| CPC H04B 7/0626 (2013.01) [H04B 7/0486 (2013.01); H04B 7/0634 (2013.01); H04B 7/0639 (2013.01)] | 12 Claims |

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1. A method performed by a user equipment (UE), the method comprising:
receiving, from a base station (BS), configuration information including information for a codebook;
receiving, from the BS, a channel state information reference signal (CSI-RS);
measuring channel state information (CSI) based on the CSI-RS; and
transmitting, to the BS, the CSI including a rank indicator (RI) and a precoding matrix indicator (PMI),
wherein the CSI is measured based on the codebook including a linear combination based on multiple matrices,
wherein a type of the codebook is configured as a port selection codebook based on the information for the codebook,
wherein at least one index of indices of the codebook related to the PMI is an index representing antenna ports selected for each polarization of antenna ports,
wherein the antenna ports are selected at regular intervals based on a specific step size, and
wherein the codebook is used based on a value of the RI being 3 or more.
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