Method and apparatus for transmitting HARQ ACK/NACK

1. A User Equipment (UE) transmitting a Hybrid Automatic Repeat reQuest (HARQ) response in a wireless communication system, the UE comprising:

a receiving unit configured to:

receive an Radio Resource Control (RRC) message from a base station through a first serving cell supporting a Time Division Duplex (TDD) mode, the RRC message comprising carrier aggregation (CA) configuration information, the CA configuration information comprising information of a second serving cell supporting a Frequency Division Duplex (FDD) mode, and the first serving cell and the second serving cell being aggregated by a FDD-TDD CA scheme;

receive a Physical Downlink Control Channel (PDCCH) transmission or an Enhanced PDCCH (EPDCCH) transmission through the second serving cell; and

receive a Physical Downlink Shared Channel (PDSCH) transmission through the second serving cell;

a processor operationally coupled to the receiving unit and configured to:

determine a downlink (DL) reference timing for transmitting an HARQ response signal based on information received through the first serving cell, the HARQ response signal being responsive to the PDSCH transmission through the second serving cell;

recognize, from the PDCCH or the EPDCCH, a 2-bit uplink (UL) downlink assignment index (DAI) field configured in a UL downlink control information (DCI) format, the UL DCI format indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell, and the 2-bit UL DAI field indicating the number of PDSCHs scheduled in downlink subframes associated with one uplink subframe of the second serving cell; and

generate an HARQ response signal based on the number of PDSCHs scheduled in the downlink subframes indicated by the UL DAI field and the number of total downlink subframes associated with the one uplink subframe, the HARQ response signal being generated in association with PUCCH format 3 if the number of total downlink subframes associated with the one uplink sub frame is 5 or 6; and

a transmitting unit configured to transmit the HARQ response signal through a PUSCH in the one uplink subframe.

2. The UE of claim 1 , wherein the processor is further configured to generate HARQ bits for PDSCHs received through the 5 or 6 downlink subframes associated with the one uplink subframe.

3. The UE of claim 1 , wherein the processor is further configured to determine the DL reference timing based on one of TDD UL/DL configurations 2, 3, and 4 of the first serving cell.

4. The UE of claim 3 , wherein, if the TDD UL/DL configuration of the first serving cell is TDD UL/DL configuration 2, an uplink subframe having an index N is associated with 5 downlink subframes having indexes N-4, N-5, N-6, N-7, and N-8, and

wherein N is at least one of 2 and 7.

5. The UE of claim 3 , wherein, if the TDD UL/DL configuration of the first serving cell is TDD UL/DL configuration 3, an uplink subframe having an index N is associated with 6 downlink subframes having indexes N-6, N-7, N-8, N-9, N-10, and N-11, and

wherein N is 2.

6. The UE of claim 3 , wherein, if the TDD UL/DL configuration of the first serving cell is TDD UL/DL configuration 4, an uplink subframe having an index N is associated with 6 downlink subframes having indexes N-7, N-8, N-9, N-10, N-11, and N-12, and

wherein N is 2.

7. The UE of claim 1 , wherein the processor is further configured to:

retrieve values of most significant bit (MSB) and least significant bit (LSB) of the UL DAI field;

confirm the number of PDSCHs scheduled in the downlink subframes associated with the one uplink subframe W DAI UL , as 5 when the MSB and the LSB are zero, respectively; and

confirm the number of scheduled PDSCHs in downlink subframes associated with the one uplink subframe, W DAI UL , as 6 when the MSB is zero and the LSB is one.

8. The UE of claim 1 , wherein PUCCH format is configured by an RRC signaling.

9. The UE of claim 1 , wherein, when the self-scheduling scheme is configured, the PDCCH and the PDSCH indicated by the PDCCH are transmitted through one downlink component carrier or the EPDCCH and the PDSCH indicated by the EPDCCH are transmitted through one downlink component carrier.

10. A base station receiving a Hybrid Automatic Repeat reQuest (HARQ) response in a wireless communication system, the base station comprising:

a transmitting unit configured to:

transmit, to a User Equipment (UE), an RRC message through the first serving cell, the first serving cell supporting a Time Division Duplex (TDD) mode, the RRC message comprising carrier aggregation (CA) configuration information, the CA configuration information comprising information of a second serving cell supporting a Frequency Division Duplex (FDD) mode, the first serving cell and the second serving cell being aggregated by a TDD-FDD CA scheme, and the second serving cell being configured for the UE according to a self-scheduling scheme;

