Base station device and beam selecting method

1. A base station device comprising: a central unit; and a distributed unit, wherein

the distributed unit includes a first processor configured to:

form beams in plural directions by using plural antenna elements; and transmit and receive a data signal addressed to a terminal device, and

the central unit includes a second processor configured to:

select a first beam and a second beam set, by using: relevant information on the beams, the relevant information being notified by the distributed unit that forms the beams; and reception quality of the beams in the terminal device;

cause the distributed unit to transmit a reference signal by application of a beam group formed of: one or more beams in the second beam set; and the first beam; and

select a beam group to be applied to the data signal addressed to the terminal device, by using a reception state of the reference signal from the terminal device in a predetermined interval.

2. The base station device according to claim 1 , wherein the second processor is further configured to select, as the first beam, a beam with a maximum reception quality, refer to relevant information on the first beam, and select, as the second beam set, a beam set excluding a beam that interferes with the first beam.

3. The base station device according to claim 1 , wherein the second processor is further configured to select the beam group to be applied to the data signal addressed to the terminal device, by using the reception state of the reference signal in the predetermined interval, the beam group being a beam group corresponding to a reception state with a maximum reception quality included in reception states with a maximum suitability rank included in reception states.

4. The base station device according to claim 1 , wherein the second processor is further configured to refer to the reception state of the reference signal transmitted by application of the beam group, and select the beam group to be applied to the data signal addressed to the terminal device, the beam group being a beam group having a suitability rank included in the reception state, the suitability rank being equal to or larger than a predetermined value.

5. The base station device according to claim 1 , wherein the second processor is further configured to sequentially select one or more beams in the second beam set, and cause the distributed unit to transmit the reference signal while changing the beam group formed of: the beam/beams sequentially selected; and the first beam.

6. A beam selecting method comprising:

forming, by using a distributed unit of a base station device, beams in plural directions by using plural antenna elements and transmitting and receiving a data signal addressed to a terminal device;

selecting, by using a central unit of the base station device, a first beam and a second beam set, by using: relevant information on the beams, the relevant information being notified by the distributed unit that forms the beams; and reception quality of the beams in the terminal device;

causing, by using the central unit, the distributed unit to transmit a reference signal by application of a beam group formed of: one or more beams in the second beam set; and the first beam; and

selecting, by using the central unit, a beam group to be applied to the data signal addressed to the terminal device, by using a reception state of the reference signal from the terminal device in a predetermined interval.