Provided is a communication system that transmits a control channel using a downlink. The communication system may transmit, to the terminal, transmission information of uplink allocation information that indicates whether uplink allocation information is transmitted using a downlink, and the terminal may determine whether the uplink allocation information is included in a downlink frame, based on the transmission information of uplink allocation information. The base station may transmit, to the terminal, information associated with a resource which has a possibility of being used for transmission of a physical downlink control channel (PDCCH), and the terminal may decode the PDCCH in the resource which has a possibility of being used for transmission of the PDCCH.