Method for triggering a BSR for sidelink data in a D2D communication system and device therefor

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

configuring a sidelink logical channel;

receiving a sidelink data of the sidelink logical channel from upper layer;

checking whether the sidelink data of the sidelink logical channel is received from an eNB or not; and

triggering a buffer status reporting according to a result of the checking,

wherein if the sidelink data of the sidelink logical channel is received from the eNB, the buffer status reporting is not triggered, and

wherein the UE triggers the buffer status reporting when a certain time period is passed after the sidelink data of the sidelink logical channel is received from the eNB.

2. The method according to claim 1 , wherein the UE does not transmit the sidelink data of the sidelink logical channel until a sidelink grant is received from the eNB.

3. The method according to claim 1 , wherein a sidelink grant for transmitting the sidelink data is not received from the eNB during the certain time period.

4. The method according to claim 1 , wherein the sidelink data received from the eNB is a data to be relayed from the eNB to another UE via the UE.

5. The method according to claim 1 , wherein if the sidelink data of the sidelink logical channel is not received from the eNB, the UE triggers the buffer status reporting when the sidelink data of the sidelink logical channel is received from upper layer.

6. The method according to claim 5 , wherein the sidelink data of the sidelink logical channel not received from the eNB is a sidelink data generated by the UE.

7. The method according to claim 1 , wherein when the sidelink data of the sidelink logical channel becomes available for transmission in a Packet Data Convergence Protocol (PDCP) entity, the UE checks whether the sidelink data of the sidelink logical channel is received from the eNB or not.

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

a Radio Frequency (RF) module including a transceiver; and

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

configure a sidelink logical channel;

receive a sidelink data of the sidelink logical channel from upper layer;

check whether the sidelink data of the sidelink logical channel is received from an eNB or not; and

trigger a buffer status reporting according to a result of the checking,

wherein if the sidelink data of the sidelink logical channel is received from the eNB, the buffer status reporting is not triggered, and

wherein the processor triggers the buffer status reporting when a certain time period is passed after the sidelink data of the sidelink logical channel is received from the eNB.

9. The UE according to claim 8 , wherein the processor does not transmit the sidelink data of the sidelink logical channel until a sidelink grant is received from the eNB.

10. The UE according to claim 8 , wherein a sidelink grant for transmitting the sidelink data is not received from the eNB during the certain time period.

11. The UE according to claim 8 , wherein the sidelink data received from the eNB is a data to be relayed from the eNB to another UE via the UE.

12. The UE according to claim 8 , wherein if the sidelink data of the sidelink logical channel is not received from the eNB, the processor triggers the buffer status reporting when the sidelink data of the sidelink logical channel is received from upper layer.

13. The UE according to claim 12 , wherein the sidelink data of the sidelink logical channel not received from the eNB is a sidelink data generated by the UE.

14. The UE according to claim 8 , wherein when the sidelink data of the sidelink logical channel becomes available for transmission in a Packet Data Convergence Protocol (PDCP) entity, the processor checks whether the sidelink data of the sidelink logical channel is received from the eNB or not.