Demodulation method for MIMO systems

1. A method for processing a plurality of data streams from a transmitter, the method including:

(a) receiving symbols via the plurality of data streams, the received symbols being represented by a received symbol vector y;

(b) generating an N×N channel matrix H, using a signal model y=Hx+n, where x is the N×1 transmitted symbols and n is the N×1 Gaussian noise vector, and where N is the number of data streams;

(c) sorting the N×N channel matrix H to provide an N×N sorted channel matrix H(S);

(d) performing QR decomposition on the sorted channel matrix H(S) to compute a Q(S) matrix and an R(S) matrix such that H(S)=Q(S)R(S), the Q(S) matrix being a unitary matrix and the R(S) matrix being an upper triangular matrix;

(e) performing QR decomposition on a column-row-swapped-sorted-channel matrix H ({tilde over (S)}) to compute the corresponding Q({tilde over (S)}) matrix and R({tilde over (S)}) matrix such that H({tilde over (S)})=Q({tilde over (S)})×R({tilde over (S)}), the Q({tilde over (S)}) matrix being a unitary matrix and the R({tilde over (S)}) matrix being an upper triangular matrix;

(f) performing QR equalization on a sorted received symbol vector y(S), which is produced by sorting the receiving symbol vector y to provide a equalized-sorted vector z(S);

(g) performing QR equalization on a swapped received symbol vector y({tilde over (S)}) to provide a equalized-swapped-sorted vector z({tilde over (S)});

(h) processing a first portion of z(S) and z({tilde over (S)}) via a QR-maximum likelihood detection (MLD) demodulation scheme to determine soft bits and soft symbols;

(I) processing a second portion of z(S) and z({tilde over (S)}) via a QR-maximum likelihood detection (MLD) demodulation scheme to determine soft bits and soft symbols;

(j) rearrange soft bits in steps (h) and (I) to provide an output vector b.

2. The method of claim 1 , wherein N=4 and sorting of the 4×4 channel matrix H to provide a 4×4 sorted channel matrix H(S) at step (c) includes the following steps:

(a) generating pre-arranged matrices H( 1 ), H( 2 ), H( 3 ) and H( 4 );

(b) performing QR decomposition on H(t)=Q(t)×R(t), tε{1, 2, 3, 4},

(c) utilizing an element of each R matrix for sorting such that S=└s 1 ,s 2 ,s 3 ,s 4 ┘.

3. The method of claim 1 , wherein N=4 and sorting of the 4×4 channel matrix H to provide a 4×4 sorted channel matrix H(S) at step (c) includes the following steps:

(a) calculating a norm of each column of the channel matrix H;

(b) comparing the norm of each column to obtain a sorted vector S=└s 1 ,s 2 ,s 3 ,s 4 ┘.

4. The method of claim 1 , wherein N=4 and the sorted channel matrix H(S) is given by the expression: H(S)=└h(s 1 )h(s 2 )h(s 3 )h(s 4 )┘=Q(S)×R(S).

5. The method of claim 1 , wherein N=4 and the column-row-swapped-sorted-channel matrix H({tilde over (S)}) is obtained.

6. The method of claim 1 , wherein N=4 and performing QR equalization on a sorted received symbol vector y(S) to provide a equalized-sorted vector z(S) is determined by the following steps:

(a) multiplying a sorted received symbol vector y(S) by a Hermitian Q H (S) of the Q(S) matrix such that z(S)=Q H (S)y(S);

(b) obtaining the equalized-sorted vector z(S).

7. The method of claim 1 , wherein N=4 and performing QR equalization by multiplying the swapped received symbol vector y({tilde over (S)}) by a Hermitian Q H ({tilde over (S)}) of the Q({tilde over (S)}) matrix such that z({tilde over (S)})=Q H ({tilde over (S)})×y (S) where z({tilde over (S)}) is the equalized-swapped-sorted vector.

8. The method of claim 7 , wherein the first portion of z(S) and z ({tilde over (S)}) is used to calculate soft bits x S 3 , x S 4 .

9. The method of claim 8 , wherein a total distance metric d total j is calculated to provide soft symbol {circumflex over (x)} s 4 and {circumflex over (x)} s 3 .

10. The method of claim 7 , wherein the second portion of z(S) and z({tilde over (S)}) with the calculated soft symbol {circumflex over (x)} s 4 and {circumflex over (x)} s 3 are used to calculate soft bits x S 1 , x S 2 .

11. The method of claim 10 , wherein the soft bits x S 1 , x S 2 , x S 3 , x S 4 are fed into a Forward Error Correction (FEC) decoder for further processing.

12. The method of claim 11 , wherein the soft bits x S 1 , x S 2 , x S 3 , x S 4 , are rearranged to provide an output vector b.