Iterative interference canceller for wireless multiple-access systems employing closed loop transmit diversity

• US 7,623,602 B2
• Filed: 08/25/2006
• Issued: 11/24/2009
• Est. Priority Date: 11/15/2005
• Status: Active Grant

• Current Assignee: III Holdings 1, LLC
• Original Assignee: TensorComm, Inc. (Rambus Inc.)
• Inventors: McCloud, Michael L, Guess, Tommy
• Primary Examiner(s): KIM, KEVIN
• Application Number:
  US11/509,920
• Publication Number:
  US 20070110137A1
• Time in Patent Office: 1,187 Days
• Field of Search: 375/347, 375/299
• US Class Current: 375/347
• CPC Class Codes: H04B 1/00 Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
• CPC Class Codes: H04B 1/7107 Subtractive interference cancellation
• CPC Class Codes: H04B 1/71072 Successive interference cancellation
• CPC Class Codes: H04B 1/71075 Parallel interference cancellation
• CPC Class Codes: H04B 1/7115 Constructive combining of multi-path signals, i.e. RAKE receivers
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04L 2025/03375 Passband transmission
• CPC Class Codes: H04L 25/03006 Arrangements for removing intersymbol interference

Abstract

An interference-canceling receiver processes coded, multiple-access, spread-spectrum transmissions that propagate through frequency-selective communication channels from multiple transmit antennas to multiple receive antennas in a closed-loop transmit-diversity channel. The receiver provides for repeated use of symbol-estimate weighting, subtractive cancellation with a stabilizing step-size, and mixed-decision symbol estimation. Receivers may be designed, adapted, and implemented explicitly in software or programmed hardware, or implicitly in standard Rake-based hardware, either within a Rake receiver at the finger level or outside the Rake at the user or subchannel symbol level. The receiver may be employed in user equipment on the forward link or in a base station on the reverse link.

Claims

1. An interference canceller coupled to a plurality of receive antennas configured for receiving signals from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the interference canceller comprising:

a front-end module configured for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources;

the front-end module comprising,

a combiner configured for combining signals from the plurality of receive antennas for each of the plurality of transmit sources for producing a plurality of combined signals,

a despreading module configured for employing the set of dominant beamforming weights and resolving the plurality of combined signals onto a signal basis for the plurality of transmit sources to produce soft symbol estimates, and

a mixed-decision module configured for performing a mixed decision on each of the soft symbol estimates to produce initial symbol decisions.

2. The interference canceller recited in claim 1, configured for canceling at least one of intra-cell interference and inter-cell interference.

3. The interference canceller recited in claim 1, configured for canceling interference from each of a plurality of base stations.

4. The interference canceller recited in claim 1, further comprising a sequence of interference-cancellation units configured for producing interference-cancelled versions of the initial symbol decisions, the sequence of interference-cancellation units being configured for summing constituent signals for each of the plurality of receive antennas to a corresponding scaled error signal to produce a combined signal, followed by resolving the combined signals across antennas onto the signal basis for the plurality of transmit sources, the resolving being performed with respect to multipath structure determined from the set of dominant beamforming weights.

5. The interference canceller recited in claim 4, wherein the sequence of interference-cancellation units is configured for performing finger-level interference cancellation in a Rake receiver, the sequence of interference-cancellation units comprising:

a plurality of synthesizers, each corresponding to one of the plurality of receive antennas and configured to produce synthesized Rake finger signals that would be received in response to weighted symbol decisions employed by at least one of the plurality of transmit sources, and

a subtractive canceller configured for performing per-antenna subtraction of a sum of the synthesized Rake finger signals from a corresponding received signal to produce an error signal.

6. The interference canceller recited in claim 4, wherein the constituent signals comprise received signals on each of a plurality of Rake fingers or received signals associated with each transmit source.

7. The canceller recited in claim 4, wherein each of the sequence of interference-cancellation units comprises:

a resolving module configured to resolve a residual signal from each of the plurality of antennas onto the signal basis for the plurality of transmit sources for producing a plurality of per-antenna resolved signals,

a first combiner configured to combine the per-antenna resolved signals for producing a combined signal,

a step-size module configured to scale the combined signals with a stabilizing step size for producing a scaled signal, and

a second combiner configured to sum weighted input symbol decisions with the scaled signal for generating a set of interference-cancelled constituents.

8. The canceller recited in claim 1, configured to reside in at least one of a set of devices, the set comprising a subscriber-side device configured for processing forward-link signals, and a server-side device configured for processing reverse-link signals.

9. A method of canceling interference from signals in a plurality of receive antennas received from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the method comprising:

providing for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources, wherein providing for determining the set of dominant beamforming weights comprises;

providing for combining signals from the plurality of receive antennas for each of the plurality of transmit sources for producing a plurality of combined signals,

providing for despreading by employing the set of dominant beamforming weights and resolving the plurality of combined signals onto a signal basis for the plurality of transmit sources to produce soft symbol estimates, and

providing for performing a mixed decision on each of the soft symbol estimates to produce initial symbol decisions.

10. The method recited in claim 9, configured for canceling at least one of intra-cell interference and inter-cell interference.

11. The method recited in claim 9, configured for canceling interference from each of a plurality of base stations.

12. The method recited in claim 9, further comprising providing for sequential interference cancellation to produce interference-cancelled versions of the initial symbol decisions, whereby providing for sequential interference cancellation comprises summing constituent signals for each of the plurality of receive antennas to a corresponding scaled error signal to produce a combined signal, followed by resolving the combined signals across antennas onto the signal basis for the plurality of transmit sources, the resolving being performed with respect to multipath structure determined from the set of dominant beamforming weights.

