Method and apparatus for receiving digital wireless transmissions using multiple-antenna communication schemes

1. A method for detecting a plurality, M, of transmitted signals transmitted across a channel by respective transmitting antenna elements in a multiple-input multiple-output MIMO communications system, the method comprising the steps of:

(a) collecting a plurality of received signals from respective receiving antenna elements in said MIMO communications system;

(b) determining a channel matrix H of estimated channel coefficients based on said plurality of received signals;

(c) computing an estimate of a selected one of said plurality of transmitted signals, said estimate based on said plurality of received signals and on an intermediate matrix Q, thereby resulting in detection of the selected one of said plurality of transmitted signals, wherein said intermediate matrix Q is a function of the channel matrix H; and

(d) repeating at least step (c) one or more times to detect an additional one or more of said plurality of transmitted signals, wherein said intermediate matrix Q as used in step (c) for each such repeated execution thereof is re-computed based on a function of an inverse of a Schur complement of an element in the inverse of a modified version of the intermediate matrix Q used in the previous execution of step (c).

2. The method of claim 1 further comprising the step of:

modifying one or more of said received signals by at least partially canceling an effect of the detected signal from said received signals based on the computed estimated of said detected signal,

and wherein said modified received signals are used in a subsequent repetition of step (c).

3. The method of claim 1 wherein said selected one of said transmitted signals detected in each execution of step (c) is selected in accordance with a preferred order, and wherein said preferred order is based on signal-to-noise ratios of said transmitted signals as determined at each execution of step (c).

4. The method of claim 1 wherein said channel matrix H is initially determined based on a transmission of a predetermined training sequence.

5. The method of claim 1 wherein the intermediate matrix Q as used in step (c) in a first execution thereof is Q M =[H M H H M +αI M×M ] −1 , where H M is the determined channel matrix H, the operator H represents a conjugate transpose of a matrix, I M×M represents an M×M identity matrix, and α is a predetermined constant based on a signal-to-noise ratio of the transmitted signals.

6. The method of claim 1 wherein the modified version of the intermediate matrix Q is derived from the intermediate matrix Q by permuting

(i) a matrix row and a matrix column which corresponds to said transmitted signal detected by said previous execution of step (c) with

(ii) a matrix row and a matrix column which corresponds to a last one of said transmitted signals which has not yet been detected, respectively.

7. The method of claim 6 wherein the intermediate matrix Q as used in step (c) in each repeated execution thereof is Q=Q m−1 where

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m

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where

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is the Schur complement of β p M−m+1 in Q m −1 , where the operator H represents a conjugate transpose of a matrix, and where the modified version of the intermediate matrix Q as used in step (c) in each corresponding execution immediately preceding said repeated execution thereof, is Q m where

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8. An apparatus for detecting a plurality, M, of transmitted signals transmitted across a channel by respective transmitting antenna elements in a multiple-input multiple-output MIMO communications system, the apparatus comprising:

a plurality of receiving antenna elements in said MIMO communications system for collecting a corresponding plurality of received signals; and

a processor adapted to perform the steps of:

(a) determining a channel matrix H of estimated channel coefficients based on said plurality of received signals;

(b) computing an estimate of a selected one of said plurality of transmitted signals, said estimate based on said plurality of received signals and on an intermediate matrix Q, thereby resulting in detection of the selected one of said plurality of transmitted signals, wherein said intermediate matrix Q is a function of the channel matrix H; and

(c) repeating at least step (c) one or more times to detect an additional one or more of said plurality of transmitted signals, wherein said intermediate matrix Q as used in step (b) for each such repeated execution thereof is re-computed based on a function of an inverse of a Schur complement of an element in the inverse of a modified version of the intermediate matrix Q used in the previous execution of step (b).

9. The apparatus of claim 8 , wherein said processor is further adapted to perform the additional step of:

modifying one or more of said received signals by at least partially cancelling an effect of the detected signal from said received signals based on the computed estimated of said detected signal, and wherein said modified received signals are used in a subsequent repetition of step (b).

10. The apparatus of claim 8 wherein said selected one of said transmitted signals detected in each execution of step (b) is selected in accordance with a preferred order, and wherein said preferred order is based on signal-to-noise ratios of said transmitted signals as determined at each execution of step (b).

11. The apparatus of claim 8 wherein said channel matrix H is initially determined based on a transmission of a predetermined training sequence.

12. The apparatus of claim 8 wherein the intermediate matrix Q as used in step (b) in a first execution thereof is Q M =[H M H H M +αI M×M ] −1 , where H M is the determined channel matrix H, the operator H represents a conjugate transpose of a matrix, I M×M represents an M×M identity matrix, and α is a predetermined constant based on a signal-to-noise ratio of the transmitted signals.

13. The apparatus of claim 8 wherein the modified version of the intermediate matrix Q is derived from the intermediate matrix Q by permuting

(i) a matrix row and a matrix column which corresponds to said transmitted signal detected by said previous execution of step (b) with

(ii) a matrix row and a matrix column which corresponds to a last one of said transmitted signals which has not yet been detected, respectively.

14. The apparatus of claim 8 wherein the intermediate matrix Q as used in step (b) in each repeated execution thereof is Q=Q m−1 where

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m

-

1

=

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where

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=

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v

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v

m

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1

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is the Schur complement of β p M−m+1 in Q m −1 , where the operator H represents a conjugate transpose of a matrix, and where the modified version of the intermediate matrix Q as used in step (b) in each corresponding execution immediately preceding said repeated execution thereof, is Q m where

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m

=

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.