Soft weighted interference cancellation for CDMA systems

• US 20060227854A1
• Filed: 11/04/2005
• Published: 10/12/2006
• Est. Priority Date: 04/07/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC (Intellectual Ventures LLC)
• Original Assignee: Rambus Inc.
• Inventors: McCloud, Michael L., Nagarajan, Vijay
• Granted Patent: US 7,876,810 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/712 Weighting of fingers for combining, e.g. amplitude control or phase rotation using an inner loop

Abstract

Interference is cancelled from a baseband signal by synthesizing interference from estimated symbols in interfering subchannels. The estimated symbols are hard-coded, soft weighted, or zeroed, depending on the value of an estimated pre-processed signal-to-interference-and-noise ratio (SINR) in each subchannel in order to maximize a post-processed SINR. The estimated pre-processed SINR is obtained from averages of estimated symbol energies and estimated noise variances, or from related statistical procedures.

Claims

1. A CDMA receiver, comprising:

an SINR-estimation module configured for producing a plurality of pre-processed SINR estimates corresponding to a plurality of pre-processed symbol estimates from a received multipath signal,

a thresholding module configured for comparing each of the plurality of pre-processed SINR estimates to a predetermined threshold for determining whether to employ a weighted soft decision or a hard decision,

a companding module configured for generating the weighted soft decision or the hard decision for each of the plurality of pre-processed symbol estimates, and

a canceller configured for producing at least one interference-cancelled signal corresponding to at least one multipath signal.

2. The receiver recited in claim 1, wherein the SINR-estimation module is configured for producing the plurality of pre-processed SINR estimates by averaging symbol amplitudes over at least one of a set of parameters, the set of parameters including time and a plurality of subchannels.

3. The receiver recited in claim 1, wherein the thresholding module is configured for determining an estimated 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 1, wherein the thresholding module is configured for determining a second cutoff SINR, below which corresponding pre-processed symbol estimates are set to zero.

5. The receiver recited in claim 1, wherein the thresholding module is configured for determining an estimation strategy based on whether subchannel constellations are known.

6. The receiver recited in claim 1, wherein the companding module is configured for producing at least one weight expressed by an estimate of

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

where SINR_k⁽¹⁾ is a pre-processed signal-to-interference-and-noise ratio for a user or subchannel k.

7. The receiver recited in claim 6, wherein SINR_k⁽¹⁾ is estimated via a function of the plurality of soft symbol estimates.

8. The receiver recited in claim 1, further comprising a synthesizer configured for producing a synthesized interference signal.

9. The receiver recited in claim 8, wherein the synthesizer comprises a channel emulator configured for providing channel distortions to the synthesized interference signal.

10. The receiver recited in claim 1, further comprising a channel emulator configured to perform channel emulation.

11. The receiver recited in claim 1, wherein the canceller is configured to perform scaling.

12. The receiver recited in claim 1, wherein the canceller is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

13. The receiver recited in claim 1, further comprising a rake combiner configured to perform maximal ratio combining across a plurality of rake fingers.

14. The receiver recited in claim 13, wherein the SINR-estimation module is coupled to the Rake combiner.

15. The receiver recited in claim 1 configured to operate in at least one of a handset and a base station.

16. A method of receiving a CDMA signal, comprising:

providing for producing a plurality of pre-processed SINR estimates corresponding to a plurality of pre-processed symbol estimates from a received multipath signal,

providing for comparing each of the plurality of pre-processed SINR estimates to a predetermined threshold for determining whether to employ a weighted soft decision or a hard decision,

providing for generating the weighted soft decision or the hard decision for each of the plurality of pre-processed symbol estimates to produce at least one interference-symbol estimate, and

providing for producing at least one interference-cancelled signal from a received baseband signal and the at least one interference-symbol estimate.

17. The method recited in claim 16, wherein providing for producing a plurality of pre-processed SINR estimates is configured for producing the plurality of pre-processed SINR estimates by averaging symbol amplitudes over at least one of a set of parameters, the set of parameters including time and a plurality of subchannels.

18. The method recited in claim 16, wherein providing for comparing 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.

19. The method recited in claim 16, wherein providing for comparing is configured for determining a second cutoff SINR, below which corresponding pre-processed symbol estimates are set to zero.

