A method is provided for a User Equipment (UE) operating in a wireless communication system. The method includes monitoring a control channel candidate with a downlink control information (DCI) format size in a plurality of search spaces. Each of the plurality of search spaces corresponds to a respective carrier indicator field (CIF) value. The method further includes transmitting or receiving data using downlink control information which is detected by monitoring the control channel candidate. In a state that control channel candidates have different values of carrier indicator field for the DCI format size, the control channel candidate with the DCI format size is received in any search space corresponding to any of the different values of carrier indicator field for the DCI format size.