Interference selection and cancellation for CDMA communications

• US 20060229051A1
• Filed: 04/07/2005
• Published: 10/12/2006
• Est. Priority Date: 04/07/2005
• Status: Abandoned Application

• Current Assignee: Rambus Inc.
• Original Assignee: Rambus Inc.
• Inventors: Narayan, Anand P., Nagarajan, Vijay
• Application Number:
  US11/100,940
• Publication Number:
  US 20060229051A1
• Time in Patent Office: Days
• US Class Current: 455/296
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04L 25/06 Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection

Abstract

Interference cancellation for CDMA handsets comprises projecting a received signal onto a subspace that is substantially orthogonal to an interference subspace. Selection of the interference subspace includes extracting at least one interfering signal from the received signal. Interference selection may include calculating a signal-power threshold from which the presence or absence of interfering channels is determined. Receiver embodiments are configured for transmit and receive diversity.

Claims

1. A cancellation system comprising:

a projection canceller configured to project a down-converted signal onto a subspace substantially orthogonal or oblique to an interference subspace corresponding to at least one interference signal, and

an interference selector coupled to the projection canceller and configured to extract the at least one interference signal from the down-converted signal.

2. The cancellation system recited in claim 1 configured to receive the baseband signal from at least one radio receiver.

3. The cancellation system recited in claim 1 configured to receive the baseband signal from a receiver antenna array.

4. The cancellation system recited in claim 1 further comprising an RF-to-baseband module.

5. The cancellation system recited in claim 1 further comprising a path-information module.

6. The cancellation system recited in claim 1 wherein the projection canceller is configured to up-sample at least one of the down-converted signal and the at least one interference signal.

7. The cancellation system recited in claim 1 wherein the interference selector includes at least one down sampler.

8. The cancellation system recited in claim 1 wherein the interference selector further comprises a scrambler configured to scramble the at least one interference signal.

9. The cancellation system recited in claim 1 configured to cancel interference over at least one of a set of signal durations, including a data symbol duration, an integer multiple of a symbol duration, a chip duration, an integer multiple of a chip duration, a fraction of a symbol duration, and a fraction of a chip duration.

10. The cancellation system recited in claim 1 configured to process at least one of a set of signals, including IS95 signals, CDMA2000 signals, and W-CDMA signals.

11. The cancellation system recited in claim 1 further comprising a Rake receiver, the projection canceller including at least one signal output coupled to at least one finger of the Rake receiver.

12. The cancellation system recited in claim 1 wherein the interference selector includes at least one S-matrix construction block, and the interference subspace is characterized by at least one S-matrix produced by the at least one S-matrix construction block.

13. The cancellation system recited in claim 12 wherein the at least one S-matrix construction block is configured to add a dc-signal component to the interference subspace.

14. The cancellation system recited in claim 12 wherein the at least one S-matrix construction block is configured to compare baseband data in the down-converted signal to at least one threshold to determine which of a plurality of multiple-access channels is present.

15. The cancellation system recited in claim 12 wherein the at least one S-matrix construction block is configured to process baseband data to produce a function of at least one of a real part of the baseband data and an imaginary part of the baseband data, the S-matrix construction block being further configured to compare the function to at least one threshold.

16. The cancellation system recited in claim 15 wherein the function includes at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

17. The cancellation system recited in claim 15 further including a threshold detector wherein the function produced by the at least one S-matrix construction block is similar to a function employed by the threshold detector to produce at least one threshold.

18. The cancellation system recited in claim 15 wherein the S-matrix construction block is further configured to replace with zero any multiple-access channel value having a corresponding function that does not satisfy a predetermined threshold criterion.

19. The cancellation system recited in claim 15 wherein the S-matrix construction block is further configured to include in the interference subspace any multiple-access channel values corresponding to a function satisfying a predetermined threshold criterion.

20. The cancellation system recited in claim 12 wherein the S-matrix construction block is further configured to include in the interference subspace only a predetermined number of multiple-access channel values corresponding to a function satisfying a predetermined threshold criterion.

21. The cancellation system recited in claim 20 wherein the predetermined number of multiple-access channel values selected by the S-matrix comprises multiple-access channel values having greater signal strength than non-selected channel values.

22. The cancellation system recited in claim 1 wherein the interference selector further comprises a threshold detector.

23. The cancellation system recited in claim 22 wherein the threshold detector is configured to derive at least one threshold from a function of real and imaginary parts of the down-converted signal.

