Receiving Node and Method for Determining Channel Estimate
The present invention relates to a receiving node, and to 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 ( 10 ) a matched filter channel estimate based on a known reference signal and a received reference signal in a frequency domain, transforming ( 20 ) the matched filter channel estimate into an over-sampled transform domain channel estimate, applying ( 30 ) a window to the over-sampled transform domain channel estimate to achieve a windowed transform domain channel estimate, transforming ( 40 ) the windowed transform domain channel estimate into a frequency domain channel estimate, and compensating ( 50 ) for a bias in the over-sampled frequency domain channel estimate based on a digital sine function.
1 - 12 . (canceled)
13 . 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, and
compensating for a bias in the over-sampled frequency domain channel estimate based on a digital sinc function, wherein the compensating for the bias comprises:
calculating de-biasing values 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
)
-
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, and compensating for the bias in the over-sampled frequency domain channel estimate based on the calculated de-biasing values.
14 . The method according to claim 13 , 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.
15 . The method according to claim 13 , wherein the window is applied so that a centre of the window substantially coincides with the group delay of the radio channel.
16 . The method according to claim 13 , wherein the de-biasing values 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
)
-
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.
17 . The method according to claim 13 , wherein the de-biasing values 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.
18 . 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, and
a compensating circuit adapted to compensate for a bias in the over-sampled frequency domain channel estimate based on a digital sinc function, by calculating de-biasing values 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
)
-
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, and by compensating for the bias in the over-sampled frequency domain channel estimate based on the calculated de-biasing values.
19 . The receiving node according to claim 18 , 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.
20 . The receiving node according to claim 18 , wherein the windowing circuit is further adapted to apply the window so that a centre of the window substantially coincides with the group delay of the radio channel.
21 . The receiving node according to claim 18 , wherein the compensating circuit is adapted to calculate the de-biasing values 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
)
-
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.
22 . The receiving node according to claim 18 , wherein the compensating circuit is adapted to calculate the de-biasing values 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.
23 . A computer readable medium storing a computer program comprising computer readable code that when executed on a receiving node configures the receiving node to determine a channel estimate of a radio channel in a radio communication system, based on configuring 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, and
compensate for a bias in the over-sampled frequency domain channel estimate based on a digital sinc function, wherein the compensating for the bias comprises:
calculate de-biasing values 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
)
-
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, and compensating for the bias in the over-sampled frequency domain channel estimate based on the calculated de-biasing values.