Method for QR-MLD demodulation
View Patent ↗A method for QR-maximum likelihood detection (QR-MLD) demodulation is provided. The method includes determining a transmission reception mode, receiving symbols represented by a received symbol vector, generating a channel matrix, and performing QR decomposition on the channel matrix to compute a unitary matrix and an upper triangular matrix. The method further includes the steps of processing the received symbol vector by multiplying the received symbol vector by the Hermitian of the unitary matrix, determining whether a conjugate calculation will be required to set a conjugate flag, computing a first distance metric by performing a conjugate or non-conjugate first distance metric calculation depending on the conjugate flag, and computing an estimated symbol by performing a conjugate or non-conjugate estimated symbol calculation depending on the conjugate flag. The method provided is less complex than existing demodulation methods, and it may be used to at least demodulate data transmitted via different modes.
1. A method for QR-maximum likelihood detection (QR-MLD) demodulation, including the steps of:
(a) determining a transmission reception mode as being one of single input—single output (SISO), single input—multiple output (SIMO), multiple input—multiple output (MIMO) or space frequency block codes (SFBC);
(b) receiving symbols simultaneously via multiple streams, the simultaneously received symbols being represented by a received symbol vector y;
(c) generating a channel matrix H;
(d) performing QR decomposition on the channel matrix H to compute a Q matrix and an R matrix such that H=QR, the Q matrix being a unitary matrix and the R matrix being an upper triangular matrix;
(e) processing the received symbol vector y by multiplying the received symbol vector y by the Hermitian Q H of the Q matrix such that z=Q H y where z is the processed received symbol vector;
(f) determining, for a SFBC mode determined at step (a), whether a conjugate calculation will be required and setting a conjugate flag having either a true or false value;
(g) computing a first distance metric d 1,j by using the processed received symbol vector z and the R matrix of the QR decomposition and performing a conjugate first distance metric calculation if the conjugate flag is true, else performing a non-conjugate first distance metric calculation if the conjugate flag is false;
(h) computing an estimated symbol {circumflex over (x)} j by performing a conjugate estimated symbol calculation if the conjugate flag is true, else performing a non-conjugate estimated symbol calculation if the conjugate flag is false;
(i) mapping the estimated symbol to a constellation as {circumflex over (x)} map,j ;
(j) computing a second distance metric d 2,j by performing a conjugate second distance metric calculation if the conjugate flag is true; else performing a non-conjugate second distance metric calculation if the conjugate flag is false;
(k) computing a total distance metric d totalj by summing the first and second distance metrics in steps (g) and (j); and
(l) calculating the soft bits.
2. The method of claim 1 , wherein at step (f), the SFBC mode includes a frequency tone index f=(0,f max ) ranging from 0 to f max and the conjugate flag is determined by the expression f=(0,f max ) such that the conjugate flag is set to true if f is odd and set to false otherwise.
3. The method of claim 1 , wherein at step (g) the conjugate first distance metric calculation is calculated from the expression d 1,j =|z 2 −r 2,2 c j *| 2 where c j is a symbol drawn from a constellation set.
4. The method of claim 1 , wherein at step (g) the non-conjugate first distance metric calculation is calculated from the expression d 1,j =|z 2 −r 2,2 c j | 2 where c j is a symbol drawn from a constellation set.
5. The method of claim 3 , wherein the constellation set includes any constellation set commonly used in wireless communications, including BPSK, QPSK, 8-PSK, 16QAM, 64QAM.
6. The method of claim 1 , wherein at step (h) the conjugate estimated symbol calculation is calculated from the expression
x
^
j
=
z
1
-
r
1
,
2
c
j
*
r
1
,
1
.
7. The method of claim 1 , wherein at step (h) the non-conjugate estimated symbol calculation is calculated from the expression
x
^
j
=
z
1
-
r
1
,
2
c
j
r
1
,
1
.
8. The method of claim 1 , wherein at step (j) the conjugate second distance metric calculation is calculated from the expression d 2,j =|z 1 −r 1,1 {circumflex over (x)} map,j −r 1,2 c j *| 2 .
9. The method of claim 1 , wherein at step (j) the non-conjugate second distance metric calculation is calculated from the expression d 2,j =|z 1 −r 1,1 {circumflex over (x)} map,j −r 1,2 c j | 2 .
10. The method of claim 1 , wherein at step (k) the total distance metric d totalj is calculated by the expression d totalj =d 1,j +d 2,j .
11. The method of claim 1 , wherein at step (l), the soft bits are calculated by:
(m) calculating the minimum distance from the symbols in the constellation that have a 1 in the i-th bit position (denoted B i 1 ) from the expression
d
min
,
i
(
B
i
1
)
=
min
j
∈
B
i
1
(
d
total
j
)
;
(n) calculating the minimum distance from the symbols in the constellation that have an 0 in the i-th bit position (denoted B i 0 ) from the expression and
d
min
,
i
(
B
i
0
)
=
min
j
∈
B
i
0
(
d
total
j
)
;
and
(o) calculating the two minimum distances from the expression
{circumflex over (b)} i =d min,i ( B i 1 ) −d min,i ( i B i 0 ).
12. The method of claim 4 , wherein the constellation set includes any constellation set commonly used in wireless communications, including BPSK, QPSK, 8-PSK, 16QAM, 64QAM.