24. The cancellation system recited in claim 23 wherein the threshold detector is configured to average at least one of the real and the imaginary parts of the down-converted signal over at least one symbol interval.

25. The cancellation system recited in claim 23 wherein the threshold detector is configured to derive the at least one threshold from at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

26. The cancellation system recited in claim 25 wherein the threshold detector is configured to derive the at least one threshold from a sum of the absolute value of the real part of the baseband data and the absolute value of the imaginary part of the baseband data.

27. The cancellation system recited in claim 22 wherein the threshold detector is configured to derive at least one threshold from a weighted average of a plurality of multiple-access channels.

28. The cancellation system recited in claim 22 wherein the threshold detector is configured to provide at least one threshold value with a corrective term to compensate for data estimates obtained via threshold determination.

29. The cancellation system recited in claim 22 wherein the threshold detector is configured to multiply an input descrambled baseband signal with at least one orthogonal channel code to obtain baseband data.

30. The cancellation system recited in claim 29 wherein the threshold detector is configured to employ a fast Walsh Transform.

31. The cancellation system recited in claim 29 wherein at least one of the threshold detector and an S-matrix construction block is configured to determine which multiple-access channels are present.

32. A cancellation system comprising:

a projection cancellation means configured to project a down-converted signal onto a subspace substantially orthogonal or oblique to an interference subspace corresponding to at least one interference signal, and

an interference selection means configured to process the down-converted signal for extracting therefrom the at least one interference signal.

33. The cancellation system recited in claim 32 configured to receive the baseband signal from at least one radio receiver.

34. The cancellation system recited in claim 32 configured to receive the baseband signal from a receiver antenna array.

35. The cancellation system recited in claim 32 further comprising an RF-to-baseband means.

36. The cancellation system recited in claim 32 further comprising a path-information means.

37. The cancellation system recited in claim 32 wherein the projection cancellation means is configured to up-sample at least one of the down-converted signal and the at least one interference signal.

38. The cancellation system recited in claim 32 wherein the interference selection means includes at least one down-sampler means.

39. The cancellation system recited in claim 32 wherein the interference selection means further comprises a scrambler means configured to scramble the at least one interference signal.

40. The cancellation system recited in claim 32 configured to cancel interference over at least one of a set of signal durations, including a data symbol duration, an integer multiple of a symbol duration, a chip duration, an integer multiple of a chip duration, a fraction of a symbol duration, and a fraction of a chip duration.

41. The cancellation system recited in claim 32 configured to process at least one of a set of signals, including IS95 signals, CDMA2000 signals, and W-CDMA signals.

42. The cancellation system recited in claim 32 further comprising a Rake reception means, the projection cancellation means including at least one signal output coupled to at least one finger of the Rake reception means.

43. The cancellation system recited in claim 32 wherein the interference selection means includes an S-matrix construction means, and the interference subspace is characterized by at least one S-matrix produced by the S-matrix construction means.

44. The cancellation system recited in claim 43 wherein the S-matrix construction means is configured to add a dc-signal component to the interference subspace.

45. The cancellation system recited in claim 43 wherein the S-matrix construction means is configured to compare baseband data in the down-converted signal to at least one threshold to determine which of a plurality of multiple-access channels is present.

46. The cancellation system recited in claim 43 wherein the S-matrix construction means is configured to process baseband data to produce a function of at least one of a real part of the baseband data and an imaginary part of the baseband data, the S-matrix construction means being further configured to compare the function to at least one threshold.

47. The cancellation system recited in claim 46 wherein the function includes at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

48. The cancellation system recited in claim 46 further including a threshold detection means wherein the function produced by the S-matrix construction means is similar to a function employed by the threshold detection means to produce at least one threshold.

49. The cancellation system recited in claim 46 wherein the S-matrix construction means is further configured to replace with zero any multiple-access channel value having a corresponding function that does not satisfy a predetermined threshold criterion.

50. The cancellation system recited in claim 46 wherein the S-matrix construction means is further configured to include in the interference subspace any multiple-access channel values corresponding to a function satisfying a predetermined threshold criterion.

51. The cancellation system recited in claim 43 wherein the S-matrix construction means is further configured to include in the interference subspace only a predetermined number of multiple-access channel values corresponding to a function satisfying a predetermined threshold criterion.

52. The cancellation system recited in claim 51 wherein the predetermined number of multiple-access channel values selected by the S-matrix comprises multiple-access channel values having greater signal strength than non-selected channel values.

