Method and apparatus for handling link failure in wireless communication system

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

receiving, from a second wireless device over a first link, information informing a preliminary radio link failure (RLF) detected on a second link;

upon receiving the information informing the preliminary RLF, transmitting discovery messages for searching one or more other wireless devices; and

establishing a connection with a third wireless device among the one or more other wireless devices,

wherein the preliminary RLF is detected on the second link based on that a relaxed condition with respect to the RLF condition for detecting an RLF on the second link is satisfied,

wherein the first link is a link between the first wireless device and the second wireless device, and

wherein the second link is a link between the second wireless device and a node other than the first wireless device.

2. The method of claim 1 , wherein the node comprises a base station, and the second link comprises an access link.

3. The method of claim 2 , wherein the RLF condition comprises at least one of:

a first condition that i) consecutive out-of-synchronization (sync) indications of a threshold out-of-sync number are identified for a cell related to the base station, upon which an RLF timer starts, ii) consecutive in-sync indications of a threshold in-sync number are not identified for the cell related to the base station while the RLF timer is running, and iii) the RLF timer expires;

a second condition that a random access problem is identified for the cell related to the base station; or

a third condition that a maximum number of retransmissions has been reached for the cell related to the base station.

4. The method of claim 3 , wherein the relaxed condition is satisfied upon starting the RLF timer.

5. The method of claim 3 , wherein the relaxed condition comprises the first condition with the threshold in-sync number set to a lower value.

6. The method of claim 3 , wherein the relaxed condition comprises the third condition with the maximum number of retransmissions set to a lower value.

7. The method of claim 1 , wherein the node comprises a fourth wireless device, and the second link comprises a sidelink.

8. The method of claim 7 , wherein the RLF condition comprises a sidelink RLF condition that a number of consecutive discontinuous transmissions (DTXs) on the second link reaches a maximum consecutive DTX number configured by a network.

9. The method of claim 8 , wherein the relaxed condition comprises the sidelink RLF condition with the maximum consecutive DTX number set to a lower value.

10. The method of claim 7 , wherein the relaxed condition is satisfied based on that a number of consecutive negative-acknowledgements (NACKs) on the second link during a time period reaches a maximum consecutive NACK number configured by a network.

11. The method of claim 1 , further comprising:

upon receiving the information informing the preliminary RLF, monitoring an access link to search a cell; and

establishing a connection with the cell.

12. The method of claim 1 , further comprising:

upon receiving the information informing the preliminary RLF, performing a transmission resource reselection; and

performing a transmission on a resource determined based on the transmission resource reselection.

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

14. 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 second wireless device over a first link, information informing a preliminary radio link failure (RLF) detected on a second link;

upon receiving the information informing the preliminary RLF, control the transceiver to transmit discovery messages for searching one or more other wireless devices; and

establish a connection with a third wireless device among the one or more other wireless devices,

wherein the preliminary RLF is detected on the second link based on that a relaxed condition with respect to the RLF condition for detecting an RLF on the second link is satisfied,

wherein the first link is a link between the first wireless device and the second wireless device, and

wherein the second link is a link between the second wireless device and a node other than the first wireless device.

15. 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 second wireless device over a first link, information informing a preliminary radio link failure (RLF) detected on a second link;

upon receiving the information informing the preliminary RLF, transmit discovery messages for searching one or more other wireless devices; and

establish a connection with a third wireless device among the one or more other wireless devices,

wherein the preliminary RLF is detected on the second link based on that a relaxed condition with respect to the RLF condition for detecting an RLF on the second link is satisfied,

wherein the first link is a link between the first wireless device and the second wireless device, and

wherein the second link is a link between the second wireless device and a node other than the first wireless device.