To reduce the number of base stations in a mobile telecommunication network, an analog type repeater has been used until now. But nowadays a digital type repeater began to be used, wherein it has the following merits, i.e., for IMT-2000 service a number of repeaters can be connected in cascade, and the total distance in the repeater network can be widely expanded too, and the add/drop control at every repeater can be done flexibly, and the time delay in the various network can be compensated, and the monitoring and controlling of transmission environment can be processed by software