53. The cancellation system recited in claim 32 wherein the interference selection means further comprises a threshold detector.

54. The cancellation system recited in claim 53 wherein the threshold detection means is configured to derive at least one threshold from a function of real and imaginary parts of the down-converted signal.

55. The cancellation system recited in claim 54 wherein the threshold detection means is configured to average at least one of the real and the imaginary parts of the down-converted signal over at least one symbol interval.

56. The cancellation system recited in claim 54 wherein the threshold detection means is configured to derive the at least one threshold from at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

57. The cancellation system recited in claim 56 wherein the threshold detection means is configured to derive the at least one threshold from a sum of the absolute value of the real part of the baseband data and the absolute value of the imaginary part of the baseband data.

58. The cancellation system recited in claim 53 wherein the threshold detection means is configured to derive at least one threshold from a weighted average of a plurality of multiple-access channels.

59. The cancellation system recited in claim 53 wherein the threshold detection means is configured to provide at least one threshold value with a corrective term to compensate for data estimates obtained via threshold determination.

60. The cancellation system recited in claim 53 wherein the threshold detection means is configured to multiply an input descrambled baseband signal with at least one orthogonal channel code to obtain baseband data.

61. The cancellation system recited in claim 60 wherein the threshold detection means is configured to employ a fast Walsh Transform.

62. The cancellation system recited in claim 60 wherein at least one of the threshold detection means and an S-matrix construction means is configured to determine which multiple-access channels are present.

63. A handset comprising:

a projection canceller configured to project a down-converted signal onto a subspace substantially orthogonal or oblique to an interference subspace corresponding to at least one interference signal, and

an interference selector coupled to the projection canceller and configured to extract the at least one interference signal from the down-converted signal.

64. The handset recited in claim 63 configured to receive the baseband signal from at least one radio receiver.

65. The handset recited in claim 63 configured to receive the baseband signal from a receiver antenna array.

66. The handset recited in claim 63 further comprising an RF-to-baseband module.

67. The handset recited in claim 63 further comprising a path-information module.

68. The handset recited in claim 63 wherein the projection canceller is configured to up-sample at least one of the down-converted signal and the at least one interference signal.

69. The handset recited in claim 63 wherein the interference selector includes at least one down sampler.

70. The handset recited in claim 63 wherein the interference selector further comprises a scrambler configured to scramble the at least one interference signal.

71. The handset recited in claim 63 configured to cancel interference over at least one of a set of signal durations, including a data symbol duration, an integer multiple of a symbol duration, a chip duration, an integer multiple of a chip duration, a fraction of a symbol duration, and a fraction of a chip duration.

72. The handset recited in claim 63 configured to process at least one of a set of signals, including IS95 signals, CDMA2000 signals, and W-CDMA signals.

73. The handset recited in claim 63 further comprising a Rake receiver, the projection canceller including at least one signal output coupled to at least one finger of the Rake receiver.

74. The handset recited in claim 63 wherein the interference selector includes at least one S-matrix construction block, and the interference subspace is characterized by at least one S-matrix produced by the at least one S-matrix construction block.

75. The handset recited in claim 74 wherein the at least one S-matrix construction block is configured to add a dc-signal component to the interference subspace.

76. The handset recited in claim 74 wherein the at least one S-matrix construction block is configured to compare baseband data in the down-converted signal to at least one threshold to determine which of a plurality of multiple-access channels is present.

77. The handset recited in claim 74 wherein the at least one S-matrix construction block is configured to process baseband data to produce a function of at least one of a real part of the baseband data and an imaginary part of the baseband data, the S-matrix construction block being further configured to compare the function to at least one threshold.

78. The handset recited in claim 77 wherein the function includes at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

79. The handset recited in claim 77 further including a threshold detector wherein the function produced by the at least one S-matrix construction block is similar to a function employed by the threshold detector to produce at least one threshold.

80. The handset recited in claim 77 wherein the S-matrix construction block is further configured to replace with zero any multiple-access channel value having a corresponding function that does not satisfy a predetermined threshold criterion.

81. The handset recited in claim 77 wherein the S-matrix construction block is further configured to include in the interference subspace any multiple-access channel values corresponding to a function satisfying a predetermined threshold criterion.

82. The handset recited in claim 74 wherein the S-matrix construction block is further configured to include in the interference subspace only a predetermined number of multiple-access channel values corresponding to a function satisfying a predetermined threshold criterion.