13. The method recited in claim 12, wherein providing for sequential interference cancellation is configured for performing finger-level interference cancellation in a Rake receiver, the sequence of interference-cancellation units comprising:

providing for producing synthesized Rake finger signals for each of the plurality of receive antennas, the synthesized Rake finger signals emulating signals that would be received in response to weighted symbol decisions being employed by at least one of the plurality of transmit sources, and

providing for performing per-antenna subtraction of a sum of the synthesized Rake finger signals from a corresponding received signal to produce an error signal.

14. The method recited in claim 12, wherein the constituent signals comprise received signals on each of a plurality of Rake fingers, or received signals associated with each transmit source.

15. The method recited in claim 12, wherein providing for sequential interference cancellation comprises:

providing for resolving a residual signal from each of the plurality of antennas onto the signal basis for the plurality of transmit sources for producing a plurality of per-antenna resolved signals,

providing for combining the per-antenna resolved signals for producing a combined signal,

providing for scaling the combined signals with a stabilizing step size for producing a scaled signal, and

providing for summing weighted input symbol decisions with the scaled signal for generating a set of interference-cancelled constituents.

16. A handset configured to perform the method recited in claim 9.

17. A chipset configured to perform the method recited in claim 9.

18. A digital computer system programmed to perform the method recited in claim 9.

19. A computer-readable medium storing a computer program implementing the method of claim 9.

20. A base station configured to perform the method of claim 9.

21. A system configured for canceling interference from signals in a plurality of receive antennas received from a plurality of transmit antennas wherein closed loop transmit waveform shaping is employed, the system comprising:

a calculation means configured for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources, the calculation means comprising;

a combining means for combining signals from the plurality of receive antennas for each of the plurality of transmit sources for producing a plurality of combined signals,

a despreading means configured for employing the set of dominant beamforming weights to resolve the plurality of combined signals onto a signal basis for the plurality of transmit sources to produce soft symbol estimates, and

a mixed-decision means for performing a mixed decision on each of the soft symbol estimates to produce initial symbol decisions.

22. The system recited in claim 21, configured for canceling at least one of intra-cell interference and inter-cell interference.

23. The system recited in claim 21, configured for canceling interference from each of a plurality of base stations.

24. The system recited in claim 21, further comprising a sequential interference cancellation means configured for producing interference-cancelled versions of the initial symbol decisions, the sequential interference cancellation means comprising a summing means for summing constituent signals for each of the plurality of receive antennas to a corresponding scaled error signal to produce a combined signal, and a resolving means configured for resolving the combined signals across antennas onto the signal basis for the plurality of transmit sources, whereby the resolving is performed with respect to multipath structure determined from the set of dominant beamforming weights.

25. The system recited in claim 24, wherein the constituent signals comprise received signals on each of a plurality of Rake fingers, or received signals associated with each transmit source.

26. The system recited in claim 24, wherein the sequential interference cancellation means comprises:

a Rake-synthesis means configured for producing synthesized Rake finger signals for each of the plurality of receive antennas, the synthesized Rake finger signals emulating signals that would be received in response to weighted symbol decisions being employed by at least one of the plurality of transmit sources, and

a subtraction means configured for performing per-antenna subtraction of a sum of the synthesized Rake finger signals from a corresponding received signal to produce an error signal.

27. The system recited in claim 24, wherein the sequential interference cancellation means comprises:

a resolving means configured for resolving a residual signal from each of the plurality of antennas onto the signal basis for the plurality of transmit sources for producing a plurality of per-antenna resolved signals,

a combining means configured for combining the per-antenna resolved signals for producing a combined signal,

a stabilizing step size means configured for scaling the combined signals with a stabilizing step size for producing a scaled signal, and

a summing means configured for summing weighted input symbol decisions with the scaled signal for generating a set of interference-cancelled constituents.

28. The system recited in claim 21, configured to reside in at least one of a set of devices, the set comprising a subscriber-side device configured for processing forward-link signals, and a server-side device configured for processing reverse-link signals.

29. An interference canceller coupled to a plurality of receive antennas configured for receiving signals from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the interference canceller comprising:

a front-end module configured for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources, the front-end module further configured for generating initial symbol decisions, and

a sequence of interference-cancellation units configured for processing the initial symbol decisions;

each of the sequence of interference-cancellation units comprising;

a weighting module configured for applying weights to a plurality of input symbol decisions to produce weighted symbol decisions,

a synthesis block configured for processing the weighted symbol decisions and the set of dominant beamforming weights for generating synthesized constituent signals for each of the plurality of receive antennas,

a subtraction module configured for subtracting the synthesized constituent signals from the received signal to produce residual signals,

a step-size module configured for scaling the residual signals by a stabilizing step size for producing scaled residual signals,

a combining module configured for combining the synthesized constituent signals with the scaled residual signals to produce interference-cancelled constituents,

a despreading module configured for employing the set of dominant beamforming weights and resolving the interference-cancelled constituents onto a signal basis for the plurality of transmit sources to produce soft symbol estimates, and

a mixed-decision module configured for performing a mixed decision on each of the soft symbol estimates to produce updated symbol decisions.

30. The canceller recited in claim 29, configured for canceling at least one of intra-cell interference and inter-cell interference.

