Apparatus and method for transmitting/receiving data in a multi-antenna system, and system using the same

A closed-loop multi-antenna system that defines multiple antenna groups by antenna grouping on multiple antennas, and performs data transmission individually via each of the multiple antenna groups, the closed-loop multi-antenna system comprising:

• a transmitter comprising a feedback information processor and a first transmit unit;
• and
• a receiver including a channel estimator, a feedback information generator and a second transmit unit,
• wherein the feedback information processor is configured to receive feedback information from the receiver, calculate each of a sum rate (R_MU) in a multi-user mode and a sum rate (R_SU) in a single-user mode using the feedback information, and select one of the single-user mode and the multi-user mode as a transmission mode depending on a comparison result between the sum rate (R_MU) in the multi-user mode and the sum rate (R_SU) in the single-user mode,
• the first transmit unit is configured to transmit a data stream according to the selected transmission mode,
• the channel estimator is configured to acquire channel quality information (CQI) for each data stream transmitted individually via each antenna group,
• the feedback information generator is configured to determine the CQI associated information from the CQI acquired individually for each antenna group corresponding to the transmission mode;
• and
• the second transmit unit is configured to transmit the feedback information to the transmitter,
• wherein the CQI associated information includes maximum CQI, an antenna group index associated with the maximum CQI, rank information, and remaining CQI associated the rank information.