Apparatus and method for transmitting HARQ ACK/NACK

1. A User Equipment (UE) comprising:

a transceiver; and

a processor operationally coupled to the transceiver and configured to establish a Radio Resource Control (RRC) connection with a base station through a first serving cell, the first serving cell supporting a Time Division Duplex (TDD) mode,

wherein: the transceiver receives an RRC message from the base station through the first serving cell, 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 TDD-FDD CA scheme;

the processor is further configured to check a 2-bit downlink (DL) downlink assignment index (DAI) field configured in a DL downlink control information (DCI) format, the DL DCI format indicating a Physical Downlink Shared Channel (PDSCH) transmission on the second serving cell, and the 2-bit DL DAI field indicating that ten downlink subframes for the second serving cell are associated with a uplink subframe of the first serving cell, wherein the DL DCI format is comprised in at least one of a Physical Downlink Control Channel (PDCCH) and an Enhanced PDCCH (EPDCCH);

the transceiver receives data through the first serving cell and the second serving cell;

in response to the received data, the processor is further configured to generate a Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement/Negative Acknowledgement (ACK/NACK) signal, the HARQ ACK/NACK signal being indexed based on a value of the 2-bit DL DAI field; and

the transceiver transmits the HARQ ACK/NACK signal through the uplink subframe of the first serving cell.

2. The UE of claim 1 , wherein the processor is further configured to check a 2-bit uplink (UL) DAI field configured in a UL DCI format, the UL DCI format indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell.

3. The UE of claim 1 , wherein, if the value of the 2-bit DL DAI field corresponds to 2, the processor is configured to determine that the value of the 2-bit DL DAI field indicates that at least one of the number of subframes with the PDSCH transmission and the number of subframes with the PDCCH or the EPDCCH indicating DL Semi-Persistent Scheduling (SPS) release is 2, 6, or 10.

4. The UE of claim 1 , wherein the processor is further configured to check that a value of a most significant bit (MSB) of the 2-bit DL DAI field is zero (0) and a value of a least significant bit (LSB) of the 2-bit DL DAI field is one (1).

5. The UE of claim 1 , wherein the 2-bit DL DAI field is defined in the following Table:

Number of subframes having PDSCH and

number of subframes having

DAI

V UL DAI or

PDCCH/EPDCCH indicating DL Semi-

MSB,LSB

V DL DAI

Persistent Scheduling (SPS) release

0,0

1

1 or 5 or 9

0,1

2

2 or 6 or 10

1,0

3

3 or 7

1,1

4

0 or 4 or 8

wherein the MSB is a most significant bit, the LSB is a least significant bit, V UL DAI denotes a value of a UL DAI field, and V DL DAI denotes the value of the DL DAI field.

6. The UE of claim 1 , wherein in generating the HARQ ACK/NACK signal, the processor is configured to:

generate first HARQ ACK/NACKs indexed based on the value of the 2-bit DL DAI field, the first HARQ ACK/NACKs being responsive to the data received through subframes of the first serving cell;

generate second HARQ ACK/NACKs indexed based on the value of the 2-bit DL DAI field, the second HARQ ACK/NACKs being responsive to the data received through subframes of the second serving cell; and

generate the HARQ ACK/NACK signal comprising the first HARQ ACK/NACKs and the second HARQ ACK/NACKs.

7. The UE of claim 6 , wherein the processor is further configured to combine the first HARQ ACK/NACKs and the second HARQ ACK/NACKs based on a Physical Uplink Control Channel (PUCCH) resource index and a constellation of a modulation symbol, and

wherein the processor is further configured to process the first HARQ ACK/NACKs and the second HARQ ACK/NACKs to be transmitted through a PUCCH format 1/1a/1b with a channel selection, a PUCCH format 3, or a Physical Uplink Shared Channel (PUSCH).

8. A base station comprising:

a transceiver; and

a processor operationally coupled to the transceiver and configured to establish a Radio Resource Control (RRC) connection with a User Equipment (UE) through a first serving cell, the first serving cell supporting a Time Division Duplex (TDD) mode,

wherein: the transceiver transmits an RRC message to the UE through the first serving cell, 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 TDD-FDD CA scheme;

the processor is further configured to configure a 2-bit downlink (DL) downlink assignment index (DAI) field in a DL downlink control information (DCI) format, the DL DCI format indicating a Physical Downlink Shared Channel (PDSCH) transmission on the second serving cell, and the 2-bit DL DAI field indicating that ten downlink subframes for the second serving cell are associated with a uplink subframe of the first serving cell, wherein the DL DCI format is comprised in at least one of a Physical Downlink Control Channel (PDCCH) and an Enhanced PDCCH (EPDCCH);

the transceiver transmits, to the UE, data through the first serving cell and the second serving cell;

in response to the transmitted data, the transceiver receives a Hybrid Automatic Repeat reQuest (HARQ) Acknowledgement/Negative Acknowledgement (ACK/NACK) signal, the HARQ ACK/NACK signal being indexed based on a value of the 2-bit DL DAI field; and

the HARQ ACK/NACK signal is received through the uplink subframe of the first serving cell.

9. The base station of claim 8 , wherein the processor is further configured to configure a 2-bit uplink (UL) DAI field in a UL DCI format, the UL DCI format indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell.

10. The base station of claim 8 , wherein, the processor is configured to determine the value of the 2-bit DL DAI field as 2, when the value of the 2-bit DL DAI field indicates that at least one of the number of subframes with the PDSCH transmission and the number of subframes with the PDCCH or the EPDCCH indicating DL Semi-Persistent Scheduling (SPS) release is 2, 6, or 10.

11. The base station of claim 8 , wherein the processor is further configured to configure a most significant bit (MSB) of the 2-bit DL DAI field as zero (0) and a least significant bit (LSB) of the 2-bit DL DAI field as one (1).

12. The base station of claim 8 , wherein the 2-bit DL DAI field is defined in the following Table:

Number of subframes having PDSCH and

number of subframes having

DAI

V UL DAI or

PDCCH/EPDCCH indicating DL Semi-

MSB,LSB

V DL DAI

Persistent Scheduling (SPS) release

0,0

1

1 or 5 or 9

0,1

2

2 or 6 or 10

1,0

3

3 or 7

1,1

4

0 or 4 or 8

wherein the MSB is a most significant bit, the LSB is a least significant bit, V UL DAI denotes a value of a UL DAI field, and V DL DAI denotes the value of the DL DAI field.

13. The base station of claim 8 , wherein the HARQ ACK/NACK signal comprising:

first HARQ ACK/NACKs indexed based on the value of the 2-bit DL DAI field, the first HARQ ACK/NACKs being responsive to the data transmitted through subframes of the first serving cell; and

second HARQ ACK/NACKs indexed based on the value of the 2-bit DL DAI field, the second HARQ ACK/NACKs being responsive to the data transmitted through subframes of the second serving cell.

14. The base station of claim 13 , wherein the processor is further configured to determine the first HARQ ACK/NACKs and the second HARQ ACK/NACKs combined based on a Physical Uplink Control Channel (PUCCH) resource index and a constellation of a modulation symbol, and

wherein the first HARQ ACK/NACKs and the second HARQ ACK/NACKs are formatted through a PUCCH format 1/1a/1b with a channel selection, a PUCCH format 3, or a Physical Uplink Shared Channel (PUSCH).