Disclosed are operation methods of communication nodes supporting superposition transmission in a cellular communication system. An operation method of a base station comprises dividing a transmission block used for communications in the communication system into a plurality of sub transmission blocks each of which includes at least one resource block; setting transmit power allocation coefficients respectively for the plurality of sub transmission blocks; and transmitting the transmission block to which a superimposed signal is mapped, the superimposed signal including information indicating a number of resource blocks included in each of the plurality of sub transmission blocks, information indicating the transmit power allocation coefficients, first data units for the first terminal, and second data units for the second terminal. The first data units and the second data units are mapped to a same resource in the transmission block.