31. The canceller recited in claim 29, configured for canceling interference from each of a plurality of base stations.

32. The canceller recited in claim 29, wherein the weighting module is further configured to calculate the weights as scale constants having magnitudes that depend on merits of the input symbol decisions.

33. The canceller recited in claim 29, wherein the step-size module is further configured to calculate the stabilizing step size as a scalar that improves convergence rate for iterative interference cancellation.

34. The canceller recited in claim 29 wherein the mixed-decision module is configured to produce each of the updated symbol decisions, irrespective of other symbol decisions, as a hard decision that quantizes the soft symbol estimates onto a nearby constellation point or a soft decision that scales the soft symbol estimates without quantizing to a constellation point.

35. The canceller recited in claim 29, further comprising a de-bias module configured to remove bias, as computed on the soft symbol estimates, prior to performing the mixed decision.

36. The canceller recited in claim 29, configured for employing a direct implementation of a one-step matrix update equation to perform symbol-level interference cancellation, the direct implementation including an explicit matrix representation of at least one users'"'"' received correlation matrix for received signals combined across the plurality of receive antennas, the correlation matrix being calculated with respect to multipath structure determined from the set of dominant beamforming weights, an implementation matrix, a soft-weighting matrix, a de-biasing matrix, and a scalar stabilizing step size.

37. The canceller recited in claim 36, whereby the one-step matrix update equation is expressed by

${\underset{\_}{\hat{b}}}^{\left[i+1\right]}=\Psi$

⁢

{ D [ i ] ⁡

( μ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) + F ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) } ,

wherein {circumflex over (b)}^[i] is a column vector containing the input symbol decisions corresponding to each of the plurality of transmit sources after an i^th iteration of interference cancellation, q is a vector of the soft symbol estimates that have been combined across the plurality of receive antennas, μ

^[i] is a scalar stabilizing step, Γ

^[i] is a weighting matrix used for scaling the input symbol decisions, R is a correlation matrix for received signals combined across antennas that is a sum of per-antenna received-signal correlation matrices with respect to multipath structure determined by the set of dominant beamforming weights, F is an implementation matrix, D^[i] is a de-biasing matrix, and Ψ

is a mixed-decision operator that returns a mixed symbol decision for each element of its input vector to produce the updated symbol decisions, {circumflex over (b)}^[i+1].

38. The canceller of claim 36, wherein the implementation matrix comprises an identity matrix or a correlation matrix.

39. The canceller recited in claim 29, configured to reside in at least one of a set of devices, the set comprising a subscriber-side device configured for processing forward-link signals and a server-side device configured for processing reverse-link signals.

40. An interference cancellation method for processing signals from a plurality of receive antennas configured for receiving signals from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the method comprising:

providing for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources, and generating initial symbol decisions, and

providing for sequential interference cancellation for processing the initial symbol decisions;

whereby providing for sequential interference cancellation comprises;

providing for applying weights to a plurality of input symbol decisions to produce weighted symbol decisions,

providing for processing the weighted symbol decisions and the set of dominant beamforming weights for generating synthesized constituent signals for each of the plurality of receive antennas,

providing for subtracting the synthesized constituent signals from the received signal to produce residual signals,

providing for scaling the residual signals by a stabilizing step size for producing scaled residual signals,

providing for combining the synthesized constituent signals with the scaled residual signals to produce interference-cancelled constituents,

providing for despreading by employing the set of dominant beamforming weights and resolving the interference-cancelled constituents onto a signal basis for the plurality of transmit sources to produce soft symbol estimates, and

providing for performing a mixed decision on each of the soft symbol estimates to produce updated symbol decisions.

41. The method recited in claim 40, configured for canceling at least one of intra-cell interference and inter-cell interference.

42. The method recited in claim 40, configured for canceling interference from each of a plurality of base stations.

43. The method recited in claim 40, wherein providing for applying weights is further configured for calculating the weights as scale constants having magnitudes that depend on merits of the input symbol decisions.

44. The method recited in claim 40, wherein providing for scaling is further configured for calculating the stabilizing step size as a scalar that improves convergence rate for iterative interference cancellation.

45. The method recited in claim 40 wherein providing for performing the mixed decision comprises producing each of the updated symbol decisions, irrespective of other symbol decisions, as a hard decision that quantizes the soft symbol estimates onto a nearby constellation point or a soft decision that scales the soft symbol estimates without quantizing to a constellation point.

46. The method recited in claim 40, further comprising removing bias from the soft symbol estimates prior to performing the mixed decision.

47. The method recited in claim 40, configured for employing a direct implementation of a one-step matrix update equation to perform symbol-level interference cancellation, the direct implementation including an explicit matrix representation of at least one users'"'"' received correlation matrix for received signals combined across the plurality of receive antennas, the correlation matrix being calculated with respect to multipath structure determined from the set of dominant beamforming weights, an implementation matrix, a soft-weighting matrix, a de-biasing matrix, and a scalar stabilizing step size.

