Method for transmitting and receiving channel state information (CSI) in wireless communication system, and apparatus therefor

1. A method for transmitting Channel State Information (CSI) by a user equipment (UE) in a wireless communication system that supports Multiuser Superposition Transmission (MUST), the method comprising:

reporting, to a base station, UE capability information related to a MUST operation;

reporting, to the base station, a first precoding matrix indicator (PMI) indicating a precoding matrix that is the most preferred by the UE, and a first channel quality indicator (CQI) that is calculated assuming use of the first PMI; and

reporting, to the base station, a second PMI indicating a precoding matrix that is secondly preferred by the UE, and a second CQI that is calculated assuming use of the second PMI.

2. The method of claim 1 , wherein:

the first PMI and the first CQI are calculated assuming a rank indicator (RI) that is reported by the UE to the base station, and

the second PMI and the second CQI are calculated assuming the RI or a predefined RI.

3. The method of claim 2 , wherein both the first PMI and the second PMI are selected from a codebook for beam selection and co-phasing.

4. The method of claim 1 , wherein a periodicity and/or a granularity of the first PMI and the first CQI is identical to a periodicity and/or a granularity of the second PMI and the second CQI.

5. The method of claim 1 , wherein the second CQI is reported as a differential CQI value relative to the first CQI.

6. The method of claim 1 , wherein the second PMI indicates a precoding matrix that is selected from a subset of a codebook from which the first PMI is selected.

7. The method of claim 6 , wherein the subset is composed of a precoding matrix that generates a beam of which correlation with a beam formed by the first PMI is equal to or greater than a preset threshold.

8. The method of claim 6 , wherein the subset is composed of a precoding matrix which generates a beam orthogonal to a beam formed by the first PMI.

9. The method of claim 6 , wherein the subset is composed of a precoding matrix which generates a beam having co-phasing identical to co-phasing of a beam formed by the first PMI.

10. The method of claim 6 , wherein the subset is composed of a precoding matrix which generates a beam not orthogonal to the beam formed by the first PMI.

11. The method of claim 6 , wherein the subset is composed of or a precoding matrix which generates a beam having other co-phasing except for co-phasing being orthogonal to the beam formed by the first PMI.

12. The method of claim 1 , wherein a granularity of the second PMI and the second CQI is determined to be different from a granularity of the first PMI and the first CQI, or restricted only to a wideband.

13. The method of claim 1 , wherein the first CQI and the second CQI are calculated using a power allocation factor that is used for the MUST transmission to the UE.

14. The method of claim 1 , further comprising: reporting, to the base station, an absolute value of a variance of channel estimation error to correct the first CQI and the second CQI.

15. The method of claim 1 , wherein the UE capability information may include at least one of the following: a UE-supportable MUST transmission technique; a number of Successive Interference Cancellation (SIC)-capable spatial layers; a receiver type, whether SIC is supported depending on a layer received by a UE; a number of superposed UEs per supportable layer; a total number of cancellation-capable superposed UEs; a total number of cancellation-capable spatial layers; whether MUST CSI reporting is supported; and a unit or number of blind detection (BD)-capable MUST power offsets.

16. A user equipment (UE) that transmits channel state information (CSI) in a wireless communication system supporting multiuser superposition transmission (MUST), the UE comprising:

a transmitter and a receiver; and

a processor operatively coupled to the transmitter and the receiver,

wherein the processor is configured to:

report, to a base station, UE capability information related to a MUST operation,

report, to the base station, a first precoding matrix indicator (PMI) indicating a precoding matrix that is the most preferred by the UE, and a first channel quality indicator (CQI) that is calculated assuming use of the first PMI; and

report, to the base station, a second PMI indicating a precoding matrix that is secondly preferred by the UE, and a second CQI that is calculated assuming use of the second PMI.