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

1. 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 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

the transceiver transmits, 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 base station of claim 1 , wherein the processor is further configured to configure 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 base station of claim 1 , wherein the processor is further configured to generate the at least one of the PDCCH and the EPDCCH, and

wherein the transceiver transmits the at least one of the PDCCH and the EPDCCH through the second serving cell.

4. The base station of claim 1 , wherein the processor is further configured to configure the first serving cell as a primary serving cell (PCell) and the second serving cell as a secondary serving cell (SCell).

5. The base station of claim 1 , wherein the processor is further configured to configure 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, and

wherein the transceiver transmits the at least one of the PDCCH and the EPDCCH through the first serving cell.

6. The base station of claim 1 , wherein the processor is further configured to configure the DL DCI format 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 base station of claim 2 , wherein the processor is further configured to configure the UL DCI format as at least one of UL DCI format 0 and UL DCI format 4.

8. The base station of claim 1 , wherein the processor is further configured to determine that 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 base station of claim 2 , wherein the processor s further configured to determine that the 2-bit UL DAI field indicates information associated with the PDSCH transmission within DL subframes corresponding to UL subframe on the second serving cell.

10. A base station comprising:

a transceiver; and

a processor operationally coupled to the transceiver and configured to establish a RadioResource Control (RRC) connection with a User Equipment (UE) through a first serving cell, the first serving cell supporting a Frequency Division Duplex (FDD) 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 Time Division Duplex (TDD) mode, and the first serving cell and the second serving cell being aggregated by an FDD-TDD CA scheme;

the processor is further configured to configure 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

the transceiver transmits, 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 base station of claim 10 , wherein the processor is further configured to configure an uplink (UL) DCI format for indicating a Physical Uplink Shared Channel (PUSCH) transmission on the second serving cell, and

wherein, when the FDD-TDD CA scheme is configured, the processor is further configured to configure either a 0-bit UL DAI field in the UL DCI format or to determine that a UL DAI field is not configured in the UL DCI format.

12. The base station of claim 10 , wherein the processor is further configured to generate the at least one of the PDCCH and the EPDCCH, and

wherein the transceiver transmits the at least one of the PDCCH and the EPDCCH through the second serving cell.

13. The base station of claim 10 , wherein the processor is further configured to configure the first serving cell as a primary serving cell (PCell) and the second serving cell as a secondary serving cell (SCell).

14. The base station of claim 10 , wherein the processor is further configured to configure 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, and

wherein the transceiver transmits the at least one of the PDCCH and the EPDCCH through the first serving cell.

15. The base station of claim 10 , wherein the processor is further configured to configure the DL DCI format 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 base station of claim 11 , wherein the processor is further configured to configure the UL DCI format as at least one of UL DCI format 0 and UL DCI format 4.

17. A User Equipment (UE) supporting a carrier aggregation of a Time Division Duplex (TDD) cell and a Frequency Division Duplex (FDD) cell, the 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 primary serving cell (PCell);

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

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

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

when a TDD cell is configured as the PCell and an FDD cell is configured as the SCell, retrieve a 2-bit downlink assignment index (DAI) field from the UL DCI format, and retrieve 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, retrieve a 3-bit HARQ process number field from the DL DCI format.

18. The UE of claim 17 , wherein the processor is further configured to retrieve, when a TDD cell is configured as the PCell and an FDD cell is configured as the SCell, a 2-bit downlink assignment index (DAI) field from the DL DCI format, and

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