48. The method recited in claim 47, whereby the one-step matrix update equation is expressed by

${\underset{\_}{\hat{b}}}^{\left[i+1\right]}=\Psi$

⁢

{ D [ i ] ⁡

( μ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b _ ^ [ i ] ) + F ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) } ,

wherein {circumflex over (b)}^[i] is a column vector containing the input symbol decisions corresponding to each of the plurality of transmit sources after an i^th iteration of interference cancellation, q is a vector of the soft symbol estimates that have been combined across the plurality of receive antennas, μ

^[i] is a scalar stabilizing step, Γ

^[i] is a weighting matrix used for scaling the input symbol decisions, R is a correlation matrix for received signals combined across antennas that is a sum of per-antenna received-signal correlation matrices with respect to multipath structure determined by the set of dominant beamforming weights, F is an implementation matrix, D^[i] is a de-biasing matrix, and Ψ

is a mixed-decision operator that returns a mixed symbol decision for each element of its input vector to produce the updated symbol decisions, {circumflex over (b)}^[i+1].

49. The method of claim 47, wherein the implementation matrix comprises an identity matrix or a correlation matrix.

50. A handset configured to perform the method recited in claim 40.

51. A chipset configured to perform the method recited in claim 40.

52. A digital computer system programmed to perform the method recited in claim 40.

53. A computer-readable medium storing a computer program implementing the method of claim 40.

54. A base station configured to perform the method of claim 40.

55. A subscriber-side device configured to perform the method recited in claim 40.

56. A server-side device configured to perform the method recited in claim 40.

57. An interference cancellation system for processing signals from a plurality of receive antennas configured for receiving signals from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the system comprising:

a calculation means configured for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources, and generating initial symbol decisions, and

a sequential interference cancellation means configured for processing the initial symbol decisions;

sequential interference cancellation means comprising;

a weighting means configured for applying weights to a plurality of input symbol decisions to produce weighted symbol decisions,

a synthesizing means configured for processing the weighted symbol decisions and the set of dominant beamforming weights for generating synthesized constituent signals for each of the plurality of receive antennas,

a subtraction means configured for subtracting the synthesized constituent signals from the received signal to produce residual signals,

a stabilizing step size means configured for scaling the residual signals by a stabilizing step size for producing scaled residual signals,

a combining means configured for combining the synthesized constituent signals with the scaled residual signals to produce interference-cancelled constituents,

a despreading means configured for employing the set of dominant beamforming weights and resolving the interference-cancelled constituents onto a signal basis for the plurality of transmit sources to produce soft symbol estimates, and

a mixed-decision means configured for performing a mixed decision on each of the soft symbol estimates to produce updated symbol decisions.

58. The system recited in claim 57, configured for canceling at least one of intra-cell interference and inter-cell interference.

59. The system recited in claim 57, configured for canceling interference from each of a plurality of base stations.

60. The system recited in claim 57, wherein the weighting means is further configured for calculating the weights as scale constants having magnitudes that depend on merits of the input symbol decisions.

61. The system recited in claim 57, wherein the stabilizing step size means is further configured for calculating the stabilizing step size as a scalar that improves convergence rate for iterative interference cancellation.

62. The system recited in claim 57 wherein the mixed-decision means is configured for producing each of the updated symbol decisions, irrespective of other symbol decisions, as a hard decision that quantizes the soft symbol estimates onto a nearby constellation point or a soft decision that scales the soft symbol estimates without quantizing to a constellation point.

63. The system recited in claim 57, further comprising a de-bias means configured for removing bias from the soft symbol estimates prior to performing the mixed decision.

64. The system recited in claim 57, configured for employing a direct implementation of a one-step matrix update equation to perform symbol-level interference cancellation, the direct implementation including an explicit matrix representation of at least one users'"'"' received correlation matrix for received signals combined across the plurality of receive antennas, the correlation matrix being calculated with respect to multipath structure determined from the set of dominant beamforming weights, an implementation matrix, a soft-weighting matrix, a de-biasing matrix, and a scalar stabilizing step size.

65. The system recited in claim 64, whereby the one-step matrix update equation is

${\underset{\_}{\hat{b}}}^{\left[i+1\right]}=\Psi$

⁢

{ D [ i ] ⁡

( μ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) + F ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) } ,

wherein {circumflex over (b)}^[i] is a column vector containing the input symbol decisions corresponding to each of the plurality of transmit sources after an i^th iteration of interference cancellation, q is a vector of the soft symbol estimates that have been combined across the plurality of receive antennas, μ

^[i] is a scalar stabilizing step, Γ

^[i] is a weighting matrix used for scaling the input symbol decisions, R is a correlation matrix for received signals combined across antennas that is a sum of per-antenna received-signal correlation matrices with respect to multipath structure determined by the set of dominant beamforming weights, F is an implementation matrix, D^[i] is a de-biasing matrix, and Ψ

is a mixed-decision operator that returns a mixed symbol decision for each element of its input vector to produce the updated symbol decisions, {circumflex over (b)}^[i+1].

66. The system recited in claim 64, wherein the implementation matrix comprises an identity matrix or a correlation matrix.

67. An interference canceller coupled to a plurality of receive antennas configured for receiving signals from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the interference canceller comprising:

a front-end module configured for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources, the front-end module further configured for generating initial symbol decisions, and

a sequence of interference-cancellation units configured for processing the initial symbol decisions;

each of the sequence of interference-cancellation units comprising;

a weighting module configured for applying soft weights to a plurality of input symbol decisions,

a mixed decision module configured for performing mixed decisions on soft symbol estimates, and

a step-size module configured to scale a residual signal with a stabilizing step size, the step-size module further configured to produce the stabilizing step size with a magnitude representing how far the input symbol decisions are from desired interference-cancelled symbol decisions in a step of iterative interference cancellation.

