A method of generating Acknowledgement/Negative Acknowledgement (ACK/NACK) information by a user equipment (UE) in a wireless communication system is discussed. The method includes receiving, by the UE from a base station (BS), a plurality of codewords through a plurality of downlink frequency bands related to a plurality of downlink carriers, wherein the UE is configured with a 1-codeword mode or a 2-codeword mode for each of the plurality of downlink frequency bands independently, and wherein a number of supported codewords is one for the 1-codeword mode or two for the 2-codeword mode; determining, by the UE, a total number of ACK/NACK bits, wherein the total number of ACK/NACK bits is determined based on a total number of the plurality of downlink carriers and the number of supported codewords; and generating, by the UE, a sequence of the ACK/NACK bits based on the total number of the ACK/NACK bits.