Method and apparatus for handling sidelink identifier change in a wireless communication system

1. A method for a second UE (User Equipment) to change sidelink identity associated with a first UE for a sidelink unicast link, comprising:

establishing the sidelink unicast link with the first UE, wherein a first lower-layer identity of the first UE and a second lower-layer identity of the second UE are used for communicating between the first UE and the second UE via the sidelink unicast link;

receiving a Link Identifier Update Request message from the first UE, wherein the Link Identifier Update Request message includes a new first lower-layer identity of the first UE and the Link Identifier Update Request message is transmitted using the first lower-layer identity as a source;

transmitting a Link Identifier Update Response message to the first UE in response to reception of the Link Identifier Update Request message, wherein the Link Identifier Update Response message is transmitted using the first lower-layer identity as a destination; and

continuing, after the Link Identifier Update Response message is transmitted, to use the first lower-layer identity for examining the source of each sidelink data frame received from the first UE until a sidelink data frame with the source set to the new first lower-layer identity is received from the first UE, wherein only the new first lower-layer identity is used for receiving following one or more sidelink data frames after the sidelink data frame is received.

2. The method of claim 1 , further comprising:

using the first lower-layer identity as a source and the new first lower-layer identity as a source for filtering received sidelink data frames before a very first sidelink data frame with the new first lower-layer identity is received from the first UE or successful transmission of the Link Identifier Update Response message has been confirmed.

3. The method of claim 1 , further comprising:

using the new first lower-layer identity as a source for filtering received sidelink data frames after a very first sidelink data frame with the new first lower-layer identity is received from the first UE or successful transmission of the Link Identifier Update Response message has been confirmed.

4. The method of claim 1 , wherein a lower-layer identity of the first lower-layer identity, the new first lower-layer identity, and/or the second lower-layer identity is a Layer-2 identity or a Layer-1 identity.

5. A method for a first UE (User Equipment) to change sidelink identity for a sidelink unicast link associated with a second UE, comprising:

establishing the sidelink unicast link with the second UE, wherein a first lower-layer identity of the first UE and a second lower-layer identity of the second UE are used for communicating between the first UE and the second UE via the sidelink unicast link;

transmitting a Link Identifier Update Request message to the second UE, wherein the Link Identifier Update Request message includes a new first lower-layer identity of the first UE and the Link Identifier Update Request message is transmitted using the first lower-layer identity as a source;

receiving a Link Identifier Update Response message from the second UE, wherein the Link Identifier Update Response message is transmitted using the first lower-layer identity as a destination; and

continuing, after the Link Identifier Update Response message is received, to use the first lower-layer identity for examining the destination of each sidelink data frame received from the second U E until a sidelink data frame with the destination set to the new first lower-layer identity is received from the second UE, wherein only the new first lower-layer identity is used for receiving following one or more sidelink data frames after the sidelink data frame is received.

6. The method of claim 5 , further comprising:

using the first lower-layer identity as a destination and the new first lower-layer identity as a destination for filtering received sidelink data frames before a very first sidelink data frame with the new first lower-layer identity is received from the second UE.

7. The method of claim 5 , further comprising:

using the new first lower-layer identity as a destination for filtering received sidelink data frames after a very first sidelink data frame with the new first lower-layer identity is received from the second UE.

8. The method of claim 5 , wherein a lower-layer identity of the first lower-layer identity, the new first lower-layer identity, and/or the second lower-layer identity is a Layer-2 identity or a Layer-1 identity.

9. A second UE (User Equipment), comprising:

a processor; and

a memory operatively coupled to the processor, wherein the processor is configured to execute a program code stored in the memory to:

establish the sidelink unicast link with the first UE, wherein a first lower-layer identity of the first UE and a second lower-layer identity of the second UE are used for communicating between the first UE and the second UE via the sidelink unicast link;

receive a Link Identifier Update Request message from the first UE, wherein the Link Identifier Update Request message includes a new first lower-layer identity of the first UE and the Link Identifier Update Request message is transmitted using the first lower-layer identity as a source;

transmit a Link Identifier Update Response message to the first UE in response to

reception of the Link Identifier Update Request message, wherein the Link Identifier Update Response message is transmitted using the first lower-layer identity as a destination; and

continue, after the Link Identifier Update Response message is transmitted, to use the first lower-layer identity for examining the source of each sidelink data frame received from the first UE until a sidelink data frame with the source set to the new first lower-layer identity is received from the first UE, wherein only the new first lower-layer identity is used for receiving following one or more sidelink data frames after the sidelink data frame is received.

10. The second UE of claim 9 , wherein the processor is further configured to execute a program code stored in the memory to:

use the first lower-layer identity as a source and the new first lower-layer identity as a source for filtering received sidelink data frames before a very first sidelink data frame with the new first lower-layer identity is received from the first UE or successful transmission of the Link Identifier Update Response message has been confirmed.

11. The second UE of claim 9 , wherein the processor is further configured to execute a program code stored in the memory to:

use the new first lower-layer identity as a source for filtering received sidelink data frames after a very first sidelink data frame with the new first lower-layer identity is received from the first UE or successful transmission of the Link Identifier Update Response message has been confirmed.

12. The second UE of claim 9 , wherein a lower-layer identity of the first lower-layer identity, the new first lower-layer identity, and/or the second lower-layer identity is a Layer-2 identity or a Layer-1 identity.

13. 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 stored in the memory to:

establish the sidelink unicast link with the second UE, wherein a first lower-layer identity of the first UE and a second lower-layer identity of the second UE are used for communicating between the first UE and the second UE via the sidelink unicast link;

transmit a Link Identifier Update Request message to the second UE, wherein the Link Identifier Update Request message includes a new first lower-layer identity of the first UE and the Link Identifier Update Request message is transmitted using the first lower-layer identity as a source;

receive a Link Identifier Update Response message from the second UE, wherein the Link Identifier Update Response message is transmitted using the first lower-layer identity as a destination; and

continue, after the Link Identifier Update Response message is received, to use the first lower-layer identity for examining the destination of each sidelink data frame received from the second UE until a sidelink data frame with the destination set to the new first lower-layer identity is received from the second UE, wherein only the new first lower-layer identity is used for receiving following one or more sidelink data frames after the sidelink data frame is received.

14. The first UE of claim 13 , wherein the processor is further configured to execute a program code stored in the memory to:

use the first lower-layer identity as a destination and the new first lower-layer identity as a destination for filtering received sidelink data frames before a very first sidelink data frame with the new first lower-layer identity is received from the second UE.

15. The first UE of claim 13 , wherein the processor is further configured to execute a program code stored in the memory to:

use the new first lower-layer identity as a destination for filtering received sidelink data frames after a very first sidelink data frame with the new first lower-layer identity is received from the second UE.

16. The first UE of claim 13 , wherein a lower-layer identity of the first lower-layer identity, the new first lower-layer identity, and/or the second lower-layer identity is a Layer-2 identity or a Layer-1 identity.