Signal transmission method and apparatus using codebook in wireless communication system supporting multiple antennas
The present invention relates to a method for transmitting, by a base station, a downlink signal using a plurality of transmission antennas comprises the steps of: applying a precoding matrix indicated by the PMI, received from a terminal, in a codebook to a plurality of layers, and transmitting the precoded signal to the terminal through a plurality of transmission antennas. Among precoding matrices included in the codebook, a precoding matrix for even number transmission layers can be a 2×2 matrix containing four matrices (W1s), the matrix (W1) having rows of a number of transmission antennas and columns of half the number of transmission layers, the first and second columns of the first row in the 2×2 matrix being multiplied by 1, the first column of the second row being multiplied by coefficient “a” of a phase, and the first column of the second row being multiplied by “−a”.
1. A method for transmitting precoding matrix index (PMI) by a user equipment (UE), the method comprising:
transmitting a first PMI and a second PMI to a base station (BS),
wherein a codebook includes precoding matrices applicable to a downlink transmission of R layers (where 1≦R≦8) transmitted via through 2·N (N is a natural number) transmit (Tx) antennas, and a precoding matrix in the codebook is indicated by a combination of the first PMI and the second PMI,
wherein, when R is an even number, the codebook includes precoding matrices configured in the form of
[
W
1
W
1
aW
1
-
aW
1
]
,
where W 1 is an N×(R/2) matrix and α is a coefficient of a phase, and
wherein N is greater than or equal to 2.
2. The method according to claim 1 , wherein W 1 is a Discrete Fourier Transform (DFT) matrix.
3. The method according to claim 1 , wherein:
if R is an even number, then W 1 is configured as a matrix of [v1 . . . v(R/2)], and each of v1 . . . v(R/2) is an N×1 matrix.
4. The method according to claim 3 , wherein each of v1 . . . v(R/2) is configured as a DFT matrix.
5. The method according to claim 4 , wherein:
if R is equal to 4 (R=4), then the codebook includes precoding matrices that are configured in the form of
[
v
1
v
2
v
1
v
2
a
·
v
1
a
·
v
2
-
a
·
v
1
-
a
·
v
2
]
.
6. The method according to claim 1 , wherein:
if R is denoted by 3≦R≦7, the precoding matrix of the R layers is comprised of a column subset of precoding matrices of (R+1) layers.
7. The method according to claim 1 , wherein N is set to 4 (N=4).
8. A user equipment (UE) for p transmitting precoding matrix index (PMI), the UE comprising:
a reception (Rx) module;
a transmission (Tx) module;
a memory; and
a processor;
wherein the processor is configured to control the Tx module to transmit a first PMI and a second PMI to a base station (BS),
wherein the memory stores a codebook including precoding matrices applicable to a downlink transmission of R layers (where 1≦R≦8) transmitted via through 2·N (N is a natural number) transmit (Tx) antennas, and a precoding matrix in the codebook is indicated by a combination of the first PMI and the second PMI,
wherein, when R is an even number, the codebook includes precoding matrices configured in the form of
[
W
1
W
1
aW
1
-
aW
1
]
where W 1 is an N×(R/2) matrix and a is a coefficient of a phase, and
wherein N is greater than or equal to 2.
9. The method according to claim 1 , wherein the precoding matrix is determined based on two codebook indices.