Wireless base station, wireless communication method, and wireless communication system

1. A wireless base station comprising:

a transmitter that employs a plurality of antenna elements to form a beam in each of a plurality of transmission directions and transmit a reference signal;

a receiver that receives a value representing reception quality of the reference signal for a user device that has received the reference signal;

a memory; and

a processor connected to the memory, the processor being configured to employ an indicator value, representing reception quality for a user device group computed from values received by the receiver that represent reception quality for each of a plurality of user devices, in order to select a combination of beams to employ in user data transmission from a plurality of beams transmitted by the transmitter.

2. The wireless base station of claim 1 , wherein in a case of transmitting the user data, the transmitter:

transmits the user data to a plurality of the user devices that receive a same selected beam by multiplexing using a multiplexing technique other than space-division multiplexing; and

transmits the user data to a plurality of the user devices that receive different beams but use a same multiplexing resource by performing space-division multiplexing using digital precoding.

3. The wireless base station of claim 2 , wherein in a case of transmitting the user data, and in a case in which a number of the user devices receiving a single one of the beams is greater than a number of allocable multiplexing resources for the single beam, the transmitter transmits the user data by allocating the multiplexing resources and multiplexing in sequence from a user device having a highest reference signal reception quality.

4. The wireless base station of claim 1 , wherein the transmitter transmits the reference signal to a plurality of the user devices for which a connection has been established with the wireless base station.

5. The wireless base station of claim 1 , wherein the value representing reception quality is a value quantizing the reference signal reception quality, or is a value quantizing a received power value of the reference signal.

6. The wireless base station of claim 1 , wherein:

the value representing reception quality becomes larger as reception quality increases; and

the indicator value is a number of the user devices included in the user device group for which the value representing reception quality is at least a specific value, is a sum of the values representing reception quality for such user devices, or is a product of the values representing reception quality for such user devices.

7. The wireless base station of claim 1 , wherein:

the value representing reception quality becomes larger as reception quality increases;

the indicator value is a number of the user devices included in the user device group for which the value representing reception quality is at least a specific value; and

in a case of selecting a combination of the beams to give a greatest number of the user devices included in the user device group for which the value representing reception quality is at least the specific value, the processor lowers the specific value until the number of such user devices is greater than or equal to a value obtained by multiplying a number of selected beams by a number of multiplexing resources for each beam, and then the processor selects the combination of the beams.

8. A wireless communication method employed by a wireless base station provided with a plurality of antenna elements, the wireless communication method comprising:

forming a beam in each of a plurality of transmission directions and transmitting a reference signal by employing the plurality of antenna elements;

receiving a value representing reception quality of the reference signal for a user device that has received the reference signal; and

by a processor, by employing an indicator value representing reception quality for a user device group computed from received values that represent reception quality for each of a plurality of user devices, selecting a combination of beams to employ in user data transmission from a plurality of transmitted beams.

9. The wireless communication method of claim 8 , wherein in a case of transmitting the user data:

the user data is transmitted to a plurality of the user devices that receive a same selected beam by multiplexing using a multiplexing technique other than space-division multiplexing; and

the user data is transmitted to a plurality of the user devices that receive different beams but use a same multiplexing resource by performing space-division multiplexing using digital precoding.

10. The wireless communication method of claim 9 , wherein in a case of transmitting the user data, and in a case in which a number of the user devices receiving a single one of the beams is greater than a number of allocable multiplexing resources for the single beam, the user data is transmitted by allocating the multiplexing resources and multiplexing in sequence from a user device having a highest reference signal reception quality.

11. The wireless communication method of claim 8 , wherein the reference signal is transmitted to a plurality of the user devices for which a connection has been established with the wireless base station.

12. The wireless communication method of claim 8 , wherein the value representing reception quality is a value quantizing the reference signal reception quality, or is a value quantizing a received power value of the reference signal.

13. The wireless communication method of claim 8 , wherein:

the value representing reception quality becomes larger as reception quality increases; and

the indicator value is a number of the user devices included in the user device group for which the value representing reception quality is at least a specific value, is a sum of the values representing reception quality for such user devices, or is a product of the values representing reception quality for such user devices.

14. The wireless communication method of claim 8 , wherein:

the value representing reception quality becomes larger as reception quality increases;

the indicator value is a number of the user devices included in the user device group for which the value representing reception quality is at least a specific value; and

in a case of selecting a combination of the beams to give a greatest number of the user devices included in the user device group for which the value representing reception quality is at least the specific value, the specific value is lowered by the processor until the number of such user devices is greater than or equal to a value obtained by multiplying a number of selected beams by a number of multiplexing resources for each beam, and then the combination of the beams is selected by the processor.

15. A wireless communication system comprising:

a wireless base station including:

a transmitter that employs a plurality of antenna elements to form a beam in each of a plurality of transmission directions and transmit a reference signal,

a receiver that receives a value representing reception quality of the reference signal for a user device that has received the reference signal,

a memory, and

a processor connected to the memory, the processor being configured to employ an indicator value, representing reception quality for a user device group computed from values received by the receiver that represent reception quality for each of a plurality of user devices, in order to select a combination of beams to employ in user data transmission from a plurality of beams transmitted by the transmitter; and

the plurality of user devices, each user device including:

a receiver that receives the reference signal, and

a transmitter that transmits the value representing the reference signal reception quality to the wireless base station.