# Patent

## Title
Order recursive computation for a MIMO equalizer

## Abstract

A receiver module includes an input that receives a data message from a wireless communication channel. The data message has a plurality of training fields and data. A channel estimator module recursively estimates a matrix H that represents the channel based on the plurality of training fields. The recursive estimation is performed as the plurality of training fields are being received. An equalizer module applies coefficients to the data based on the matrix H.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Application No. 60/759,453, filed on Jan. 17, 2006. The disclosure of the above application is incorporated herein by reference in its entirety.


FIELD
The present disclosure relates to channel estimation in a wireless communication system.
BACKGROUND
The Background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
Some multiple input, multiple output (MIMO) wireless communication systems can estimate channel conditions, or gains, in the communication path between the transmitting and receiving antennas. The channel estimation process can include transmitting known training symbols, receiving the known training symbols, and processing the received symbols to estimate the channel conditions. The estimation is based on differences between the known training symbols and the received symbols. Information regarding the channel conditions can then be used to program coefficients of an equalizer of the receiver. The equalizer then compensates for the channel conditions.
Referring now to FIG. 1, an example is shown of a MIMO communication system 10 that complies with the Institute of Electrical and Electronics Engineers (IEEE) 802.11n specification, which is hereby incorporated by reference in its entirety. A transmitter module 12 communicates with a receiver module 14 via a wireless communication channel 16. A matrix H represents signal gains through channel 16.
Transmitter module 12 periodically generates a plurality of long training fields (LTFs) 18-1, . . . , 18-j, referred to collectively as LTFs 18. Each LTF 18 includes a plurality of training symbols 20-1, . . . , 20-k, referred to collectively as training symbols 20. A multiplier module 22 multiplies each training symbol 20 by a corresponding column of a preamble steering matrix P. A number of rows n of matrix P corresponds with a number of transmit antennas 26-1, . . . , 26-n, collectively referred to as antennas 26. The number of columns j of matrix P corresponds with the number of LTFs 18. Matrix P assures the orthogonality of training symbols 20 as they are transmitted from antennas 26. Matrix P has a condition number of 1, i.e. cond(P)=1.
Receiver module 14 includes receiver antennas 30-1, . . . , 30-n, collectively referred to as antennas 30, that receive the training symbols via channel 16. After receiving all of the training symbols, receiver module 14 generates matrix H based on known training symbols 20, matrix P, and the received training symbols. Receiver module 14 can then use matrix H to adjust coefficients of an internal equalization module for signals from antennas 30. It is generally desirable for receiver module 14 to generate matrix H as quickly as possible.
A sample estimation of matrix H will now be described. Assume that n=3 and j=4. Transmitter module 12 then sends 4 LTFs 18 and matrix P is a 3×4 matrix




  P
  =
  
    
      [
      
        
          
            1
          
          
            
              -
              1
            
          
          
            1
          
          
            1
          
        
        
          
            1
          
          
            1
          
          
            
              -
              1
            
          
          
            1
          
        
        
          
            1
          
          
            1
          
          
            1
          
          
            
              -
              1
            
          
        
        
          
            
              -
              1
            
          
          
            1
          
          
            1
          
          
            1
          
        
      
      ]
    
    .
  




The effective MIMO channel estimated at receiver module 14 is given by Hest=HPH=HestP−1, where Hest represents an estimation of matrix H. For the data associated with each LTF 18 the transmitter-to-receiver communication model can be described by y=HestP−1x+n, where x represents transmitted data symbols. The ZF solution is applied to the matrix HestP−1.
If the matrix P were not used, y=Hx+n{circumflex over (x)}=R−1Q*y, where y represents received data symbols. With matrix P, y=HestP−1x+n. Receiver module 14 uses each LTF 18 to estimate a column of matrix Hest. Matrix H can therefore be estimated by waiting until all columns have been estimated and then estimating the matrix HestP−1. Receiver module 14 can then perform orthogonal-triangular decomposition (QR) on HestP−1, i.e QR(HestP−1). However, the computational density increases to the order of n3, i.e. O(n3). To meet the processing latency the hardware burden would also increase based on O(n3).
The effect of matrix P will now be described to shed light on the above equations. Let Hest=QR. Without matrix P the equalized vector is given by




  
    
      x
      ^
    
    =
    
      
        1
        
          diag
          ⁡
          
            (
            
              
                R
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  *
                
              
            
            )
          
        
      
      ⁢
      
        R
        
          -
          1
        
      
      ⁢
      
        Q
        *
      
      ⁢
      y
    
  
  ,
  
    
      where
      ⁢
      
        
      
      ⁢
      
        W
        
      
    
    =
    
      
        1
        
          diag
          ⁡
          
            (
            
              
                R
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  *
                
              
            
            )
          
        
      
      .
    
  




With matrix P the equalized vector is given by:




  
    
      
        x
        ^
      
      =
      
        
          1
          
            diag
            ⁡
            
              (
              
                
                  
                    (
                    
                      RP
                      
                        -
                        1
                      
                    
                    )
                  
                  
                    -
                    1
                  
                
                ⁢
                
                  
                    (
                    
                      RP
                      
                        -
                        1
                      
                    
                    )
                  
                  
                    -
                    *
                  
                
              
              )
            
          
        
        ⁢
        
          PR
          
            -
            1
          
        
        ⁢
        
          Q
          *
        
        ⁢
        y
      
    
    ,
    
      

    
    ⁢
    where
  




  
    
      W
      
    
    =
    
      
        1
        
          diag
          ⁡
          
            (
            
              
                
                  (
                  
                    RP
                    
                      -
                      1
                    
                  
                  )
                
                
                  -
                  1
                
              
              ⁢
              
                
                  (
                  
                    RP
                    
                      -
                      1
                    
                  
                  )
                
                
                  -
                  *
                
              
            
            )
          
        
      
      .
    
  



The equivalent matrix RP−1 is a full matrix and it is difficult to compute its inverse for an n×n communication system.

