Method and apparatus of transmitting control information considering TDD-FDD CA

1. A method of transmitting control information from a base station to a user equipment (UE), the method comprising:

establishing a Radio Resource Control (RRC) connection with the UE through a first serving cell, the first serving cell supporting a Time Division Duplex (TDD) mode;

transmitting 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;

configuring a downlink (DL) downlink control information (DCI) format for indicating a Physical Downlink Shared Channel (PDSCH) transmission on the second serving cell, a 4-bit Hybrid Automatic Repeat reQuest (HARQ) process number field and a 2-bit DL downlink assignment index (DAI) field being configured in the DL DCI format; and

transmitting, to the UE, at least one of a Physical Downlink Control Channel (PDCCH) and an Enhanced PDCCH (EPDCCH), the at least one of the PDCCH and the EPDCCH comprising the DL DCI format.

2. The method of claim 1 , further comprising:

configuring an uplink (UL) DCI format for indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell, a 2-bit UL DAI field being configured in the UL DCI format.

3. The method of claim 1 , wherein the at least one of the PDCCH and the EPDCCH is transmitted through the second serving cell.

4. The method of claim 1 , wherein the first serving cell is a primary serving cell (PCell), and the second serving cell is a secondary serving cell (SCell).

5. The method of claim 1 , further comprising:

configuring a cross-carrier scheduling between the first serving cell and the second serving cell, the first serving cell being configured as a scheduling cell, and the second serving cell being configured as a scheduled cell that is scheduled by the scheduling cell,

wherein the at least one of the PDCCH and the EPDCCH is transmitted through the first serving cell.

6. The method of claim 1 , wherein the DL DCI format is configured as at least one of DL DCI format 1, DL DCI format 1A, DL DCI format 1B, DL DCI format 1D, DL DCI format 2, DL DCI format 2A, DL DCI format 2B, DL DCI format 2C, and DL DCI format 2D.

7. The method of claim 2 , wherein the UL DCI format is configured as at least one of UL DCI format 0, and UL DCI format 4.

8. The method of claim 1 , wherein the 4-bit HARQ process number field indicates an HARQ process number, and the 2-bit DL DAI field indicates information associated with scheduling for the PDSCH transmission on the second serving cell.

9. The method of claim 2 , wherein the 2-bit UL DAI field indicates information associated with the PDSCH transmission within DL subframes corresponding to a UL subframe on the second serving cell.

10. A method of transmitting control information from a base station to a user equipment (UE), the method comprising:

establishing a Radio Resource Control (RRC) connection with the UE through a first serving cell, the first serving cell supporting a Frequency Division Duplex (FDD) mode;

transmitting 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 Time Division Duplex (TDD) mode, and the first serving cell and the second serving cell being aggregated by an FDD-TDD CA scheme;

configuring a downlink (DL) downlink control information (DCI) format for indicating a Physical Downlink Shared Channel (PDSCH) transmission on the second serving cell, a 3-bit Hybrid Automatic Repeat reQuest (HARQ) process number field being configured in the DL DCI format, wherein a DL downlink assignment index (DAI) field is not configured in the DL DCI format; and

transmitting, to the UE, at least one of a Physical Downlink Control Channel (PDCCH) and an Enhanced PDCCH (EPDCCH), the at least one of the PDCCH and the EPDCCH comprising the DL DCI format.

11. The method of claim 10 , further comprising:

configuring an uplink (UL) DCI format for indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell,

wherein either a 0-bit UL DAI field is configured in the UL DCI format or a UL DAI field is not configured in the UL DCI format.

12. The method of claim 10 , wherein the at least one of the PDCCH and the EPDCCH is transmitted through the second serving cell.

13. The method of claim 10 , wherein the first serving cell is a primary serving cell (PCell), and the second serving cell is a secondary serving cell (SCell).

14. The method of claim 10 , further comprising:

configuring a cross-carrier scheduling between the first serving cell and the second serving cell, the first serving cell being configured as a scheduling cell, and the second serving cell being configured as a scheduled cell that is scheduled by the scheduling cell,

wherein the at least one of the PDCCH and the EPDCCH is transmitted through the first serving cell.

15. The method of claim 10 , wherein the DL DCI format is configured as at least one of DL DCI format 1, DL DCI format 1A, DL DCI format 1B, DL DCI format 1D, DL DCI format 2, DL DCI format 2A, DL DCI format 2B, DL DCI format 2C, and DL DCI format 2D.

16. The method of claim 11 , wherein the UL DCI format is configured as at least one of UL DCI format 0, and UL DCI format 4.

17. A method of receiving a downlink control information (DCI) by a User Equipment (UE), the UE supporting a carrier aggregation of a Time Division Duplex (TDD) cell and a Frequency Division Duplex (FDD) cell, the method comprising:

establishing a Radio Resource Control (RRC) connection with a base station through a primary serving cell (PCell);

configuring an FDD cell as a secondary serving cell (SCell) when the PCell is a TDD cell or configuring a TDD cell as the SCell when the PCell is an FDD cell;

monitoring a physical downlink control channel (PDCCH) or an Enhanced PDCCH (EPDCCH) to retrieve DCI, the DCI comprising an uplink (UL) DCI format and a downlink (DL) DCI format;

decoding the DCI according to the configuration of the PCell and the SCell;

when a TDD cell is configured as the PCell and an FDD cell is configured as the SCell, retrieving a 2-bit downlink assignment index (DAI) field from the UL DCI format, and retrieving a 4-bit hybrid automatic repeat request (HARQ) process number field from the DL DCI format; and

when an FDD cell is configured as the PCell and a TDD cell is configured as the SCell, retrieving a 3-bit HARQ process number field from the DL DCI format.

18. The method of claim 17 , further comprising:

when a TDD cell is configured as the PCell and an FDD cell is configured as the SCell, retrieving a 2-bit downlink assignment index (DAI) field from the DL DCI format,

wherein, when the FDD cell is configured as the PCell and the TDD cell is configured as the SCell, a DAI field is not configured in the DL DCI format or the UL DCI format.