Method and apparatus for transmitting signals using codebooks in a wireless communication system that supports multiple antennas
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for transmitting signals using codebooks in a wireless communication system that supports multiple antennas. A method in which a base station transmits downlink signals according to one embodiment of the present invention comprises the following steps: receiving a first precoding matrix indicator (PMI) and a second precoding matrix indicator from a terminal; determining a first matrix (W1) from a first codebook including precoding matrixes indicated by the first PMI, determining a second matrix (W2) from a second codebook, including precoding matrices indicated by the second PMI, and determining a precoding matrix (W) based on the first matrix (W1) and second matrix (W2); performing precoding on one or more layers, to which the downlink signals are mapped, using the determined precoding matrix (W); and transmitting the precoded signals to the terminal. Each of the precoding matrices included in the first codebook is a block diagonal matrix, and one block has, as compared to the other block, a form multiplied by a predetermined phase value.
1. A method of transmitting a downlink signal, which is transmitted by a base station, comprising the steps of:
receiving a 1 st PMI (precoding matrix indicator) and a 2 nd PMI from a user equipment;
determining a 1 st matrix (W1) from a 1 st codebook including precoding matrixes indicated by the 1 st PMI, determining a 2 nd matrix (W2) from a 2 nd codebook including precoding matrixes indicated by the 2 nd PMI, determining a precoding matrix (W) based on the 1 st matrix (W1) and the 2 nd matrix (W2);
performing a precoding on at least one layer having the downlink signal mapped thereto using the determined precoding matrix (W); and
transmitting the precoded signal to the user equipment,
wherein each of the precoding matrixes included in the 1 st code book is configured with a block diagonal matrix, the block diagonal matrix including a first block and a second block on a diagonal,
wherein the second block is multiplied by a prescribed phase value while the first block is not multiplied by the prescribed phase value, and
wherein the 1 st matrix (W1) is configured as a following formula:
w
1
(
n
)
=
[
X
(
n
)
0
0
α
(
n
)
X
(
n
)
]
,
wherein the X (n) and the α (n) X (n) respectively correspond to the first and the second blocks of the block diagonal matrix, and wherein the α (n) corresponds to the prescribed phase value.
2. The method of claim 1 , wherein the X (n) is configured with a DFT (Discrete Fourier Transform) vector defined as a following formula:
X
(
n
)
=
1
K
ⅇ
j
2
π
nk
N
n
=
0
,
…
,
N
-
1
k
=
0
,
…
,
K
-
1
,
wherein the N indicates the number of the DFT vectors, and wherein the K indicates a length of the DFT vector.
3. The method of claim 1 , wherein the α (n) is defined as a following formula:
α
(
n
)
=
ⅇ
j
2
π
nk
N
n
=
0
,
…
,
N
-
1.
4. The method of claim 1 , wherein the α (n) is defined as a phase diagonal matrix represented as a following formula:
α
(
n
)
=
diag
(
ⅇ
j
θ
0
(
n
)
…
ⅇ
jθ
K
-
1
(
n
)
)
=
[
ⅇ
j
θ
0
(
n
)
0
…
0
0
ⅇ
jθ
1
(
n
)
…
0
⋮
⋮
⋱
⋮
0
0
…
ⅇ
jθ
K
-
1
(
n
)
]
.
5. A method of receiving a downlink signal, which is received by a user equipment, comprising the steps of:
transmitting a 1 st PMI (precoding matrix indicator) and a 2 nd PMI to a base station;
receiving a signal having a precoding performed on at least one layer having the downlink signal mapped thereto from the base station using a precoding matrix (W) determined based on a 1 st matrix (W1) determined from a 1 st codebook including precoding matrixes indicated by the 1 st PMI and a 2 nd matrix (W2) determined from a 2 nd codebook including precoding matrixes indicated by the 2 nd PMI; and
processing the received downlink signal using the precoding matrix (W),
wherein each of the precoding matrixes included in the 1 st code book is configured with a block diagonal matrix, the block diagonal matrix including a first block and a second block on a diagonal,
wherein the second block is multiplied by a prescribed phase value while the first block is not multiplied by the prescribed phase value, and
wherein the 1 st matrix (W1) is configured as a following formula:
W
1
(
n
)
=
[
X
(
n
)
0
0
α
(
n
)
X
(
n
)
]
,
wherein the X (n) and the α (n) X (n) respectively correspond to the first and the second blocks of the block diagonal matrix, and wherein the α (n) corresponds to the prescribed phase value.
