresponding to a plurality of soft symbol estimates from a received multipath signal,

a weight and threshold module configured for producing a plurality of processed symbol estimates corresponding to pluralities of multipaths and subchannels, each processed symbol estimate comprising a hard estimate or a weighted soft estimate based on a predetermined SINR threshold,

an interference-cancellation module configured for producing a plurality of interference-cancelled signals, each corresponding to a different multipath, and

a combining module configured for combining the plurality of interference-cancelled signals.

2. The receiver recited in claim 1, further comprising a threshold calculation module for determining the predetermined SINR threshold.

3. The receiver recited in claim 2, wherein the threshold calculation module is configured for determining an SINR below which weighted soft decisions provide better performance than hard decisions, and above which hard decisions provide better performance than weighted soft decisions.

4. The receiver recited in claim 2, wherein the threshold calculation module is configured for determining a second cutoff SINR, below which the processed symbol estimates are set to zero.

5. The receiver recited in claim 1, further comprising a weight computation module configured for generating at least one weight for weighting at least one of the plurality of soft symbol estimates.

6. The receiver recited in claim 5, wherein the weight is expressed by

$\frac{1}{1+1/\left({\mathrm{SINR}}_k\right)},$

where SINR_k is an average signal-to-noise ratio measured for a user or subchannel k.

7. The receiver recited in claim 6, wherein SINR_k is estimated via a function of the plurality of soft symbol estimates.

8. The receiver recited in claim 5, wherein the SINR measurement module is coupled to a MIMO receiver, and the weight is an optimal weighting matrix given by Λ

_k′

=R_QQ(R_QQ+R_k)<sup>−

1</sup>, where R_QQ is a transmit constellation correlation matrix and R_k is an effective interference-plus-noise correlation matrix in subchannel k.

9. The receiver recited in claim 1, further comprising an interference synthesis module configured for synthesizing the estimated interference signal.

10. The receiver recited in claim 9, wherein the interference synthesis module is configured to perform channel emulation.

11. The receiver recited in claim 1, wherein the SINR measurement module is configured for estimating an error vector magnitude.

12. The receiver recited in claim 1, wherein the weight and threshold module is configured to perform quantized scaling.

13. The receiver recited in claim 1, wherein the interference-cancellation module is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

14. The receiver recited in claim 1, wherein the interference-cancellation module is configured to generate a synthesized interference signal from the plurality of processed symbol estimates.

15. The receiver recited in claim 1, wherein the combining module is configured for performing maximal ratio combining.

16. The receiver recited in claim 1 being configured to process at least one of a set of signals, the set including CDMA, OFDM, MIMO, UWB, and narrowband single-carrier signals.

17. The receiver recited in claim 1, wherein the SINR measurement module is coupled to a Rake receiver.

18. The receiver recited in claim 1, wherein the receiver is included as part of at least one of a handset and a base station.

19. A receiving method, comprising:

providing for producing a plurality of SINR measurements corresponding to a plurality of soft symbol estimates from a received multipath signal,

providing for producing a plurality of processed symbol estimates, each processed symbol estimate comprising a hard estimate or a weighted soft estimate based on a comparison to a predetermined SINR threshold,

providing for producing a plurality of interference-cancelled signals, each corresponding to a different multipath, and

providing for combining the plurality of interference-cancelled signals.

20. The receiving method recited in claim 19, further comprising providing for determining the predetermined SINR threshold.

21. The receiving method recited in claim 20, wherein providing for determining the predetermined SINR threshold includes determining an SINR below which weighted soft decisions provide better performance than hard decisions, and above which hard decisions provide better performance than weighted soft decisions.

22. The receiving method recited in claim 20, wherein providing for determining the predetermined SINR threshold includes determining a second cutoff SINR, below which the processed symbol estimates are set to zero.

23. The receiving method recited in claim 19, further comprising providing for generating at least one weight for weighting at least one of the plurality of soft symbol estimates.

24. The receiving method recited in claim 23, wherein the weight is expressed by

$\frac{1}{1+1/\left({\mathrm{SINR}}_k\right)},$

where SINR_k is an average signal-to-noise ratio for a user or subchannel k.

25. The receiving method recited in claim 24, wherein SINR_k is estimated via a function of the plurality of soft symbol estimates.

26. The receiving method recited in claim 23 being configured for MIMO reception, and providing for generating at least one weight comprises generating an optimal weighting matrix expressed by Λ

_k′

=R_QQ(R_QQ+R_k)<sup>−

1</sup>, where R_QQ is a transmit constellation correlation matrix and R_k is an effective interference-plus-noise correlation matrix in subchannel k.

27. The receiving method recited in claim 19, wherein providing for producing a plurality of interference-cancelled signals includes performing channel emulation.

28. The receiving method recited in claim 19, wherein providing for producing a plurality of interference-cancelled signals includes producing a synthesized interference signal from the plurality of processed symbol estimates.

