Base station

A base station configured to perform time-division duplex radio communication with a terminal, using part of a frequency band shared with another system, the base station comprising:

• a receiver that receives an uplink signal from the terminal for each frequency band in use;
• a guard-time-length setter that sets a length of a guard time;
• a reception level measurer that measures, for the frequency band in use, a reception level of the uplink signal and a reception level of the guard time having a predetermined length;
• a frequency band selector that selects a frequency band in which the reception level of the guard time is not greater than a first threshold;
• a control signal generator that generates, for the frequency band in use, a control signal including information indicating the set length of the guard time, and information indicating the selected frequency band;
• and
• a transmitter that transmits a downlink signal including the control signal to the terminal for the frequency band in use,
• wherein the guard-time-length setter sets a first length for the guard time based on the reception level of the uplink signal during a period until a timer that is set for a predetermined period of time expires, and the guard-time-length setter sets a second length for the guard time when the timer that is set for the predetermined period of time has expired, the second length being longer than the first length.