A method for transmitting an ACK/NACK by a user equipment, UE, which is configured with a primary cell, a first secondary cell in a long term evolution, LTE, network, characterized in that the UE is further configured with a second secondary cell, the method comprising: receiving (S151) scheduling information on the first secondary cell, wherein the primary cell and the first secondary cell use a time division duplex, TDD, frame, and the second secondary cell uses a frequency division duplex, FDD, frame; receiving (S152) a data channel on the second secondary cell based on the scheduling information received on the first secondary cell; and transmitting (S153) an ACK/NACK for the data channel through the primary cell, wherein the data channel received on the second secondary cell using the FDD frame is scheduled by the scheduling information received on the first secondary cell using the TDD frame,wherein an uplink-downlink configuration for the TDD frame is one of uplink-downlink configurations 0 to 6 such that: Uplink-downlink configuration subframe number 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U 1 D S U U D D S U U D 2 D S U D D D S U D D 3 D S U U U D D D D D 4 D S U U D D D D D D 5 D S U D D D D D D D 6 D S U U U D S U U D where D indicates a downlink subframe, S indicates a special subframe, and U indicates an uplink subframe; wherein the primary cell and the first secondary cell use different uplink-downlink configurations among the uplink-downlink configurations 0 to 6, wherein one of the uplink-downlink configurations is determined as a reference uplink-downlink configuration, and the ACK/NACK for the data channel is transmitted according to the HARQ timing of the reference uplink-downlink configuration. receiving (S151) scheduling information on the first secondary cell, wherein the primary cell and the first secondary cell use a time division duplex, TDD, frame, and the second secondary cell uses a frequency division duplex, FDD, frame; receiving (S152) a data channel on the second secondary cell based on the scheduling information received on the first secondary cell; and transmitting (S153) an ACK/NACK for the data channel through the primary cell, wherein the data channel received on the second secondary cell using the FDD frame is scheduled by the scheduling information received on the first secondary cell using the TDD frame,wherein an uplink-downlink configuration for the TDD frame is one of uplink-downlink configurations 0 to 6 such that: Uplink-downlink configuration subframe number 0 1 2 3 4 5 6 7 8 9 0 D S U U U D S U U U 1 D S U U D D S U U D 2 D S U D D D S U D D 3 D S U U U D D D D D 4 D S U U D D D D D D 5 D S U D D D D D D D 6 D S U U U D S U U D where D indicates a downlink subframe, S indicates a special subframe, and U indicates an uplink subframe; wherein the primary cell and the first secondary cell use different uplink-downlink configurations among the uplink-downlink configurations 0 to 6, wherein one of the uplink-downlink configurations is determined as a reference uplink-downlink configuration, and the ACK/NACK for the data channel is transmitted according to the HARQ timing of the reference uplink-downlink configuration. <EOS>