Maintenance of multi-beam unicast link for sidelink communications

1. An apparatus for wireless communications at a first user equipment (UE), comprising:

a memory comprising instructions; and

one or more processors configured to execute the instructions and cause the apparatus to:

send a first sidelink communication to a second UE using a first beam pair of a unicast link with the second UE, wherein the first beam pair includes a first transmission beam and a first reception beam;

detect a fault associated with at least one of the first transmission beam or the first reception beam;

based on the detected fault, update a value of at least one discontinuous transmission (DTX) count associated with at least one of the first transmission beam or the first reception beam;

determine that the value of the at least one DTX count meets a threshold; and

based on the value of the at least one DTX count meeting the threshold, initiate at least one of beam refinement or beam recovery of the first beam pair.

2. The apparatus of claim 1 , wherein the one or more processors are further configured to cause the apparatus to:

send a second sidelink communication to the second UE, wherein the fault is based on whether a response to the second sidelink communication is received.

3. The apparatus of claim 2 , wherein the second sidelink communication includes a hybrid automatic repeat request (HARQ) associated with the first sidelink communication.

4. The apparatus of claim 3 , wherein the one or more processors are further configured to cause the apparatus to:

obtain a response to the HARQ indicating successful reception of the first sidelink communication; and

determine that the fault is associated with the first reception beam.

5. The apparatus of claim 3 , wherein the one or more processors are further configured to cause the apparatus to:

obtain a response to the HARQ indicating failed reception of the first sidelink communication; and

determine that the fault is associated with the first transmission beam.

6. The apparatus of claim 5 , wherein the response to the HARQ indicates failed reception of at least one of a control message or a data message associated with the first sidelink communication.

7. The apparatus of claim 2 , wherein the second sidelink communication includes a sidelink control information (SCI) codebook request.

8. The apparatus of claim 7 , wherein the SCI codebook request includes one or more slot indices associated with a first SCI corresponding to the first sidelink communication.

9. The apparatus of claim 7 , wherein the one or more processors are further configured to cause the apparatus to:

obtain an SCI codebook indicating a reception status of a first SCI corresponding to the first sidelink communication.

10. The apparatus of claim 1 , wherein the one or more processors are further configured to cause the apparatus to:

determine, based on the fault, a second beam pair of the unicast link with the second UE; and

send a second sidelink communication to the second UE using the second beam pair.

11. The apparatus of claim 10 , wherein, to determine the second beam pair of the unicast link with the second UE, the one or more processors are further configured to cause the apparatus to:

initiate beam refinement of at least one of the first transmission beam or the first reception beam.

12. The apparatus of claim 10 , wherein the second beam pair includes the first transmission beam and a second reception beam.

13. The apparatus of claim 12 , wherein the one or more processors are further configured to cause the apparatus to:

obtain an acknowledgment (ACK) corresponding to the second sidelink communication; and

determine that the fault is associated with the first reception beam.

14. The apparatus of claim 13 , wherein, to update the at least one DTX count, the one or more processors are further configured to cause the apparatus to:

update DTX count associated with the first reception beam.

15. The apparatus of claim 14 , wherein, to determine that the value of the at least one DTX count meets the threshold, the one or more processors are further configured to cause the apparatus to:

determine that a value of the DTX count associated with the first reception beam meets a beam refinement threshold; and

based on the value of the DTX count associated with the first reception beam meeting the beam refinement threshold, initiate beam refinement of the first reception beam.

16. The apparatus of claim 1 , wherein, to update the at least one DTX count, the one or more processors are further configured to cause the apparatus to:

update a DTX count associated with the first beam pair.

17. The apparatus of claim 16 , wherein, to determine that the value of the at least one DTX count meets the threshold, the one or more processors are further configured to cause the apparatus to:

determine that a value of the DTX count associated with the first beam pair meets a beam failure threshold; and

based on the value of the DTX count associated with the first beam pair meeting the beam failure threshold, initiate beam recovery of the first beam pair.

18. The apparatus of claim 1 , further comprising at least one transceiver configured to transmit the first sidelink communication, wherein the apparatus is configured as the first UE.