83. The handset recited in claim 82 wherein the predetermined number of multiple-access channel values selected by the S-matrix comprises multiple-access channel values having greater signal strength than non-selected channel values.

84. The handset recited in claim 63 wherein the interference selector further comprises a threshold detector.

85. The handset recited in claim 84 wherein the threshold detector is configured to derive at least one threshold from a function of real and imaginary parts of the down-converted signal.

86. The handset recited in claim 85 wherein the threshold detector is configured to average at least one of the real and the imaginary parts of the down-converted signal over at least one symbol interval.

87. The handset recited in claim 85 wherein the threshold detector is configured to derive the at least one threshold from at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

88. The handset recited in claim 87 wherein the threshold detector is configured to derive the at least one threshold from a sum of the absolute value of the real part of the baseband data and the absolute value of the imaginary part of the baseband data.

89. The handset recited in claim 84 wherein the threshold detector is configured to derive at least one threshold from a weighted average of a plurality of multiple-access channels.

90. The handset recited in claim 84 wherein the threshold detector is configured to provide at least one threshold value with a corrective term to compensate for data estimates obtained via threshold determination.

91. The handset recited in claim 84 wherein the threshold detector is configured to multiply an input descrambled baseband signal with at least one orthogonal channel code to obtain baseband data.

92. The handset recited in claim 91 wherein the threshold detector is configured to employ a fast Walsh Transform.

93. The handset recited in claim 91 wherein at least one of the threshold detector and an S-matrix construction block is configured to determine which multiple-access channels are present.

94. A method for canceling interference in a received signal comprising:

providing for extracting at least one interference signal from a down-converted signal, and

providing for projecting the down-converted signal onto a subspace substantially orthogonal or oblique to an interference subspace corresponding to the at least one interference signal.

95. The method recited in claim 94 wherein providing for extracting at least one interference signal comprises:

providing for demultiplexing the down-converted signal into a plurality of multiple-access channel values including one or more interference values,

providing for selecting at least one of the one or more interference values to produce at least one selected interference value, and

providing for multiplexing the at least one selected interference value to produce the at least one interference signal.

96. The method recited in claim 95 wherein providing for selecting at least one of the one or more interference values provides for selecting the one or more interference values relative to a predetermined threshold.

97. The method recited in claim 95 wherein providing for selecting at least one of the one or more interference values includes selecting a predetermined number of the one or more interference values.

98. The method recited in claim 94 preceded by providing for performing RF-to-baseband conversion on the received signal to produce the down-converted signal.

99. The method recited in claim 94 preceded by providing for receiving the received signal with an antenna array.

100. The method recited in claim 94 preceded by providing for receiving the received signal wherein the received signal originates from at least one transmit antenna.

101. The method recited in claim 94 wherein providing for extracting at least one interference signal further comprises providing for alignment of the received signal relative to at least one of delay information, symbol boundaries, and chip boundaries.

102. The method recited in claim 94 wherein providing for projecting the down-converted signal further comprises providing for up-sampling at least one of the down-converted signal and the at least one interference signal.

103. The method recited in claim 94 wherein providing for extracting at least one interference signal includes providing for down sampling the down-converted signal.

104. The method recited in claim 94 wherein providing for extracting at least one interference signal further comprises providing for scrambling the at least one interference signal.

105. The method recited in claim 94 configured to cancel interference over at least one of a set of signal durations, including a data symbol duration, an integer multiple of a symbol duration, a chip duration, an integer multiple of a chip duration, a fraction of a symbol duration, and a fraction of a chip duration.

106. The method recited in claim 94 configured to process at least one of a set of down-converted signals, including IS95 signals, CDMA2000 signals, and W-CDMA signals.

107. The method recited in claim 94 wherein providing for projecting the down-converted signal generates at least one interference-canceled signal, the method further comprising providing for coupling the at least one interference-canceled signal into at least one finger of a Rake receiver.

108. The method recited in claim 94 wherein providing for extracting at least one interference signal comprises providing for generating an S-matrix.

109. The method recited in claim 108 wherein providing for generating the S-matrix includes providing for adding a dc-signal component.

110. The method recited in claim 108 wherein providing for generating the S-matrix includes providing for including a predetermined number of data values

111. The method recited in claim 108 wherein providing for generating the S-matrix includes providing for comparing baseband data in the down-converted signal to at least one threshold to determine which of a plurality of channels is present.

