Method and apparatus for mobility in wireless communication system

1. A method performed by a wireless device in a wireless communication system, the method comprising:

receiving, from a source cell, information for a dual active protocol stack (DAPS) mobility procedure;

performing, in the DAPS mobility procedure, a random access to a target cell while maintaining a connection with the source cell;

performing, by the wireless device while performing the random access to the target cell in the DAPS mobility procedure, a radio link monitoring (RLM) on a radio link for the source cell, wherein the RLM comprises monitoring a number of consecutive out-of-sync indications received on the radio link for the source cell;

after detecting a radio link failure (RLF) for the source cell based on the RLM, stopping a transmission on the radio link for the source cell during the DAPS mobility procedure; and

transmitting, to the target cell, an RLF indication indicating the RLF for the source cell,

wherein the RLF indication comprises at least one of measurement results, or a cause of the RLF for the source cell.

2. The method of claim 1 , wherein the detecting of the RLF comprises:

detecting the RLF for the source cell based on that the number of received consecutive out-of-sync indications reaches a threshold number,

wherein the threshold number comprises at least one of a predetermined threshold value, or a threshold value received from a network.

3. The method of claim 2 , wherein the detecting of the RLF comprises:

declaring the RLF upon an expiry of a timer,

wherein the timer starts upon receiving the consecutive out of sync indications of the threshold number on the radio link for the source cell.

4. The method of claim 1 , wherein the transmitting of the RLF indication comprises transmitting, to the target cell, a mobility complete message comprising the RLF indication.

5. The method of claim 1 , further comprising:

communicating with the source cell based on a source cell configuration during the DAPS mobility procedure; and

releasing the source cell configuration after detecting the RLF on the radio link for the source cell.

6. The method of claim 5 , wherein the releasing of the source cell configuration comprises:

releasing the source cell configuration without receiving, from the target cell, an indication to release the source cell configuration.

7. The method of claim 1 , further comprising:

receiving, from the source cell, an indication to perform operations related to a DAPS handover; and

initiating the DAPS handover procedure upon a reception of the indication.

8. The method of claim 1 , further comprising:

performing an RLM on a radio link for the target cell.

9. The method of claim 8 , wherein the performing of the RLM on the radio link for the source cell comprises performing the RLM on the radio link for the source cell until transmitting a mobility complete message to the target cell, and

wherein the performing of the RLM on the radio link for the target cell comprises performing the RLM on the radio link for the target cell after transmitting the mobility complete message to the target cell.

10. The method of claim 1 , wherein the DAPS mobility procedure is a mobility procedure in which:

both of protocol stacks in the source cell and protocol stacks in the target cell are active; or

radio bearers and a configuration of the source cell and the target cell are maintained until the source cell is released.

11. The method of claim 1 , wherein the wireless device is in communication with at least one of a user equipment, a network, or autonomous vehicles other than the wireless device.

12. A wireless device in a wireless communication system comprising:

a transceiver;

a memory; and

at least one processor operatively coupled to the transceiver and the memory, and configured to:

control the transceiver to receive, from a source cell, information for a dual active protocol stack (DAPS) mobility procedure;

perform, in the DAPS mobility procedure, a random access to a target cell while maintaining a connection with the source cell;

perform, by the wireless device while performing the random access to the target cell in the DAPS mobility procedure, a radio link monitoring (RLM) on a radio link for the source cell, wherein the RLM comprises monitoring a number of consecutive out-of-sync indications received on the radio link for the source cell;

after detecting a radio link failure (RLF) for the source cell based on the RLM, stop a transmission on the radio link for the source cell during the DAPS mobility procedure; and

control the transceiver to transmit, to the target cell, an RLF indication indicating the RLF for the source cell,

wherein the RLF indication comprises at least one of measurement results, or a cause of the RLF for the source cell.

13. A non-transitory computer-readable medium having stored thereon a plurality of instructions, wherein the plurality of instructions, when executed by a processor of a wireless device, cause the wireless device to:

receive, from a source cell, information for a dual active protocol stack (DAPS) mobility procedure;

perform, in the DAPS mobility procedure, a random access to a target cell while maintaining a connection with the source cell;

perform, by the wireless device while performing the random access to the target cell in the DAPS mobility procedure, a radio link monitoring (RLM) on a radio link for the source cell, wherein the RLM comprises monitoring a number of consecutive out-of-sync indications received on the radio link for the source cell;

after detecting a radio link failure (RLF) for the source cell based on the RLM, stop a transmission on the radio link for the source cell during the DAPS mobility procedure; and

transmit, to the target cell, an RLF indication indicating the RLF for the source cell,

wherein the RLF indication comprises at least one of measurement results, or a cause of the RLF for the source cell.