Method for counting a DRX (discontinuous reception) timer in a carrier aggregation system and a device therefor

1. A method for performing Discontinuous Reception (DRX) operation by a User Equipment (UE) configured with at least one Frequency Division Duplex (FDD) serving cell and at least one Time Division Duplex (TDD) serving cell, the method comprising:

receiving a Radio Resource Control (RRC) signal for configuring the DRX operation from a base station;

configuring the DRX operation by setting a timer related to the DRX operation according to the RRC signal; and

operating the timer related to the DRX operation by counting subframes when subframes for all TDD serving cells configured to the UE are uplink subframes and the at least one FDD serving cell is not configured with cross carrier scheduling for both uplink and downlink.

2. The method according to claim 1 , wherein the timer related to the DRX timer includes at least one of a drx-Inactivity timer, a drx-Retransmission timer or an onDuration timer.

3. The method according to claim 1 , further comprising:

monitoring a Physical Downlink Control Channel (PDCCH) in one of the subframes which are uplink subframes for all TDD serving cells configured to the UE.

4. The method according to claim 1 , wherein the subframes counted by the UE are downlink subframes for all FDD serving cells configured to the UE, and

the at least one FDD serving cell is not configured with schedulingCellld.

5. The method according to claim 1 , wherein the at least one TDD serving cell is not configured with schedulingCellId.

6. The method according to claim 1 , wherein the at least one FDD serving cell and the at least one TDD serving cell are served by the base station.

7. The method according to claim 1 , wherein the at least one FDD serving cell comprises a Primary Cell (PCell).

8. A User Equipment (UE) for performing Discontinuous Reception (DRX) operation and configured with at least one Frequency Division Duplex (FDD) serving cell and at least one Time Division Duplex (TDD) serving cell, the UE comprising:

a Radio Frequency (RF) module; and

a processor operably coupled with the RF module and configured to:

receive a Radio Resource Control (RRC) signal for configuring the DRX operation from a base station;

configure the DRX operation by setting a timer related to the DRX operation according to the RRC signal; and

operate the timer related to the DRX operation by counting subframes when subframes for all TDD serving cells configured to the UE are uplink subframes and the at least one FDD serving cell is not configured with cross carrier scheduling for both uplink and downlink.

9. The UE according to claim 8 , wherein the timer related to the DRX timer includes at least one of a drx-Inactivity timer, a drx-Retransmission timer or an onDuration timer.

10. The UE according to claim 8 , wherein the processor is further configured to:

monitor a Physical Downlink Control Channel (PDCCH) in one of the subframes which are uplink subframes for all TDD serving cells configured to the UE.

11. The UE according to claim 8 , wherein the subframes counted by the UE are downlink subframes for all FDD serving cells configured to the UE, and

the at least one FDD serving cell is not configured with schedulingCellId.

12. The UE according to claim 8 , wherein the at least one TDD serving cell is not configured with schedulingCellId.

13. The UE according to claim 12 , wherein the at least one FDD serving cell and the at least one TDD serving cell are served by the base station.

14. The UE according to claim 12 , wherein the at least one FDD serving cell comprises a Primary Cell (PCell).