6. The method of claim 5 , wherein the X (n) is configured with a DFT (Discrete Fourier Transform) vector defined as a following formula:
X
(
n
)
=
1
K
ⅇ
j
2
π
nk
N
n
=
0
,
…
,
N
-
1
k
=
0
,
…
,
K
-
1
,
wherein the N indicates the number of the DFT vectors, and wherein the K indicates a length of the DFT vector.
7. The method of claim 5 , wherein the α (n) is defined as a following formula:
α
(
n
)
=
ⅇ
j
2
π
nk
N
n
=
0
,
…
,
N
-
1.
8. The method of claim 5 , wherein the α (n) is defined as a phase diagonal matrix represented as a following formula:
α
(
n
)
=
diag
(
ⅇ
j
θ
0
(
n
)
…
ⅇ
jθ
K
-
1
(
n
)
)
=
[
ⅇ
j
θ
0
(
n
)
0
…
0
0
ⅇ
jθ
1
(
n
)
…
0
⋮
⋮
⋱
⋮
0
0
…
ⅇ
jθ
K
-
1
(
n
)
]
.
9. A base station, which transmits a downlink signal, comprising:
a transmitting module transmitting a downlink signal to a user equipment;
a receiving module receiving an uplink signal from the user equipment;
a memory storing a codebook including precoding matrixes; and
a processor controlling the base station, the processor configured to receive a 1 st PMI (precoding matrix indicator) and a 2 nd PMI from the user equipment via the receiving module,
the processor configured to determine a 1 st matrix (W1) from a 1 st codebook including precoding matrixes indicated by the 1 st PMI, determine a 2 nd matrix (W2) from a 2 nd codebook including precoding matrixes indicated by the 2 nd PMI, and determine a precoding matrix (W) based on the 1 st matrix (W1) and the 2 nd matrix (W2),
the processor configured to perform a precoding on at least one layer having the downlink signal mapped thereto using the determined precoding matrix (W),
the processor configured to transmit the precoded signal to the user equipment,
wherein each of the precoding matrixes included in the 1 st code book is configured with a block diagonal matrix, the block diagonal matrix including a first block and a second block on a diagonal and
wherein the second block is multiplied by a prescribed phase value while the first block is not multiplied by the prescribed phase value,
wherein the 1 st matrix (W1) is configured as a following formula:
W
1
(
n
)
=
[
X
(
n
)
0
0
α
(
n
)
X
(
n
)
]
,
wherein the X (n) and the α (n) X (n) respectively correspond to the first and the second blocks of the block diagonal matrix, and wherein the α (n) corresponds to the prescribed phase value.
10. A user equipment, which receives a downlink signal, comprising:
a receiving module receiving the downlink signal from a base station;
a transmitting module transmitting an uplink signal to the base station;
a memory storing a codebook including precoding matrixes; and
a processor controlling the user equipment,
the processor configured to transmit a 1 st PMI (precoding matrix indicator) and a 2 nd PMI to the base station via the transmitting module,
the processor configured to receive a signal having a precoding performed on at least one layer having the downlink signal mapped thereto from the base station via the receiving module using a precoding matrix (W) determined based on a 1 st matrix (W1) determined from a 1 st codebook including precoding matrixes indicated by the 1 st PMI and a 2 nd matrix (W2) determined from a 2 nd codebook including precoding matrixes indicated by the 2 nd PMI,
the processor configured to process the received downlink signal using the precoding matrix (W),
wherein each of the precoding matrixes included in the 1 st code book is configured with a block diagonal matrix, the block diagonal matrix including a first block and a second block on a diagonal and
wherein the second block is multiplied by a prescribed phase value while the first block is not multiplied by the prescribed phase value,
wherein the 1 st matrix (W1) is configured as a following formula:
W
1
(
n
)
=
[
X
(
n
)
0
0
α
(
n
)
X
(
n
)
]
,
wherein the X (n) and the α (n) X (n) respectively correspond to the first and the second blocks of the block diagonal matrix, and wherein the α (n) corresponds to the prescribed phase value.