Mobile communication system, base station, and user terminal

A mobile communication system to perform communication between a base station and a user terminal, wherein

• the base station transmits a first radio signal including a reference signal at a predetermined timing according to a formed directivity,
• the user terminal transmits a second radio signal including communication quality information when receiving the reference signal after a lapse of a predetermined period from the reception of the first radio signal,
• the base station receives the second radio signal and determines a directivity to be formed based on the timing at which the user terminal transmits the second radio signal and the quality information, and
• the base station detects mobility of the user terminal based on the second radio signal received from the user terminal or information included in the second radio signal, and determines a directivity wider than the directivity to be formed when the mobility indicates a predetermined movement amount per unit time or a movement amount greater than the predetermined movement amount.

A base station to perform communication with a user terminal, the base station comprising:

• a transceiver configured to transmit and receive a radio signal;
• a formation unit configured to form a directivity of the radio signal to be transmitted by the transceiver;
• and
• a controller configured to determine the directivity to be formed by the formation unit, wherein
• the transceiver transmits a first radio signal including identification information to identify a directivity and a reference signal with the directivity formed by the formation unit, and receives a second radio signal transmitted by the user terminal,
• the controller determines the directivity to be formed by the formation unit based on the identification information and quality information based on the reference signal transmitted by the base station which are included in the second radio signal transmitted by the user terminal, and
• the controller detects mobility of the user terminal based on the second radio signal transmitted by the user terminal or information included in the second radio signal, and determines a directivity wider than the directivity to be formed when the mobility indicates a predetermined movement amount per unit time or a movement amount greater than the predetermined movement amount.