Patent ID: 8787469

Claim:
A base station, comprising: a grouping unit configured to group a plurality of data signals into a plurality of data signal groups, each of the data signal groups comprising selected ones of the plurality of data signals; a multiplexer configured to select one of the data signal groups to be transmitted by performing beamforming; a control unit configured to control the grouping unit and the multiplexer to perform beamforming using a codebook to generate a signal, the codebook comprising a plurality of matrices; a multi-antenna configured to transmit the data signal; and a codebook generator configured to generate the codebook, wherein: the codebook is generated by following requirements of: (1) for all of the plurality of matrices, all column vectors of the same matrix of the plurality of matrices are orthogonal to each other, (2) for all columns of the plurality of matrices, each column vector of all of the plurality of matrices of the same column is spaced apart from each other by a distance greater than a predetermined amount, and (3) each of a plurality of mobile terminals, which corresponds to a group served by the base station, corresponds to a different column vector of the same matrix, and the codebook generator is further configured to: designate a plurality of column vectors as first column vectors of the plurality of matrices, the plurality of column vectors being configured to satisfy a Grassmannian line packing (GLP) criterion; and generate a second column vector of each of the matrices by multiplying the first column vector of each of the matrices by a rotation matrix according to the following equation: w k , 2 = [ 0 1 - 1 0 ] ⁢ w k , 1 * , where w k,1 is the first column vector of a k-th matrix of the plurality of matrices that satisfies the GLP criterion with respect to the first column vectors of all other matrices of the plurality of matrices, and w k,2 is the second column vector of the k-th matrix generated by multiplying w k,1 by the rotation matrix.