68. The interference canceller recited in claim 67, wherein the stabilizing step size is measured as a ratio of distance measures between received signals combined across the plurality of receive antennas and synthesized received signals combined across the plurality of receive antennas, the synthesized received signals and combining weights being determined with respect to a multipath structure determined from the set of dominant beamforming weights.

69. The interference canceller recited in claim 68, wherein the ratio comprises a numerator and a denominator, the numerator being calculated by:

evaluating a residual signal for each of the plurality of receive antennas, the residual signal being a difference between a received signal for one of the plurality of receive antennas and a synthesized received signal for the one of the plurality of receive antennas, the synthesized receive signal comprising multipath structure determined by the set of dominant beamforming weights;

resolving the residual signal onto a signal basis for the plurality of transmit sources, the signal basis comprising the multipath structure determined by the dominant beamforming weights;

providing for maximal ratio combining and despreading to produce a plurality of error vectors, each corresponding to one of the plurality of receive antennas;

summing the plurality of error vectors to produce a total error vector; and

evaluating a sum of square magnitudes of elements of the total error vector;

the denominator being calculated by;

synthesizing for each of the plurality of receive antennas a signal that would be received in response to elements of the total error vector being employed as symbols at the plurality of transmit sources,

using a signal basis for all symbol sources in the channel;

evaluating an integral of square magnitudes for the synthesized received signal for each of the plurality of receive antennas for producing a plurality of integral values, and

summing the integral values.

70. The interference canceller recited in claim 69, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = ( q _ - RF ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

( q _ - RF ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

R ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ,

wherein μ

^[i] is a stabilizing step size after an i^th iteration of the interference canceller;

q is a vector of despread received signals that have been combined across the plurality of receive antennas, Γ

^[i] is a weighting matrix for scaling the plurality of input symbol decisions, {circumflex over (b)}^[i], R is a correlation matrix for received signals combined across the plurality of receive antennas that is a sum of per-antenna received-signal correlation matrices calculated with respect to the multipath structure determined by the set of dominant beamforming weights;

F is an implementation matrix that may comprise an identity matrix or a transmit-signal correlation matrix; and

superscript H denotes complex-conjugate matrix transposition.

71. The interference canceller recited in claim 67, wherein the step-size module is further configured to measure the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of receive antennas and two differently synthesized received signals combined across the plurality of receive antennas, the synthesized received signals comprising multipath structure determined by the set of dominant beamforming weights.

72. The interference canceller recited in claim 71, wherein the stabilizing step size is a ratio comprising a numerator and a denominator, the step-size module being configured for

evaluating for each one of the plurality of receive antennas a residual signal as a difference between a received signal on the one of the plurality of receive antennas and a first synthesized received signal for the one of the plurality of receive antennas, the first synthesized received signal comprising multipath structure determined by the set of dominant beamforming weights;

resolving the residual signal onto a signal basis for the plurality of transmit sources for producing resolved signals, wherein resolving employs the multipath structure determined by the set of dominant beamforming weights;

maximal ratio combining and despreading the resolved signals to produce a plurality of error vectors;

summing the plurality of error vectors to produce a first total error vector;

scaling the input symbol decisions by the square of the soft weights to produce scaled input symbol decisions;

producing synthesized signals that emulate signals that would be received by the plurality of receive antennas in response to the scaled input symbol decisions being employed as symbols at the plurality of transmit sources;

evaluating a difference between received signals and the first synthesized received signal for each of the plurality of receive antennas to produce a plurality of error signals;

resolving each of the plurality of error signals onto a signal basis for the plurality of transmit sources to produce resolved signals, the signal basis employing the multipath structure determined by the set of dominant beamforming weights;

maximal ratio combining and despreading the resolved signals to produce a plurality of error vectors;

summing the plurality of error vectors to produce a second total error vector;

calculating the denominator by;

scaling the first total error vector with the soft weights to produce a scaled error vector;

producing synthesized signals that would be received by the plurality of receive antennas in response to the scaled error vector being employed as symbols at the plurality of transmit sources, the synthesized signals being determined with respect to the multipath structure determined by the set of dominant beamforming weights; and

integrating square magnitudes of the synthesized signals for producing integrated signals; and

summing the integrated signals; and

calculating the numerator by calculating an inner product between the first total error vector scaled by the soft weights and the second total error vector.

73. The interference canceller recited in claim 71, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

F ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

Γ

[ i ] ⁡

( q ^ _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

( Γ

[ i ] ) H ⁢

R ⁢

⁢

Γ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) .

wherein μ

^[i] is a stabilizing step size after an i^th iteration of iterative interference cancellation, q is a vector representing despread received signals that have been combined across the plurality of receive antennas, Γ

^[i] is a diagonal soft-weighting matrix used for scaling the input symbol decisions {circumflex over (b)}^[i], R is a correlation matrix for received signals combined across the plurality of receive antennas that is a sum of per-antenna received-signal correlation matrices, and is determined with respect to the multipath structure determined by the set of dominant beamforming weights;

F is an implementation matrix comprising an identity matrix or a transmit-signal correlation matrix; and

superscript H denotes complex-conjugate matrix transposition.

74. The interference canceller recited in claim 67, wherein the step-size module is further configured for measuring the stabilizing step size as a function of channel quality.

