Base station, radio communications system, and processing method in base station

A base station includes a determining unit, and a change unit. The determining unit determines, for each terminal, whether reception quality of an uplink signal from the terminal is equal to or smaller than a certain threshold. The change unit performs first processing or second processing when the reception quality is equal to or smaller than the certain threshold. The first processing is the processing of instructing a first terminal, a terminal of a transmission source of an uplink signal, to change the frequency of the uplink signal of the first terminal to the frequency of either an uplink or a downlink signal assigned to each terminal. The second processing is the processing of changing the frequency of a downlink signal identical to that of the uplink signal from the first terminal to the frequency of either an uplink or a downlink signal assigned to each terminal.