Radio base station

A radio base station configured to perform a MIMO multiplexing transmission in which multiple different streams are simultaneously transmitted in a downlink data channel to a mobile station by using multiple antennas, the radio base station comprising:

• a rank indicator acquisition unit configured to acquire, from the mobile station, a rank indicator indicating number of streams determined by the mobile station;
• a rank indicator adjustment unit configured to adjust the rank indicator acquired by the rank indicator acquisition unit, by using an offset value unique to the mobile station,
• wherein the rank indicator adjustment unit is configured to adjust the rank indicator, according to a reception error rate in the downlink data channel calculated based on an ACKINACK signal for the downlink data channel notified by using an uplink channel;
• a stream-number determination unit configured to determine the number of streams to be simultaneously transmitted to the mobile station, based on the rank indicator adjusted by the rank indicator adjustment unit;
• a channel quality information acquisition unit configured to acquire, from the mobile station, channel quality information in the downlink data channel through which the streams are transmitted;
• a channel quality information adjustment unit configured to adjust the channel quality information according to the reception error rate;
• and
• a determination unit configured to determine a modulation scheme used and the number of bits that can be transmitted by a predetermined radio resource used in the downlink data channel, based on the channel quality information adjusted by the channel quality information adjustment unit.