Method and apparatus for handling radio link failure

1. A method performed by an integrated access and backhaul (IAB) node, the method comprising:

determining a failure in a backhaul link between the IAB node and an uplink IAB node;

in response to determining the failure in the backhaul link, determining whether there is another IAB node available for backhaul link reestablishment; and

in response to determining that there is not another IAB node available for backhaul link reestablishment, transmitting, to a downlink IAB node, a signaling message indicating the failure in the backhaul link.

2. The method of claim 1 , wherein the signaling message comprises a radio resource control (RRC) signaling message, a media access control (MAC) control element (CE) signaling message, or a physical layer signaling message.

3. The method of claim 2 , wherein the RRC signaling message comprises an indication for the failure in the backhaul link and information indicating two nodes which terminate the backhaul link, or a RRC connection release message having a release cause indication for the failure in the backhaul link;

wherein the MAC CE signaling message comprises the indication for the failure in the backhaul link or the information indicating the two nodes which terminate the backhaul link; and

wherein the physical layer signaling message comprises the indication for the failure in the backhaul link.

4. The method of claim 3 , wherein the information indicating the two nodes comprises node identifiers for the two nodes.

5. The method of claim 1 , wherein the signaling message is transmitted in response to an expiry of a timer and a determination that no candidate node is available for backhaul link re-establishment.

6. The method of claim 1 , further comprising:

selecting a candidate node for backhaul link re-establishment in response to an expiry of a timer; and

performing backhaul link re-establishment with the selected candidate node;

wherein the signaling message is transmitted in response to a failure in the backhaul link re-establishment.

7. The method of claim 1 , further comprising:

receiving the signaling message indicating the failure in the backhaul link.

8. The method of claim 7 , wherein the signaling message is transmitted in response to a determination that no candidate node is available for backhaul link re-establishment.

9. The method of claim 7 , further comprising:

selecting a candidate node for backhaul link re-establishment; and

performing backhaul link re-establishment with the selected candidate node;

wherein the signaling message is transmitted in response to a failure in the backhaul link re-establishment.

10. A method performed by an integrated access and backhaul (IAB) node, the method comprising:

receiving, from a first uplink IAB node, a signaling message indicating a failure in a backhaul link, wherein the signaling message indicates that the first uplink IAB node determined a failure in the backhaul link between the first uplink IAB node and a second uplink IAB node, and that the first uplink IAB node determined there was not another IAB node available for backhaul link reestablishment.

11. The method of claim 10 , wherein the signaling message comprises an indication for the failure in the backhaul link and information indicating two nodes which terminate the backhaul link, and the information comprises node identifiers for the two nodes.

12. A method performed by an integrated access and backhaul (IAB) node, the method comprising:

determining a failure in a backhaul link between the IAB node and an uplink IAB node;

in response to determining the failure in the backhaul link, selecting a candidate node for backhaul link re-establishment; and

transmitting a re-establishment request to the candidate node.

13. The method of claim 12 , wherein selecting the candidate node for backhaul link re-establishment comprises:

selecting the candidate node in response to an expiry of a timer or a reception of a signaling message indicating the failure in the backhaul link.

14. The method of claim 12 , further comprising:

determining that a channel quality between the candidate node and the IAB node is equal to or greater than a threshold for backhaul link selection.

15. The method of claim 14 , further comprising:

receiving a radio resource control (RRC) signaling message from a base station, wherein the RRC signaling message comprises the threshold for backhaul link selection.

16. The method of claim 14 , wherein selecting the candidate node for backhaul link re-establishment comprises:

selecting the candidate node from one or more candidate nodes for backhaul link, wherein the one or more candidate nodes and the IAB node are connected to the same base station.

17. The method of claim 14 , wherein selecting the candidate node for backhaul link re-establishment comprises:

determining one or more candidate nodes for backhaul link, wherein the one or more candidate nodes and the IAB node are connected to different base stations; and

randomly selecting the candidate node from the one or more candidate nodes for backhaul link.

18. The method of claim 12 , further comprising:

initiating a timer in response to transmission of the re-establishment request.

19. The method of claim 18 , further comprising:

stopping the timer in response to a successful link establishment between the IAB node and the candidate node; and

in response to an expiry of the timer:

transmitting, to another communication device, a signaling message indicating the failure in the backhaul link; and

entering into an idle mode.

20. An integrated access and backhaul (IAB) node, comprising:

at least one memory; and

at least one processor coupled with the at least one memory and configured to cause the IAB node to:

determine a failure in a backhaul link between the IAB node and an uplink IAB node;

in response to determining the failure in the backhaul link, determine whether there is another IAB node available for backhaul link reestablishment; and

in response to determining that there is not another IAB node available for backhaul link reestablishment, transmit, to a downlink IAB node, a signaling message indicating the failure in the backhaul link.