Method for differential precoding and base station supporting same

1. A method for differential precoding, the method comprising:

initializing a precoding matrix with a first Precoding Matrix Indicator (PMI) for a channel between a mobile station and a base station; and

updating the precoding matrix with a second PMI for the channel and side information for adaptively updating the precoding matrix according to a change speed of a state of the channel,

wherein the side information has a quantized scalar value, and

wherein the precoding matrix is repeatedly updated with the following Equation:

G ( n )= G ( n− 1)*( F sub,p ) a ,

where G(n) is a precoding matrix at an nth time, G(n−1) is a precoding matrix at an n−1st time, F sub,q denotes a factor corresponding to the second PMI “p” in a sub-codebook, * denotes an inter-matrix operator indicating one of a matrix addition, a matrix product, and a Kronecker product, and a denotes a value corresponding to the side information.

2. The method of claim 1 , further comprising:

precoding downlink data with the initialized precoding matrix or the updated precoding matrix; and

transmitting the precoded downlink data to the mobile station.

3. The method of claim 1 , wherein the precoding matrix is initialized with the following Equation:

G (0)= F main,q ,

where G(0) denotes a precoding matrix at a zeroth time, and F main,q denotes a factor corresponding to the first PMI “q” in a main codebook.

4. A method for differential precoding, the method comprising:

precoding, when first Channel State Information (CSI) on a channel between a mobile station and a base station is received from the mobile station, first downlink data with a precoding matrix initialized with the first CSI to transmit the precoded first downlink data to the mobile station;

updating, when second CSI on the channel and side information for adaptively updating the precoding matrix according to a change in a state of the channel are received from the mobile station, the precoding matrix with the side information and the second CSI; and

precoding second downlink data with the updated precoding matrix to transmit the precoded second downlink data to the mobile station,

wherein the precoding matrix is initialized with a matrix corresponding to the first CSI in a first codebook, and

wherein the precoding matrix is updated by performing a matrix product or a Kronecker product on the precoding matrix and a matrix raised to the power of the side information, the matrix corresponding to the second CSI in a second codebook.

5. The method of claim 4 , wherein each of the first and second CSI is a Precoding Matrix Indicator (PMI).

6. The method of claim 4 , wherein the side information has a quantized scalar value.

7. The method of claim 4 , wherein each of the first and second CSI comprises at least one of a Channel Quality Indicator (CQI) and a Rank Indicator.

8. A method for differential precoding, the method comprising:

determining a first Precoding Matrix Indicator (PMI) indicating a first matrix selected from a first codebook, and feeding back the first PMI to a base station;

determining a second PMI, indicating a second matrix selected from a second codebook, and side information that is used to extract the power of the second matrix, the side information having a quantized scalar value; and

feeding back the second PMI and the side information to the base station periodically or aperiodically.

9. The method of claim 8 , further comprising receiving downlink data precoded with a precoding matrix initialized with the first matrix, or downlink data precoded with a precoding matrix updated with the precoding matrix and the second matrix raised to the power of the side information.

10. The method of claim 9 , wherein the updated precoding matrix is calculated by performing a matrix product or a Kronecker product on the precoding matrix and the second matrix raised to the power of the side information.

11. A base station, comprising:

a feedback receiver receiving first Channel State Information (CSI), second CSI, and side information from a mobile station, the side information being used for adaptively updating a precoding matrix according to a change in a state of a channel;

a precoder initializing the precoding matrix with the first CSI, repeatedly updating the precoding matrix with the second CSI and the side information, and precoding downlink data with the precoding matrix; and

a data transmitter transmitting the downlink data to the mobile station,

wherein the precoder comprises:

a precoding matrix initialization unit initializing the precoding matrix with Equation “G(0)=F main,q ”; and

a precoding matrix update unit repeatedly updating the precoding matrix with Equation “G(n)=G(n−1)*(F sub,p ) a ”,

where G(0) denotes a precoding matrix at a zeroth time, F main,q denotes a factor corresponding to the first PMI “q” in a main codebook, G(n) is a precoding matrix at an nth time, G(n−1) is a precoding matrix at an n−1st time, F sub,q denotes a factor corresponding to the second PMI “p” in a sub-codebook, * denotes an inter-matrix operator indicating one of a matrix addition, a matrix product, and a Kronecker product, and a denotes a value corresponding to the side information.

12. The base station of claim 11 , wherein each of the first and second CSI is a PMI.

13. The base station of claim 11 , wherein the side information has a quantized scalar value.