A user equipment configured with at least two serving cells comprising a primary cell, PCell, and a secondary cell, SCell, the PCell and the SCell having different Time Division Duplex, TDD, Uplink-Downlink, UL-DL, configurations, the user equipment comprising: a receiver; a controller; and a transmitter configured to transmit first acknowledgement/negative acknowledgement, A/N, in an uplink subframe determined by a reference TDD configuration for the SCell, the first A/N corresponding to a physical downlink shared channel, PDSCH, transmission on the SCell, wherein the reference TDD configuration for the SCell is any of one or more reference TDD configurations for the TDD UL-DL configurations of the PCell and the SCell in Table 1 below: [Table 1] Reference TDD configuration PCell TDD UL-DL configuration 0 1 2 3 4 5 6 SCell TDD UL-DL configuration 0 0 1, 2, 4, 5 2, 5 3, 4, 5 4, 5 5 1, 2, 3, 4, 5, 6 1 1, 2, 4, 5 1 2, 5 4, 5 4, 5 5 1, 2, 4, 5 2 2, 5 2, 5 2 5 5 5 2, 5 3 3, 4, 5 4, 5 5 3 4, 5 5 3, 4, 5 4 4, 5 4, 5 5 4, 5 4 5 4, 5 5 5 5 5 5 5 5 5 6 1, 2, 3, 4, 5, 6 1, 2, 4, 5 2, 5 3, 4, 5 4, 5 5 6 where each reference TDD configuration in Table 1 indicates downlink association set indexes K: {k 0,k 1,...k M-1} for a subframe n as defined in Table 2 below: [Table 2] UL-DL Configuration Subframe n 0 1 2 3 4 5 6 7 8 9 0 - - 6 - 4 - - 6 - 4 1 - - 7, 6 4 - - - 7, 6 4 - 2 - - 8, 7, 4, 6 - - - - 8, 7, 4, 6 - - 3 - - 7, 6, 11 6, 5 5, 4 - - - - - 4 - - 12, 8, 7, 11 6, 5, 4, 7 - - - - - - 5 - - 13, 12, 9, 8, 7, 5, 4, 11, 6 - - - - - - - 6 - - 7 7 5 - - 7 7 - where A/N corresponding to PDSCH transmitted in a subframe n - k i, 0≤i≤M-1, is transmitted in the subframe n, wherein k i in Table 2 indicates the number of subframes between the reception of the PDSCH transmission of the SCell and a responsive A/N transmission, k i being determined based on a reference TDD configuration for the SCell, characterized in that the reference TDD configuration for SCell is obtained by selecting that with the greatest number of uplink frames from among the one or more reference TDD configurations in said Table 1 when the user equipment is located on the border of a cell or has a low signal to noise ratio, and the reference TDD configuration for the Scell is obtained by selecting that with the smallest number of uplink frames from among the one or more reference TDD configurations in said Table 1 when the user equipment is located in the center of a cell or has a high signal to noise ratio. a receiver; a controller; and a transmitter configured to transmit first acknowledgement/negative acknowledgement, A/N, in an uplink subframe determined by a reference TDD configuration for the SCell, the first A/N corresponding to a physical downlink shared channel, PDSCH, transmission on the SCell, wherein the reference TDD configuration for the SCell is any of one or more reference TDD configurations for the TDD UL-DL configurations of the PCell and the SCell in Table 1 below: [Table 1] Reference TDD configuration PCell TDD UL-DL configuration 0 1 2 3 4 5 6 SCell TDD UL-DL configuration 0 0 1, 2, 4, 5 2, 5 3, 4, 5 4, 5 5 1, 2, 3, 4, 5, 6 1 1, 2, 4, 5 1 2, 5 4, 5 4, 5 5 1, 2, 4, 5 2 2, 5 2, 5 2 5 5 5 2, 5 3 3, 4, 5 4, 5 5 3 4, 5 5 3, 4, 5 4 4, 5 4, 5 5 4, 5 4 5 4, 5 5 5 5 5 5 5 5 5 6 1, 2, 3, 4, 5, 6 1, 2, 4, 5 2, 5 3, 4, 5 4, 5 5 6 where each reference TDD configuration in Table 1 indicates downlink association set indexes K: {k 0,k 1,...k M-1} for a subframe n as defined in Table 2 below: [Table 2] UL-DL Configuration Subframe n 0 1 2 3 4 5 6 7 8 9 0 - - 6 - 4 - - 6 - 4 1 - - 7, 6 4 - - - 7, 6 4 - 2 - - 8, 7, 4, 6 - - - - 8, 7, 4, 6 - - 3 - - 7, 6, 11 6, 5 5, 4 - - - - - 4 - - 12, 8, 7, 11 6, 5, 4, 7 - - - - - - 5 - - 13, 12, 9, 8, 7, 5, 4, 11, 6 - - - - - - - 6 - - 7 7 5 - - 7 7 - where A/N corresponding to PDSCH transmitted in a subframe n - k i, 0≤i≤M-1, is transmitted in the subframe n, wherein k i in Table 2 indicates the number of subframes between the reception of the PDSCH transmission of the SCell and a responsive A/N transmission, k i being determined based on a reference TDD configuration for the SCell, characterized in that the reference TDD configuration for SCell is obtained by selecting that with the greatest number of uplink frames from among the one or more reference TDD configurations in said Table 1 when the user equipment is located on the border of a cell or has a low signal to noise ratio, and the reference TDD configuration for the Scell is obtained by selecting that with the smallest number of uplink frames from among the one or more reference TDD configurations in said Table 1 when the user equipment is located in the center of a cell or has a high signal to noise ratio.