Method and apparatus for requesting SIB in wireless communication system

1. A method for requesting, by a user equipment (UE), a system information block (SIB) in a wireless communication system, the method comprising:

receiving an SIB list comprising one or more SIBs supported by a cell from a radio access network (RAN);

receiving, from the RAN, SIB broadcast information informing the UE whether an SIB supported by the cell is broadcast in a broadcast control channel (BCCH) period;

detecting a missing SIB based on the SIB list and the SIB broadcast information; and

requesting the missing SIB from the RAN,

wherein the missing SIB is an SIB that is not broadcast in the BCCH period among the SIBs comprised in the SIB list.

2. The method of claim 1 , wherein the BCCH period is a current BCCH period or a next BCCH period.

3. The method of claim 1 , wherein the BCCH period is one of a BCCH modification period or a BCCH repetition period.

4. The method of claim 1 , wherein the missing SIB is an SIB that the UE needs to receive from the RAN in order to perform a particular service.

5. The method of claim 4 , wherein the particular service comprises at least one of a multimedia broadcast/multicast service (MBMS) service, a device-to-device (D2D) service, a vehicle-to-everything (V2X) service, or wireless local area network (WLAN) interworking.

6. The method of claim 1 , wherein the missing SIB is requested from the RAN by informing the RAN of a service associated with the missing SIB.

7. The method of claim 1 , wherein the SIB list and the SIB broadcast information are received by the UE via particular system information.

8. The method of claim 7 , wherein the particular system information is system information that is always broadcast by the RAN.

9. The method of claim 1 , further comprising:

receiving a probability factor from the RAN, wherein based on a random number drawn by the UE that is less than or equal to the probability factor, the missing SIB is requested from the RAN.

10. The method of claim 1 , further comprising:

receiving, from the RAN, a value tag informing the UE of system information to be requested from the RAN, wherein based on the missing SIB that is the system information informed by the value tag, the missing SIB is requested from the RAN.

11. The method of claim 1 , further comprising:

receiving, from the RAN, a number of a type of SIB to be requested from the RAN, wherein based on the missing SIB that matches the number of the type of SIB to be requested, the missing SIB is requested from the RAN.

12. The method of claim 1 , further comprising:

receiving, from the RAN, a set of SIBs to be requested from the RAN,

wherein based on the missing SIB in the set of SIBs to be requested, the missing SIB is requested from the RAN.

13. The method of claim 1 , further comprising:

receiving the missing SIB from the RAN in response to the request.

14. A user equipment (UE) for requesting a system information block (SIB) in a wireless communication system, the UE comprising:

a memory;

a transceiver; and

a processor functionally in communication with the memory and the transceiver,

wherein the processor is configured to:

control the transceiver to receive an SIB list comprising one or more SIBs supported by a cell from a radio access network (RAN);

control the transceiver to receive, from the RAN, SIB broadcast information informing the UE whether an SIB supported by the cell is broadcast in a broadcast control channel (BCCH) period;

detect a missing SIB based on the SIB list and the SIB broadcast information; and

control the transceiver to request the missing SIB from the RAN,

wherein the missing SIB is an SIB that is not broadcast in the BCCH period among the SIBs comprised in the SIB list.