Method of handling communication operation and related communication device

1. A communication device for handling a communication operation, comprising:

a storage device; and

a processing circuit, coupled to the storage device, wherein the storage device stores instructions, and the processing circuit is configured to execute the instructions of:

performing a reception in a first subframe of a time-division duplexing (TDD) carrier from a network; and

performing a transmission for responding to the reception via a second subframe of a uplink (UL) carrier to the network;

wherein the UL carrier is a frequency-division duplexing (FDD) UL carrier, or is another TDD carrier with an UL/downlink (DL) configuration where all subframes are UL subframes;

wherein the reception comprises at least one packet, and the transmission comprises a hybrid automatic repeat request (HARQ) feedback for responding to the at least one packet in the reception;

wherein a HARQ process number of the HARQ feedback is not greater than a maximum number of HARQ processes, M DL _ HARQ , determined according to the reception and the transmission;

wherein M DL _ HARQ for a UL/DL configuration 4 is 8, or M DL _ HARQ for a UL/DL configuration 5 is 8.

2. The communication device of claim 1 , wherein the TDD carrier is another FDD carrier configured with a TDD UL/DL configuration.

3. The communication device of claim 1 , wherein the reception comprises a UL grant, and the transmission is performed according to the UL grant.

4. The communication device of claim 1 , wherein the second subframe is a number of subframes after the first subframe, and the number of subframes is a constant regardless of a subframe index of the first subframe.

5. The communication device of claim 1 , wherein the second subframe is determined according to a reference timeline.

6. The communication device of claim 5 , wherein the reference timeline is determined according to a UL/DL configuration of the TDD carrier, or is determined according to a UL/DL configuration configured by a higher layer signaling.

7. The communication device of claim 5 , wherein the reference timeline is a newly defined timeline.

8. The communication device of claim 1 , wherein the reception is performed via a physical DL shared channel (PDSCH) of the first subframe of the TDD carrier or via a physical DL control channel (PDCCH) of the first subframe of the TDD carrier.

9. The communication device of claim 1 , wherein the transmission is performed via a physical UL shared channel (PUSCH) of the second subframe of the UL carrier or via a physical UL control channel (PUCCH) of the second subframe of the UL carrier.

10. A communication device for handling a communication operation, comprising:

a storage device; and

a processing circuit, coupled to the storage device, wherein the storage device stores instructions, and the processing circuit is configured to execute the instructions of:

performing a transmission in a first subframe of a uplink (UL) carrier to a network; and

performing a reception for responding to the transmission via a second subframe of a time-division duplexing (TDD) carrier from the network;

wherein the UL carrier is a frequency-division duplexing (FDD) UL carrier, or is another TDD carrier with an UL/downlink (DL) configuration where all subframes are UL subframes;

wherein the second subframe is a number of subframes after the first subframe and the number of subframes is a constant regardless of a subframe index of the first subframe;

wherein the reception is performed via a physical HARQ indicator channel (PHICH) of the second subframe of the TDD carrier.

11. The communication device of claim 10 , wherein the TDD carrier is another FDD carrier configured with a TDD UL/DL configuration.

12. The communication device of claim 10 , wherein the transmission comprises at least one packet, and the reception comprises a hybrid automatic repeat request (HARQ) feedback for responding to the at least one packet in the transmission.

13. The communication device of claim 12 , wherein if the HARQ feedback is not received successfully due to that the second subframe is not valid for performing the reception, the communication device determines that the HARQ feedback which is not received is an acknowledgement (ACK).

14. The communication device of claim 10 , wherein the transmission is performed via a physical UL shared channel (PUSCH) of the first subframe of the UL carrier.

15. A communication device for handling a communication operation, comprising:

a storage device; and

a processing circuit, coupled to the storage device, wherein the storage device stores instructions, and the processing circuit is configured to execute the instructions of:

performing a reception in a first subframe of a downlink (DL) carrier from a network; and

performing a transmission for responding to the reception via a second subframe of a time-division duplexing (TDD) carrier to the network;

wherein the DL carrier is a frequency-division duplexing (FDD) DL carrier, or is another TDD carrier with an uplink (UL)/DL configuration where all subframes are DL subframes;

wherein the reception comprises at least one packet, and the transmission comprises a hybrid automatic repeat request (HARQ) feedback for responding to the at least one packet in the reception;

wherein a HARQ process number of the HARQ feedback is not greater than a maximum number of HARQ processes, M DL _ HARQ , determined according to the reception and the transmission;

wherein M DL _ HARQ for a UL/DL configuration 0 is 10, M DL _ HARQ for a UL/DL configuration 1 is 11, M DL _ HARQ for a UL/DL configuration 2 is 12, M DL _ HARQ for a UL/DL configuration 3 is 15, or M DL _ HARQ for a UL/DL configuration 4 is 16.

16. The communication device of claim 15 , wherein the TDD carrier is another FDD carrier configured with a TDD UL/DL configuration.

17. The communication device of claim 15 , wherein M DL _ HARQ for a UL/DL configuration 5 is 16, or M DL _ HARQ for a UL/DL configuration 6 is 11.

18. The communication device of claim 15 , wherein the reception comprises a UL grant, and the transmission is performed according to the UL grant.

19. The communication device of claim 15 , wherein the second subframe is a number of subframes after the first subframe, and the number of subframes is a constant regardless of a subframe index of the first subframe.

20. The communication device of claim 15 , wherein the second subframe is determined according to a reference timeline.

21. The communication device of claim 20 , wherein the reference timeline is determined according to a UL/DL configuration of the TDD carrier, or is determined according to a UL/DL configuration configured by a higher layer signaling.

22. The communication device of claim 20 , wherein the reference timeline is a newly defined timeline.

23. The communication device of claim 15 , wherein the reception is performed via a physical DL shared channel (PDSCH) of the first subframe of the DL carrier or via a physical DL control channel (PDCCH) of the first subframe of the DL carrier.

24. The communication device of claim 15 , wherein the transmission is performed via a physical UL shared channel (PUSCH) of the second subframe of the TDD carrier or via a physical UL control channel (PUCCH) of the second subframe of the TDD carrier.

25. The communication device of claim 10 , wherein the second subframe is determined according to a reference timeline.

26. The communication device of claim 25 , wherein the reference timeline is determined according to a UL/DL configuration of the TDD carrier, or is determined according to a UL/DL configuration configured by a higher layer signaling.

27. The communication device of claim 25 , wherein the reference timeline is a newly defined timeline.