29. The receiving method recited in claim 19, wherein providing for producing a plurality of SINR measurements is configured for estimating an error vector magnitude.

30. The receiving method recited in claim 19, wherein providing for producing a plurality of processed symbol estimates includes performing quantized scaling.

31. The receiving method recited in claim 19, wherein providing for producing a plurality of interference-cancelled signals includes performing at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

32. The receiving method recited in claim 19, wherein providing for combining comprises providing for performing maximal ratio combining.

33. The receiving method recited in claim 19 being configured to process at least one of a set of signals, the set including CDMA, OFDM, MIMO, UWB, and narrowband single-carrier signals.

34. The receiving method recited in claim 19, configured to perform Rake reception.

35. A chipset configured to perform the receiving method recited in claim 19.

36. A digital computer system programmed to perform the method recited in claim 19.

37. A computer-readable medium storing a computer program implementing the method of claim 19.

38. A base station configured to perform the method of claim 19.

39. A handset configured to perform the method of claim 19.

40. A receiver, comprising:

a means for producing a plurality of SINR measurements corresponding to a plurality of soft symbol estimates for a received multipath signal,

a means for producing a plurality of processed symbol estimates, each processed symbol estimate comprising a hard estimate or a weighted soft estimate based on a predetermined SINR threshold,

a means for producing a plurality of interference-cancelled signals, each corresponding to a different multipath, and

a means for combining the plurality of interference-cancelled signals.

41. The receiver recited in claim 40, further comprising a means for determining the predetermined SINR threshold.

42. The receiver recited in claim 41, wherein the means for determining the predetermined SINR threshold includes a means for determining an SINR below which weighted soft decisions provide better performance than hard decisions, and above which hard decisions provide better performance than weighted soft decisions.

43. The receiver recited in claim 41, wherein the means for determining the predetermined SINR threshold includes a means for determining a second cutoff SINR, below which the processed symbol estimates are set to zero.

44. The receiver recited in claim 40, further comprising a means for generating at least one weight for weighting at least one of the plurality of soft symbol estimates.

45. The receiver recited in claim 44, wherein the weight is expressed by

$\frac{1}{1+1/\left({\mathrm{SNIR}}_k\right)},$

where SINR_k is an average signal-to-noise ratio measured for a user or subchannel k.

46. The receiver recited in claim 45, wherein SINR_k is estimated via a function of the plurality of soft symbol estimates.

47. The receiver recited in claim 44 further comprising a MIMO receiver, wherein the means for generating at least one weight comprises a means for generating an optimal weighting matrix expressed by Λ

_k′

=R_QQ(R_QQ+R_k)<sup>−

1</sup>, where R_QQ is a transmit constellation correlation matrix and R_k is an effective interference-plus-noise correlation matrix in subchannel k.

48. The receiver recited in claim 40, wherein the means for producing a plurality of interference-cancelled signals includes a means for performing channel emulation.

49. The receiver recited in claim 40, wherein the means for producing a plurality of SINR measurements is configured for estimating an error vector magnitude.

50. The receiver recited in claim 40, wherein the means for producing a plurality of processed symbol estimates is configured for performing quantized scaling.

51. The receiver recited in claim 40, wherein the means for producing a plurality of interference-cancelled signals includes at least one of a means for performing subtractive cancellation, a means for performing weighted subtractive cancellation, a means for performing projective cancellation, and a means for performing weighted projective cancellation.

52. The receiver recited in claim 40, wherein the means for producing a plurality of interference-cancelled signals is configured for generating a synthesized interference signal from the plurality of processed symbol estimates.

53. The receiver recited in claim 40, wherein the means for combining comprises a means for performing maximal ratio combining.

54. The receiver recited in claim 40 configured to process at least one of a set of signals, the set including CDMA, OFDM, MIMO, UWB, and narrowband single-carrier signals.

55. The receiver recited in claim 40 further comprising a means for performing Rake reception.

56. A chipset, comprising:

an SINR measurement module configured for producing a plurality of SINR measurements corresponding to a plurality of soft symbol estimates from a received multipath signal,

a weight and threshold module configured for producing a plurality of processed symbol estimates corresponding to pluralities of multipaths and subchannels, each processed symbol estimate comprising a hard estimate or a weighted soft estimate based on a predetermined SINR threshold,

an interference-cancellation module configured for producing a plurality of interference-cancelled signals, each corresponding to a different multipath, and

a combining module configured for combining the plurality of interference-cancelled signals.

57. The chipset recited in claim 56, further comprising a threshold calculation module for determining the predetermined SINR threshold.

58. The chipset recited in claim 57, wherein the threshold calculation module is configured for determining an SINR below which weighted soft decisions provide better performance than hard decisions, and above which hard decisions provide better performance than weighted soft decisions.

