Receiving node and method for determining channel estimate
View Patent ↗The teachings herein disclose a receiving node and a related method for determining a channel estimate of a radio channel in a receiving node of a radio communication system. The method comprises calculating a matched filter channel estimate based on a known reference signal and a received reference signal in a frequency domain, transforming the matched filter channel estimate into an over-sampled transform domain channel estimate, applying a window to the over-sampled transform domain channel estimate to achieve a windowed transform domain channel estimate, transforming the windowed transform domain channel estimate into a frequency domain channel estimate, and compensating for a bias in the over-sampled frequency domain channel estimate based on a digital sinc function.
1. A method for determining a channel estimate of a radio channel in a receiving node of a radio communication system, the method comprising:
calculating a matched filter channel estimate based on a known reference signal and a received reference signal in a frequency domain;
transforming the matched filter channel estimate into an over-sampled transform domain channel estimate;
applying a window to the over-sampled transform domain channel estimate to achieve a windowed transform domain channel estimate;
transforming the windowed transform domain channel estimate into a frequency domain channel estimate, the frequency domain channel estimate corresponding to a number of sub-carriers; and
compensating for a bias in the over-sampled frequency domain channel estimate by applying de-biasing values that are calculated based on a digital sinc function, wherein for each individual sub-carrier, a corresponding de-biasing value is calculated and applied individually for that sub-carrier.
2. The method according to claim 1 , wherein the compensating for the bias comprises:
calculating the de-biasing values based on the digital sinc function and a set of values for at least one of a group delay of the radio channel, an over-sampling factor, a right and a left channel tap index of the applied window, and the number of sub-carriers for which the channel estimate is determined; and
compensating for the bias in the over-sampled frequency domain channel estimate based on the calculated de-biasing values.
3. The method according to claim 2 , wherein the compensating for the bias further comprises:
storing the calculated de-biasing values; and
wherein the compensation for the bias is based on the stored calculated de-biasing values.
4. The method according to claim 2 , wherein the window is applied so that a center of the window substantially coincides with the group delay of the radio channel.
5. The method according to claim 1 , wherein the matched filter channel estimate is transformed based on a Discrete Fourier Transform, DFT.
6. The method according to claim 1 , wherein the matched filter channel estimate is transformed based on a Discrete Cosine Transform, DCT.
7. The method according to claim 2 , wherein the de-biasing values, denoted as B(k), are calculated based on the following equation:
B
(
k
)
=
1
N
c
K
os
∑
k
′
=
0
N
c
-
1
sin
(
π
(
k
-
k
′
)
(
m
R
-
m
L
+
1
)
N
c
K
os
)
sin
(
π
(
k
-
k
′
)
N
c
K
os
)
ⅇ
-
j
π
(
k
-
k
′
)
(
m
R
+
m
L
-
2
m
0
(
k
)
)
N
c
K
os
wherein k and k′ are sub-carrier indices, N c is the number of sub-carriers for which the channel estimate is determined, K os is the over-sampling factor, m R is the right channel tap index of the applied window, m L is the left channel tap index of the applied window, and m 0 (k) is the group delay of the radio channel as function of sub-carrier index k.
8. The method according to claim 2 , wherein the de-biasing values, denoted as B(k), are calculated based on the following equation:
B
(
k
)
=
1
N
c
K
os
∑
m
=
m
L
m
R
sin
(
π
(
m
-
m
0
(
k
)
)
K
os
)
sin
(
π
(
m
-
m
0
(
k
)
)
N
c
K
os
)
ⅇ
-
j
π
(
m
-
m
0
(
k
)
)
(
2
k
-
N
+
1
)
N
c
K
os
wherein k and k′ are sub-carrier indices, N c is the number of sub-carriers for which the channel estimate is determined, K os is the over-sampling factor, m is a channel tap index, m R is the right channel tap index of the applied window, m L is the left channel tap index of the applied window, and m 0 (k) is the group delay of the radio channel as function of sub-carrier index k.
9. The method according to claim 2 , wherein the de-biasing values, denoted as B(k), are calculated based on the following equation:
B
(
k
)
=
1
N
c
K
os
∑
k
′
=
0
N
c
-
1
sin
(
2
π
(
k
-
k
′
)
L
2
N
c
K
os
)
sin
(
2
π
(
k
-
k
′
)
2
N
c
K
os
)
wherein k and k′ are sub-carrier indices, N c is the number of sub-carriers for which the channel estimate is determined, K os is the over-sampling factor, and L is the length of the applied window in number of channel taps.