75. The interference canceller recited in claim 74, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = μ

= max ⁢

{ C , 

max a , s , n , l ⁢



w ^ s , n ⁢

α

a , s , n , l 

p ∑

a = 1 A ⁢

⁢

∑

s = 1 B ⁢

⁢

∑

n = 1 N ⁢

⁢

∑

l = 1 L a , s , n ⁢

⁢



w ^ s , n ⁢

α

a , s , n , l 

p 

r } ,

where μ

is a stabilizing step size fixed for every iteration, A is a number of receive antennas, B is a number of base stations, L_a,s,n is a number of multipaths from a plurality N of transmit antennas of an s^th base station received by an a^th receive antenna, α

_a,s,n,l is a multipath gain corresponding to an l^th path from an n^th transmit antenna of the s^th base station received by the a^th receive antenna, ŵ

_s,n is a dominant beamforming scalar corresponding to the n^th transmit antenna of the s^th base station, max { } denotes a maximum function, and C, p, and r are non-negative constants.

76. The interference canceller recited in claim 67, wherein the step-size module is configured to set the stabilizing step to a predetermined fixed value.

77. A method for canceling interference in signals from a plurality of receive antennas configured for receiving transmissions from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the method comprising:

providing for front-end processing for determining a set of dominant beam forming weights for transmit antennas of each of a plurality of transmit sources, and generating initial symbol decisions, and

providing for performing sequential interference cancellation on the initial symbol decisions;

performing sequential interference cancellation comprising;

providing for applying soft weights to a plurality of input symbol decisions for producing soft symbol estimates,

providing for performing mixed decisions on the soft symbol estimates, and

providing for scaling a residual signal with a stabilizing step size, the step-size having a magnitude representing how far the input symbol decisions are from desired interference-cancelled symbol decisions in a step of iterative interference cancellation.

78. The method recited in claim 77, wherein the stabilizing step size is measured as a ratio of distance measures between received signals combined across the plurality of receive antennas and synthesized received signals combined across the plurality of receive antennas, the synthesized received signals and combining weights being determined with respect to a multipath structure determined from the set of dominant beamforming weights.

79. The method recited in claim 78, wherein the ratio comprises a numerator and a denominator, the numerator being calculated by:

providing for evaluating a residual signal for each of the plurality of receive antennas, the residual signal being a difference between a received signal for one of the plurality of receive antennas and a synthesized received signal for the one of the plurality of receive antennas, the synthesized receive signal comprising multipath structure determined by the set of dominant beamforming weights;

providing resolving the residual signal onto a signal basis for the plurality of transmit sources, the signal basis comprising the multipath structure determined by the dominant beamforming weights;

providing for maximal ratio combining and despreading to produce a plurality of error vectors, each corresponding to one of the plurality of receive antennas;

providing for summing the plurality of error vectors to produce a total error vector; and

providing for evaluating a sum of square magnitudes of elements of the total error vector;

the denominator being calculated by;

providing for synthesizing for each of the plurality of receive antennas a signal that would be received in response to elements of the total error vector being employed as symbols at the plurality of transmit sources,

providing for using a signal basis for all symbol sources in the channel;

providing for evaluating an integral of square magnitudes for the synthesized received signal for each of the plurality of receive antennas for producing a plurality of integral values, and

providing for summing the integral values.

80. The method recited in claim 79, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = ( q _ - RF ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

( q _ - RF ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

R ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ,

wherein μ

^[i] is a stabilizing step size after an i^th iteration of the interference canceller;

q is a vector of despread received signals that have been combined across the plurality of receive antennas, Γ

^[i] is a weighting matrix for scaling the plurality of input symbol decisions, {circumflex over (b)}^[i], R is a correlation matrix for received signals combined across the plurality of receive antennas that is a sum of per-antenna received-signal correlation matrices calculated with respect to the multipath structure determined by the set of dominant beamforming weights;

F is an implementation matrix that may comprise an identity matrix or a transmit-signal correlation matrix; and

superscript H denotes complex-conjugate matrix transposition.

81. The method recited in claim 77, wherein providing for scaling is further configured to measure the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of receive antennas and two differently synthesized received signals combined across the plurality of receive antennas, the synthesized received signals comprising multipath structure determined by the set of dominant beamforming weights.

82. The method recited in claim 81, wherein the stabilizing step size is a ratio comprising a numerator and a denominator, the providing for scaling further comprising:

providing for evaluating a residual signal for each one of the plurality of receive antennas, the residual signal being a difference between a received signal on the one of the plurality of receive antennas and a first synthesized received signal for the one of the plurality of receive antennas, the first synthesized received signal comprising multipath structure determined by the set of dominant beamforming weights;

providing for resolving the residual signal onto a signal basis for the plurality of transmit sources for producing resolved signals, wherein providing for resolving employs the multipath structure determined by the set of dominant beamforming weights;

providing for maximal ratio combining and despreading of the resolved signals to produce a plurality of error vectors;

providing for summing the plurality of error vectors to produce a first total error vector;

providing for scaling the input symbol decisions by the square of the soft weights to produce scaled input symbol decisions;

providing for producing synthesized signals that emulate signals that would be received by the plurality of receive antennas in response to the scaled input symbol decisions being employed as symbols at the plurality of transmit sources;

providing for evaluating a difference between received signals and the first synthesized received signal for each of the plurality of receive antennas to produce a plurality of error signals;

providing for resolving each of the plurality of error signals onto a signal basis for the plurality of transmit sources to produce resolved signals, the signal basis employing the multipath structure determined by the set of dominant beamforming weights;

providing for performing maximal ratio combining and despreading of the resolved signals to produce a plurality of error vectors;

providing for summing the plurality of error vectors to produce a second total error vector;

providing for calculating the denominator by;

scaling the first total error vector with the soft weights to produce a scaled error vector;

producing synthesized signals that would be received by the plurality of receive antennas in response to the scaled error vector being employed as symbols at the plurality of transmit sources, the synthesized signals being determined with respect to the multipath structure determined by the set of dominant beamforming weights; and

integrating square magnitudes of the synthesized signals for producing integrated signals; and

providing for summing the integrated signals; and

providing for calculating the numerator by calculating an inner product between the first total error vector scaled by the soft weights and the second total error vector.