59. The chipset recited in claim 57, wherein the threshold calculation module is configured for determining a second cutoff SINR, below which the processed symbol estimates are set to zero.

60. The chipset recited in claim 56, further comprising a weight computation module configured for generating at least one weight for weighting at least one of the plurality of soft symbol estimates.

61. The chipset recited in claim 60, wherein the weight is expressed by

$\frac{1}{1+1/\left({\mathrm{SINR}}_k\right)},$

where SINR_k is an average signal-to-noise ratio measured for a user or subchannel k.

62. The chipset recited in claim 61, wherein SINR_k is estimated via a function of the plurality of soft symbol estimates.

63. The chipset recited in claim 60, wherein the SINR measurement module is coupled to a MIMO receiver, and the weight is an optimal weighting matrix given by Λ

_k′

=R_QQ(R_QQ+R_k)<sup>−

1</sup>, where R_QQ is a transmit constellation correlation matrix and R_k is an effective interference-plus-noise correlation matrix in subchannel k.

64. The chipset recited in claim 56, further comprising an interference synthesis module configured for producing a synthesized interference signal from at least one of the plurality of processed symbol estimates.

65. The chipset recited in claim 64, wherein the interference synthesis module is configured to perform channel emulation.

66. The chipset recited in claim 56, wherein the SINR measurement module is configured for estimating an error vector magnitude.

67. The chipset recited in claim 56, wherein the weight and threshold module is configured to perform quantized scaling.

68. The chipset recited in claim 56, wherein the interference-cancellation module is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

69. The chipset recited in claim 56, wherein the interference-cancellation module is configured to generate a synthesized interference signal from the plurality of processed symbol estimates.

70. The chipset recited in claim 56, wherein the combining module is configured for performing maximal ratio combining.

71. The chipset recited in claim 56 being configured to process at least one of a set of signals, the set including CDMA, OFDM, MIMO, UWB, and narrowband single-carrier signals.

72. The chipset recited in claim 56, wherein the SINR measurement module is coupled to a Rake receiver.

73. The chipset recited in claim 56 configured to operate in at least one of a handset and a base station.

74. A handset, comprising:

an SINR measurement module configured for producing a plurality of SINR measurements corresponding to a plurality of soft symbol estimates from a received multipath signal,

a weight and threshold module configured for producing a plurality of processed symbol estimates corresponding to pluralities of multipaths and subchannels, each processed symbol estimate comprising a hard estimate or a weighted soft estimate based on a predetermined SINR threshold,

an interference-cancellation module configured for producing a plurality of interference-cancelled signals, each corresponding to a different multipath, and

a combining module configured for combining the plurality of interference-cancelled signals.

75. The handset recited in claim 74, further comprising a threshold calculation module for determining the predetermined SINR threshold.

76. The handset recited in claim 75, wherein the threshold calculation module is configured for determining an SINR below which weighted soft decisions provide better performance than hard decisions, and above which hard decisions provide better performance than weighted soft decisions.

77. The handset recited in claim 75, wherein the threshold calculation module is configured for determining a second cutoff SINR, below which the processed symbol estimates are set to zero.

78. The handset recited in claim 74, further comprising a weight computation module configured for generating at least one weight for weighting at least one of the plurality of soft symbol estimates.

79. The handset recited in claim 78, wherein the weight is expressed by

$\frac{1}{1+1/\left({\mathrm{SINR}}_k\right)},$

where SINR_k is an average signal-to-noise ratio measured for a user or subchannel k.

80. The handset recited in claim 79, wherein SINR_k is estimated via a function of the plurality of soft symbol estimates.

81. The handset recited in claim 78, wherein the SINR measurement module is coupled to a MIMO receiver, and the weight is an optimal weighting matrix given by Λ

_k′

=R_QQ(R_QQ+R_k)<sup>−

1</sup>, where R_QQ is a transmit constellation correlation matrix and R_k is an effective interference-plus-noise correlation matrix in subchannel k.

82. The handset recited in claim 74, further comprising an interference synthesis module configured for generating a synthesized interference signal from at least one of the plurality of processed symbol estimates.

83. The handset recited in claim 82, wherein the interference synthesis module is configured to perform channel emulation.

84. The handset recited in claim 74, wherein the SINR measurement module is configured for estimating an error vector magnitude.

85. The handset recited in claim 74, wherein the weight and threshold module is configured to perform quantized scaling.

86. The handset recited in claim 74, wherein the interference-cancellation module is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

87. The handset recited in claim 74, wherein the interference-cancellation module is configured to generate a synthesized interference signal from the plurality of processed symbol estimates.

88. The handset recited in claim 74, wherein the combining module is configured for performing maximal ratio combining.

89. The handset recited in claim 74 being configured to process at least one of a set of signals, the set including CDMA, OFDM, MIMO, UWB, and narrowband single-carrier signals.

90. The handset recited in claim 74, wherein the SINR measurement module is coupled to a Rake receiver.