A method performed by a base station for receiving acknowledgement information in a wireless communication system, the method comprising: transmitting, to a user equipment, UE , configuration information for communicating with a secondary cell, SCell, on a primary cell, PCell, the PCell using a frequency division duplexing, FDD, and the SCell using a time division duplexing, TDD; transmitting, to the UE , downlink control information for scheduling data, said data to be transmitted on at least one of the PCell and the SCell in a first transmission time interval, TTI; transmitting, to the UE , the data on the at least one of the PCell and the SCell based on the downlink control information in the first TTI; and receiving, from the UE , acknowledgement information for the data, said acknowledgement information being received on the PCell in a second TTI. wherein a number of information bits corresponding to the acknowledgement information is determined based on whether the first TTI of the SCell is an uplink TTI or a downlink TTI, wherein the information bits include at least one HARQ-ACK bit corresponding to the first TTI on the PCell and at least one HARQ-ACK bit corresponding to the SCell in case that the first TTI of the SCell is a downlink TTI, and wherein the information bits include at least one HARQ-ACK bit corresponding to the first TTI on the PCell but no HARQ-ACK bit corresponding to the SCell in case that the first TTI of the SCell is an uplink TTI, characterized in that in case that a TDD uplink-downlink, UL-DL, configuration for the SCell is adaptively configured, whether the first TTI of the SCell is an uplink TTI or a downlink TTI is determined based on a reference TDD UL-DL configuration configured by a higher layer signaling. transmitting, to a user equipment, UE , configuration information for communicating with a secondary cell, SCell, on a primary cell, PCell, the PCell using a frequency division duplexing, FDD, and the SCell using a time division duplexing, TDD; transmitting, to the UE , downlink control information for scheduling data, said data to be transmitted on at least one of the PCell and the SCell in a first transmission time interval, TTI; transmitting, to the UE , the data on the at least one of the PCell and the SCell based on the downlink control information in the first TTI; and receiving, from the UE , acknowledgement information for the data, said acknowledgement information being received on the PCell in a second TTI. wherein a number of information bits corresponding to the acknowledgement information is determined based on whether the first TTI of the SCell is an uplink TTI or a downlink TTI, wherein the information bits include at least one HARQ-ACK bit corresponding to the first TTI on the PCell and at least one HARQ-ACK bit corresponding to the SCell in case that the first TTI of the SCell is a downlink TTI, and wherein the information bits include at least one HARQ-ACK bit corresponding to the first TTI on the PCell but no HARQ-ACK bit corresponding to the SCell in case that the first TTI of the SCell is an uplink TTI, characterized in that in case that a TDD uplink-downlink, UL-DL, configuration for the SCell is adaptively configured, whether the first TTI of the SCell is an uplink TTI or a downlink TTI is determined based on a reference TDD UL-DL configuration configured by a higher layer signaling. <EOS>