20. The method recited in claim 16, wherein providing for comparing is configured for determining an estimation strategy based on whether subchannel constellations are known.

21. The method recited in claim 16, wherein providing for generating the weighted soft decision or the hard decision is configured for producing at least one weight expressed by an estimate of

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

where SINR_k⁽¹⁾ is a pre-processed signal-to-interference-and-noise ratio for a user or subchannel k.

22. The method recited in claim 21, wherein SINR_k⁽¹⁾ is estimated via a function of the plurality of soft symbol estimates.

23. The method recited in claim 16, further comprising providing for producing a synthesized interference signal.

24. The method recited in claim 23, further comprising providing for emulating channel distortions in the synthesized interference signal.

25. The method recited in claim 16, further comprising providing for performing channel emulation.

26. The method recited in claim 16, wherein providing for producing at least one interference-cancelled signal includes providing for scaling.

27. The method recited in claim 16, wherein providing for producing at least one interference-cancelled signal comprises performing at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

28. The method recited in claim 16, further comprising providing for maximal ratio combining across a plurality of rake fingers.

29. The receiver recited in claim 28, wherein providing for producing a plurality of pre-processed SINR estimates includes receiving the plurality of pre-processed symbol estimates from a Rake combiner.

30. A chipset configured to perform the receiving method recited in claim 16.

31. A digital computer system programmed to perform the method recited in claim 16.

32. A computer-readable medium storing a computer program implementing the method of claim 16.

33. A base station configured to perform the method of claim 16.

34. A handset configured to perform the method of claim 16.

35. A CDMA receiver, comprising:

a means for determining a pre-processed SINR estimate for each of a plurality of pre-processed symbol estimates corresponding to a plurality of subchannels,

a means for determining whether to use weighted soft decisions or hard decisions for each subchannel,

a means for generating at least one interference-symbol estimate, wherein each of the at least one interference-symbol estimate comprises a hard decision or a weighted soft decision of a corresponding pre-processed symbol estimate, and

a means for producing an interference-cancelled signal from a received baseband signal and the at least one interference-symbol estimate.

36. The receiver recited in claim 35, further comprising a means for determining at least one pre-processed SINR threshold.

37. The receiver recited in claim 36, wherein the means for determining the pre-processed SINR threshold 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.

38. The receiver recited in claim 36, wherein the means for determining the pre-processed SINR threshold includes a means for determining a cutoff SINR, below which the processed symbol estimates are set to zero.

39. The receiver recited in claim 35, further comprising a means for generating at least one weight for weighting at least one of the plurality of soft symbol estimates.

40. The receiver recited in claim 39, wherein the at least one weight is expressed by an estimate of

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

where SINR_k⁽¹⁾ is a pre-processed signal-to-interference-and-noise ratio for a user or subchannel k.

41. The receiver recited in claim 35, wherein the means for producing an interference-cancelled signal comprises a means for producing a synthesized interference signal from the at least one interference-symbol estimate.

42. The receiver recited in claim 41, wherein the means for producing a synthesized interference signal includes a means for emulating channel distortions in the synthesized interference signal.

43. The receiver recited in claim 35, wherein the means for determining the SINR estimate is configured for estimating an SINR in each of the plurality of subchannels.

44. The receiver recited in claim 35, wherein the means for producing an interference-cancelled signal is configured for performing scaling.

45. The receiver recited in claim 35, wherein the means for producing an interference-cancelled signal is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

46. The receiver recited in claim 35, wherein the means for determining the SINR estimate is coupled to a means for producing pre-processed symbol estimates corresponding to a received baseband signal.

47. The receiver recited in claim 35, wherein the means for determining the SINR estimate is configured for averaging amplitudes of the plurality of pre-processed symbol estimates over at least one of a set of parameters, the set of parameters including time and a plurality of subchannels.

48. The receiver recited in claim 35, wherein the means for determining whether to use weighted soft decisions or hard decisions is further configured for determining an estimation strategy based on whether subchannel constellations are known.

49. A chipset, comprising:

an SINR-estimation module configured for producing a plurality of pre-processed SINR estimates corresponding to a plurality of pre-processed symbol estimates from a received multipath signal,

a thresholding module configured for comparing each of the plurality of pre-processed SINR estimates to a predetermined threshold for determining whether to employ a weighted soft decision or a hard decision,

a companding module configured for generating the weighted soft decision or the hard decision for each of the plurality of pre-processed symbol estimates, and

a canceller configured for producing at least one interference-cancelled signal corresponding to at least one multipath signal.