83. The method recited in claim 81, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

F ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

Γ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

( Γ

[ i ] ) H ⁢

R ⁢

⁢

Γ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) .

wherein μ

^[i] is a stabilizing step size after an i^th iteration of iterative interference cancellation, q is a vector representing despread received signals that have been combined across the plurality of receive antennas, Γ

^[i] is a diagonal soft-weighting matrix used for scaling the input symbol decisions {circumflex over (b)}^[i], R is a correlation matrix for received signals combined across the plurality of receive antennas that is a sum of per-antenna received-signal correlation matrices, and is determined with respect to the multipath structure determined by the set of dominant beamforming weights;

F is an implementation matrix comprising an identity matrix or a transmit-signal correlation matrix; and

superscript H denotes complex-conjugate matrix transposition.

84. The method recited in claim 77, wherein providing for scaling is further configured for measuring the stabilizing step size as a function of channel quality.

85. The method recited in claim 84, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = μ

= max ⁢

{ C , 

max a , s , n , l ⁢



w ^ s , n ⁢

α

a , s , n , l 

p ∑

a = 1 A ⁢

⁢

∑

s = 1 B ⁢

⁢

∑

n = 1 N ⁢

⁢

∑

l = 1 L a , s , n ⁢

⁢



w ^ s , n ⁢

α

a , s , n , l 

p 

r } ,

where μ

is a stabilizing step size fixed for every iteration, A is a number of receive antennas, B is a number of base stations, L_a,s,n is a number of multipaths from a plurality N of transmit antennas of an s^th base station received by an a^th receive antenna, α

_a,s,n,l is a multipath gain corresponding to an l^th path from an n^th transmit antenna of the s^th base station received by the a^th receive antenna, ŵ

_s,n is a dominant beamforming scalar corresponding to the n^th transmit antenna of the s^th base station, max { } denotes a maximum function, and C, p, and r are non-negative constants.

86. The method recited in claim 77, wherein providing for scaling is configured to set the stabilizing step to a predetermined fixed value.

87. A handset configured to perform the method recited in claim 77.

88. A chipset configured to perform the method recited in claim 77.

89. A digital computer system programmed to perform the method recited in claim 77.

90. A computer-readable medium storing a computer program implementing the method of claim 77.

91. A base station configured to perform the method of claim 77.

92. A system configured for canceling interference in signals from a plurality of receive antennas receiving transmissions from a plurality of transmit antennas in a system wherein closed loop transmit waveform shaping is employed, the system comprising:

a front-end processing means configured for determining a set of dominant beamforming weights for transmit antennas of each of a plurality of transmit sources and generating initial symbol decisions, and

a sequential interference cancellation means configured for operating on the initial symbol decisions;

the sequential interference cancellation means comprising;

a soft-weighting means configured for applying soft weights to a plurality of input symbol decisions for producing soft symbol estimates,

a mixed-decision means configured for performing mixed decisions on the soft symbol estimates, and

a stabilizing step size means configured for scaling a residual signal with a stabilizing step size, the step-size having a magnitude representing how far the input symbol decisions are from desired interference-cancelled symbol decisions in a step of iterative interference cancellation.

93. The system recited in claim 92, wherein the stabilizing step size means is configured for measuring the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of receive antennas and synthesized received signals combined across the plurality of receive antennas, the synthesized received signals and combining weights being determined with respect to a multipath structure determined from the set of dominant beamforming weights.

94. The system recited in claim 93, wherein the ratio comprises a numerator and a denominator, the numerator being calculated by:

providing for evaluating a residual signal for each of the plurality of receive antennas, the residual signal being a difference between a received signal for one of the plurality of receive antennas and a synthesized received signal for the one of the plurality of receive antennas, the synthesized receive signal comprising multipath structure determined by the set of dominant beamforming weights;

providing resolving the residual signal onto a signal basis for the plurality of transmit sources, the signal basis comprising the multipath structure determined by the dominant beamforming weights;

providing for maximal ratio combining and despreading to produce a plurality of error vectors, each corresponding to one of the plurality of receive antennas;

providing for summing the plurality of error vectors to produce a total error vector; and

providing for evaluating a sum of square magnitudes of elements of the total error vector;

the denominator being calculated by;

providing for synthesizing for each of the plurality of receive antennas a signal that would be received in response to elements of the total error vector being employed as symbols at the plurality of transmit sources,

providing for using a signal basis for all symbol sources in the channel;

providing for evaluating an integral of square magnitudes for the synthesized received signal for each of the plurality of receive antennas for producing a plurality of integral values, and

providing for summing the integral values.

