Mobile communication systems have been required to ensure service qualities in accordance with the contents of communication requests randomly made by mobile stations (users). Thus, when installing a base station, a mobile telecommunications carrier generally estimates the size of a service area and traffic generated in the service area, and use means such as simulation to design the installation location and configuration of the base station as well as radio parameters such as a transmission level of a downlink common control channel transmitted from the base station.
The designing of a base station involves determining an in-out threshold that is a threshold for determining whether a mobile station is to camp on a cell formed by the base station. For example, in a W-CDMA system, based on Qqualmin broadcasted from a cell whose Ec/N0 measured is the highest, the mobile station determines to camp on the cell when the measured Ec/N0 exceeds Qqualmin. When Ec/N0 periodically measured after completion of the procedure to camp on the cell becomes equal to or lower than Qqualmin, the mobile station attempts to camp on another cell.
In recent years, in addition to base stations for public communications installed by the mobile telecommunications carriers as described above, there has been an increase in small base stations (Home Nodes) installed at home and the like by users of mobile stations. As compared with the base stations for public communications, such a small base station is used by only limited users and can form a small sized cell. Accordingly, the throughput can be expected to increase (see. Non-Patent Document 1).