112. The method recited in claim 111 wherein providing for generating the S-matrix includes providing for generating the at least one threshold from a sum of an absolute value of a real part of the baseband data and an absolute value of an imaginary part of the baseband data.

113. The method recited in claim 111 wherein providing for generating the S-matrix includes providing for deriving the at least one threshold from a weighted average of the plurality of channels.

114. The method recited in claim 111 wherein providing for generating the S-matrix includes providing the at least one threshold with a corrective term to compensate for data estimates obtained via threshold determination.

115. The method recited in claim 111 wherein providing for generating the S-matrix includes providing for processing the baseband data to produce a function of at least one of a real part of the baseband data and an imaginary part of the baseband data, and providing for comparing the function to at least one threshold.

116. The method recited in claim 115 wherein the function produced by providing for processing the baseband data includes at least one of an absolute value of the real part of the baseband data and an absolute value of the imaginary part of the baseband data.

117. The method recited in claim 115 wherein the function produced by providing for processing the baseband data and a function employed to produce the at least one threshold are substantially identical.

118. The method recited in claim 115 wherein providing for comparing the function to at least one threshold further comprises setting to zero any of the baseband data having a corresponding function that does not satisfy a predetermined threshold criterion.

119. The method recited in claim 115 wherein providing for generating the S-matrix further comprises including in the S-matrix any spreading codes of the baseband data having a corresponding function that satisfies a predetermined threshold criterion.

133. A digital computer system programmed to perform the method recited in claim 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, or 124.

134. A computer-readable medium storing a computer program implementing the method of claim 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, or 124.

120. A method for calculating a threshold for a receiver configured to operate in a communication system employing transmit-diversity, the method comprising:

providing for determining channel estimates,

providing for estimating transmit antenna weights,

providing for estimating at least one transmitted symbol, and

providing for constructing the threshold from the channel estimates, the estimated antenna weights, and the at least one transmitted symbol.

121. The method recited in claim 120 wherein providing for estimating transmit antenna weights comprises estimating the antenna weights from a predetermined set of possible antenna weights.

122. The method recited in claim 120 wherein providing for estimating the at least one transmitted symbol includes estimating at least one transmitted symbol transmitted in at least one common channel.

123. The method recited in claim 120 wherein providing for determining channel estimates includes measuring at least one common channel.

124. The method recited in claim 120 wherein providing for constructing the threshold comprises generating the threshold from an average of absolute values of a real part and an imaginary part of a quantity derived from the channel estimates, the estimated antenna weights, and the at least one transmitted symbol.

125. An apparatus configured for calculating a threshold in a receiver configured to operate in a communication system employing transmit-diversity, the apparatus comprising:

a channel estimator configured to determine channel estimates,

a weight estimator configured to estimate transmit antenna weights to produce estimated channel weights,

a symbol estimator configured to estimate at least one transmitted symbol to produce at least one transmitted symbol estimate, and

a threshold determination module configured to calculate the threshold from the channel estimates, the estimated antenna weights, and the at least one transmitted symbol estimate.

126. The apparatus recited in claim 125 wherein the weight estimator is configured to estimate the transmit antenna weights from a predetermined set of possible antenna weights.

127. The apparatus recited in claim 125 wherein the symbol estimator is configured to estimate at least one transmitted symbol transmitted in at least one common channel.

128. The apparatus recited in claim 125 wherein the threshold determination module is configured to generate the threshold from an average of absolute values of a real part and an imaginary part of a quantity derived from the channel estimates, the estimated antenna weights, and the at least one transmitted symbol.

129. A handset configured to operate in a communication system employing transmit-diversity, the handset comprising:

a channel estimator configured to determine channel estimates,

a weight estimator configured to estimate transmit antenna weights to produce estimated channel weights,

a symbol estimator configured to estimate at least one transmitted symbol to produce at least one transmitted symbol estimate, and

a threshold determination module configured to calculate the threshold from the channel estimates, the estimated antenna weights, and the at least one transmitted symbol estimate.

130. The handset recited in claim 129 wherein the weight estimator is configured to estimate the transmit antenna weights from a predetermined set of possible antenna weights.

131. The handset recited in claim 129 wherein the symbol estimator is configured to estimate at least one transmitted symbol transmitted in at least one common channel.

132. The handset recited in claim 129 wherein the threshold determination module is configured to generate the threshold from an average of absolute values of a real part and an imaginary part of a quantity derived from the channel estimates, the estimated antenna weights, and the at least one transmitted symbol.