SUMMARY
A receiver module includes an input that receives a data message from a wireless communication channel. The data message has a plurality of training fields and data. A channel estimator module recursively estimates a matrix H that represents the channel based on the plurality of training fields. The recursive estimation is performed as the plurality of training fields are being received. An equalizer module applies coefficients to the data based on the matrix H.
In other features the channel estimator module begins the recursive estimation upon receiving a first one of the training fields and finishes the recursive estimation upon receiving a final one of the plurality of training fields. The channel estimator module estimates the matrix H based on a matrix P. the plurality of training symbols are processed in accordance with the matrix P prior to being transmitted to the receiver module. The recursive estimation of matrix H includes recursively estimating a matrix Hest based on the plurality of training fields and estimating matrix H based on an inverse of matrix P and a final value of the matrix Hest. Each iteration of the recursive estimation of matrix Hest occurs after receiving a corresponding one of the plurality of training fields.
In other features the receiver module further includes a plurality of FFT modules that convert the data from time domain signals to frequency domain signals. Respective outputs of the plurality of FFT modules communicate with respective inputs of the equalizer module. The receiver module includes a Viterbi decoder module that generates data symbols based on the frequency domain signals communicated from an output of the equalizer module. The plurality of training fields are compliant with IEEE 802.11n.
In other features a transceiver module includes the receiver module and further includes a transmitter module. The transmitter module generates training symbols that are to be included in the plurality of training fields and includes a multiplier module that multiplies the training symbols by a matrix P. The matrix P has a condition number equal to 1.
A method of operating a receiver includes receiving a data message from a wireless communication channel. The data message has a plurality of training fields and data. The method includes recursively estimating a matrix H that represents the channel based on the plurality of training fields. The recursive estimating is performed as the plurality of training fields are being received. The method also includes applying coefficients to the data based on the matrix H.
In other features the recursive estimating step begins upon receiving a first one of the training fields and finishes upon receiving a final one of the plurality of training fields. The matrix H is based on a matrix P and the plurality of training symbols are processed in accordance with the matrix P prior to being transmitted. The recursive estimation of matrix H includes recursively estimating a matrix Hest based on the plurality of training fields and estimating matrix H based on an inverse of matrix P and a final value of the matrix Hest. Each iteration of the recursive estimation of matrix Hest occurs after receiving a corresponding one of the plurality of training fields.
In other features the method includes converting the data from time domain signals to frequency domain signals. The method includes communicating the frequency domain signals to the step of applying coefficients. The method includes generating data symbols based on frequency domain signals that are output from the step of applying coefficients. The plurality of training fields are compliant with IEEE 802.11n.
In other features the method is adapted to operating a transceiver module by including transmitting a wireless signal over the wireless communication channel. The transmitting step includes generating training symbols that are to be included in the plurality of training fields and multiplying the training symbols by a matrix P. The matrix P has a condition number equal to 1.
A receiver module includes input means for receiving a data message from a wireless communication channel. The data message has a plurality of training fields and data. Channel estimator means recursively estimate a matrix H that represents the channel based on the plurality of training fields. The recursive estimation is performed as the plurality of training fields are being received. Equalizer means apply coefficients to the data based on the matrix H.
In other features the channel estimator means begins the recursive estimation upon receiving a first one of the training fields and finishes the recursive estimation upon receiving a final one of the plurality of training fields. The channel estimator means estimates the matrix H based on a matrix P. The plurality of training symbols are processed in accordance with the matrix P prior to being transmitted to the receiver module. The recursive estimation of matrix H includes recursively estimating a matrix Hest based on the plurality of training fields and estimating matrix H based on an inverse of matrix P and a final value of the matrix Hest. Each iteration of the recursive estimation of matrix Hest occurs after receiving a corresponding one of the plurality of training fields.
In other features the receiver module includes FFT means for converting the data from time domain signals to frequency domain signals. Respective outputs of the FFT means communicate with respective inputs of the equalizer means. The receiver module includes a Viterbi decoder module that generates data symbols based on frequency domain signals communicated from an output of the equalizer module. The plurality of training fields are otherwise compliant with IEEE 802.11 n.
In other features a transceiver module includes the receiver and further includes transmitter means for transmitting a wireless signal over the wireless communication channel. The transmitter means generates training symbols that are to be included in the plurality of training fields and includes multiplier means for multiplying the training symbols by a matrix P. The matrix P has a condition number equal to 1.
In still other features, a computer program executed by a processor associated with a receiver includes receiving a data message from a wireless communication channel. The data message has a plurality of training fields and data. The computer program includes recursively estimating a matrix H that represents the channel based on the plurality of training fields. The recursive estimating is performed as the plurality of training fields are being received. The computer program also includes applying coefficients to the data based on the matrix H.
In other features the recursive estimating step begins upon receiving a first one of the training fields and finishes upon receiving a final one of the plurality of training fields. The matrix H is based on a matrix P and the plurality of training symbols are processed in accordance with the matrix P prior to being transmitted. The recursive estimation of matrix H includes recursively estimating a matrix Hest based on the plurality of training fields and estimating matrix H based on an inverse of matrix P and a final value of the matrix Hest. Each iteration of the recursive estimation of matrix Hest occurs after receiving a corresponding one of the plurality of training fields.
In other features the computer program includes converting the data from time domain signals to frequency domain signals. The computer program includes communicating the frequency domain signals to the step of applying coefficients. The computer program includes generating data symbols based on frequency domain signals that are output from the step of applying coefficients. The plurality of training fields are compliant with IEEE 802.11n.
In other features the computer program is adapted to operating a transceiver module by including transmitting a wireless signal over the wireless communication channel. The transmitting step includes generating training symbols that are to be included in the plurality of training fields and multiplying the training symbols by a matrix P. The matrix P has a condition number equal to 1.
In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a computer readable medium such as but not limited to memory, non-volatile data storage and/or other suitable tangible storage mediums.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.



BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a functional block diagram of a multiple input, multiple output (MIMO) communication system according to the prior art;
FIG. 2 is a functional block diagram of a MIMO communication system that includes a receiver that employs a recursive channel estimation method;
FIG. 3 is a functional block diagram of a MIMO transceiver that includes the receiver of FIG. 2;
FIG. 4 is a data diagram of a prior art data message that is transmitted by a transmitter module of the communication system of FIG. 2;
FIG. 5 is a flowchart of the recursive channel estimation method;
FIG. 6A is a functional block diagram of a high definition television;
FIG. 6B is a functional block diagram of a vehicle control system;
FIG. 6C is a functional block diagram of a cellular phone;
FIG. 6D is a functional block diagram of a set top box; and
FIG. 6E is a functional block diagram of a media player.



DETAILED DESCRIPTION
The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module, circuit and/or device refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure.
Referring now to FIG. 2, a functional block diagram is shown of a MIMO communication system 50. Communication system 50 includes a receiver module 52 that employs a recursive channel estimation method (shown in FIG. 5). The recursive channel estimation method estimates conditions in a wireless communication channel 54. The recursive estimation method begins with a first long training sequence that is sent by a transmitter module 56. The recursive estimation method ends by generating a channel estimation matrix H when the last long training sequence has been received. Since the recursive estimation method develops a basis for generating matrix H while the long training sequences are being received, instead of starting after the long training sequences have been received, the recursive estimation method can generate matrix H faster than previously known methods. The matrix H can then be used to perform channel equalization in receiver module 52 to compensate for the effects of communication channel 54.
Communication system 50 will now be described in pertinent part. A baseband module 58 generates data messages based on m streams of incoming data. Baseband module 58 communicates the data messages (shown in FIG. 4) to an encoder module 60. The data messages include respective long training fields that are compliant with IEEE 802.11n. Encoder module 60 encodes the long training fields into n data streams based on the matrix P, which is shown in FIG. 1. Encoder module 60 communicates the n data streams to n respective transmit channels 62-1, . . . , 62-n, which are referred to collectively as transmit channels 62. Each transmit channel 62 includes a respective modulation module 64 that modulates its respective data stream, such as with quadrature-amplitude modulation (QAM), and communicates the modulated data stream to a respective inverse fast-Fourier transform (IFFT) module 66. IFFT modules 66 convert their respective data streams from a frequency domain signal to a time domain signal. IFFT modules 66 communicate the time domain signals to respective radio frequency (RF) transmitters that are represented by antennas 68.
The transmitted data streams propagate through communication channel 54. Communication channel 54 perturbs the transmitted data streams due to phenomena such as reflections, signal attenuation, and so forth. The perturbations can be represented by matrix H.
Receiver module 52 includes n RF receivers that are represented by antennas 70-1, . . . , 70-n. The RF receivers receive the transmitted data streams and communicate the perturbed time domain signals to a channel estimator module 72. Channel estimator module 72 estimates matrix H based on matrix P and the long training fields that are included in the received data streams. In some embodiments channel estimator module 72 includes a processor 73 and associated memory 75 for storing and/or executing the recursive channel estimation methods that are described below.
Channel estimator module 72 communicates the n received data streams to n respective fast-Fourier transform (FFT) modules 74 and adjusts gains of an equalizer module 76. FFT modules 74 convert the time-domain data streams to frequency-domain data streams and communicate them to equalizer module 76. Equalizer module 76 compensates the respective data streams based on the gains and communicates the compensated gains to a Viterbi decoder module 78. Viterbi decoder module 78 decodes the n data streams to generate received data streams ym.
Referring now to FIG. 3, a functional block diagram is shown of a transceiver 80 that includes transmitter module 56 and receiver module 52. Transceiver 80 can communicate with other transceivers 80 via antennas 82-1, . . . 82-n. An antennas switch module 84 selectively connects antennas 82 to transmitter module 56 or receiver module 52 based on whether transceiver 80 is transmitting or receiving.
Referring now to FIG. 4, a data diagram is shown of an IEEE 802.11n data message 90. Data message 90 includes data 92 and a preamble 94 that contains a plurality of training fields. Preamble 94 is divided into a first portion 96 and a second portion 98. First portion 96 may be used by legacy systems, e.g. non-MIMO, IEEE 802.11 communication systems. Second portion 98 includes a signal filed field 100, a short training field 102, and x long training fields (LTFs) 104-1, . . . , 104-x, where x is an integer. Each LTF 104 includes k training symbols 106 or tones. Short training field 102 is generally used by receiver module 52 to establish symbol timing of data message 90. Channel estimator module 72 uses LTFs 104 and their k respective training symbols 106 to estimate matrix H based on methods that are described below.
Referring now to FIG. 5, a method 120 is shown for estimating matrix H. Method 120 can be executed by channel estimator module 72. In some embodiments method 120 can be implemented as a computer program or firmware that is stored in memory 75 and executed by processor 73.
Control enters at a block 122 and proceeds to decision block 124. In decision block 124 control determines whether an LTF 104 is being received. If not then control returns to block 122. If an LTF 104 is being received then control branches from decision block 124 to block 126. In block 126 control receives a training symbol 106 that is associated with the current LTF 104. Control then proceeds to block 128 and updates a matrix Hest, which is described below in more detail, based on the current training symbol 106. Control then proceeds to decision block 130 and determines whether the current training symbol 106 was the last training symbol 106 of the present LTF 104. If not then control branches to block 132 and waits for the next training symbol 106 of the current LTF 104. When the next training symbol 106 is received control returns to block 126 and repeats the aforementioned steps for the new training symbol 106. On the other hand, if the training symbol 106 in decision block 130 was the last training symbol 106 of the present LTF 104 then control branches to decision block 134.
In decision block 134 control determines whether the current LTF 104 was the last LTF 104 (i.e. LTF 104-x) of the current group of LTFs 104. If not then control branches to block 136 and waits for the next LTF 104 to begin before returning to block 126. On the other hand, if the current LTF 104 was the last LTF 104-x then control branches from decision block 134 to block 138. In block 138 control generates matrix H based on matrix Hest and matrix P. Control then proceeds to block 140 and adjusts the gains of equalizer module 76 based on matrix H. Control then returns to other processes via termination block 142.
As channel estimator module 72 executes method 120 it performs distributed QR across LTFs 104. That is, QR(Hest). Computational density therefore increases as O(n2) and the processing latency of associated hardware and/or processor 73 would increase by about O(n2). This represents an improvement, e.g. reduced need for processing power, over the prior art. Example estimations of matrix Hest will now be provided for various MIMO dimensions of communications system 50.
2×2 And 2×3 Mimo Cases
In 2×2 and 2×3 MIMO cases the equalized vector is given by




