Generating channel estimates in a radio receiver
A method and system for generating channel estimates for processing signals received through first and second transmission channels in a wireless communications network, each channel corresponding to a separate transmit antenna, and each signal comprising a plurality of samples derived from symbols transmitted in the signal by: generating first variable z1 (k) and second variable z2 (k); and providing a set of filter coefficients (I) and generating first and second channel estimates using first and second variables and a set of filter coefficients.
1. A method of generating channel estimates for processing signals received through first and second transmission channels in a wireless communications network, each channel corresponding to a separate transmit antenna, and each signal comprising a plurality of samples derived from symbols transmitted in the signal, the method comprising:
generating a first variable z 1 (k) and a second variable z 2 (k), the first variable being a sequence of values, each k-th value being a function of the 2k-th and 2k+1-th samples and the complex conjugate of a symbol S, the second variable being a sequence of values each k-th value being a function of the 2k-th and 2k+1-th samples, the sign of the 2k-th and 2k+1-th symbols transmitted on one of the antennas and the complex conjugate of the symbol S; and
providing a set of filter coefficients {w(l)} l=−L 1 L 2 and generating first and second channel estimates using the first and second variables and the set of filter coefficients.
2. A method according to claim 1 , comprising generating a third variable y 1 (k) and a fourth variable y 2 (k) by repeating in time the first variable z 1 (k) and the second variable z 2 (k), respectively; and
generating the channel estimates by applying a single set of filter coefficients {w(l)} l=−L 1 L 2 to the fourth and third variables.
3. A method according to claim 1 , comprising providing a first set of filter coefficients {w 0 (l)} and a second set of filter coefficients {w 1 (l)} derived from a single set of filter coefficients {w(l)} l=−L 1 L 2 by combining respectively adjacent pairs of said single set, the first set commencing from a first value from the single set and the second set commencing from the second value of the single set; and
generating the channel estimates by applying the first and second sets of filter coefficients to the first and second variables.
4. A method according to claim 1 , comprising the step of selectively using the single set of filter coefficients for generating a channel estimate in the case where a signal is received through one transmission channel from a single antenna.
5. A method according to claim 1 , wherein the first and second variables are generated according to:
z
1
(
k
)
=
y
(
2
k
)
+
y
(
2
k
+
1
)
2
·
S
*
Equation
1
z
2
(
k
)
=
ξ
(
2
k
)
y
(
2
k
)
+
ξ
(
2
k
+
1
)
y
(
2
k
+
1
)
2
·
S
*
.
Equation
2
6. A method according to claim 3 , wherein the first and second filter coefficients are provided according to:
w
0
(
-
L
1
/
2
)
=
w
(
-
L
1
)
+
w
(
-
L
1
+
1
)
w
1
(
-
L
1
/
2
)
=
w
(
-
L
1
)
⋮
w
1
(
-
L
1
/
2
+
1
)
=
w
(
-
L
1
+
1
)
+
w
(
L
1
+
2
)
w
0
(
L
2
/
2
-
1
)
=
w
(
L
2
-
2
)
+
w
(
L
2
-
1
)
⋮
w
0
(
L
2
/
2
)
=
w
(
L
2
)
w
1
(
L
2
/
2
)
=
w
(
L
2
-
1
)
+
w
(
L
2
)
.
7. A method according to claim 3 , wherein the step of generating the channel estimates comprises generating even indexes for the channel estimates using the first set of filter coefficients and generating odd indexes for the channel coefficients using the second set of filter coefficients.
8. A method according to claim 6 , wherein the channel estimates are generated according to:
h
^
1
(
2
k
)
=
∑
l
=
-
L
1
/
2
L
2
/
2
w
0
(
l
)
z
1
(
k
-
l
)
,
h
^
1
(
2
k
+
1
)
=
∑
I
=
-
L
1
/
2
L
2
/
2
w
1
(
l
)
z
1
(
k
-
l
)
Equation
3
h
^
2
(
2
k
)
=
∑
l
=
-
L
1
/
2
L
2
/
2
w
0
(
l
)
z
2
(
k
-
l
)
,
h
^
2
(
2
k
+
1
)
=
∑
l
=
-
L
1
/
2
L
2
/
2
w
1
(
l
)
z
2
(
k
-
l
)
.
Equation
4
9. Circuitry for generating channel estimates for first and second transmission channels in a receiver of a wireless communications system, each channel corresponding to a separate transmit antenna, the circuitry comprising:
a variable generation unit operable to generate first and second variables, the first variable being a sequence of values, each k-th value being a function of the 2k-th and 2k+1-th samples and the complex conjugate of a symbol S, the second variable being a sequence of values, each k-th value being a function of the 2k-th and 2k+1-th samples, the sign of 2k-th and 2k+1-th symbols transmitted on one of the antennas and the complex conjugate of the symbol S;
storage means holding a set of filter coefficients; and
means for generating first and second channel estimates for the first and second transmission channels using the set of filter coefficients and the first and second variables.
