Method and apparatus for handling connection re-establishment in wireless communication system

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

receiving a conditional handover (CHO) command comprising a CHO execution condition for a target cell, and a T304 timer;

evaluating the CHO execution condition for the target cell;

initiating a CHO from a source cell to the target cell based on the CHO execution condition for the target cell being satisfied;

starting the T304 timer upon initiating the CHO to the target cell;

performing an access to the target cell while the T304 timer is running, wherein the wireless device monitors a number of consecutive out-of-sync indications for the source cell while the T304 timer is running;

starting a T310 timer upon the number of consecutive out-of-sync indications reaching a number N310;

detecting a radio link failure (RLF) for the source cell upon an expiry of the T310 timer;

determining whether the T304 timer is still running when the RLF is detected;

based on a determination that the T304 timer is still running when the RLF is detected, delaying performing a radio resource control (RRC) re-establishment; and

performing the RRC re-establishment upon an expiry of the T304 timer.

2. The method of claim 1 , wherein the performing of the RRC re-establishment is prohibited while the T304 timer is running.

3. The method of claim 2 , wherein the performing of the RRC re-establishment is prohibited before the expiry of the T304 timer and after the RLF is detected.

4. The method of claim 1 , wherein the number N310 comprises at least one of a predetermined threshold value, or a threshold value received from a network.

5. The method of claim 4 , wherein the RLF timer starts upon receiving the consecutive out of sync indications of the threshold number on the radio link for the source cell.

6. The method of claim 1 , wherein the CHO execution condition for the target cell is satisfied based on an entering condition being satisfied for at least a time-to-trigger (TTT), and

wherein the entering condition comprises at least one of:

an event A2 entering condition that a signal quality for the source cell is worse than a serving cell threshold;

an event A3 entering condition that a signal quality for the target cell is better than that for the source cell more than or equal to an offset value;

an event A4 entering condition that a signal quality for the target cell is better than a neighbor cell threshold; or

an event A5 entering condition that a signal quality for the target cell is better than a neighbor cell threshold and a signal quality for the source cell is lower than a serving cell threshold.

7. The method of claim 1 , wherein the performing of the RRC re-establishment comprises performing the RRC re-establishment upon the expiry of the T304 timer after the T310 timer expires.

8. The method of claim 1 , wherein the performing of the RRC re-establishment is prohibited based on the T304 timer running and the expiry of the T310 timer.

9. 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.

10. The method of claim 1 , wherein the CHO fails upon the expiry of the T304 timer.

11. 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, wherein the memory stores instructions that, based on being executed by the at least one processor, perform operations comprising:

receiving a conditional handover (CHO) command comprising a CHO execution condition for a target cell, and a T304 timer;

evaluating the CHO execution condition for the target cell;

initiating a CHO from a source cell to the target cell based on the CHO execution condition for the target cell being satisfied;

starting the T304 timer upon initiating the CHO to the target cell;

performing an access to the target cell while the T304 timer is running, wherein the wireless device monitors a number of consecutive out-of-sync indications for the source cell while the T304 timer is running;

starting a T310 timer upon the number of consecutive out-of-sync indications reaching a number N310;

detecting a radio link failure (RLF) for the source cell upon an expiry of the T310 timer;

determining whether the T304 timer is still running when the RLF is detected;

based on a determination that the T304 timer is still running when the RLF is detected, delaying performing a radio resource control (RRC) re-establishment; and

performing the RRC re-establishment upon an expiry of the T304 timer.

12. A processor for a wireless device in a wireless communication system, wherein the processor is configured to control the wireless device to perform operations comprising:

receiving a conditional handover (CHO) command comprising a CHO execution condition for a target cell, and a T304 timer;

evaluating the CHO execution condition for the target cell;

initiating a CHO from a source cell to the target cell based on the CHO execution condition for the target cell being satisfied;

starting the T304 timer upon initiating the CHO to the target cell;

performing an access to the target cell while the T304 timer is running, wherein the wireless device monitors a number of consecutive out-of-sync indications for the source cell while the T304 timer is running;

starting a T310 timer upon the number of consecutive out-of-sync indications reaching a number N310;

detecting a radio link failure (RLF) for the source cell upon an expiry of the T310 timer;

determining whether the T304 timer is still running when the RLF is detected;

based on a determination that the T304 timer is still running when the RLF is detected, delaying performing a radio resource control (RRC) re-establishment; and

performing the RRC re-establishment upon an expiry of the T304 timer.