  
    x
    ^
  
  =
  
    
      1
      
        diag
        ⁡
        
          (
          
            
              P
              
                2
                ×
                2
              
            
            ⁢
            
              R
              
                2
                ×
                2
              
              
                -
                1
              
            
            ⁢
            
              R
              
                2
                ×
                2
              
              
                -
                *
              
            
            ⁢
            
              P
              
                2
                ×
                2
              
              T
            
          
          )
        
      
    
    ⁢
    
      P
      
        2
        ×
        2
      
    
    ⁢
    
      R
      
        2
        ×
        2
      
      
        -
        1
      
    
    ⁢
    
      Q
      *
    
    ⁢
    y
  




It can be seen that




  
    
      
        x
        ^
      
      =
      
        
          
            
              [
              
                
                  
                    
                      
                        
                          r
                          11
                          2
                        
                        ⁢
                        
                          r
                          22
                          2
                        
                      
                      
                        
                          r
                          22
                          2
                        
                        +
                        
                          
                            
                            
                              
                                r
                                11
                              
                              +
                              
                                r
                                12
                              
                            
                            
                          
                          2
                        
                      
                    
                  
                  
                    0
                  
                
                
                  
                    0
                  
                  
                    
                      
                        
                          r
                          11
                          2
                        
                        ⁢
                        
                          r
                          22
                          2
                        
                      
                      
                        
                          r
                          22
                          2
                        
                        +
                        
                          
                            
                            
                              
                                r
                                11
                              
                              -
                              
                                r
                                12
                              
                            
                            
                          
                          2
                        
                      
                    
                  
                
              
              ]
            
            ⁡
            
              [
              
                
                  
                    1
                  
                  
                    
                      -
                      1
                    
                  
                
                
                  
                    1
                  
                  
                    1
                  
                
              
              ]
            
          
          ⁡
          
            [
            
              
                
                  
                    1
                    
                      r
                      11
                    
                  
                
                
                  
                    -
                    
                      
                        r
                        12
                      
                      
                        
                          r
                          11
                        
                        ⁢
                        
                          r
                          22
                        
                      
                    
                  
                
              
              
                
                  0
                
                
                  
                    1
                    
                      r
                      22
                    
                  
                
              
            
            ]
          
        
        ⁢
        
          Q
          *
        
        ⁢
        y
      
    
    ,
    
      

    
    ⁢
    where
  




  
    
      
        W
        
      
      =
      
        [
        
          
            
              
                
                  
                    r
                    11
                    2
                  
                  ⁢
                  
                    r
                    22
                    2
                  
                
                
                  
                    r
                    22
                    2
                  
                  +
                  
                    
                      
                      
                        
                          r
                          11
                        
                        +
                        
                          r
                          12
                        
                      
                      
                    
                    2
                  
                
              
            
            
              0
            
          
          
            
              0
            
            
              
                
                  
                    r
                    11
                    2
                  
                  ⁢
                  
                    r
                    22
                    2
                  
                
                
                  
                    r
                    22
                    2
                  
                  +
                  
                    
                      
                      
                        
                          r
                          11
                        
                        -
                        
                          r
                          12
                        
                      
                      
                    
                    2
                  
                
              
            
          
        
        ]
      
    
    ,
    
      

    
    ⁢
    
      
        P
        
          2
          ×
          2
        
      
      =
      
        [
        
          
            
              1
            
            
              
                -
                1
              
            
          
          
            
              1
            
            
              1
            
          
        
        ]
      
    
    ,
    and
  




  
    
      R
      
        2
        ×
        2
      
      
        -
        1
      
    
    =
    
      
        [
        
          
            
              
                1
                
                  r
                  11
                
              
            
            
              
                -
                
                  
                    r
                    12
                  
                  
                    
                      r
                      11
                    
                    ⁢
                    
                      r
                      22
                    
                  
                
              
            
          
          
            
              0
            
            
              
                1
                
                  r
                  22
                
              
            
          
        
        ]
      
      .
    
  



4×4 Spatial-Multiplexing (SM) Mimo Case
For a general n×n MIMO communication system 50 the equalized vector is given by



  
    
      
        x
        ^
      
      n
    
    =
    
      
        1
        
          diag
          ⁡
          
            (
            
              
                P
                n
              
              ⁢
              
                R
                n
                
                  -
                  1
                
              
              ⁢
              
                R
                n
                
                  -
                  *
                
              
              ⁢
              
                P
                n
                T
              
            
            )
          
        
      
      ⁢
      
        P
        n
      
      ⁢
      
        R
        n
        
          -
          1
        
      
      ⁢
      
        Q
        n
        *
      
      ⁢
      y
    
  




  where




  
    
      H
      
        est
        ,
        n
      
    
    =
    
      
        Q
        n
      
      ⁢
      
        
          R
          n
        
        .
      
    
  



Methods are known in the art for recursively solving the Qn*y term of the above equation. Recursive computation of the PnRn−1 and




  
    
      w
      
        ll
        ,
        n
      
    
    _
  
  =
  
    1.
    /
    
      diag
      ⁡
      
        (
        
          
            P
            n
          
          ⁢
          
            R
            n
            
              -
              1
            
          
          ⁢
          
            R
            n
            
              -
              *
            
          
          ⁢
          
            P
            n
            T
          
        
        )
      
    
  




terms of the above equation will now be described.

4×4 SM Mimo Case—Substream Signal-to Noise Ratio (SNR) Recursion
Let w∥,n=1./diag(Pn×nRn×n−1Rn×n−*Pn×nT). It can be seen that for 1≦j<n the jth element of the w∥ vector for n streams can be recursively computed as follows:



  
    
      1
      
        w
        
          ll
          ,
          n
        
        j
      
    
    =
    
      
        1
        
          w
          
            ll
            ,
            
              n
              -
              1
            
          
          j
        
      
      +
      
        k
        j
      
    
  




  where




  
    
      
        k
        j
      
      =
      
        
          (
          
            
              P
              
                n
                ×
                n
              
            
            ⁢
            
              v
              _
            
            ⁢
            
              
                v
                _
              
              *
            
            ⁢
            
              P
              
                n
                ×
                n
              
              T
            
          
          )
        
        jj
      
    
    ,
    
      

    
    ⁢
    
      
        R
        
          n
          ×
          n
        
        
          -
          1
        
      
      =
      
        
          
            
              [
              
                
                  
                    
                      
                        R
                        
                          n
                          -
                          
                            1
                            ×
                            n
                          
                          -
                          1
                        
                        
                          -
                          1
                        
                      
                    
                  
                  
                    
                      
                        
                          
                        
                        ⁢
                        
                          0
                          _
                        
                      
                    
                  
                
                ⁢
                
                  v
                  _
                
              
              ]
            
            .
            