10. Circuitry according to claim 9 , comprising a filter coefficient generation unit for providing first and second sets of filter coefficients from a single set of filter coefficients by combining respectively adjacent pairs of said single set, the first set commencing from a first value from the single set and the second set commencing from the second value of the single set.
11. Circuitry according to claim 9 , comprising a further variable generation unit for generating a third variable y 1 (k) and a fourth variable y 2 (k) by repeating in time the first variable z 1 (k) and the second variable z 2 (k) respectively.
12. A wireless receiver for a communications system, the receiver comprising circuitry according to claim 9 .
13. A wireless communications system comprising first and second transmit antennas each arranged to transmit signals via first and second transmission channels; and
a wireless receiver according to claim 12 .
14. A computer program product for generating channel estimates for processing signals received through first and second transmission channels in a wireless communications network, each channel corresponding to a separate transmit antenna, and each signal comprising a plurality of samples derived from symbols transmitted in the signal, the computer program product comprising program code embodied on a computer readable medium and configured so as when executed on a processor to:
generate a first variable z 1 (k) and a second variable z 2 (k), the first variable being a sequence of values, each k-th value being a function of the 2k-th and 2k+1-th samples and the complex conjugate of a symbol S, the second variable being a sequence of values each k-th value being a function of the 2k-th and 2k+1-th samples, the sign of the 2k-th and 2k+1-th symbols transmitted on one of the antennas and the complex conjugate of the symbol S; and
provide a set of filter coefficients {w(l)} l=−L 1 L 2 and generating first and second channel estimates using the first and second variables and the set of filter coefficients.
15. A computer program product according to claim 14 , wherein the code is configured to:
generate a third variable y 1 (k) and a fourth variable y 2 (k) by repeating in time the first variable z 1 (k) and the second variable z 2 (k), respectively; and
generate the channel estimates by applying a single set of filter coefficients {w(l)} l=−L 1 L 2 to the fourth and third variables.
16. A computer program product according to claim 14 , wherein the code is configured to:
provide a first set of filter coefficients {w 0 (l)} and a second set of filter coefficients {w 1 (l)} derived from a single set of filter coefficients {w(l)} l=−L 1 L 2 by combining respectively adjacent pairs of said single set, the first set commencing from a first value from the single set and the second set commencing from the second value of the single set; and
generate the channel estimates by applying the first and second sets of filter coefficients to the first and second variables.
17. A computer program product according to claim 14 , wherein the code is configured to selectively use the single set of filter coefficients for generating a channel estimate in the case where a signal is received through one transmission channel from a single antenna.
18. A computer program product according to claim 14 , wherein the first and second variables are generated according to:
z
1
(
k
)
=
y
(
2
k
)
+
y
(
2
k
+
1
)
2
·
S
*
Equation
1
z
2
(
k
)
=
ξ
(
2
k
)
y
(
2
k
)
+
ξ
(
2
k
+
1
)
y
(
2
k
+
1
)
2
·
S
*
.
Equation
2
19. A computer program product according to claim 16 , wherein the first and second filter coefficients are provided according to:
w
0
(
-
L
1
/
2
)
=
w
(
-
L
1
)
+
w
(
-
L
1
+
1
)
w
1
(
-
L
1
/
2
)
=
w
(
-
L
1
)
⋮
w
1
(
-
L
1
/
2
+
1
)
=
w
(
-
L
1
+
1
)
+
w
(
L
1
+
2
)
w
0
(
L
2
/
2
-
1
)
=
w
(
L
2
-
2
)
+
w
(
L
2
-
1
)
⋮
w
0
(
L
2
/
2
)
=
w
(
L
2
)
w
1
(
L
2
/
2
)
=
w
(
L
2
-
1
)
+
w
(
L
2
)
.
20. A computer program product according to claim 16 , wherein the generation of the channel estimates comprises generating even indexes for the channel estimates using the first set of filter coefficients and generating odd indexes for the channel coefficients using the second set of filter coefficients.
21. A computer program product according to claim 19 , wherein the channel estimates are generated according to:
h
^
1
(
2
k
)
=
∑
l
=
-
L
1
/
2
L
2
/
2
w
0
(
l
)
z
1
(
k
-
l
)
,
h
^
1
(
2
k
+
1
)
=
∑
I
=
-
L
1
/
2
L
2
/
2
w
1
(
l
)
z
1
(
k
-
l
)
Equation
3
h
^
2
(
2
k
)
=
∑
l
=
-
L
1
/
2
L
2
/
2
w
0
(
l
)
z
2
(
k
-
l
)
,
h
^
2
(
2
k
+
1
)
=
∑
l
=
-
L
1
/
2
L
2
/
2
w
1
(
l
)
z
2
(
k
-
l
)
.
Equation
4