Method and apparatus for establishing sidelink radio bearer for UE-to-UE relay communication in a wireless communication system

1. A method for a first User Equipment (UE), comprising:

establishing a Sidelink (SL) Data Radio Bearer (DRB) for transmission to a second UE directly or via a relay UE, wherein a configuration of the SL DRB is identified by a configuration index, and the SL DRB is mapped to a SL Radio Link Control (RLC) channel established between the first UE and the second UE or between the first UE and the relay UE, and wherein the SL RLC channel is identified by a logical channel identity (LCID);

ciphering, using at least the LCID as input to ciphering algorithm, a sidelink packet to be sent to the second UE on the SL DRB if the SL DRB is established for transmission to the second UE directly; and

ciphering, using at least the configuration index as input to ciphering algorithm, the sidelink packet to be sent to the second UE on the SL DRB if the SL DRB is established for transmission to the second UE via the relay UE.

2. The method of claim 1 , wherein the configuration index is included in a header of an adaptation layer Protocol Data Unit (PDU).

3. The method of claim 2 , wherein the header and the sidelink packet are included in the adaptation layer PDU.

4. A method for a second User Equipment (UE), comprising:

establishing a Sidelink (SL) Data Radio Bearer (DRB) for reception from a first UE directly or via a relay UE, wherein a configuration of the SL DRB is identified by a configuration index, and the SL DRB is mapped to a SL Radio Link Control (RLC) channel established between the first UE and the second UE or between the second UE and the relay UE, and wherein the SL RLC channel is identified by a logical channel identity (LCID);

deciphering, using at least the LCID as input to deciphering algorithm, a sidelink packet received from the first UE on the SL DRB if the SL DRB is established for reception from the first UE directly; and

deciphering, using at least the configuration index as input to deciphering algorithm, the sidelink packet received from the first UE on the SL DRB if the SL DRB is established for reception from the first UE via the relay UE.

5. The method of claim 4 , wherein the configuration index is included in a header of an adaptation layer Protocol Data Unit (PDUI.

6. The method of claim 5 , wherein the header and the sidelink packet are included in the adaptation layer PDU.

7. A first UE (User Equipment), comprising:

a processor; and a memory operatively coupled to the processor, wherein the processor is configured to execute a program code to: establish a Sidelink (SL) Data Radio Bearer (DRB) for transmission to a second UE directly or via a relay UE, wherein a configuration of the SL DRB is identified by a configuration index, and the SL DRB is mapped to a SL Radio Link Control (RLC) channel established between the first UE and the second UE or between the first UE and the relay UE, and wherein the SL RLC channel is identified by a logical channel identity (LCID);

cipher, using at least the LCID as input to ciphering algorithm, a sidelink packet to be sent to the second UE via the relay UE on the SL DRB if the SL DRB is established for transmission to the second UE directly; and

cipher, using at least the configuration index as input to ciphering algorithm, the sidelink packet to be sent to the second UE on the SL DRB if the SL DRB is established for transmission to the second UE via the relay UE.

8. The first UE of claim 7 , wherein the configuration index is included in a header of an adaptation layer Protocol Data Unit (PDU).

9. The first UE of claim 8 , wherein the header and the sidelink packet are included in the adaptation layer PDU.