Patent ID: 8526538

Claim:
A method of transmitting a signal, which is transmitted to a base station by a user equipment configured to use 4 antennas, the method comprising: obtaining transmission rank information; outputting a precoded signal by precoding a number of layer signals, the number corresponding to a transmission rank included in the transmission rank information, using a specific precoding matrix corresponding to the transmission rank, wherein the specific precoding matrix is selected from a 4-antenna codebook; and transmitting the precoded signal to the base station, wherein the 4 antennas are grouped into a first antenna group including two of the 4 antennas and a second antenna group including the other two of the 4 antennas, and wherein the 4-antenna codebook includes a first type precoding matrix, in which two components corresponding to one of the first and second antenna groups are zero and two components corresponding to the other one of the first and second antenna groups construct a discrete Fourier transform (DFT) matrix, and a second type precoding matrix, in which two components corresponding to the first antenna group and two components corresponding to the second antenna group construct DFT matrixes for a rank of 1.