Base station

A base station used in a mobile communication system comprising a user terminal capable of performing communication in a licensed band and an unlicensed band, comprising:

• a controller configured to measure interference power in a predetermined frequency out of a plurality of frequencies available for data transmission and reception in the mobile communication system in the unlicensed band;
• and
• a transmitter configured to transmit, based on a measurement result of the interference power, a reference signal, wherein
• the unlicensed band includes the plurality of frequencies and an unused frequency other than the plurality of frequencies, and
• the transmitter transmits the reference signal in the unused frequency.

A base station capable of performing communication, in an unlicensed band, with a user terminal capable of performing communication in a licensed band and the unlicensed band, wherein

• the unlicensed band includes a plurality of frequency channels,
• each of the plurality of frequency channels includes a plurality of frequency resources divided in a frequency direction,
• the base station includes:
• a controller configured to measure the interference power in a frequency resource unit;
• and
• a transmitter configured to transmit, based on a measurement result of the interference power, a reference signal by using a predetermined frequency resource included in the plurality of frequency resources, and
• the controller notifies the user terminal of resource information indicating the predetermined frequency resource.

A base station capable of performing communication, in a licensed band, with a user terminal capable of performing communication in the licensed band and an unlicensed band, comprising:

• a controller configured to measure interference power in the unlicensed band;
• and
• a transmitter configured to transmit, in the unlicensed band, a reference signal, wherein
• the controller schedules a transmission timing of the reference signal at any timing.