Method and apparatus for quantizing channel state information

A method of operating a user equipment, said method comprising:

• receiving antenna configuration of a base station, wherein the antenna configuration comprises an antenna port in a vertical direction and an antenna port in a horizontal direction;
• selecting a vertical codebook that is applied to the antenna port in the vertical direction and a horizontal codebook that is applied to the antenna port in the horizontal direction;
• constructing a combined codebook for the antenna configuration by using the selected vertical codebook and horizontal codebook;
• receiving a reference signal (RS), and estimating channel state information (CSI) based on the received RS;
• selecting a precoder from the combined codebook based on the estimated CSI;
• and
• based on the selected precoder, feeding back a vertical precoder corresponding to the antenna port in the vertical direction and a horizontal precoder corresponding to the antenna port in the horizontal direction.

A base station, comprising:

• a broadcaster, which broadcasts antenna configuration of the base station to a user equipment, wherein the antenna configuration comprises an antenna port in a vertical direction and an antenna port in a horizontal direction;
• a transmitter, which sends a reference signal (RS) to the user equipment;
• a receiver, which receives a vertical precoder corresponding to the antenna port in a vertical direction and a horizontal precoder corresponding to the antenna port in a horizontal direction that are fed back by the user equipment, wherein said vertical precoder and said horizontal precoder that are fed back by the user equipment are based upon a precoder selected from a combined codebook which combined codebook is constructed from a vertical codebook corresponding to the antenna port in the vertical direction and a horizontal codebook corresponding to the antenna port in the horizontal direction, said precoder being selected from the combined codebook based upon a channel state information (CSI) estimated from the RS;
• and
• a reconstructor, which reconstructs, based on the received vertical precoder and horizontal precoder, a precoder by using the vertical codebook corresponding to the antenna port in the vertical direction and the horizontal codebook corresponding to the antenna port in the horizontal direction.

A user equipment, comprising:

• a receiver, which receives antenna configuration of a base station, wherein the antenna configuration comprises an antenna port in a vertical direction and an antenna port in a horizontal direction;
• a codebook selector, which selects a vertical codebook that is applied to the antenna port in the vertical direction and a horizontal codebook that is applied to the antenna port in the horizontal direction;
• a constructor, which constructs a combined codebook for the antenna configuration by using the selected vertical codebook and horizontal codebook;
• an estimator, which receives a reference signal (RS), and estimates channel state information (CSI) based on the received RS;
• a precoder selector, which selects a precoder from the combined codebook based on the estimated CSI;
• and
• a feedback device, which feeds back, based on the selected precoder, a vertical precoder corresponding to the antenna port in the vertical direction and a horizontal precoder corresponding to the antenna port in the horizontal direction.