Frequency-domain method for joint equalization and decoding of space-time block codes
View Patent ↗Space-time block coding is combined with single-carrier, minimum-mean-square-error, frequency-domain equalization for wireless communication through a medium characterized by multi-paths. The transmitter encodes incoming symbols into two or more streams that are transmitted over a corresponding number of transmitting antennas. The encoding employs modulo arithmetic. Decoding in the receiver proceeds by converting received signals to frequency domain, linearly combining the signals to separate contribution of the signals from the two or more transmitting antennas equalizing the separated signals, converting the equalized signals to time domain, and applying the converted signals to a decision circuit.
1. A receiver comprising:
a time-domain to frequency-domain converter responsive to a signal received by an antenna in frames k and k+1, for developing signals Y k in frame k and signals Y k+1 in frame k+1;
a linear combiner for creating a first linear combination signal, {tilde over (Y)} k , from signals related to Y k and Y k+1 , and a second linear combination signal, {tilde over (Y)} k+1 , from signals related to Y k and Y k+1 , where said first linear combination is different from said second linear combination;
an equalizer that pre-multiplies signal {tilde over (Y)} k by a diagonal matrix W to form signal {tilde over (X)} k , and pre-multiplies signal {tilde over (Y)} k+1 by said diagonal matrix W to form signal {tilde over (Z)} k+1 ;
a frequency-domain to time-domain converter for converting signals {tilde over (Z)} k and {tilde over (Z)} k+1 to time-domain signals; and
a slicer responsive to said time domain signals.
2. The receiver of claim 1 where said time-domain to frequency-domain converter implements a Fast Fourier Transform algorithm.
3. The receiver of claim 1 where said frequency-domain to time-domain converter implements an inverse Fast Fourier Transform algorithm.
4. The receiver of claim 1 where said linear combiner, in creating signal {tilde over (Y)} k from component signals related to Y k and Y k+1 , multiplies at least one of said component signals by a diagonal matrix.
5. The receiver of claim 1 where said linear combiner, in creating signal {tilde over (Y)} k from component signals related to Y k and Y k+1 , multiplies each of said component signals by a different diagonal matrix.
6. The receiver of claim 1 where said linear combiner, in creating signal {tilde over (Y)} k from component signals related to Y k and Y k+1 , employs diagonal matrices Λ 1 and Λ 2 where diagonal matrix Λ 1 is related to characteristics of transmission medium between a first antenna of a transmitter of signals received by said receiver, and Λ 2 is related to characteristics of transmission medium between a first antenna of a transmitter of signals received by said receiver.
7. The receiver of claim 6 where said linear combiner, in creating signal {tilde over (Y)} k+1 from component signals related to Y k and Y k+1 , employs diagonal matrices that are related to said matrices Λ 1 and Λ 2 through operations taken from a set that includes negations and complex conjugations.
8. The receiver of claim 1 where said linear combiner creates signal {tilde over (Y)} l =Λ 1 *Y k +Λ 2 {overscore (Y)} k+1 , and signal {tilde over (Y)} k+1 =Λ 2 *Y k −Λ 1 {overscore (Y)} k+1 , where {overscore (Y)} k+1 is a complex conjugate of Y k+1 .
9. The receiver of claim 8 where elements of said diagonal matrix W are related to matrices Λ 1 and Λ 2 .
10. The receiver of claim 8 where said diagonal matrix W has elements
W
(
i
,
i
)
=
1
Λ
~
(
i
,
i
)
+
1
S
N
R
,
where
Λ
~
(
i
,
i
)
=
Λ
1
(
i
,
i
)
Λ
1
*
(
i
,
i
)
+
Λ
2
(
i
,
i
)
Λ
2
*
(
i
,
i
)
,
and (.)* represents a complex conjugate operation, and SNR is a computed value.
