Method and apparatus for UL synchronization handling for satellite switch in a wireless communication system

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

receiving, from an upper layer, an indication of an uplink synchronization loss; and

in response to receiving the indication of the uplink synchronization loss:

not performing uplink transmission on a serving cell; and

determining whether to flush one or more Hybrid Automatic Repeat Request (HARQ) buffers based on whether the uplink synchronization loss is due to a satellite switch.

2. The method of claim 1 , further comprising:

not flushing the one or more HARQ buffers if at least the uplink synchronization loss is due to the satellite switch; and

flushing the one or more HARQ buffers if at least the uplink synchronization loss is not due to the satellite switch.

3. The method of claim 1 , further comprising:

receiving a system information, wherein the system information includes at least an indication for a satellite switch;

initiating a procedure of satellite switch based on the indication for the satellite switch being included in the system information; and

indicating the uplink synchronization loss, in response to initiating the procedure of the satellite switch.

4. The method of claim 3 , wherein the indication for the satellite switch is satSwitchWithResync and/or the system information is SIB19.

5. The method of claim 1 , further comprising:

starting or restarting a timer upon receiving a system information; and

indicating the uplink synchronization loss, in response to expiry of the timer.

6. The method of claim 5 , wherein the timer is T430 and/or the system information is SIB19.

7. A method of a User Equipment (UE), comprising:

receiving a system information, wherein the system information includes at least a first Non-Terrestrial Network (NTN) configuration, a time information, and an indication for a satellite switch;

starting or restarting a timer based on the first NTN configuration, in response to receiving the system information;

initiating a procedure of satellite switch based on the indication for the satellite switch being included in the system information;

stopping the timer upon a timing indicated by the time information;

considering Uplink (UL) synchronization is lost, after stopping the timer;

determining whether to flush one or more Hybrid Automatic Repeat Request (HARQ) buffers based on whether the UL synchronization is lost due to satellite switch;

performing Downlink (DL) synchronization with a cell served by a satellite indicated in the indication for the satellite switch;

starting the timer based on a second NTN configuration included in the indication for the satellite switch, after performing the DL synchronization; and

considering the UL synchronization is obtained, after starting the timer.

8. The method of claim 7 , wherein the time information indicates when an NTN cell is going to stop serving an area the NTN cell is currently covering and/or the time information is t-Service.

9. The method of claim 7 , wherein the first NTN configuration includes at least a first validity duration and a first epoch time, and/or the second NTN configuration includes at least a second validity duration and a second epoch time.

10. The method of claim 9 , wherein the UE starts or restarts the timer with a timer value set to the first validity duration from a subframe indicated by the first epoch time, and/or the UE starts the timer with a timer value set to the second validity duration from a subframe indicated by the second epoch time.

11. A User Equipment (UE), comprising:

a memory; and

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

receive, from an upper layer, an indication of an uplink synchronization loss;

in response to receiving the indication of the uplink synchronization loss:

not perform uplink transmission on a serving cell; and

determine whether to flush one or more Hybrid Automatic Repeat Request (HARQ) buffers based on whether the uplink synchronization loss is due to a satellite switch.

12. The UE of claim 11 , wherein the processor is further configured to execute the program code to:

not flush the one or more HARQ buffers if at least the uplink synchronization loss is due to the satellite switch; and

flush the one or more HARQ buffers if at least the uplink synchronization loss is not due to the satellite switch.

13. The UE of claim 11 , wherein the processor is further configured to execute the program code to:

receive a system information, wherein the system information includes at least an indication for a satellite switch;

initiate a procedure of satellite switch based on the indication for the satellite switch being included in the system information; and

indicate the uplink synchronization loss, in response to initiating the procedure of the satellite switch.

14. The UE of claim 13 , wherein the indication for the satellite switch is satSwitchWithResync and/or the system information is SIB19.

15. The UE of claim 11 , wherein the processor is further configured to execute the program code to:

start or restart a timer upon receiving a system information; and

indicate the uplink synchronization loss, in response to expiry of the timer.

16. The UE of claim 15 , wherein the timer is T430 and/or the system information is SIB19.