              

            
            ⁢
            For
          
          ⁢
          
            
          
          ⁢
          j
        
        =
        n
      
    
    ,
    
      
        w
        
          ll
          ,
          n
        
        n
      
      =
      
        1
        
          
            λ
            n
          
          +
          
            k
            n
          
        
      
    
  




  where




  
    
      λ
      n
    
    =
    
      
        P
        ⁡
        
          (
          
            n
            ,
            
              
                1
                ⁢
                
                  :
                
                ⁢
                n
              
              -
              1
            
          
          )
        
      
      ⁢
      
        R
        
          n
          -
          1
        
        
          -
          1
        
      
      ⁢
      
        R
        
          n
          -
          1
        
        
          -
          *
        
      
      ⁢
      
        
          
            P
            ⁡
            
              (
              
                n
                ,
                
                  
                    1
                    ⁢
                    
                      :
                    
                    ⁢
                    n
                  
                  -
                  1
                
              
              )
            
          
          T
        
        .
      
    
  



A proof of the immediately preceding equations will now be provided.



  
    
      R
      
        n
        ×
        n
      
      
        -
        1
      
    
    =
    
      [
      
        
          
            
              
                R
                
                  n
                  -
                  
                    1
                    ×
                    n
                  
                  -
                  1
                
                
                  -
                  1
                
              
            
          
          
            
              
                
                  
                
                ⁢
                
                  0
                  _
                
              
            
          
        
        ⁢
        
          v
          _
        
      
      ]
    
  




  
    
      
        
          
            diag
            ⁡
            
              (
              
                
                  P
                  
                    n
                    ×
                    n
                  
                
                ⁢
                
                  R
                  
                    n
                    ×
                    n
                  
                  
                    -
                    1
                  
                
                ⁢
                
                  R
                  
                    n
                    ×
                    n
                  
                  
                    -
                    *
                  
                
                ⁢
                
                  P
                  
                    n
                    ×
                    n
                  
                  T
                
              
              )
            
          
          =
          
          ⁢
          
            diag
            ⁡
            
              (
              
                
                  
                    
                      
                        P
                        n
                      
                      ⁡
                      
                        [
                        
                          
                            
                              
                                
                                  R
                                  
                                    n
                                    -
                                    1
                                  
                                  
                                    -
                                    1
                                  
                                
                              
                            
                            
                              
                                
                                  
                                    
                                  
                                  ⁢
                                  
                                    0
                                    _
                                  
                                
                              
                            
                          
                          ⁢
                          
                            v
                            _
                          
                        
                        ]
                      
                    
                    ⁡
                    
                      [
                      
                        
                          
                            
                              
                                R
                                
                                  n
                                  -
                                  1
                                
                                
                                  -
                                  1
                                
                              
                            
                          
                          
                            
                              
                                
                                  
                                
                                ⁢
                                
                                  0
                                  _
                                
                              
                            
                          
                        
                        ⁢
                        
                          v
                          _
                        
                      
                      ]
                    
                  
                  *
                
                ⁢
                
                  P
                  n
                  T
                
              
              )
            
          
        
      
    
    
      
        
          =
          
          ⁢
          
            diag
            ⁡
            
              (
              
                
                  
                    P
                    n
                  
                  ⁡
                  
                    (
                    
                      
                        [
                        
                          
                            
                              
                                
                                  
                                    R
                                    
                                      n
                                      -
                                      1
                                    
                                    
                                      -
                                      1
                                    
                                  
                                  ⁢
                                  
                                    R
                                    
                                      n
                                      -
                                      1
                                    
                                    
                                      -
                                      *
                                    
                                  
                                
                              
                            
                            
                              
                                
                                  
                                    
                                  
                                  ⁢
                                  
                                    0
                                    _
                                  
                                
                              
                            
                          
                          ⁢
                          
                            0
                            _
                          
                        
                        ]
                      
                      +
                      
                        
                          v
                          _
                        
                        ⁢
                        
                          
                            v
                            _
                          
                          *
                        
                      
                    
                    )
                  
                
                ⁢
                
                  P
                  n
                  T
                
              
              )
            
          
        
      
    
    
      
        
          =
          
          ⁢
          
            diag
            (
            
              
                
                  P
                  
                    n
                    -
                    1
                  
                
                ⁢
                
                  R
                  
                    n
                    -
                    1
                  
                  
                    -
                    1
                  
                
                ⁢
                
                  R
                  
                    n
                    -
                    1
                  
                  
                    -
                    *
                  
                
                ⁢
                
                  P
                  
                    n
                    -
                    1
                  
                  T
                
              
              ,
              
                P
                
                  (
                  
                    n
                    ,
                    
                      
                        1
                        ⁢
                        
                          :
                        
                        ⁢
                        n
                      
                      -
                      1
                    
                  
                  )
                
              
            
          
        
      
    
    
      
        
          
            
            ⁢
            
              
                R
                
                  n
                  -
                  1
                
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  n
                  -
                  1
                
                
                  -
                  *
                
              
              ⁢
              
                P
                
                  (
                  
                    n
                    ,
                    
                      
                        1
                        ⁢
                        
                          :
                        
                        ⁢
                        n
                      
                      -
                      1
                    
                  
                  )
                
                T
              
            
            )
          
          +
          
            diag
            ⁡
            
              (
              
                
                  P
                  n
                
                ⁢
                
                  v
                  _
                
                ⁢
                
                  
                    v
                    _
                  
                  *
                
                ⁢
                
                  P
                  n
                  T
                
              
              )
            
          
        
      
    
  



4×4 SM Mimo Case—Processing the 2nd LTF 104




  
    Compute
    ⁢
    
      
    
    ⁢
    
      
        R
        
          2
          ×
          2
        
      
      .
      
        

      
      ⁢
      Compute
    
    ⁢
    
      
    
    ⁢
    
      
        
          R
          
            2
            ×
            2
          
          
            -
            1
          
        
        ⁡
        
          [
          
            
              
                
                  1
                  /
                
              
              
                
                  
                    
                      -
                      
                        r
                        12
                      
                    
                    /
                    
                      r
                      11
                    
                  
                  ⁢
                  
                    r
                    22
                  
                
              
            
            
              
                0
              
              
                
                  1
                  /
                  
                    r
                    22
                  
                
              
            
          
          ]
        
      
      .
      
        

      
      ⁢
      Compute
    
    ⁢
    
      
    
    ⁢
    
      1
      /
      
        w
        
          ll
          ,
          1
        
      
    
  
  =
  
    
      
        
          (
          
            
              r
              22
              2
            
            +
            
              
                
                
                  
                    r
                    11
                  
                  +
                  
                    r
                    12
                  
                
                
              
              2
            
          
          )
        
        /
        
          r
          11
          2
        
      
      ⁢
      
        
          r
          22
          2
        
        .
        
          

        
        ⁢
        Compute
      
      ⁢
      
        
      
      ⁢
      
        1
        /
        
          w
          
            ll
            ,
            2
          
        
      
    
    =
    
      
        
          
            (
            
              
                r
                22
                2
              
              +
              
                
                  
                  
                    
                      r
                      11
                    
                    -
                    
                      r
                      12
                    
                  
                  
                
                2
              
            
            )
          
          /
          
            r
            11
            2
          
        
        ⁢
        
          
            r
            22
            2
          
          .
          
            

          
          ⁢
          Let
        
        ⁢
        
          
        
        ⁢
        λ
      
      =
      
        1
        /
        
          
            w
            
              ll
              ,
              2
            
          
          .
        