11. A receiver comprising:
a time-domain to frequency-domain converter responsive to a signal received by an antenna in frames k, k+1, . . . k+m, where m is a selected integer greater than 0, for developing signals Y k , Y k+1 , . . . Y k+m , in frames k, k+1, . . . . k+m, respectively;
a linear combiner for creating signals {tilde over (Y)} k , {tilde over (Y)} k+1 , . . . {tilde over (Y)} k+m from linear combinations of signals related to Y k , Y k+1 , . . . Y k+m ;
an equalizer that pre-multiplies each signal {tilde over (Y)} j ,j=k, k+1, . . . k+m by a diagonal matrix W to form signals {overscore (Z)} l , j=k, k+1, . . . k+m;
a frequency-domain to time-domain converter for converting signals {tilde over (Z)} j to time domain signals; and
a slicer responsive to said time domain signals.
12. The receiver of claim 11 where said signals related to signals Y k , Y k+1 , . . . y k+m are related to said signals Y k , Y k+1 , . . . Y k+m through operations from a set that includes negations and complex conjugations.
13. A receiver comprising:
p antennas, where p is an integer greater than 1;
a time-domain to frequency-domain converter responsive to a signal received by each of said antennas in frames k, k+1, . . . k+m, where m is a selected integer greater than 0, for developing signals Y j k , Y j k+1 , . . . y h k+m , in frames k, k+1, . . . k+m, respectively, where subscript j identifies a j th antennas of said p antennas;
a linear combiner for creating groups of signals {tilde over (Y)} n k , {tilde over (Y)} n k+1 , . . . {tilde over (Y)} n k+m for each value of subscript j=1, 2, . . . p, from linear combinations of signals related to said signals {tilde over (Y)} n k , {tilde over (Y)} n k+1 , . . . {tilde over (Y)} n k+m , when n is an index designating a transmitting unit that supplies signals to said p antennas;
an equalizer that pre-multiplies each signal {tilde over (Y)} n q , q=k, k+1, . . . k+m by a diagonal matrix W to form signals {tilde over (Z)} n q , q=k, k+1, . . . k+m;
a frequency-domain to time-domain converter for converting signals {tilde over (Z)} n q to time-domain signals; and
a slicer responsive to said time domain signals.
14. The receiver of claim 13 where p=2, and where said linear combiner obtains signals {tilde over (Y)} n k and {tilde over (Y)} n k+1 by computing
[
Y
^
1
k
Y
^
2
k
]
=
[
I
-
Λ
2
-
1
Λ
1
-
2
-
1
-
Λ
2
-
2
Λ
1
-
1
-
1
I
]
[
Y
1
k
Y
2
k
]
where Ŷ 1 k represents signal received at said receiver, in frame k, from transmitting unit 1 , and Ŷ 2 k represents signal received at said receiver, in frame k, from transmitting unit 1 , Λ 1-1 is a diagonal matrix representing transmission medium between transmitting unit 1 and a first one of said two antennas, Λ 2-1 is a diagonal matrix representing transmission medium between transmitting unit 2 and said first one of said two antennas Λ t-2 −1 is a diagonal matrix representing transmission medium between said transmitting unit 1 and a second one of said two antennas Λ 2-2 is a diagonal matrix representing transmission medium between said transmitting unit 1 and said second one of said two antennas.
15. A method carried out in a receiver for decoding received frame signals of a unit that transmits over p antennas, comprising the steps of:
converting each received frame signal to frequency domain;
in groups of p consecutive converted frame signals, combining said converted frame signals to form p intermediate signals;
multiplying said intermediate signals by values related to transfer characteristics between said p antennas and said receiver, to obtain thereby equalized signals;
converting said equalized signals to time domain, to obtain time domain estimate signals; and
carrying out a decision regarding information symbols transmitted by said unit, based on said estimate signals.
16. The method of claim 15 where said combining is linear combining.
17. The method of claim 15 where said transfer characteristics employed in said step of multiplying are frequency domain characteristics of transmission channel between said p antennas and said receiver.