Indicating cancelation of transmissions of sidelink messages

1. An apparatus for wireless communication at a sidelink device, comprising:

at least one memory; and

at least one processor coupled to the at least one memory and configured to cause the sidelink device to:

transmit sidelink control information (SCI) reserving a set of resources for one or more retransmissions of a message, the set of resources identifying one or more reserved resources in a time domain;

identify a skipped transmission associated with one or more of the set of resources reserved by the sidelink device for the one or more retransmissions; and

transmit a cancelation indication including a backward indication indicating the skipped transmission after at least one of the one or more reserved resources has occurred, the cancelation indication indicating that the skipped transmission corresponds to a previous reserved resource that has already occurred in the time domain for the one or more retransmissions.

2. The apparatus of claim 1 , wherein the at least one processor is configured to cause the sidelink device to transmit the cancelation indication using one or more of an additional SCI message, a data channel, and radio resource control signaling.

3. The apparatus of claim 1 , wherein the at least one processor is configured to cause the sidelink device to identify the skipped transmission based on an interference measurement associated with a reserved resource, collision detection, or congestion control.

4. The apparatus of claim 1 , wherein the at least one processor is configured to cause the sidelink device to further identify a second skipped transmission before transmitting a second retransmission of a second message using a corresponding reserved resource of a second set of resources, and transmitting a second cancelation indication that indicates that the corresponding reserved resource corresponds to a current reserved resource in the time domain or a future reserved resource in the time domain.

5. The apparatus of claim 1 , wherein the at least one processor is configured to cause the sidelink device to transmit an additional SCI and the cancelation indication using a reserved resource of the set of resources.

6. The apparatus of claim 5 , wherein the at least one processor is configured to cause the sidelink device to transmit the additional SCI and the cancelation indication based on identifying the skipped transmission.

7. The apparatus of claim 5 , wherein the at least one processor is further configured to cause the sidelink device to:

schedule a cancelation indication monitoring occasion with a receiving sidelink device; and

transmit the additional SCI and the cancelation indication to the receiving sidelink device at the cancelation indication monitoring occasion.

8. The apparatus of claim 7 , wherein the cancelation indication monitoring occasion comprises one or more resources in the time domain, and the at least one processor is configured to cause the sidelink device to transmit the additional SCI and the cancelation indication using at least one resource of the one or more resources in the time domain.

9. The apparatus of claim 7 , wherein the cancelation indication monitoring occasion overlaps with at least one reserved resource of the set of resources, and the cancelation indication monitoring occasion is periodic.

10. The apparatus of claim 1 , wherein the cancelation indication indicating the skipped transmission comprises a quantity of reserved resources, and the cancelation indication indicating the skipped transmission comprises a bitmap.

11. The apparatus of claim 1 , wherein the at least one processor is configured to cause the sidelink device to transmit the cancelation indication during a cancelation indication monitoring occasion.

12. The apparatus of claim 11 , wherein the cancelation indication indicates a reason for the skipped transmission.

13. The apparatus of claim 11 , wherein the at least one processor is further configured to cause the sidelink device to:

schedule the cancelation indication monitoring occasion with a receiving sidelink device, the cancelation indication monitoring occasion comprising one or more time domain resources; and

use at least one resource of the one or more time domain resources to transmit the cancelation indication.

14. The apparatus of claim 1 , wherein the at least one processor is configured to cause the sidelink device to receive the cancelation indication from a base station via at least one of downlink control information (DCI), a medium access control—control element (MAC-CE), or radio resource control (RRC) signaling.

15. An apparatus for wireless communication of a first sidelink device, comprising:

at least one memory; and

at least one processor coupled to the at least one memory and configured to cause the first sidelink device to:

receive, from a second sidelink device, sidelink control information (SCI) reserving a set of resources for retransmissions of a message, the set of resources identifying one or more reserved resources in a time domain; and

receive, from the second sidelink device, a cancelation indication including a backward indication indicating a skipped transmission after at least one of the one or more reserved resources has occurred, the cancelation indication indicating that the skipped transmission corresponds to a previous reserved resource that has already occurred in the time domain for the retransmissions.

16. The apparatus of claim 15 , wherein the at least one processor is further configured to cause the first sidelink device to:

decode the message based on reception of the message and without at least one retransmission of the message indicated by the cancelation indication.

17. The apparatus of claim 15 , wherein the at least one processor is configured to cause the first sidelink device to receive the cancelation indication via one or more of an additional SCI, a data channel, and radio resource control signaling.

18. The apparatus of claim 15 , wherein the at least one processor is configured to cause the first sidelink device to forego using a prior retransmission occasion corresponding to the skipped transmission indicated via the cancelation indication when decoding the message.

19. The apparatus of claim 15 , wherein the at least one processor is configured to cause the first sidelink device to receive an additional SCI and the cancelation indication from the second sidelink device via a reserved resource of the set of resources.

20. The apparatus of claim 19 , wherein the at least one processor is configured to cause the first sidelink device to monitor for the additional SCI and the cancelation indication using blind decoding techniques at the reserved resource of the set of resources.

21. The apparatus of claim 19 , wherein the at least one processor is further configured to cause the first sidelink device to:

schedule a cancelation indication monitoring occasion with the second sidelink device; and

receive the additional SCI and the cancelation indication from the second sidelink device at the cancelation indication monitoring occasion.

22. The apparatus of claim 21 , wherein the cancelation indication monitoring occasion comprises one or more resources in the time domain, and wherein the at least one processor is configured to cause the first sidelink device to receive the SCI and the cancelation indication via at least one resource of the one or more resources in the time domain.

23. The apparatus of claim 21 , wherein the cancelation indication monitoring occasion overlaps with at least one reserved resource of the set of resources, and the cancelation indication monitoring occasion is periodic.

24. The apparatus of claim 19 , wherein the at least one processor is further configured to cause the first sidelink device to:

perform de-rate-matching based on the cancelation indication from the second sidelink device.

25. The apparatus of claim 15 , wherein the cancelation indication indicating the skipped transmission comprises a quantity of reserved resources, and the cancelation indication indicating the skipped transmission comprises a bitmap.

26. The apparatus of claim 15 , wherein the at least one processor is configured to cause the first sidelink device to receive the cancelation indication from the second sidelink device at a cancelation indication monitoring occasion.

27. The apparatus of claim 26 , wherein the cancelation indication comprises a reason for the skipped transmission.

28. The apparatus of claim 26 , wherein the at least one processor is further configured to cause the first sidelink device to:

schedule the cancelation indication monitoring occasion with the second sidelink device, the cancelation indication monitoring occasion comprising one or more resources in the time domain; and

receive the cancelation indication via at least one resource of the one or more resources in the time domain.

29. The apparatus of claim 15 , wherein the at least one processor is further configured to cause the first sidelink device to:

receive a second cancelation indication that indicates a cancelation of a current reserved resource in the time domain or a future reserved resource in the time domain; and

transmit an additional message using a previously reserved resource that is canceled by the second cancelation indication.