      
    
  




4×4 SM Mimo Case—Processing the 3rd LTF 104
Update the inverse of the triangular matrix based on



  
    
      R
      
        3
        ×
        3
      
    
    =
    
      [
      
        
          
            
              
                
                  R
                  
                    2
                    ×
                    2
                  
                
              
            
            
              
                
                  
                    
                  
                  ⁢
                  
                    0
                    _
                  
                
              
            
          
          ⁡
          
            [
            
              
                r
                13
              
              ⁢
              
                
              
              ⁢
              
                r
                23
              
              ⁢
              
                
              
              ⁢
              
                r
                33
              
            
            ]
          
        
        T
      
      ]
    
  




  
    
      R
      
        3
        ×
        3
      
      
        -
        1
      
    
    =
    
      [
      
        
          
            
              
                
                  R
                  
                    2
                    ×
                    2
                  
                  
                    -
                    1
                  
                
              
            
            
              
                
                  
                    
                  
                  ⁢
                  
                    0
                    _
                  
                
              
            
          
          ⁡
          
            [
            
              
                ρ
                1
              
              ⁢
              
                
              
              ⁢
              
                ρ
                2
              
              ⁢
              
                
              
              ⁢
              
                ρ
                3
              
            
            ]
          
        
        T
      
      ]
    
  



where ρ1=(r12r23−r13r22)/r11r22r33  ρ2=−r23/r22r33  ρ3=1/r33.

Update the substream SNRs based on

1/w∥,1→1/w∥,1+∥ρ1−ρ2+ρ3∥2 

1/w∥,2→1/w∥,2+∥ρ1+ρ2−ρ3∥2 

1/w∥,3→λ+∥ρ1+ρ2+ρ3∥2.

Update the lamda factor based on

λ=1/w∥,1+1/w∥,1−1/w∥,3+8real(ρ2)ρ3.

4×4 SM Mimo Case—Processing the 4th LTF 104
Update the inverse of the triangular matrix based on



  
    
      R
      
        4
        ×
        4
      
    
    =
    
      [
      
        
          
            
              
                
                  R
                  
                    3
                    ×
                    3
                  
                
              
            
            
              
                
                  
                    
                  
                  ⁢
                  
                    0
                    _
                  
                
              
            
          
          ⁡
          
            [
            
              
                r
                14
              
              ⁢
              
                
              
              ⁢
              
                r
                24
              
              ⁢
              
                
              
              ⁢
              
                r
                34
              
              ⁢
              
                
              
              ⁢
              
                r
                44
              
            
            ]
          
        
        T
      
      ]
    
  




  
    
      R
      
        4
        ×
        4
      
    
    =
    
      [
      
        
          
            
              
                
                  R
                  
                    3
                    ×
                    3
                  
                
              
            
            
              
                
                  
                    
                  
                  ⁢
                  
                    0
                    _
                  
                
              
            
          
          ⁡
          
            [
            
              
                r
                14
              
              ⁢
              
                
              
              ⁢
              
                r
                24
              
              ⁢
              
                
              
              ⁢
              
                r
                34
              
              ⁢
              
                
              
              ⁢
              
                r
                44
              
            
            ]
          
        
        T
      
      ]
    
  



where

ρ1=(r33(r12r24−r14r22)−(r12r23−r13r22)r34)/r11r22r33r44, ρ2=(r34r23−r24r33)/r22r33r44, ρ3=−r33/r33r44, ρ4=1/r44 

Update the substream SNR based on

1/w∥,2→1/w∥,2+∥ρ1+ρ2−ρ3+ρ4∥2 

1/w∥,3→1/w∥,3+∥ρ1+ρ2+ρ3−ρ4∥2 

1/w∥,4→λ+∥−ρ1+ρ2+ρ3+ρ4∥2 

1/w∥,4→λ+∥−ρ1+ρ2+ρ3+ρ4∥2.

Compute their inverses and store them in a memory that can be included in channel estimator module 72.
3×3 SM Mimo Case—Processing the 4th LTF 104
The 3×3 MIMO case employs a non-square matrix P. For 3 streams transmitter module 56 sends 4 LTFs 104 and employs matrix P of




  
    P
    3
  
  =
  
    
      [
      
        
          
            1
          
          
            
              -
              1
            
          
          
            1
          
          
            1
          
        
        
          
            1
          
          
            1
          
          
            
              -
              1
            
          
          
            1
          
        
        
          
            1
          
          
            1
          
          
            1
          
          
            
              -
              1
            
          
        
      
      ]
    
    .
  




Channel estimator module 72 estimates channel matrix Hest3×4 and the real matrix is H=Hest3×4P3×4⊥. The received vector can be based on y=Hest3×4P3×4⊥x=Hx.
A distributed solution may also be employed by working directly with Hest3×4 without forming H. In the distributed solution let

Hest3×4=QR3×4 and

Hest3×4=[Hest3×3h4].

Then Q*Hest3×4=└R Q*h4┘ where QR=Hest3×3.

In some embodiments the equalized vector can be based on

{circumflex over (x)}=(Hest,3×4P3×4⊥)⊥y. 

It can be seen that

{circumflex over (x)}=P1−1z−μv where u=R−1Q*h4, and μ=[1−1 1]z. 

The vector v is based on

v=kP1−1u where u=R−1Q*h4.

The scalar k is based on

k=1/(1+[1−1 1]u).

The matrix P1−1 is based on





  
    P
    1
    
      -
      1
    
  
  =
  
    
      2
      ⁡
      
        [
        
          
            
              1
            
            
              
                -
                1
              
            
            
              0
            
          
          
            
              1
            
            
              0
            
            
              
                -
                1
              
            
          
          
            
              0
            
            
              1
            
            
              1
            
          
        
        ]
      
    
    .
  




A proof of the immediately preceding equations will now be provided.
A solution is given by {circumflex over (x)}=(Hest,3×4P3×4⊥)−1y.
Let




  
    P
    
      3
      ×
      4
    
    ⊥
  
  =
  
    [
    
      
        
          
            P
            1
          
        
      
      
        
          
            P
            2
          
        
      
    
    ]
  




and write the matrix as





  
    
      
        
          
            (
            
              
                H
                
                  est
                  ,
                  
                    3
                    ×
                    4
                  
                
              
              ⁢
              
                P
                
                  3
                  ×
                  4
                
                ⊥
              
            
            )
          
          
            -
            1
          
        
        =
        
          
            [
            
              
                
                  H
                  
                    est
                    ,
                    
                      3
                      ×
                      3
                    
                  
                
                ⁢
                
                  P
                  1
                
              
              +
              
                
                  h
                  4
                
                ⁢
                
                  p
                  1
                
              
            
            ]
          
          
            -
            1
          
        
      
    
  
  
    
      
        =
        
          
            [
            
              
                QRP
                1
              
              +
              
                
                  h
                  4
                
                ⁢
                
                  p
                  1
                
              
            
            ]
          
          
            -
            1
          
        
      
    
  
  
    
      
        =
        
          
            
              P
              1
              
                -
                1
              
            
            ⁢
            
              R
              
                -
                1
              
            
            ⁢
            
              Q
              *
            
          
          -
          
            
              
                P
                1
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  1
                
              
              ⁢
              
                Q
                *
              
              ⁢
              
                h
                4
              
              ⁢
              
                p
                1
              
              ⁢
              
                P
                1
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  1
                
              
              ⁢
              
                Q
                *
              
            
            
              1
              +
              
                
                  p
                  1
                
                ⁢
                
                  P
                  1
                  
                    -
                    1
                  
                
                ⁢
                
                  R
                  
                    -
                    1
                  
                
                ⁢
                
                  Q
                  *
                
                ⁢
                
                  h
                  4
                
              
            
          
        
      
    
  
  
    
      
        =
        
          
            [
            
              I
              -
              
                
                  vp
                  1
                
                
                  1
                  +
                  
                    
                      p
                      1
                    
                    ⁢
                    v
                  
                
              
            
            ]
          
          ⁢
          
            P
            1
            
              -
              1
            
          
          ⁢
          
            R
            
              -
              1
            
          
          ⁢
          
            Q
            *
          
        
      
    
  




where v=P1−1R−1Q*h4.





