Method for performing inter PLMN discovery by a user equipment (UE) in device-to-device (D2D) communication

1. A method for performing discovery, by a user equipment (UE), the method comprising:

transmitting, by a user equipment (UE), a discovery service authorization request to a device to device (D2D) function in a home public land mobile network (home PLMN);

receiving, from the D2D function in the home PLMN, authorization information for a list of PLMNs where the UE is authorized to perform a discovery, wherein the authorization information is transferred from a D2D function in a visited PLMN to the D2D function in the home PLMN; and

performing the discovery based on the authorization information.

2. The method of claim 1 , wherein performing the discovery based on the authorization information comprises:

receiving first information including a list of frequencies and PLMN identifiers (IDs) from a serving cell;

receiving second information through at least one frequency of the list of frequencies for monitoring a discovery message on the at least one frequency;

identifying discovery configuration in the second information; and

monitoring the discovery message based on the discovery configuration.

3. The method of claim 2 , wherein the first information is broadcast in a system information block (SIB).

4. The method of claim 2 , wherein the first information is signaled by the serving cell of the UE in dedicated signaling.

5. The method of claim 2 , wherein the UE monitors the discovery message during a discontinuous reception (DRX) mode.

6. The method of claim 1 , wherein the discovery service authorization request includes at least one of a D2D App ID, a UE Identity, a monitor command and an Application ID for monitoring.

7. The method of claim 6 , wherein the UE Identity is set to an International Mobile Subscriber Identity (IMSI).

8. The method of claim 1 , wherein the authorization information includes at least one of a related D2D application code or a D2D Application mask for a PLMN from the list of PLMNs where the UE is authorized to perform the discovery.

9. The method of claim 1 , further comprising, storing the list of PLMNs where the UE is authorized to perform a discovery in a universal integrated circuit card (UICC) module of the UE.

10. A user equipment (UE) for monitoring a discovery message, the UE comprising:

a receiver configured to:

transmit a discovery service authorization request to a device to device (D2D) function in a home public land mobile network (home PLMN), and

receive, from the D2D function in the home PLMN, authorization information for a list of PLMNs where the UE is authorized to perform a discovery, wherein the authorization information is transferred from a D2D function in a visited PLMN to the D2D function in the home PLMN; and

a controller configured to perform the discovery based on the authorization information.

11. The UE of the claim 10 , wherein:

the receiver is further configured to:

receive first information including a list of frequencies and PLMN identifiers (IDs) from a serving cell; and

receive second information through at least one frequency of the list of frequencies for monitoring a discovery message on the at least one frequency, and

the controller is further configured to:

identify discovery configuration in the second information; and

monitor the discovery message based on the discovery configuration.

12. The UE of claim 11 , wherein the first information is broadcast in a system information block (SIB).

13. The UE of claim 11 , wherein the first information is signaled by the serving cell of the UE in dedicated signaling.

14. The UE of claim 11 , wherein the controller is configured to monitor the discovery message during a discontinuous reception (DRX) mode.

15. The UE of claim 10 , wherein the discovery service authorization request includes at least one of a D2D App ID, a UE Identity, a monitor command and an Application ID for monitoring.

16. The UE of claim 15 , wherein the UE Identity is set to an International Mobile Subscriber Identity (IMSI).

17. The UE of claim 10 , wherein the authorization information includes at least one of a related D2D application code or a D2D Application mask for a PLMN from the list of PLMNs where the UE is authorized to perform the discovery.

18. The UE of claim 10 , further comprising a universal integrated circuit card module storing the list of PLMNs where the UE is authorized to perform a discovery.

19. A method of a device to device (D2D) function in a home public land mobile network (home PLMN), the method comprising:

receiving, from a user equipment (UE), a discovery service authorization request;

receiving, from a home subscriber server (HSS), a subscription information of the UE if there is no associated UE context in D2D function in the home PLMN; and

transmitting, to the UE, authorization information for a list of PLMNs where the UE is authorized to perform a discovery, wherein the authorization information is transferred from a D2D function in a visited PLMN to the D2D function in the home PLMN.

20. An apparatus of a device to device (D2D) function in a home public land mobile network (home PLMN), the apparatus comprising:

a controller configured to:

receive, from a user equipment (UE), a discovery service authorization request;

receive, from a home subscriber server (HSS), a subscription information of the UE if there is no associated UE context in D2D function in the home PLMN; and

transmit, to the UE, authorization information for a list of PLMNs where the UE is authorized to perform a discovery, wherein the authorization information is transferred from a D2D function in a visited PLMN to the D2D function in the home PLMN.