Method for performing DRX operation in wireless communication system and a device therefor

1. A method for a user equipment (UE) operating in a wireless communication system, the method comprising:

generating a Medium Access Control (MAC) Protocol Data Unit (PDU) including an indicator indicating the MAC PDU is a last MAC PDU to be transmitted to an eNB if the generated MAC PDU is a last MAC PDU to be transmitted to the eNB;

transmitting the MAC PDU including the indicator; and

starting using a Discontinuous Reception (DRX) cycle right after the UE considers that the transmission of MAC PDU is successful, even if a drx inactivity timer is running or DRX command MAC Control element (CE) is not received.

2. The method according to claim 1 , wherein the UE considers that the generated MAC PDU is the last MAC PDU to be transmitted to the eNB if there is no data available for transmission in a Packet Data Convergence Protocol (PDCP) and a Radio Link Control (RLC) entities after transmitting the generated MAC PDU.

3. The method according to claim 1 , wherein the indicator is at least one of:

a buffer status reporting including a buffer size set to zero; or

a Radio Link Control (RLC) PDU including an RLC Frame Info field set to a value indicating that a last byte of a data field of RLC PDU corresponds to a last byte of a RLC Service Data Unit (SDU).

4. The method according to claim 1 , wherein the indicator is transmitted via at least one of a MAC subheader, a MAC control element, an RLC subheader, or an RLC control PDU.

5. The method according to claim 1 , wherein the UE considers that the transmission of MAC PDU is successful, when the MAC PDU including the indicator is transmitted.

6. The method according to claim 1 , wherein the UE considers that the transmission of MAC PDU is successful, when Acknowledgement Information for the last MAC PDU transmission is received.

7. The method according to claim 6 , wherein the Acknowledgement Information for the last MAC PDU is one of Hybrid-ARQ (HARD) Acknowledgement feedback for the last MAC PDU, or an UL grant for a new transmission, or any form of feedback indicating that the last MAC PDU is successfully received or decoded by the eNB.

8. The method according to claim 1 , wherein the UE is a Narrow Band Internet of Things (NB-IoT) UE.

9. A user equipment (UE) for operating in a wireless communication system, the UE comprising

a transmitter;

a receiver; and

a processor operably coupled with the transmitter and receiver,

wherein the processor is configured to,

generate a Medium Access Control (MAC) Protocol Data Unit (PDU) including an indicator indicating the MAC PDU is a last MAC PDU to be transmitted to an eNB if the generated MAC PDU is a last MAC PDU to be transmitted to the eNB,

wherein the transmitter is configured to transmit the MAC PDU including the indicator, and

wherein the processor is configured to start using a Discontinuous Reception (DRX) cycle right after the UE considers that the transmission of MAC PDU is successful even if a drx inactivity timer is running or DRX command MAC Control element (CE) is not received.

10. The UE according to claim 9 , wherein the processor considers that the generated MAC PDU is the last MAC PDU to be transmitted to the eNB if there is no data available for transmission in a Packet Data Convergence Protocol (PDCP) and a Radio Link Control (RLC) entities after transmitting the generated MAC PDU.

11. The UE according to claim 9 , wherein the indicator is at least one of:

a buffer status reporting including a buffer size set to zero; or

a Radio Link Control (RLC) PDU including an RLC Frame Info field set to a value indicating that a last byte of a data field of RLC PDU corresponds to a last byte of a RLC Service Data Unit (SDU).

12. The UE according to claim 9 , wherein the indicator is transmitted via at least one of a MAC subheader, a MAC control element, an RLC subheader, or an RLC control PDU.

13. The UE according to claim 9 , wherein the processor considers that the transmission of MAC PDU is successful, when the MAC PDU including the indicator is transmitted.

14. The UE according to claim 9 , wherein the processor considers that the transmission of MAC PDU is successful, when Acknowledgement Information for the last MAC PDU transmission is received.

15. The UE according to claim 14 , wherein the Acknowledgement Information for the last MAC PDU is one of Hybrid-ARQ (HARD) Acknowledgement feedback for the last MAC PDU, or an UL grant for a new transmission, or any form of feedback indicating that the last MAC PDU is successfully received or decoded by the eNB.

16. The UE according to claim 9 , wherein the UE is a Narrow Band Internet of Things (NB-IoT) UE.