In a radio communication system where there are a plurality of femtocells within a macro cell controlled by a macro base station, the downlink transmission power of each femto base station affects a macro mobile station in the macro cell. Accordingly, some measures have been taken to prevent the downlink transmission power of each femto base station from interfering in the communication of the macro mobile station. For example, Patent Literature 1 discloses processing for controlling the downlink transmission power of each femto base station in consideration of a reception level of a reference signal transmitted from a macro base station.
Incidentally, in a case where a femto base station is located in a building and a femto base station is located indoors, it is possible to prevent interference to a macro mobile station located outdoors even if the downlink transmission power of the femto base station is increased by the amount corresponding to a building penetration loss due to e.g., walls of buildings and a space propagation loss. Therefore, in Patent Literature 2, a femto base station measures the reception power at the femto base station of a reference signal from a macro base station, and the reception power at the femto base station of an uplink transmission power from a macro mobile station to the macro base station. Then, the femto base station obtains a path loss (=building penetration loss+ space propagation loss) between the femto base station and the macro mobile station based on the estimated transmission power of the macro mobile station and the reception power of the uplink transmission power measured by the femto base station. The transmission power of the femto base station is obtained in consideration of this path loss. Further, in Patent Literature 3, a femto base station firstly measures the reception quality of a reference signal from a macro base station, and adds a power offset to thereby set an initial value of transmission power (transmission power of the reference signal and a maximum value of the transmission power). Next, upon receiving from a femto mobile station a report on the measurement result of the reception quality using the initial value, the femto base station reconfigures the transmission power of the femto base station so that the reception quality in the femto mobile station approaches a target level. This allows the reception quality in the femto mobile station to be maintained while preventing interference to the macro mobile station.
On the other hand, in Patent Literature 4, under a predetermined condition in which an unregistered macro mobile equipment exists in a femtocell, a femto base station changes a downlink perch channel signal to thereby change the radius of a downlink femtocell. The uplink reception sensitivity is changed, as needed, in accordance with the change in the radius of the downlink femtocell, thereby controlling the radius of an uplink femtocell to be prevented from being greatly different from the radius of the downlink femtocell. This control prevents interference to the femto base station due to the uplink transmission power from the macro mobile equipment to the macro base station.