Base station, communication control method, and processor

1. A base station for managing a cell in a mobile communication system that supports downlink multi-antenna transmission, comprising:

a receiver configured to receive beamforming control information fed back from each of a plurality of beamforming target terminals connected to the cell, and null steering control information fed back from a null steering target terminal; and

a controller configured to select, as a pair terminal to be paired with the null steering target terminal, a beamforming target terminal that feeds back the beamforming control information that coincides with the null steering control information, wherein

the beamforming control information contains a rank indicator that indicates preferred number of signal sequences to be applied to the downlink multi-antenna transmission, and

when there exists no beamforming target terminal that feeds back the beamforming control information that coincides with the null steering control information, the controller selects, as the pair terminal, a beamforming target terminal that feeds back the beamforming control information containing a predefined rank indicator.

2. The base station according to claim 1 , wherein the predefined rank indicator is a rank indicator that indicates a largest number of the signal sequences, from among a plurality of rank indicators available in the mobile communication system.

3. The base station according to claim 1 , wherein the predefined rank indicator is a rank indicator having a smallest interfering level deviation, from among a plurality of rank indicators available in the mobile communication system, in a case where the rank indicator is combined with each of a plurality of precoder matrix indicators available in the mobile communication system.

4. A communication control method used in a mobile communication system that supports downlink multi-antenna transmission, comprising the steps of:

receiving, by a base station configured to manage a cell, beamforming control information fed back from each of a plurality of beamforming target terminals connected to the cell, and null steering control information fed back from a null steering target terminal; and

selecting, by the base station, as a pair terminal to be paired with the null steering target terminal, a beamforming target terminal that feeds back the beamforming control information that coincides with the null steering control information, wherein

the beamforming control information contains a rank indicator that indicates preferred number of signal sequences to be applied to the downlink multi-antenna transmission, and

when there exists no beamforming target terminal feeding back the beamforming control information that coincides with the null steering control information, the base station selects in the selecting step, as the pair terminal, a beamforming target terminal that feeds back the beamforming control information containing a predefined rank indicator.

5. A processor provided in a base station for managing a cell in a mobile communication system that supports downlink multi-antenna transmission, the processor performing the processes of:

receiving beamforming control information fed back from each of a plurality of beamforming target terminals connected to the cell, and null steering control information fed back from a null steering target terminal; and

selecting, as a pair terminal to be paired with the null steering target terminal, a beamforming target terminal that feeds back the beamforming control information that coincides with the null steering control information, wherein

the beamforming control information contains a rank indicator that indicates preferred number of signal sequences to be applied to the downlink multi-antenna transmission, and

when there exists no beamforming target terminal feeding back the beamforming control information that coincides with the null steering control information, the processor selects in the selecting process, as the pair terminal, a beamforming target terminal that feeds back the beamforming control information containing a predefined rank indicator.