Method for reporting channel state information in wireless communication system and apparatus therefor

A user equipment (UE) reporting channel state information (CSI) in a wireless communication system, the UE comprising:

• a radio frequency (RF) unit for transmitting/receiving a radio signal;
• and
• a processor controlling the RF unit,
• wherein the processor is configured to:
• measure a CSI-reference signal (RS) transmitted from a base station;
• and
• report, to the base station, CSI generated based on the CSI-RS measurement,
• wherein the CSI comprises a precoding matrix index (PMI) for indicating a precoding matrix and a rank indicator (RI) for indicating a rank from a codebook,
• wherein the PMI comprises a first PMI for a beam group selected by the UE and a second PMI including beam subgroup selection information for beams included in the beam group and co-phase information for each antenna port polarization for the selected beam subgroup, and
• wherein the co-phase information is indicated with different granularities for a case where beam subgroups selected within the beam group are same and a case where beam subgroups selected within the beam group are different as the rank increases.