10. A receiving node for a radio communication system, comprising a channel estimator configured to determine a channel estimate of a radio channel, the channel estimator comprising:
a calculating circuit adapted to calculate a matched filter channel estimate based on a known reference signal and a received reference signal in a frequency domain;
a first transforming circuit adapted to transform the matched filter channel estimate into an over-sampled transform domain channel estimate;
a windowing circuit adapted to apply a window to the over-sampled transform domain channel estimate to achieve a windowed transform domain channel estimate;
a second transforming circuit adapted to transform the windowed transform domain channel estimate into a frequency domain channel estimate, the frequency domain channel estimate corresponding to a number of sub-carriers; and
a compensating circuit adapted to compensate for a bias in the over-sampled frequency domain channel estimate by applying de-biasing values that are calculated based on a digital sinc function, wherein for each individual sub-carrier, a corresponding de-biasing value is calculated and applied individually for that sub-carrier.
11. The receiving node according to claim 10 , wherein the compensating circuit is adapted to:
calculate the de-biasing values based on the digital sinc function and a set of values for at least one of a group delay of the radio channel, an over-sampling factor, a right and a left position of the applied window, and the number of sub-carriers for which the channel estimate is determined; and
compensate for the bias in the over-sampled frequency domain channel estimate based on the calculated de-biasing values.
12. The receiving node according to claim 11 , wherein the compensating circuit is further adapted to store the calculated de-biasing values, and to compensate for the bias based on the stored calculated de-biasing values.
13. The receiving node according to claim 11 , wherein the windowing circuit is further adapted to apply the window so that a center of the window substantially coincides with the group delay of the radio channel.
14. The receiving node according to claim 10 , wherein the first transforming circuit is adapted to transform the matched filter channel estimate based on a Discrete Fourier Transform, DFT.
15. The receiving node according to claim 10 , wherein the first transforming circuit is adapted to transform the matched filter channel estimate based on a Discrete Cosine Transform, DCT.
16. The receiving node according to claim 11 , wherein the compensating circuit is adapted to calculate the de-biasing values, denoted as B(k), based on the following equation:
B
(
k
)
=
1
N
c
K
os
∑
k
′
=
0
N
c
-
1
sin
(
π
(
k
-
k
′
)
(
m
R
-
m
L
+
1
)
N
c
K
os
)
sin
(
π
(
k
-
k
′
)
N
c
K
os
)
ⅇ
-
j
π
(
k
-
k
′
)
(
m
R
+
m
L
-
2
m
0
(
k
)
)
N
c
K
os
wherein k and k′ are sub-carrier indices, N c is the number of sub-carriers for which the channel estimate is determined, K os is the over-sampling factor, m R is the right channel tap index of the applied window, m L is the left channel tap index of the applied window, and m 0 (k) is the group delay of the radio channel as function of sub-carrier index k.
17. The receiving node according to claim 11 , wherein the compensating circuit is adapted to calculate the de-biasing values, denoted as B(k), based on the following equation:
B
(
k
)
=
1
N
c
K
os
∑
m
=
m
L
m
R
sin
(
π
(
m
-
m
0
(
k
)
)
K
os
)
sin
(
π
(
m
-
m
0
(
k
)
)
N
c
K
os
)
ⅇ
-
j
π
(
m
-
m
0
(
k
)
)
(
2
k
-
N
c
+
1
)
N
c
K
os
wherein k and k′ are sub-carrier indices, N c is the number of sub-carriers for which the channel estimate is determined, K os is the over-sampling factor, m is a channel tap index, m R is the right channel tap index of the applied window, m L is the left channel tap index of the applied window, and m 0 (k) is the group delay of the radio channel as function of sub-carrier index k.
18. The receiving node according to claim 11 , wherein the compensating circuit is adapted to calculate the de-biasing values, denoted as B(k), based on the following equation:
B
(
k
)
=
1
N
c
K
os
∑
k
′
=
0
N
c
-
1
sin
(
2
π
(
k
-
k
′
)
L
2
N
c
K
os
)
sin
(
2
π
(
k
-
k
′
)
2
N
c
K
os
)
wherein k and k′ are sub-carrier indices, N c is the number of sub-carriers for which the channel estimate is determined, K os is the over-sampling factor, and L is the length of the applied window in number of channel taps.
19. A non-transitory computer-readable medium storing a computer program comprising computer readable code that, when executed by processing circuitry at a receiving node of a radio communication system, configures the receiving node to determine a channel estimate of a radio channel, said computer readable code including program instructions causing the receiving node to:
calculate a matched filter channel estimate based on a known reference signal and a received reference signal in a frequency domain;
transform the matched filter channel estimate into an over-sampled transform domain channel estimate;
apply a window to the over-sampled transform domain channel estimate to achieve a windowed transform domain channel estimate;
transform the windowed transform domain channel estimate into a frequency domain channel estimate, the frequency domain channel estimate corresponding to a number of sub-carriers; and
compensate for a bias in the over-sampled frequency domain channel estimate by applying de-biasing values that are calculated based on a digital sinc function, wherein for each individual sub-carrier, a corresponding de-biasing value is calculated and applied individually for that sub-carrier.