19. A method for wireless communications performed at a first user equipment (UE), comprising:

sending a first sidelink communication to a second UE using a first beam pair of a unicast link with the second UE, wherein the first beam pair includes a first transmission beam and a first reception beam;

detect a fault associated with at least one of the first transmission beam or the first reception beam;

based on the detected fault, updating a value of at least one discontinuous transmission (DTX) count associated with at least one of the first transmission beam or the first reception beam;

determining that the value of the at least one DTX count meets a threshold; and

based on the value of the at least one DTX count meeting the threshold, initiating at least one of beam refinement or beam recovery of the first beam pair.

20. The method of claim 19 , further comprising:

sending a second sidelink communication to the second UE, wherein the fault is based on whether a response to the second sidelink communication is received.

21. The method of claim 19 , further comprising:

determining, based on the fault, a second beam pair of the unicast link with the second UE; and

sending a second sidelink communication to the second UE using the second beam pair.

22. The method of claim 21 , wherein the second beam pair includes the first transmission beam and a second reception beam.

23. The method of claim 22 , further comprising:

obtaining an acknowledgment (ACK) corresponding to the second sidelink communication; and

determining that the fault is associated with the first reception beam.

24. The method of claim 23 , wherein updating the at least one DTX count comprises:

updating DTX count associated with the first reception beam.

25. The method of claim 24 , wherein determining that the value of the at least one DTX count meets the threshold comprises:

determining that a value of the DTX count associated with the first reception beam meets a beam refinement threshold; and

based on the value of the DTX count associated with the first reception beam meeting the beam refinement threshold, initiating beam refinement of the first reception beam.

26. A non-transitory computer-readable medium having stored thereon instructions that, when executed by one or more processors, cause the one or more processors to:

send a first sidelink communication to a user equipment (UE) using a first beam pair of a unicast link with the UE, wherein the first beam pair includes a first transmission beam and a first reception beam;

detect a fault associated with at least one of the first transmission beam or the first reception beam;

based on the detected fault, update a value of at least one discontinuous transmission (DTX) count associated with at least one of the first transmission beam or the first reception beam;

determine that the value of the at least one DTX count meets a threshold; and

based on the value of the at least one DTX count meeting the threshold, initiate at least one of beam refinement or beam recovery of the first beam pair.

27. The non-transitory computer-readable medium of claim 26 , wherein the instructions, when executed by the one or more processors, cause the one or more processors to:

determine, based on the fault, a second beam pair of the unicast link with the UE, wherein the second beam pair includes the first transmission beam and a second reception beam; and

send a second sidelink communication to the UE using the second beam pair.

28. The non-transitory computer-readable medium of claim 27 , wherein the instructions, when executed by the one or more processors, cause the one or more processors to:

obtain an acknowledgment (ACK) corresponding to the second sidelink communication; and

determine that the fault is associated with the first reception beam.

29. The non-transitory computer-readable medium of claim 28 , wherein:

to update the at least one DTX count, the instructions, when executed by the one or more processors, cause the one or more processors to update a DTX count associated with the first reception beam; and

to determine that the value of the at least one DTX count meets the threshold, the instructions, when executed by the one or more processors, cause the one or more processors to:

determine that a value of the DTX count associated with the first reception beam meets a beam refinement threshold; and

based on the value of the DTX count associated with the first reception beam meeting the beam refinement threshold, initiate beam refinement of the first reception beam.

30. An apparatus for wireless communication, comprising:

means for sending a first sidelink communication to a second UE using a first beam pair of a unicast link with the second UE, wherein the first beam pair includes a first transmission beam and a first reception beam;

means for detecting a fault associated with at least one of the first transmission beam or the first reception beam;

means for, based on the detected fault, updating a value of at least one discontinuous transmission (DTX) count associated with at least one of the first transmission beam or the first reception beam;

means for determining that the value of the at least one DTX count meets a threshold; and

means for, based on the value of the at least one DTX count meeting the threshold, initiating at least one of beam refinement or beam recovery of the first beam pair.