Method and apparatus for transmitting channel state information in wireless communication system
The present invention relates to a wireless communication system. A method for a terminal for transmitting channel state information (CSI) in a wireless communication system according to an embodiment of the present invention comprises the steps of: in a reporting mode for a four-antenna port, joint-encoding a rank indicator (RI) and a first precoding matrix indicator (PMI) into a single encoding value; and transmitting channel state information comprising the encoding value, wherein if RI is 1, then a codebook index may have the same value as the encoding value, and if RI is 2, then the codebook index may be less than the encoding value by 8.
1. A method for reporting channel state information (CSI) by a user equipment (UE) in a wireless communication system, the method comprising:
jointly-encoding a rank indicator (RI) and a first precoding matrix indicator (PMI) into an encoded value to provide a specific CSI report mode with 4 antenna ports,
wherein a reporting field indicating the encoded value is represented in 5 bits, and the encoded value is an integer ranging from 0 to 17 reporting the encoded value via the reporting field, and
wherein the RI and the first PMI are jointly encoded into the encoded value in a way that following conditions are satisfied:
when the encoded value is an integer ranging from 0 to 7, the RI is 1 and a codebook index for the first PMI is the same as the encoded value,
when the encoded value is an integer ranging from 8 to 15, the RI is 2 and the codebook index for the first PMI is the encoded value minus 8,
when the encoded value is 16, the RI is 3 and a first precoding matrix corresponding to the first PMI is an identity matrix, and
when the encoded value is 17, the RI is 4 and the first precoding matrix corresponding to the first PMI is the identity matrix.
2. The method according to claim 1 , wherein when the encoded value is an integer ranging from 0 to 15, the codebook index for the first PMI is only among 8 codebook indices out of 16 codebook indices associated with the first PMI.
3. The method according to claim 2 , wherein the 8 codebook indices correspond to an integer ranging from 0 to 7.
4. The method according to claim 1 , further comprising:
reporting a second PMI and a wideband channel quality indicator (CQI) in another subframe different from a subframe for reporting the encoded value into which the RI and the first PMI are jointly-encoded.
5. The method according to claim 4 , wherein a final precoding matrix is to be determined based on the first PMI and the second PMI.
6. A user equipment (UE) for reporting channel state information (CSI) in a wireless communication system, the UE comprising:
a radio frequency (RF) unit; and
a processor operably coupled with the RF unit and configured to:
jointly encode a rank indicator (RI) and a first precoding matrix indicator (PMI) into an encoded value to provide a specific CSI report mode with 4 antenna ports, wherein a reporting field indicating the encoded value is represented in 5 bits, and the encoded value is an integer ranging from 0 to 17 reporting the encoded value via the reporting field,
wherein the RI and the first PMI are jointly encoded into the encoded value in a way that following conditions are satisfied:
when the encoded value is an integer ranging from 0 to 7, the RI is 1 and a codebook index for the first PMI is the same as the encoded value,
when the encoded value is integer ranging from 8 to 15, the RI is 2 and the codebook index is the encoded value minus 8,
when the encoded value is 16, the RI is 3 and a first precoding matrix corresponding to the first PMI is an identity matrix, and
when the encoded value is 17, the RI is 4 and the first precoding matrix corresponding to the first PMI is the identity matrix.
7. The UE according to claim 6 , wherein when the encoded value is an integer ranging from 0 to 15, the codebook index for the first PMI is only among 8 codebook indices out of 16 codebook indices associated with the first PMI.
8. The UE according to claim 7 , wherein the 8 codebook indices correspond to integer ranging from 0 to 7.
9. The UE according to claim 6 , wherein the processor is further configured to report a second PMI and a wideband channel quality indicator (COI) in another subframe different from a subframe for reporting the encoded value into which the RI and the first PMI are jointly-encoded.
10. The UE according to claim 9 , wherein a final precoding matrix is to be determined based on the first PMI and the second PMI.