Method and apparatus for interference suppression with efficient matrix inversion in a DS-CDMA system
First Claim
1. A method for interference suppression, the method comprising:
- receiving as part of a signal stream in a receiver a desired signal path having symbols of a first length;
receiving as part of said signal stream in the receiver an interfering signal path having symbols of a second length, wherein said second length is less than said first length; and
forming an interference matrix in a cancellation controller having at least three interference vectors, wherein a first of said interference vectors includes a representation of at least a portion of a first interfering symbol included in said interfering signal path, wherein a last of said interference vectors comprises a representation of at least a portion of a second symbol included in said interfering signal path, and wherein an intermediate one of said interference vectors comprises a representation of all of a third symbol included in said interfering signal path;
where the interference matrix is used to substantially reduce interference from the signal stream.
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Accused Products
Abstract
The present invention is directed to signal cancellation in spread spectrum communication systems. In particular, the present invention provides method and apparatus for selectively canceling interfering signals, even where symbols to be canceled do not align with symbols associated with a desired signal path. Furthermore, the interference cancellation provided by embodiments of the present invention is capable of functioning to remove interference associated with channels utilizing a symbol length that is different than the symbol length of a desired signal path. In accordance with a further embodiment of the present invention, method and apparatus for efficiently calculating projections to enable signal cancellation are provided.
184 Citations
30 Claims
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1. A method for interference suppression, the method comprising:
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receiving as part of a signal stream in a receiver a desired signal path having symbols of a first length; receiving as part of said signal stream in the receiver an interfering signal path having symbols of a second length, wherein said second length is less than said first length; and forming an interference matrix in a cancellation controller having at least three interference vectors, wherein a first of said interference vectors includes a representation of at least a portion of a first interfering symbol included in said interfering signal path, wherein a last of said interference vectors comprises a representation of at least a portion of a second symbol included in said interfering signal path, and wherein an intermediate one of said interference vectors comprises a representation of all of a third symbol included in said interfering signal path; where the interference matrix is used to substantially reduce interference from the signal stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for suppressing interference, comprising:
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identifying an interfering signal in a searcher; tracking said interfering signal in a finger; for at least a first channel included in said interfering signal, building an estimate in a cancellation controller of at least a portion of each symbol of said interfering signal that overlaps with a symbol of interest, wherein at least three symbols of the first channel of said interfering signal at least partially overlap said signal of interest; and forming an interference matrix in the cancellation controller comprising said estimate of at least a portion of each symbol of said interfering signal that overlaps with a symbol of interest; where the interference matrix is used to substantially reduce interference contributed by the said interfering signal. - View Dependent Claims (16, 17, 18, 19, 20)
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21. An apparatus for canceling an interfering channel from a signal path, comprising:
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a first demodulation finger, wherein a first desired signal path is tracked; a second demodulation finger, wherein a first interfering signal path is tracked; and a cancellation controller, operable to form an interference matrix comprising at least a first interference vector, an intermediate interference vector, and a last interference vector, wherein said first and last interference vectors each correspond to a partial interfering symbol included in a first channel of said interfering signal path, wherein said intermediate interference vector contains a number of non-zero values corresponding to a complete interfering symbol included in said first channel of said interfering signal path. - View Dependent Claims (22, 23, 24)
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25. An apparatus for a signal stream including suppression interference from a signal, comprising:
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means for receiving a desired signal path and an interfering signal path; means for detecting an active channel in said interfering signal path; means for forming at least three interference vectors for each portion of a symbol in said interfering symbol path that overlaps with a desired signal; and means for calculating a projection of a reference signal that is orthogonal to a matrix of vectors comprising said at least three interference vectors. - View Dependent Claims (26)
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27. A method for canceling interference, comprising:
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receiving as part of a signal stream a desired signal path in a receiver; receiving as part of said signal stream an interfering signal path in a receiver; identifying in a cancellation controller at least a first active channel in said interfering signal path by; 1) obtaining a first number of chip values from said interfering signal stream, wherein said first number is equal to a number of chips included in a longest valid symbol; 2) performing a fast Walsh transform on said first number of chip values to obtain a first set of transformed values, wherein a first result includes a first number of elements equal to said first number of chip values; 3) comparing a value of each of said first number of elements of said first set of transformed values to a threshold; and 4) creating a modified set of values, wherein for each element of said first set of transformed values; a) in response to a first result of said comparison, a value of said element is changed to a zero; b) in response to a second result of said comparison, a value of said element is not changed to zero; forming an interference matrix in the cancellation controller comprising a plurality of interference vectors, wherein at least a first of said interference vectors comprises at least a portion of a first interfering symbol included in said identified at least a first channel of said interfering signal path and wherein a second of said interference vectors comprises at least a portion of a second symbol included in said at least a first channel of said interfering signal path; where the interference matrix is used to substantially reduce interference from the signal stream. - View Dependent Claims (28, 29)
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30. A method for canceling interference, comprising:
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receiving as part of a signal stream a desired signal in a receiver; receiving as part of said signal stream an interfering signal path in the receiver; identifying at least a first active channel in said interfering signal path in a cancellation controller; forming an interference matrix in the cancellation controller comprising a plurality of interference vectors, wherein at least a first of said interference vectors comprises at least a portion of a first interfering symbol included in said identified at least a first channel of said interfering signal path and wherein a second of said interference vectors comprises at least a portion of a second symbol included in said at least a first channel of said interfering signal path; determining in the cancellation controller a projection operator Ps⊥
where;
Ps⊥
=I−
U(UTU)−
1UT, where I is the identity matrix and where the vectors of the interference matrix U form an orthogonal basis; andapplying said projection operator to a reference signal.
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Specification