Method for handling of a RRC connection request message of a remote UE by a relay UE in wireless communication system and a device therefor

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

receiving a first Radio Resource Control (RRC) connection request message for establishing RRC connection of a remote UE from the remote UE which is configured to connect to the relay UE via sidelink,

wherein the first RRC connection request message includes a service request message, an identity of the remote UE, a cause value, a call type, and Non Access Stratum (NAS) information,

wherein the cause value and the call type are provided by a first RRC layer of the remote UE, and the cause value and the call type are included in a header of the first RRC connection request message by a first adaptation layer of the remote UE,

wherein based on the relay UE being in RRC idle state, a second adaptation layer of the relay UE forwards the NAS information, the cause value and the call type to a NAS layer of the relay UE, only when an indication indicates that the NAS information is included in the first RRC connection request message, wherein the NAS information, the cause value and the call type are de-capsulated by a second RRC layer of the relay UE, and

wherein the indication is included in the first RRC connection request message by the first adaptation layer,

wherein the NAS layer of the relay UE triggers service request for the remote UE by transmitting the NAS information, the cause value and the call type to the second adaptation layer;

transmitting a second RRC connection request message with the identity of the remote UE to an eNB;

transmitting a first RRC connection setup message for the remote UE to the remote UE, after receiving a second RRC connection setup message for the relay UE from the eNB; and

transmitting a RRC connection setup complete message with the NAS information to the eNB.

2. The method according to claim 1 , wherein based on the NAS information for establishing RRC connection of the remote UE further including information related to a RRC connection setup complete message (Msg.5), the relay UE doesn't need to receive the RRC connection setup complete message from the remote UE to forward it to the eNB after RRC connection is setup by the remote UE.

3. The method according to claim 1 , wherein based on the second adaptation layer forwarding the received NAS information to the NAS layer of the relay UE, the second adaptation layer doesn't store the received NAS information.

4. The method according to claim 1 , wherein the remote UE is connected to a core network while the relay UE is not connected to the core network so that there is no establishment of EPC bearers between the relay UE and the core network.

5. The method according to claim 4 , wherein based on the NAS layer of the relay UE triggering service request for the relay UE in addition to the service request for the remote UE, the relay UE is configured to be connected to the core network so that there is establishment of EPC bearers between the relay UE and the core network.

6. The method according to claim 1 , wherein the relay UE relays data between the remote UE and the eNB.

7. A relay User Equipment (UE) configured to operate in a wireless communication system, the relay UE comprising:

a Radio Frequency (RF) module; and

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

receive a first Radio Resource Control (RRC) connection request message for establishing RRC connection of a remote UE from the remote UE which is configured to connect to the relay UE via sidelink,

wherein the first RRC connection request message includes a service request message, an identity of the remote UE, a cause value, a call type, and Non Access Stratum (NAS) information,

wherein the cause value and the call type are provided by a first RRC layer of the remote UE, and the cause value and the call type are included in a header of the first RRC connection request message by a first adaptation layer of the remote UE,

wherein based on the relay UE being in RRC idle state, a second adaptation layer of the relay UE is configured to forward the NAS information, the cause value and the call type to a NAS layer of the relay UE, only when an indication indicates that the NAS information is included in the first RRC connection request message, wherein the NAS information, the cause value and the call type are de-capsulated by a second RRC layer of the relay UE,

wherein the indication is included in the first RRC connection request message by the first adaptation layer,

wherein the NAS layer of the relay UE is configured to trigger service request for the remote UE by transmitting the NAS information, the cause value and the call type to the second adaptation layer;

transmit a second RRC connection request message with the identity of the remote UE to an eNB,

transmit a first RRC connection setup message for the remote UE to the remote UE, after receiving a second RRC connection setup message for the relay UE from the eNB, and

transmit a RRC connection setup complete message with the NAS information to the eNB.

8. The relay UE according to claim 7 , wherein based on the NAS information for establishing RRC connection of the remote UE further including information related to a RRC connection setup complete message (Msg.5), the relay UE doesn't need to receive the RRC connection setup complete message from the remote UE to forward it to the eNB after RRC connection is setup by the remote UE.

9. The relay UE according to claim 7 , wherein based on the second adaptation layer forwarding the received NAS information to the NAS layer of the relay UE, the second adaptation layer doesn't store the received NAS information.

10. The relay UE according to claim 7 , wherein the remote UE is connected to a core network while the relay UE is not connected to the core network so that there is no establishment of EPC bearers between the relay UE and the core network.

11. The relay UE according to claim 10 , wherein based on the NAS layer of the relay UE triggering service request for the relay UE in addition to the service request for the remote UE, the relay UE is configured to be connected to the core network so that there is establishment of EPC bearers between the relay UE and the core network.

12. The relay UE according to claim 7 , wherein the relay UE is configured to relay data between the remote UE and the eNB.

13. The method according to claim 1 , wherein the relay UE is capable of communicating with at least one of another UE, a UE related to an autonomous driving vehicle, a base station and/or a network.

14. The UE according to claim 7 , wherein the relay UE is capable of communicating with at least one of another UE, a UE related to an autonomous driving vehicle, a base station and/or a network.