Method and apparatus for configuring D2D discovery specific logical channel group in wireless communication system

1. A method for a user equipment (UE) configuring a device-to-device (D2D) discovery specific logical channel group (LCG) in a wireless communication system, the method comprising:

receiving a configuration from a network indicating a specific LCG identifier (ID) for a D2D discovery announcement;

calculating a buffer status for the D2D discovery announcement;

configuring the specific LCG ID to transmit the D2D discovery announcement;

constructing a proximity based services (ProSe) buffer status report (BSR) for the D2D discovery announcement, the ProSe BSR including the calculated buffer status and the specific LCG ID configured to transmit the D2D discovery announcement; and

transmitting the constructed ProSe BSR to an evolved NodeB (eNB).

2. The method of claim 1 , wherein the configuration further indicates a specific value of a group index for the D2D discovery announcement.

3. The method of claim 1 , wherein the configuration is received via system information or dedicated signaling.

4. The method of claim 1 , wherein the configuration is received from the eNB, a mobility management entity, or a server in the network.

5. The method of claim 1 , wherein the specific LCG ID is fixed for the D2D discovery announcement.

6. The method of claim 1 , wherein the specific LCG ID is differently configured depending on a type of the D2D discovery announcement.

7. The method of claim 1 , wherein calculating the buffer status comprises a ProSe protocol of the UE informing a media access control layer of the UE about the specific LCG ID.

8. The method of claim 1 , wherein the D2D discovery announcement includes a D2D discovery message.

9. The method of claim 1 , wherein the eNB is a master eNB or a secondary eNB.

10. A user equipment (UE) for configuring a device-to-device (D2D) discovery specific logical channel group (LCG) in a wireless communication system, the UE comprising:

a memory configured to store information;

a transceiver configured to transmit and receive information; and

a processor coupled to the memory and the transceiver, the processor configured to:

receive a configuration from a network indicating a specific LCG identifier (ID) for a D2D discovery announcement;

calculate a buffer status for the D2D discovery announcement;

configure the specific LCG ID to transmit the D2D discovery announcement;

construct a proximity based services (ProSe) buffer status report (BSR) for the D2D discovery announcement, the ProSe BSR including the calculated buffer status and the specific LCG ID configured to transmit the D2D discovery announcement and

control the transceiver to transmit the constructed ProSe BSR to an evolved NodeB (eNB).

11. The UE of claim 10 , wherein the configuration further indicates a specific value of a group index for the D2D discovery announcement.

12. The UE of claim 10 , wherein the configuration is received via system information or dedicated signaling.

13. The UE of claim 10 , wherein the configuration is received from the eNB, a mobility management entity, or a server in the network.

14. The UE of claim 10 , wherein the specific LCG ID is fixed for the D2D discovery announcement.

15. The UE of claim 10 , wherein the specific LCG ID is differently configured depending on a type of the D2D discovery announcement.

16. The UE of claim 10 , wherein calculating the buffer status for D2D discovery announcement comprises a ProSe protocol of the UE informing a media access control layer of the UE about the specific LCG ID.

17. The UE of claim 10 , wherein the D2D discovery announcement includes a D2D discovery message.

18. The UE of claim 10 , wherein the eNB is a master eNB or a secondary eNB.