a plurality of radio access units form the single cell of a first communication system , while forming respective individual multi - cells of a second communication system within the single cell . the plurality of radio access units transmit a downstream signal of the first communication system input from a main unit to a terminal using the first communication system of the single cell , while each transmitting a downstream signal of the second communication input from the main unit to a terminal using the communication system of the corresponding respective one of the multi - cells .