  
    
      P
      1
      
        -
        1
      
    
    =
    
      2
      ⁡
      
        [
        
          
            
              1
            
            
              
                -
                1
              
            
            
              0
            
          
          
            
              1
            
            
              0
            
            
              
                -
                1
              
            
          
          
            
              0
            
            
              1
            
            
              1
            
          
        
        ]
      
    
  
  ,
  
    
      
        p
        1
      
      ⁢
      
        P
        1
        
          -
          1
        
      
    
    =
    
      
        [
        
          1
          ⁢
          
            
          
          -
          1
          ⁢
          
            
          
          -
          1
        
        ]
      
      .
    
  




3×3 SM Mimo Case—Solution for W∥
Channel estimator module 72 computes

W∥=1/((Hest,3×4P3×4⊥)*(Hest,3×4P3×4⊥))−1 

based on terms of v=k P1−1R−1Q*h4 and R−1R−*.

Let this matrix be





  
    
      R
      
        -
        1
      
    
    ⁢
    
      R
      
        -
        *
      
    
  
  =
  
    [
    
      
        
          
            
              I
              11
            
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                11
              
            
          
        
        
          
            
              I
              21
            
            -
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                21
              
            
          
        
        
          
            
              I
              31
            
            -
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                31
              
            
          
        
      
      
        
          
            
              I
              21
            
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                21
              
            
          
        
        
          
            
              I
              22
            
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                22
              
            
          
        
        
          
            
              I
              32
            
            -
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                32
              
            
          
        
      
      
        
          
            
              I
              31
            
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                31
              
            
          
        
        
          
            
              I
              32
            
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                32
              
            
          
        
        
          
            
              I
              33
            
            +
            
              j
              ⁢
              
                
              
              ⁢
              
                Q
                33
              
            
          
        
      
    
    ]
  




and during LTFs 104 compute

S1=4(I11−2I21+I22)

S2=4(I11−2I31+I33)

S3=4(I22+2I32+I33)

S=(I11+I22+I33)−2(I21+I31−I32)

S4=I11−2I21+I22−I31+I32+j(Q11+Q22+Q31−Q32)

S5=I11−I21+I32−2I31+I33+j(Q11+Q21+Q32+Q33)

S6=I21−I22+I31−2I32−I33+j(Q21−Q22+Q31−Q32)

It can be seen that

W∥1=1/(S1+S∥v1∥2−4real(S4v1*))

W∥2=1/(S2+S∥v2∥2−4real(S5v2*))

W∥3=1/(S3+S∥v3∥2−4real(S6v3*))

and v=kP1−u.

Proof of the above solution for W∥ will now be provided. Let

H=[QR h4]P3×4⊥Q*H=└R Q*h4┘P3×4⊥=R(P1+up1), u=R−1Q*h4 

Then




  
    
      
        
          
            
              (
              
                
                  H
                  *
                
                ⁢
                H
              
              )
            
            
              -
              1
            
          
          =
          
          ⁢
          
            
              
                (
                
                  
                    P
                    1
                  
                  +
                  
                    
                      u
                      _
                    
                    ⁢
                    
                      p
                      1
                    
                  
                
                )
              
              
                -
                1
              
            
            ⁢
            
              R
              
                -
                1
              
            
            ⁢
            
              
                
                  R
                  
                    -
                    *
                  
                
                ⁡
                
                  (
                  
                    
                      P
                      1
                      T
                    
                    +
                    
                      
                        p
                        1
                        T
                      
                      ⁢
                      
                        
                          u
                          _
                        
                        *
                      
                    
                  
                  )
                
              
              
                -
                1
              
            
          
        
      
    
    
      
        
          =
          
          ⁢
          
            
              (
              
                I
                -
                
                  
                    
                      P
                      1
                      
                        -
                        1
                      
                    
                    ⁢
                    
                      u
                      _
                    
                    ⁢
                    
                      p
                      1
                    
                  
                  
                    1
                    +
                    
                      
                        [
                        
                          1
                          ⁢
                          
                            
                          
                          -
                          1
                          ⁢
                          
                            
                          
                          -
                          1
                        
                        ]
                      
                      ⁢
                      
                        u
                        _
                      
                    
                  
                
              
              )
            
            ⁢
            
              P
              1
              
                -
                1
              
            
            ⁢
            
              R
              
                -
                1
              
            
            ⁢
            
              R
              
                -
                *
              
            
            ⁢
            
              P
              1
              
                -
                T
              
            
          
        
      
    
    
      
        
          
          ⁢
          
            (
            
              I
              -
              
                
                  
                    p
                    1
                    T
                  
                  ⁢
                  
                    
                      u
                      _
                    
                    *
                  
                  ⁢
                  
                    P
                    1
                    
                      -
                      T
                    
                  
                
                
                  1
                  +
                  
                    
                      [
                      
                        1
                        ⁢
                        
                          
                        
                        -
                        1
                        ⁢
                        
                          
                        
                        -
                        1
                      
                      ]
                    
                    ⁢
                    
                      u
                      _
                    
                  
                
              
            
            )
          
        
      
    
    
      
        
          =
          
          ⁢
          
            
              (
              
                
                  P
                  1
                  
                    -
                    1
                  
                
                -
                
                  v
                  ⁡
                  
                    [
                    
                      1
                      ⁢
                      
                        
                      
                      -
                      1
                      ⁢
                      
                        
                      
                      -
                      1
                    
                    ]
                  
                
              
              )
            
            ⁢
            
              R
              
                -
                1
              
            
            ⁢
            
              R
              
                -
                *
              
            
          
        
      
    
    
      
        
          
          ⁢
          
            (
            
              
                P
                1
                
                  -
                  T
                
              
              -
              
                
                  
                    [
                    
                      1
                      ⁢
                      
                        
                      
                      -
                      1
                      ⁢
                      
                        
                      
                      -
                      1
                    
                    ]
                  
                  T
                
                ⁢
                
                  v
                  *
                
              
            
            )
          
        
      
    
    
      
        
          =
          
          ⁢
          
            
              
                P
                1
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  *
                
              
              ⁢
              
                P
                1
                
                  -
                  T
                
              
            
            +
            
              
                v
                ⁡
                
                  [
                  
                    1
                    ⁢
                    
                      
                    
                    -
                    1
                    ⁢
                    
                      
                    
                    -
                    1
                  
                  ]
                
              
              ⁢
              
                R
                
                  -
                  1
                
              
              ⁢
              
                R
                
                  -
                  *
                
              
            
          
        
      
    
    
      
        
          
          ⁢
          
            
              
                
                  [
                  
                    1
                    ⁢
                    
                      
                    
                    -
                    1
                    ⁢
                    
                      
                    
                    -
                    1
                  
                  ]
                
                T
              
              ⁢
              
                v
                *
              
            
            -
            
              2
              ⁢
              
                
              
              ⁢
              real
              ⁢
              
                
              
              ⁢
              
                (
                
                  
                    P
                    1
                    
                      -
                      1
                    
                  
                  ⁢
                  
                    R
                    
                      -
                      1
                    
                  
                  ⁢
                  
                    R
                    
                      -
                      *
                    
                  
                
              
            
          
        
      
    
    
      
        
          
          ⁢
          
            
              [
              
                1
                ⁢
                
                  
                
                -
                1
                ⁢
                
                  
                
                -
                1
              
              ]
            
            ⁢
            
              v
              *
            
          
          )
        
      
    
  




  
    v
    =
    
      
        kP
        1
        
          -
          1
        
      
      ⁢
      
        R
        
          -
          1
        
      
      ⁢
      
        Q
        *
      
      ⁢
      
        
          h
          4
        
        .
      
    
  



Channel estimator module 72 still needs to recursively update R−1R−* after determining v=kP1−1u as described above. At a time n let

Rn−1=[Rn−1−1ρ]

and apply the following identity

Rn−1Rn−*=Rn−1−1Rn−1−*+ρρ*.