transmit, through the first serving cell, information relating to a downlink (DL) reference timing, which enables the UE to trans fit an HARQ response signal based on the DL reference timing, the HARQ response signal being responsive to a Physical Downlink Shared Channel (PDSCH) transmission through the second serving cell;

transmit, to the UE, a Physical Downlink Control Channel (PDCCH) transmission or an Enhanced PDCCH (EPDCCH) transmission through the second serving cell, the PDCCH or the EPDCCH comprising a 2-bit uplink (UT) downlink assignment index (DAI) field configured in a UL downlink control information (DCI) format, the UL DCI format indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell, and the 2-bit UL DAI field indicating the number of PDSCHs scheduled in downlink subframes associated with one uplink subframe of the second serving cell; and

transmit, to the UE, the PDSCH through the second serving cell; and

a receiving unit configured to receive an HARQ response signal through a PUSCH in the one uplink subframe, the HARQ response signal being configured based on the number of PDSCHs scheduled in the downlink subframes indicated by the UL DAI field and the number of total downlink subframes associated with the one uplink subframe, the HARQ response signal being configured in association with PUCCH format 3 if the number of total downlink subframes associated with the one uplink subframe is 5 or 6.

11. The base station of claim 10 , wherein the HARQ response signal includes HARQ bits for PDSCHs received through the 5 or 6 downlink subframes associated with the one uplink subframe.

12. The base station of claim 10 , wherein the DL reference timing is determined based on one of TDD UL/DL configurations 2, 3, and 4 of the first serving cell.

13. The base station of claim 12 , wherein, if the TDD UL/DL configuration of the first serving cell is TDD UL/DL, configuration 2, an uplink subframe having an index N is associated with 5 downlink subframes having indexes N-4, N-5, N-6, N-7, and N-8, and

wherein N is at least one of 2 and 7.

14. The base station of claim 12 , wherein, if the TDD UL/DL configuration of the first serving cell is TDD UL/DL configuration 3, an uplink subframe having an index N is associated with 6 downlink subframes having indexes N-6, N-7, N-8, N-9, N-10, and N-11, and

wherein N is 2.

15. The base station of claim 12 , wherein, if the TDD UL/DL configuration of the first serving cell is TDD UL/DL configuration 4, an uplink subframe having an index N is associated with 6 downlink subframes having indexes N-7, N-8, N-9, N-10, N-11, and N-12, and

wherein N is 2.

16. The base station of claim 10 , further comprising a processor configured to determine values of most significant bit (MSB) and least significant bit (LSB) of the UL DAI field,

wherein the number of PDSCHs scheduled in the downlink subframes associated with the one uplink subframe, W DAI UL , is indicated as 5 when the MSB and the LSB are zero, respectively, and

wherein the number of scheduled PDSCHs in downlink subframes associated with the one uplink subframe, W DAI UL , is indicated as 6 when the MSB is zero and the LSB is one.

17. The base station of claim 10 , wherein PUCCH format is configured by an RRC signaling.

18. The base station of claim 10 , wherein, when the self-scheduling scheme is configured, the PDCCH and the PDSCH indicated by the PDCCH are transmitted through one downlink component carrier or the EPDCCH and the PDSCH indicated by the EPDCCH are transmitted through one downlink component carrier.

19. A User Equipment (UE) transmitting a Hybrid Automatic Repeat reQuest (HARQ) response in a wireless communication system, the UE comprising:

a receiving unit configured to:

receive an Radio Resource Control (RRC) message from a base station through a first serving cell supporting a Time Division Duplex (TDD) mode, the RRC message comprising carrier aggregation (CA) configuration information, the CA configuration information comprising information of a second serving cell supporting a Frequency Division Duplex (FDD) mode, and the first serving cell and the second serving cell being aggregated by a FDD-TDD CA scheme;

receive a Physical Downlink Control Channel (PDCCH) transmission or an Enhanced PDCCH (EPDCCH) transmission through the second serving cell; and

receive a Physical Downlink Shared Channels (PDSCHs) transmission through the second serving cell;

a processor operationally coupled to the receiving unit and configured to:

recognize, from the PDCCH or the EPDCCH, a field indicating the number of PDSCHs scheduled in downlink subframes associated with one uplink subframe of the second serving cell; and

generate an HARQ response signal based on the number of PDSCHs scheduled in the downlink subframes indicated by the field and the number of total downlink subframes associated with the one uplink subframe, the HARQ response signal being generated in association with PUCCH format 3 if the number of total downlink subframes associated with the one uplink sub frame is 5 or 6; and

a transmitting unit configured to transmit the HARQ response signal through a PUSCH in the one uplink subframe.