Patent ID: 8792586

Claim:
A method for transmitting a downlink signal using 2·N (N is a natural number) transmit (Tx) antennas by a base station (BS), the method comprising: receiving a first precoding matrix index (PMI) and a second precoding matrix index (PMI) from a user equipment (UE); determining a precoding matrix on the basis of a combination of the first PMI and the second PMI in a prestored codebook; performing precoding by applying the determined precoding matrix to the downlink signal mapped to R layers (where 1≦R≦8); and transmitting the precoded signal to the user equipment (UE) through 2·N Tx antennas, wherein the prestored codebook includes precoding matrices configured in the form of [ ⁢ W 1 W 1 a ⁢ ⁢ W 1 - a ⁢ ⁢ W 1 ] when R is an even number, where W 1 is an N×(R/2) matrix and a is a coefficient of a phase.