A method for transmitting positive-acknowledgement/negative-acknowledgement, ACK/NACK, in a time division duplex, TDD,-based wireless communication system, the method performed by a user equipment, UE, , and comprising: receiving at least one data in downlink subframes of a first serving cell and a second serving cell; and transmitting 2 bits-ACK/NACK information for the at least one data using one resource selected from four candidate resources in an uplink subframe of the first serving cell, wherein the UE informs ACK/NACK states for the at least one data by a combination of the one selected resource and the 2 bits-ACK/NACK information, wherein, on the first serving cell, if a physical downlink shared channel, PDSCH, indicated by a detection of a first physical downlink control channel, PDCCH, with a downlink assignment index, DAI, value equal to 1 or a second PDCCH with a DAI value equal to 2, is received, or if a first semi-persistent scheduling, SPS, release PDCCH with a DAI value equal to 1 or a second SPS release PDCCH with a DAI value equal to 2 is received, a first candidate resource is determined based on a first control channel element, CCE, used for transmission of the first PDCCH or the first SPS release PDCCH, and a second candidate resource is determined based on a first CCE used for transmission of the second PDCCH or the second SPS release PDCCH, and wherein, on the second serving cell, if a PDSCH, indicated by a detection of a third PDCCH with a DAI value equal to 1 or a fourth PDCCH with a DAI value equal to 2 on the first serving cell, is received, a third candidate resource is determined based on a first CCE used for transmission of the third PDCCH, and a fourth candidate resource is determined based on a first CCE used for transmission of the fourth PDCCH. receiving at least one data in downlink subframes of a first serving cell and a second serving cell; and transmitting 2 bits-ACK/NACK information for the at least one data using one resource selected from four candidate resources in an uplink subframe of the first serving cell, wherein the UE informs ACK/NACK states for the at least one data by a combination of the one selected resource and the 2 bits-ACK/NACK information, wherein, on the first serving cell, if a physical downlink shared channel, PDSCH, indicated by a detection of a first physical downlink control channel, PDCCH, with a downlink assignment index, DAI, value equal to 1 or a second PDCCH with a DAI value equal to 2, is received, or if a first semi-persistent scheduling, SPS, release PDCCH with a DAI value equal to 1 or a second SPS release PDCCH with a DAI value equal to 2 is received, a first candidate resource is determined based on a first control channel element, CCE, used for transmission of the first PDCCH or the first SPS release PDCCH, and a second candidate resource is determined based on a first CCE used for transmission of the second PDCCH or the second SPS release PDCCH, and wherein, on the second serving cell, if a PDSCH, indicated by a detection of a third PDCCH with a DAI value equal to 1 or a fourth PDCCH with a DAI value equal to 2 on the first serving cell, is received, a third candidate resource is determined based on a first CCE used for transmission of the third PDCCH, and a fourth candidate resource is determined based on a first CCE used for transmission of the fourth PDCCH. <EOS>