MIMO system and method of generating hierarchical codebook therefor

A multiple-input multiple-output (MIMO) system including a transmitting end and a receiving end, wherein a channel between the transmitting end and the receiving end is a temporally correlated channel, wherein the receiving end includes:

• a hierarchical codebook in which at least one base codebook comprising a plurality of reference codewords is designated as an upper matrix and a child codebook comprising a first child codebook and a second child codebook is designated as a lower matrix;
• a channel estimator configured to estimate a channel from signals received from the transmitting end through a plurality of antennas;
• a precoding selector configured to select precoding matrices based on channel information estimated in the channel estimator and feedbacking indexes corresponding thereto as channel state information to the transmitting end;
• and
• a demodulator configured to detect and demodulate data received through the plurality of antennas by using the channel information estimated in the channel estimator and the precoding matrices selected in the precoding selector,
• wherein, a predetermined number of reference codewords are selected based on a chordal distance between the selected any one reference codeword and other reference codewords, and the predetermined number of reference codewords are set as candidate codewords, and the candidate codewords are configured to be selected with respect to each of the reference codewords, and
• wherein the first child codebook is configured to belong to region of the selected any one reference codeword, and the second child codebook is configured to belong to each region of the candidate codewords, and
• wherein the first child codebook is configured to comprise at least one codeword selected based on centroid conditions between the selected any one reference codeword and each of primary centroid vectors, wherein each of the primary centroid vectors is calculated based on the centroid conditions between the selected any one reference codeword and each of the candidate codewords;
• and
• the second child codebook is configured to comprise at least one codeword selected based on the centroid conditions between each of candidate codewords and each of the primary centroid vectors.

A method for generating a hierarchical codebook for a multiple-input multiple-output (MIMO) system including a transmitting end and a receiving end, wherein a channel between the transmitting end and the receiving end is a temporally correlated channel, the method comprising:

• setting at least one base codebook comprising a plurality of reference codewords as an upper matrix;
• calculating a chordal distance between selected any one reference codeword and other reference codewords, with respect to each reference codeword;
• selecting candidate codewords by selecting a designated number of reference codewords from the plurality of reference codewords based on the chordal distance;
• and
• setting a child codebook including a first child codebook belonging to region of the selected any one reference codeword, and a second child codebook belonging to each region of the candidate codewords and setting the child codebook as a lower matrix,
• wherein the selecting of candidate codewords includes:
• selecting the designated number of candidate codewords having a close chordal distance;
• and
• the setting of the child codebook includes:
• calculating each of primary centroid vectors between the selected any one reference codeword and each of the candidate codewords;
• calculating each of secondary centroid vectors between the selected any one reference codeword and each of the primary centroid vectors;
• calculating each of third order centroid vectors between the candidate codewords and each of the primary centroid vectors;
• setting each of the secondary centroid vectors as the codewords of the first child codebook and each of the third order centroid vectors as the codeword of the second child codebook.