For example,




  
    
      R
      
        3
        ×
        3
      
      
        -
        1
      
    
    =
    
      [
      
        
          
            
              
                
                  R
                  
                    2
                    ×
                    2
                  
                  
                    -
                    1
                  
                
              
            
            
              
                
                  0
                  _
                
              
            
          
          ⁡
          
            [
            
              
                
                  
                    ρ
                    1
                  
                
                
                  
                    ρ
                    2
                  
                
                
                  
                    ρ
                    3
                  
                
              
            
            ]
          
        
        T
      
      ]
    
  




  
    
      ρ
      1
    
    =
    
      
        
          (
          
            
              
                r
                12
              
              ⁢
              
                r
                23
              
            
            -
            
              
                r
                13
              
              ⁢
              
                r
                22
              
            
          
          )
        
        /
        
          r
          11
        
      
      ⁢
      
        r
        22
      
      ⁢
      
        r
        33
      
    
  




  
    
      ρ
      
        2
        =
      
    
    -
    
      
        
          r
          23
        
        /
        
          r
          22
        
      
      ⁢
      
        r
        23
      
    
  




  
    
      ρ
      
        3
        =
      
    
    ⁢
    
      1
      /
      
        
          r
          33
        
        .
      
    
  



3×3 SM Mimo Case—Processing the 1st LTF 104
Channel estimator module 72 performs first column nulling by computing

R1−1=1/r11.

3×3 SM Mimo Case—Processing the 2nd LTF 104
Channel estimator module 72 performs second column QR processing based on




  
    
      R
      
        2
        ×
        2
      
      
        -
        1
      
    
    =
    
      
        
          [
          
            
              
                
                  
                    
                      R
                      1
                      
                        -
                        1
                      
                    
                  
                
                
                  
                    
                      0
                      _
                    
                  
                
              
              ⁡
              
                [
                
                  
                    
                      
                        ρ
                        1
                      
                    
                    
                      
                        ρ
                        2
                      
                    
                  
                
                ]
              
            
            T
          
          ]
        
        ⁢
        
          
        
        ⁢
        where
        ⁢
        
          
        
        ⁢
        
          ρ
          1
        
      
      =
      
        
          
            -
            
              r
              12
            
          
          /
          
            r
            11
          
        
        ⁢
        
          r
          22
        
      
    
  
  ,
  
    
      and
      ⁢
      
        
      
      ⁢
      
        ρ
        2
      
    
    =
    
      1
      /
      
        
          r
          22
        
        .
      
    
  




Channel estimator module 72 then computes μρ1∥2, ∥ρ2∥2, ρ1ρ2* and updates R−1R−* based on





  
    
      R
      
        2
        ×
        2
      
      
        -
        1
      
    
    ⁢
    
      R
      
        2
        ×
        2
      
      
        -
        *
      
    
  
  =
  
    
      [
      
        
          
            
              
                1
                /
                
                  r
                  11
                
              
              +
              
                
                  
                  
                    ρ
                    1
                  
                  
                
                2
              
            
          
          
            
              
                ρ
                1
              
              ⁢
              
                ρ
                2
                *
              
            
          
        
        
          
            
              
                ρ
                1
                *
              
              ⁢
              
                ρ
                2
              
            
          
          
            
              
                
                
                  ρ
                  2
                
                
              
              2
            
          
        
      
      ]
    
    .
  




3×3 SM Mimo Case—Processing the 3rd LTF 104
Channel estimator module 72 performs third column QR processing by recursively updating




  
    R
    
      3
      ×
      3
    
    
      -
      1
    
  
  =
  
    [
    
      
        
          
            
              
                R
                
                  2
                  ×
                  2
                
                
                  -
                  1
                
              
            
          
          
            
              
                0
                _
              
            
          
        
        ⁡
        
          [
          
            
              
                
                  ρ
                  1
                
              
              
                
                  ρ
                  2
                
              
              
                
                  ρ
                  3
                
              
            
          
          ]
        
      
      T
    
    ]
  




where ρ1=(r12r23−r13r22)/r11r22r33 ρ2=−r23/r22r33 ρ3=1/r33.

Channel estimator module 72 can then compute

∥ρ1∥2, ∥ρ2∥2, ∥ρ2∥2, ρ1ρ2*, ρ1ρ3*, ρ2ρ3*

and update R−1R−* based on

R3×3−1R3×3−*=R2×2−1R2×2−*+ρρ*.

Channel estimator module 72 can then compute the sums

S1=4(I11−2I21+I22)

S2=4(I11−2I31+I33)

S3=4(I22+2I32+I33)

S=(I11+I22+I33)−2(I21+I−I32)

S4=I11−2I21+I22−I31+I32+j(Q11+Q22+Q31−Q32)

S5=I11−I21+I32−2I31+I33+j(Q11+Q21+Q32+Q33)

S6=I21−I22+I31−2I32−I33+j(Q21−Q22+Q31−Q33)

3×3 SM Mimo Case—Processing the 4th LTF 104
Channel estimator module 72 computes

u=R−1Q*h4,

k=1/(1+[1−1 1]u), and

v=kP1−1u. 

Channel estimator module can store v in memory 75.

Channel estimator module 72 computes substream SNR based on

W∥1=1/(S1+S∥v1∥2−4real(S4v1*))

W∥2=1/(S2+S∥v2∥2−4real(S5v2*))

W∥3=1/(S3+S∥v3∥2−4real(S6v3*))

and store the substream SNR in memory 75.

3×3 SM Mimo Case—Processing Data 92
Channel estimator module 72 can compute

z=R−1Q*y and μ=[1−1 1]z

and read v from memory 75. Channel estimator module 72 can then compute

{circumflex over (x)}=P1−1z−μv

and read the substream SNR from memory 75. Equalizer module 76 can scale the equalized vector based on the SNRs.

Referring now to FIGS. 6A-6E, various exemplary implementations of the receiver module are shown. Referring now to FIG. 6A, the receiver module can be implemented in a high definition television (HDTV) 420. The receiver module may implement and/or be implemented in a WLAN interface 429. The HDTV 420 receives HDTV input signals in either a wired or wireless format and generates HDTV output signals for a display 426. In some implementations, signal processing circuit and/or control circuit 422 and/or other circuits (not shown) of the HDTV 420 may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other type of HDTV processing that may be required.
The HDTV 420 may communicate with mass data storage 427 that stores data in a nonvolatile manner such as optical and/or magnetic storage devices. Mass data storage 427 may include at least one hard disk drive (HDD) and/or at least one digital versatile disk (DVD) drive. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The HDTV 420 may be connected to memory 428 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The HDTV 420 also may support connections with a WLAN via WLAN network interface 429. The HDTV 420 also includes a power supply 423.
Referring now to FIG. 6B, the receiver module may implement and/or be implemented in a WLAN interface 448 of a vehicle 430. In some implementations WLAN interface 448 communicates with a powertrain control system 432 that receives inputs from one or more sensors. Examples of sensors includes temperature sensors, pressure sensors, rotational sensors, airflow sensors and/or any other suitable sensors and/or that generates one or more output control signals such as engine operating parameters, transmission operating parameters, and/or other control signals.
The receiver module may also be implemented in other control systems 440 of the vehicle 430. The control system 440 may likewise receive signals from input sensors 442 and/or output control signals to one or more output devices 444. In some implementations, the control system 440 may be part of an anti-lock braking system (ABS), a navigation system, a telematics system, a vehicle telematics system, a lane departure system, an adaptive cruise control system, a vehicle entertainment system such as a stereo, DVD, compact disc and the like. Still other implementations are contemplated.
The powertrain control system 432 may communicate with mass data storage 446 that stores data in a nonvolatile manner. Mass data storage 446 may include at least one HDD and/or at least one DVD drive. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The powertrain control system 432 may be connected to memory 447 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The powertrain control system 432 also may support connections with a WLAN via a WLAN network interface 448. The control system 440 may also include mass data storage, memory and/or a WLAN interface (all not shown). Vehicle 430 may also include a power supply 433.
Referring now to FIG. 6C, the receiver module can be implemented in a cellular phone 450 that may include a cellular antenna 451. The receiver module may implement and/or be implemented in a WLAN interface 468. In some implementations, the cellular phone 450 includes a microphone 456, an audio output 458 such as a speaker and/or audio output jack, a display 460 and/or an input device 462 such as a keypad, pointing device, voice actuation and/or other input device. The signal processing and/or control circuits 452 and/or other circuits (not shown) in the cellular phone 450 may process data, perform coding and/or encryption, perform calculations, format data and/or perform other cellular phone functions.
The cellular phone 450 may communicate with mass data storage 464 that stores data in a nonvolatile manner. Mass data storage 450 may include at least one HDD and/or at least one DVD drive. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The cellular phone 450 may be connected to memory 466 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The cellular phone 450 also may support connections with a WLAN via the WLAN network interface 468. The cellular phone 450 may also include a power supply 453.
Referring now to FIG. 6D, the receiver module can be implemented in a set top box 480. The receiver module may implement and/or be implemented in a WLAN interface 496. The set top box 480 receives signals from a source such as a broadband source and outputs standard and/or high definition audio/video signals suitable for a display 488 such as a television and/or monitor and/or other video and/or audio output devices. The signal processing and/or control circuits 484 and/or other circuits (not shown) of the set top box 480 may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other set top box function.
The set top box 480 may communicate with mass data storage 490 that stores data in a nonvolatile manner. Mass data storage 490 may include at least one HDD and/or at least one DVD drive. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The set top box 480 may be connected to memory 494 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The set top box 480 also may support connections with a WLAN via the WLAN network interface 496. The set top box 480 may include a power supply 483.
Referring now to FIG. 6E, the receiver module can be implemented in a media player 500. The receiver module may implement and/or be implemented in a WLAN interface 516. In some implementations, the media player 500 includes a display 507 and/or a user input 508 such as a keypad, touchpad and the like. In some implementations, the media player 500 may employ a graphical user interface (GUI) that typically employs menus, drop down menus, icons and/or a point-and-click interface via the display 507 and/or user input 508. The media player 500 further includes an audio output 509 such as a speaker and/or audio output jack. The signal processing and/or control circuits 504 and/or other circuits (not shown) of the media player 500 may process data, perform coding and/or encryption, perform calculations, format data and/or perform any other media player function.
The media player 500 may communicate with mass data storage 510 that stores data such as compressed audio and/or video content in a nonvolatile manner. In some implementations, the compressed audio files include files that are compliant with MP3 format or other suitable compressed audio and/or video formats. Mass data storage 510 may include at least one HDD and/or at least one DVD drive. The HDD may be a mini HDD that includes one or more platters having a diameter that is smaller than approximately 1.8′′. The media player 500 may be connected to memory 514 such as RAM, ROM, low latency nonvolatile memory such as flash memory and/or other suitable electronic data storage. The media player 500 also may support connections with a WLAN via the WLAN network interface 516. The media player 500 may also include a power supply 513. Still other implementations in addition to those described above are contemplated.
Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.

