Method for feeding back codebook-based precoding matrix information in wireless communication system and device therefor
A method for feeding back codebook-based precoding matrix information by a receiving side includes estimating a channel through a receiving signal received from a transmitting side; selecting first and second precoding matrix indexes for indicating precoding matrices selected in a predefined codebook based upon said estimated channel; and transmitting said selected first and second precoding matrix indexes to said transmitting side, wherein said predefined codebook supports antenna patterns at the receiving side, precoder (W) in the predefined codebook is expressed as a multiplication of two precoding matrices (W 1 and W 2 ), W 1 is constituted as an oversampled discrete Fourier transform (DFT) matrix by a diagonal matrix, an element which reflects a factor in accordance with an antenna pattern configuration of said receiving side is included, and said first precoding matrix index indicates a precoding matrix selected from W 1 and said second precoding matrix index indicates a precoding matrix selected from W 2 .
1. A method for feeding back, by a receiving side, codebook based precoding matrix information in a wireless communication system, the method comprising:
estimating a channel through a signal received from a transmitting side;
selecting a first precoding matrix index and a second precoding matrix index indicating precoding matrices selected from a predefined codebook based upon the estimated channel; and
transmitting the selected first and second precoding matrix indices to the transmitting side,
wherein the predefined codebook supports a plurality of antenna patterns at the receiving side and a precoder W in the codebook is represented by the product of two precoding matrices W 1 and W 2 ,
wherein W 1 is an oversampled discrete Fourier transform (DFT) matrix, is composed of a diagonal matrix and includes an element reflecting a factor according to an antenna pattern configuration of the receiving side,
wherein W 1 is configured as
W
1
=
[
W
~
1
(
n
1
)
0
0
φ
(
n
1
)
W
~
1
(
n
2
)
]
,
wherein {tilde over (W)} 1 (n) is an oversampled DFT matrix and φ(n) is the factor according to the antenna pattern configuration of the receiving side, and
wherein the first precoding matrix index indicates a precoding matrix selected from W 1 and the second precoding matrix index indicates a precoding matrix selected from W 2 .
2. The method according to claim 1 , wherein W 2 is configured in form of
W
2
=
1
2
[
1
α
]
,
α
∈
{
1
,
j
,
-
1
,
-
j
}
or
W
2
=
1
2
[
1
1
β
-
β
]
,
β
∈
{
1
,
j
}
.
3. The method according to claim 1 , wherein the matrix {tilde over (W)} 1 (n) is represented by
D
N
a
=
1
N
ⅇ
j
2
π
·
k
·
n
N
·
a
and
φ
(
n
)
=
ⅇ
j
2
π
·
N
·
n
N
·
a
wherein k=0, . . . , N−1, n=0, . . . , N·a−1, N=N t 2, N t denotes the number of antennas and a denotes an oversampling factor.
4. The method according to claim 1 , wherein the first precoding matrix index and the second precoding matrix index are selected for different frequency granularities or selected having different time periods and transmitted.
5. The method according to claim 4 , wherein the frequency granularity of the first precoding matrix is wideband and the frequency granularity of the second precoding matrix is subband.
6. The method according to claim 4 , wherein the frequency granularity of the first precoding matrix is subband and the frequency granularity of the second precoding matrix is wideband.
7. The method according to claim 1 , wherein the receiving side is user equipment (UE) and the transmitting side is an eNB.
8. The method according to claim 4 , wherein the selected first precoding matrix index is transmitted in a long term and the selected second precoding matrix index is transmitted in a short term.
9. The method according to claim 4 , wherein the selected first precoding matrix index is transmitted in a short term and the selected second precoding matrix index is transmitted in a long term.
10. The method according to claim 1 , wherein the selecting of the first precoding matrix index and the second precoding matrix index comprises:
determining a value n 1 or n 2 by which the state of the channel becomes optimal and selecting the first precoding matrix index corresponding to the determined value n 1 or n 2 from W 1 ; and
determining α or β according to transmission rank on the basis of the determined value n 1 or n 2 and selecting the second precoding matrix index corresponding to the determined α or β from W 2 .
11. A receiving side for feeding back codebook based precoding matrix information in a wireless communication system, the receiving side comprising:
a processor configured to estimate a channel through a signal received from a transmitting side and to select a first precoding matrix index and a second precoding matrix index indicating precoding matrices selected from a predefined codebook on the basis of the estimated channel; and
a transmitter configured to transmit the selected first and second precoding matrix indices to the transmitting side,
wherein the predefined codebook supports a plurality of antenna patterns at the receiving side and a precoder W in the codebook is represented by the product of two precoding matrices W 1 and W 2 ,
wherein W 1 is an oversampled DFT matrix, is composed of a diagonal matrix and includes an element reflecting a factor according to an antenna pattern configuration of the receiving side,
wherein W 1 is configured as
W
1
=
[
W
~
1
(
n
1
)
0
0
φ
(
n
1
)
W
~
1
(
n
2
)
]
,
wherein {tilde over (W)} 1 (n) is an oversampled DFT matrix and φ(n) is the factor according to the antenna pattern configuration of the receiving side, and
wherein the first precoding matrix index indicates a precoding matrix selected from W 1 and the second precoding matrix index indicates a precoding matrix selected from W 2 .
12. The receiving side according to claim 11 , wherein W 2 is configured in the form of
W
2
=
1
2
[
1
α
]
,
α
∈
{
1
,
j
,
-
1
,
-
j
}
or
W
2
=
1
2
[
1
1
β
-
β
]
,
β
∈
{
1
,
j
}
.
13. The receiving side according to claim 11 , wherein the matrix {tilde over (W)} 1 (n) is represented by
D
N
a
=
1
N
ⅇ
j
2
π
·
k
·
n
N
·
a
and
φ
(
n
)
=
ⅇ
j
2
π
·
N
·
n
N
·
a
wherein k=0, . . . , N−1, n=0, . . . , N·a−1, N=N 1 /2, N t denotes the number of antennas and a denotes an oversampling factor.
14. The receiving side according to claim 11 , wherein the first precoding matrix index and the second precoding matrix index are selected for different frequency granularities or selected having different time periods and transmitted.
15. The receiving side according to claim 11 , wherein the receiving side is a UE and the transmitting side is an eNB.
16. The receiving side according to claim 11 , wherein when the processor selects the first precoding matrix index and the second precoding matrix index, the processor is configured to determine a value n 1 or n 2 by which the state of the channel becomes optimal, to select the first precoding matrix index corresponding to the determined value n 1 or n 2 from W 1 , to determine α or β according to transmission rank on the basis of the determined value n 1 or n 2 and to select the second precoding matrix index corresponding to the determined α or β from W 2 .