50. The chipset recited in claim 49, wherein the SINR-estimation module is configured for producing the plurality of pre-processed SINR estimates by averaging symbol amplitudes over at least one of a set of parameters, the set of parameters including time and a plurality of subchannels.

51. The chipset recited in claim 49, wherein the thresholding 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.

52. The chipset recited in claim 49, wherein the thresholding module is configured for determining a second cutoff SINR, below which corresponding pre-processed symbol estimates are set to zero.

53. The chipset recited in claim 49, wherein the thresholding module is configured for determining an estimation strategy based on whether subchannel constellations are known.

54. The chipset recited in claim 49, wherein the companding module is configured for producing at least one weight expressed by an estimate of

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

where SINR_k⁽¹⁾ is a pre-processed signal-to-interference-and-noise ratio for a user or subchannel k.

55. The chipset recited in claim 54, wherein SINR_k⁽¹⁾ is estimated via a function of the plurality of soft symbol estimates.

56. The chipset recited in claim 49, further comprising a synthesizer configured for producing a synthesized interference signal.

57. The chipset recited in claim 56, wherein the synthesizer comprises a channel emulator configured for providing channel distortions to the synthesized interference signal

58. The chipset recited in claim 49, further comprising a channel emulator configured to perform channel emulation.

59. The chipset recited in claim 49, wherein the canceller is configured to perform scaling.

60. The chipset recited in claim 49, wherein the canceller is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

61. The chipset recited in claim 49, further comprising a rake combiner configured to perform maximal ratio combining across a plurality of rake fingers.

62. The chipset recited in claim 61, wherein the SINR-estimation module is coupled to the Rake combiner.

63. The chipset recited in claim 49 configured to operate in at least one of a handset and a base station.

64. A handset, comprising:

an SINR-estimation module configured for producing a plurality of pre-processed SINR estimates corresponding to a plurality of pre-processed symbol estimates from a received multipath signal,

a thresholding module configured for comparing each of the plurality of pre-processed SINR estimates to a predetermined threshold for determining whether to employ a weighted soft decision or a hard decision,

a companding module configured for generating the weighted soft decision or the hard decision for each of the plurality of pre-processed symbol estimates, and

a canceller configured for producing at least one interference-cancelled signal corresponding to at least one multipath signal.

65. The handset recited in claim 64, wherein the SINR-estimation module is configured for producing the plurality of pre-processed SINR estimates by averaging symbol amplitudes over at least one of a set of parameters, the set of parameters including time and a plurality of subchannels.

66. The handset recited in claim 64, wherein the thresholding 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.

67. The handset recited in claim 64, wherein the thresholding module is configured for determining a second cutoff SINR, below which corresponding pre-processed symbol estimates are set to zero.

68. The handset recited in claim 64, wherein the thresholding module is configured for determining an estimation strategy based on whether subchannel constellations are known.

69. The handset recited in claim 64, wherein the companding module is configured for producing at least one weight expressed by an estimate of

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

where SINR_k⁽¹⁾ is a pre-processed signal-to-interference-and-noise ratio for a user or subchannel k.

70. The handset recited in claim 69, wherein SINR_k⁽¹⁾ is estimated via a function of the plurality of soft symbol estimates.

71. The handset recited in claim 64, further comprising a synthesizer configured for producing a synthesized interference signal.

72. The handset recited in claim 71, wherein the synthesizer comprises a channel emulator configured for providing channel distortions to the synthesized interference signal

73. The handset recited in claim 64, further comprising a channel emulator configured to perform channel emulation.

74. The handset recited in claim 64, wherein the canceller is configured to perform scaling.

75. The handset recited in claim 64, wherein the canceller is configured to perform at least one of subtractive cancellation, weighted subtractive cancellation, projective cancellation, and weighted projective cancellation.

76. The handset recited in claim 64, further comprising a rake combiner configured to perform maximal ratio combining across a plurality of rake fingers.

77. The handset recited in claim 76, wherein the SINR-estimation module is coupled to the Rake combiner.

78. The handset recited in claim 64 configured to operate in at least one of a handset and a base station.