Method and apparatus for monitoring downlink control channel

1. A method for monitoring a downlink control channel in a wireless communication system, performed by a wireless device, the method comprising:

receiving a discontinuous reception (DRX) command from a base station, the DRX command indicating an activation of at least one DRX pattern from a plurality of DRX patterns, each of the plurality of DRX patterns including an on-duration which specifies at least one subframes to monitor a downlink control channel within a DRX cycle; and

monitoring the downlink control channel in at least one subframe which belongs to on-duration of the at least one activated DRX pattern.

2. The method of claim 1 , further comprising:

starting an inactivity timer wherein the downlink control channel indicates a transmission or reception of data; and

monitoring the downlink control channel continuously while the inactivity timer is running.

3. The method of claim 2 , wherein the DRX command is received while the inactivity timer is running.

4. The method of claim 3 , further comprising:

starting a DRX cycle timer upon receiving the DRX command, wherein the downlink control channel is monitored while the DRX cycle timer is running.

5. The method of claim 1 , wherein the DRX command includes a plurality of bits, each bit corresponding to each DRX pattern to be activated or deactivated.

6. The method of claim 5 , wherein the DRX command is received via a medium access control (MAC) control element (CE).

7. The method of claim 1 , wherein the downlink control channel is a physical downlink control channel (PDCCH).

8. The method of claim 1 , wherein the plurality of DRX patterns are configured by using a Radio Resource Control (RRC) message.

9. A wireless device for monitoring a downlink control channel in a wireless communication system, comprising:

a radio frequency unit for receiving a radio signal; and

a processor, operatively coupled with the radio frequency unit, configured to:

receive a discontinuous reception (DRX) command from a base station, the DRX command indicating an activation of at least one DRX pattern from a plurality of DRX patterns, each of the plurality of DRX patterns including an on-duration which specifies at least one subframes to monitor a downlink control channel within a DRX cycle; and

monitor the downlink control channel in at least one subframe which belongs to on-duration of the at least one activated DRX pattern.

10. The wireless device of claim 9 , wherein the processor is configured to:

start an inactivity timer wherein the downlink control channel indicates a transmission or reception of data; and

monitor the downlink control channel continuously while the inactivity timer is running.

11. The wireless device of claim 10 , wherein the DRX command is received while the inactivity timer is running.

12. The wireless device of claim 11 , the processor is configured to:

start a DRX cycle timer upon receiving the DRX command, wherein the downlink control channel is monitored while the DRX cycle timer is running.

13. The wireless device of claim 9 , wherein the DRX command includes a plurality of bits, each bit corresponding to each DRX pattern to be activated or deactivated.

14. The wireless device of claim 13 , wherein the DRX command is received via a medium access control (MAC) control element (CE).

15. The wireless device of claim 9 , wherein the downlink control channel is a physical downlink control channel (PDCCH).