A method of reporting Channel State Information, CSI, performed by a user equipment, UE, in a wireless communication system, the method comprising: receiving, from a base station, BS,, a Channel State Information Reference Signal, CSI-RS, through multiple antenna ports; and reporting, to the BS, the CSI using a Physical Uplink Control Channel, PUCCH, format 2, wherein the CSI includes i) a Rank Indicator, RI, ii) a Precoding Matrix Indicator, PMI, and iii) a Channel Quality Indicator, CQI, wherein the PMI includes first PMI information and second PMI information, and wherein the RI, the first PMI information and the CQI + the second PMI information are transmitted in three different CSI reporting instances, wherein the first PMI information includes i) a leading beam index, ii) information for selecting a second beam for a linear combination and iii) information for a power combining coefficient of the second beam, wherein the second PMI information includes combining coefficients applied to a leading beam and the second beam, wherein a payload size of the leading beam index is determined by log 2 N 1 N 2 O 1 O 2, wherein each of the N1 and N2 is a number of antenna ports for each polarization in each of a first dimension and a second dimension, and a number of the multiple antenna ports is 2*N1*N2, wherein each of the O 1 and the O 2, is an oversampling factor in each of the first dimension and the second dimension, wherein the power coefficient of the second beam is one of 1, 0.5, 0.25 and 0, the method being characterized in that wherein, for the number of the multiple antenna ports being 12 or 16: (the O 1, the O 2) include i) (4, 2) for the N1 greater than the N2, ii) (2,4) for the N2 greater than the N1 and iii) (2,2) for the N1 equal to N2, a payload size of the information for the power coefficient of the second beam is 1 bit and the power coefficient of the second beam is i) one of 1 and 0.5, or ii) one of 1 and 0, wherein, for the number of the multiple antenna ports being 20, 24, 28 or 32: (the O 1, the O 2) include i) (4, 2) for the N1 equal to or greater than the N2, ii) (2,4) for the N2 greater than the N1, amended claims the payload size of the information for the power coefficient of the second beam is 0 bit and the power coefficient of the second beam is configured as 1. receiving, from a base station, BS,, a Channel State Information Reference Signal, CSI-RS, through multiple antenna ports; and reporting, to the BS, the CSI using a Physical Uplink Control Channel, PUCCH, format 2, wherein the CSI includes i) a Rank Indicator, RI, ii) a Precoding Matrix Indicator, PMI, and iii) a Channel Quality Indicator, CQI, wherein the PMI includes first PMI information and second PMI information, and wherein the RI, the first PMI information and the CQI + the second PMI information are transmitted in three different CSI reporting instances, wherein the first PMI information includes i) a leading beam index, ii) information for selecting a second beam for a linear combination and iii) information for a power combining coefficient of the second beam, wherein the second PMI information includes combining coefficients applied to a leading beam and the second beam, wherein a payload size of the leading beam index is determined by log 2 N 1 N 2 O 1 O 2, wherein each of the N1 and N2 is a number of antenna ports for each polarization in each of a first dimension and a second dimension, and a number of the multiple antenna ports is 2*N1*N2, wherein each of the O 1 and the O 2, is an oversampling factor in each of the first dimension and the second dimension, wherein the power coefficient of the second beam is one of 1, 0.5, 0.25 and 0, the method being characterized in that wherein, for the number of the multiple antenna ports being 12 or 16: (the O 1, the O 2) include i) (4, 2) for the N1 greater than the N2, ii) (2,4) for the N2 greater than the N1 and iii) (2,2) for the N1 equal to N2, a payload size of the information for the power coefficient of the second beam is 1 bit and the power coefficient of the second beam is i) one of 1 and 0.5, or ii) one of 1 and 0, (the O 1, the O 2) include i) (4, 2) for the N1 greater than the N2, ii) (2,4) for the N2 greater than the N1 and iii) (2,2) for the N1 equal to N2, a payload size of the information for the power coefficient of the second beam is 1 bit and the power coefficient of the second beam is i) one of 1 and 0.5, or ii) one of 1 and 0, wherein, for the number of the multiple antenna ports being 20, 24, 28 or 32: (the O 1, the O 2) include i) (4, 2) for the N1 equal to or greater than the N2, ii) (2,4) for the N2 greater than the N1, amended claims the payload size of the information for the power coefficient of the second beam is 0 bit and the power coefficient of the second beam is configured as 1. (the O 1, the O 2) include i) (4, 2) for the N1 equal to or greater than the N2, ii) (2,4) for the N2 greater than the N1, amended claims the payload size of the information for the power coefficient of the second beam is 0 bit and the power coefficient of the second beam is configured as 1.