95. The system recited in claim 94, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = ( q _ - RF ⁢

⁢

Γ

[ i ] ⁢

b _ ^ [ i ] ) H ⁢

( q _ - RF ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) H ⁢

R ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b _ ^ [ i ] ) ,

wherein μ

^[i] is a stabilizing step size after an i^th iteration of the interference canceller;

q is a vector of despread received signals that have been combined across the plurality of receive antennas, Γ

^[i] is a weighting matrix for scaling the plurality of input symbol decisions, {circumflex over (b)}^[i], R is a correlation matrix for received signals combined across the plurality of receive antennas that is a sum of per-antenna received-signal correlation matrices calculated with respect to the multipath structure determined by the set of dominant beamforming weights;

F is an implementation matrix that may comprise an identity matrix or a transmit-signal correlation matrix; and

superscript H denotes complex-conjugate matrix transposition.

96. The system recited in claim 92, wherein the stabilizing step size means is further configured to measure the stabilizing step size as a ratio of distance measures between received signals combined across the plurality of receive antennas and two differently synthesized received signals combined across the plurality of receive antennas, the synthesized received signals comprising multipath structure determined by the set of dominant beamforming weights.

97. The system recited in claim 96, wherein the stabilizing step size is a ratio comprising a numerator and a denominator, the stabilizing step size further configured for:

providing for evaluating a residual signal for each one of the plurality of receive antennas, the residual signal being a difference between a received signal on the one of the plurality of receive antennas and a first synthesized received signal for the one of the plurality of receive antennas, the first synthesized received signal comprising multipath structure determined by the set of dominant beamforming weights;

providing for resolving the residual signal onto a signal basis for the plurality of transmit sources for producing resolved signals, wherein providing for resolving employs the multipath structure determined by the set of dominant beamforming weights;

providing for maximal ratio combining and despreading of the resolved signals to produce a plurality of error vectors;

providing for summing the plurality of error vectors to produce a first total error vector;

providing for scaling the input symbol decisions by the square of the soft weights to produce scaled input symbol decisions;

providing for producing synthesized signals that emulate signals that would be received by the plurality of receive antennas in response to the scaled input symbol decisions being employed as symbols at the plurality of transmit sources;

providing for evaluating a difference between received signals and the first synthesized received signal for each of the plurality of receive antennas to produce a plurality of error signals;

providing for resolving each of the plurality of error signals onto a signal basis for the plurality of transmit sources to produce resolved signals, the signal basis employing the multipath structure determined by the set of dominant beamforming weights;

providing for performing maximal ratio combining and despreading of the resolved signals to produce a plurality of error vectors;

providing for summing the plurality of error vectors to produce a second total error vector;

providing for calculating the denominator by;

scaling the first total error vector with the soft weights to produce a scaled error vector;

producing synthesized signals that would be received by the plurality of receive antennas in response to the scaled error vector being employed as symbols at the plurality of transmit sources, the synthesized signals being determined with respect to the multipath structure determined by the set of dominant beamforming weights; and

integrating square magnitudes of the synthesized signals for producing integrated signals; and

providing for summing the integrated signals; and

providing for calculating the numerator by calculating an inner product between the first total error vector scaled by the soft weights and the second total error vector.

98. The system recited in claim 96, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

F ⁢

⁢

Γ

[ i ] ⁢

b _ ^ [ i ] ) H ⁢

Γ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b ^ _ [ i ] ) ( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b _ ^ [ i ] ) H ⁢

( Γ

[ i ] ) H ⁢

R ⁢

⁢

Γ

[ i ] ⁡

( q _ - R ⁢

⁢

Γ

[ i ] ⁢

b _ ^ [ i ] ) .

wherein μ

^[i] is a stabilizing step size after an i^th iteration of iterative interference cancellation, q is a vector representing despread received signals that have been combined across the plurality of receive antennas, Γ

^[i] is a diagonal soft-weighting matrix used for scaling the input symbol decisions {circumflex over (b)}^[i], R is a correlation matrix for received signals combined across the plurality of receive antennas that is a sum of per-antenna received-signal correlation matrices, and is determined with respect to the multipath structure determined by the set of dominant beamforming weights;

F is an implementation matrix comprising an identity matrix or a transmit-signal correlation matrix; and

superscript H denotes complex-conjugate matrix transposition.

99. The system recited in claim 92, wherein the stabilizing step size means is further configured for measuring the stabilizing step size as a function of channel quality.

100. The system recited in claim 99, wherein the stabilizing step size is characterized by

${\mu }^{}$

[ i ] = μ

= max ⁢

{ C , 

max a , s , n , l ⁢



w ^ s , n ⁢

α

a , s , n , l 

p ∑

a = 1 A ⁢

⁢

∑

s = 1 B ⁢

⁢

∑

n = 1 N ⁢

⁢

∑

l = 1 L a , s , n ⁢

⁢



w ^ s , n ⁢

α

a , s , n , l 

p 

r } ,

where μ

is a stabilizing step size fixed for every iteration, A is a number of receive antennas, B is a number of base stations, L_a,s,n is a number of multipaths from a plurality N of transmit antennas of an s^th base station received by an a^th receive antenna, α

_a,s,n,l is a multipath gain corresponding to an l^th path from an n^th transmit antenna of the s^th base station received by the a^th receive antenna, ŵ

_s,n is a dominant beamforming scalar corresponding to the n^th transmit antenna of the s^th base station, max { } denotes a maximum function, and C, p, and r are non-negative constants.

101. The system recited in claim 92, wherein the stabilizing step size means is configured to set the stabilizing step to a predetermined fixed value.