## Claims

1. An input module coupled to at least one antenna, configured to receive a message from a wireless communication channel, the message including data and a plurality of training fields, the plurality of training fields having been generated based on a steering matrix P;
a computation module configured to recursively compute equalizer parameters based on the plurality of training fields, the steering matrix P, and a channel estimation matrix, wherein the computation module recursively computes the equalizer parameters as the plurality of training fields is being received; and
an equalizer module configured to apply the equalizer parameters to the data of the message to recover user data.

2. The receiver of claim 1, wherein the equalizer parameters include (i) a first set of parameters based on a first matrix and (ii) a second set of parameters based on a second matrix, wherein the first and second matrices are based on a decomposition of the channel estimation matrix.

3. The receiver of claim 2, wherein the decomposition of the channel estimation matrix is a recursive QR decomposition.

4. The receiver of claim 3, wherein the first matrix is based on a conjugate transpose of an orthogonal matrix of the QR decomposition, and wherein the second matrix is based on an inverse of an upper triangular matrix of the QR decomposition.

5. The receiver of claim 2, wherein the equalizer parameters include a substream signal-to-noise ratio vector.

6. The receiver of claim 5, wherein the equalizer module:
applies the first set of parameters to a vector of the data of the message to generate a first intermediate result;
applies the second set of parameters to the first intermediate result to generate a second intermediate result;
applies the steering matrix P to the second intermediate result to generate a third intermediate result; and
applies the substream signal-to-noise ratio vector to the third intermediate result to recover the user data.

7. The receiver of claim 1, wherein the computation module performs one iteration of the recursive computation of the equalizer parameters as each of the plurality of training fields is received.

8. The receiver of claim 1, further comprising N antennas that receive the message, wherein N is an integer greater than or equal 2, wherein the message is transmitted over M streams by M antennas, and wherein M is an integer greater than or equal to 2 and less than or equal to N.

9. A transceiver comprising:
the receiver of claim 1, and
a transmitter.

10. The transceiver of claim 9, further comprising:
N receive antennas that receive the message, wherein N is an integer greater than or equal 2; and
M transmit antennas that transmit the message over M streams, wherein M is an integer greater than or equal to 2 and less than or equal to N.

11. An integrated circuit comprising the transceiver of claim 9.

12. A system comprising:
a receiving device including the receiver of claim 8; and
a transmitting device including the M antennas.

13. The receiver of claim 1, wherein the equalizer parameters include a first set of parameters, a second set of parameters, and a substream signal-to-noise ratio vector.

14. The receiver of claim 13, wherein the equalizer module:
applies the first set of parameters to a vector of the data of the message to generate a first intermediate result;
applies the second set of parameters to the first intermediate result to generate a second intermediate result;
applies the steering matrix P to the second intermediate result to generate a third intermediate result; and
applies the substream signal-to-noise ratio vector to the third intermediate result to recover the user data.

15. The receiver of claim 14, wherein:
the first set of parameters is based on a conjugate transpose of an orthogonal matrix of a recursive QR decomposition of the channel estimation matrix, and
the second set of parameters is based on an inverse of an upper triangular matrix of the QR decomposition.

16. A method of operating a receiver, the method comprising:
wirelessly receiving a message from a wireless communication channel, the message including data and a plurality of training fields, the plurality of training fields having been generated based on a steering matrix P;
recursively computing equalizer parameters using a module of the receiver based on the plurality of training fields, the steering matrix P, and a channel estimation matrix, wherein the equalizer parameters are recursively computed while the plurality of training fields is being received; and
applying the equalizer parameters to the data of the message to recover user data.

17. The method of claim 16, wherein the equalizer parameters include (i) a first set of parameters based on a first matrix and (ii) a second set of parameters based on a second matrix, wherein the first and second matrices are based on a decomposition of the channel estimation matrix.

18. The method of claim 17, wherein the decomposition of the channel estimation matrix is a recursive QR decomposition.

19. The method of claim 18, wherein the first matrix is based on a conjugate transpose of an orthogonal matrix of the QR decomposition, and wherein the second matrix is based on an inverse of an upper triangular matrix of the QR decomposition.

20. The method of claim 17, wherein the equalizer parameters include a substream signal-to-noise ratio vector.

21. The method of claim 20, further comprising:
applying the first set of parameters to a vector of the data of the message to generate a first intermediate result;
applying the second set of parameters to the first intermediate result to generate a second intermediate result;
applying the steering matrix P to the second intermediate result to generate a third intermediate result; and
applying the substream signal-to-noise ratio vector to the third intermediate result to recover the user data.

22. The method of claim 16, wherein:
recursively computing the equalizer parameters comprises performing a plurality of computational iterations; and
as each of the plurality of training fields is received, a corresponding one of the plurality of computational iterations is performed.

23. The method of claim 16, further comprising receiving the message using N antennas, wherein N is an integer greater than or equal 2, wherein the message is transmitted over M streams by M antennas, and wherein M is an integer greater than or equal to 2 and less than or equal to N.

24. The method of claim 16, wherein the equalizer parameters include a first set of parameters, a second set of parameters, and a substream signal-to-noise ratio vector.

25. The method of claim 24, further comprising:
applying the first set of parameters to a vector of the data of the message to generate a first intermediate result;
applying the second set of parameters to the first intermediate result to generate a second intermediate result;
applying the steering matrix P to the second intermediate result to generate a third intermediate result; and
applying the substream signal-to-noise ratio vector to the third intermediate result to recover the user data.

26. The method of claim 25, wherein:
the first set of parameters is based on a conjugate transpose of an orthogonal matrix of a recursive QR decomposition of the channel estimation matrix, and
the second set of parameters is based on an inverse of an upper triangular matrix of the QR decomposition.