To provide a method and an apparatus for achieving a cell redundancy. Base stations, to which different frequency bands are assigned, have active base-station transmitter-receivers with a predetermined number of wireless zones repeated. Some base stations also have standby base-station transmitter-receivers at the rate of one in every predetermined number of sites that have the predetermined number of wireless zones. Under a normal condition, the different frequency bands, which are obtained by dividing a predetermined frequency bandwidth by the predetermined number of the wireless zones, are established at the respective base stations in the respective wireless zones. Under a troublesome condition, different frequency bands, which are obtained by dividing the predetermined frequency bandwidth by the predetermined number of the wireless zones plus the predetermined number of the sites, are assigned to base stations in the respective wireless zones and to base stations that are positioned on the periphery of a wireless zone where the trouble has occurred and that have the standby base-station transmitter-receivers. Further, the output powers of the standby base-station transmitter-receivers of the base stations, which are positioned on the periphery of the wireless zone where the trouble has occurred, are adjusted such that the output powers are overlaid on the wireless zone where the trouble has occurred.