Hybrid automatic repeat request (HARQ) handling for discontinuous reception

1. An apparatus for wireless communications, comprising:

a processor;

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

obtain a first downlink control information (DCI) message indicating a non-numeric value for a data-to-feedback timing indicator, wherein the first DCI message schedules a downlink data message and the data-to-feedback timing indicator is associated with feedback timing for the downlink data message, and wherein the non-numeric value is associated with a postponement of feedback transmission for the downlink data message;

activate a timer in a first symbol after the scheduled downlink data message based at least in part on the first DCI message and on the data-to-feedback timing indicator being the non-numeric value;

monitor a downlink control channel while the timer is active; and

obtain a second DCI message different from the first DCI message, the second DCI message indicating the feedback timing for the downlink data message based at least in part on monitoring the downlink control channel.

2. The apparatus of claim 1 , wherein:

the timer comprises a retransmission timer for downlink retransmissions and is associated with a hybrid automatic repeat request (HARD) process corresponding to the downlink data message.

3. The apparatus of claim 2 , wherein:

the timer comprises a drx-RetransmissionTimerDL.

4. The apparatus of claim 1 , wherein the instructions are further executable by the processor to cause the apparatus to:

output a feedback message for the downlink data message according to the feedback timing indicated by the second DCI message; and

activate a round-trip time timer in a first symbol after outputting the feedback message.

5. The apparatus of claim 4 , wherein the instructions are further executable by the processor to cause the apparatus to:

activate a retransmission timer in a first symbol after expiration of the round-trip time timer based at least in part on the feedback message comprising a negative acknowledgment (NACK) for the downlink data message; and

monitor the downlink control channel while the retransmission timer is active.

6. The apparatus of claim 5 , wherein:

the round-trip time timer comprises a drx-HARQ-RTT-TimerDL; and

the retransmission timer comprises a drx-RetransmissionTimerDL.

7. The apparatus of claim 1 , wherein the instructions are further executable by the processor to cause the apparatus to:

deactivate the timer based at least in part on obtaining the second DCI message indicating the feedback timing for the downlink data message.

8. The apparatus of claim 7 , wherein:

deactivating the timer comprises deactivating the timer in a first symbol after obtaining the second DCI message or in a first symbol after a feedback transmission corresponding to the feedback timing indicated by the second DCI message.

9. The apparatus of claim 1 , wherein the instructions are further executable by the processor to cause the apparatus to:

obtain the downlink data message based at least in part on the first DCI message;

store feedback information for the downlink data message based at least in part on the first DCI message indicating the non-numeric value; and

output a feedback message comprising the feedback information for the downlink data message according to the feedback timing indicated by the second DCI message.

10. The apparatus of claim 9 , wherein:

the feedback message comprises a hybrid automatic repeat request (HARQ) acknowledgment message.

11. The apparatus of claim 1 , wherein the instructions are further executable by the processor to cause the apparatus to:

obtain a radio resource control (RRC) message indicating an active duration of the timer.

12. The apparatus of claim 11 , wherein:

the active duration comprises a first active duration of the timer specific to obtaining DCI messages indicating non-numeric values; and

the RRC message further indicates a second active duration of the timer.

13. The apparatus of claim 1 , wherein:

the timer is specific to a hybrid automatic repeat request (HARQ) process for the downlink data message.

14. The apparatus of claim 1 , wherein the instructions are further executable by the processor to cause the apparatus to:

deactivate the timer based at least in part on the timer running for an active duration of the timer;

enter a low power mode based at least in part on deactivating the timer; and

refrain from monitoring the downlink control channel while in the low power mode.

15. The apparatus of claim 14 , wherein:

entering the low power mode is further based at least in part on a user equipment (UE) being outside of an ON duration of a discontinuous reception (DRX) mode and each timer corresponding to monitoring the downlink control channel being deactivated.

16. The apparatus of claim 1 , wherein the instructions are further executable by the processor to cause the apparatus to:

operate according to a discontinuous reception (DRX) mode; and

monitor the downlink control channel during an ON duration of the DRX mode, wherein the first DCI message is obtained based at least in part on monitoring the downlink control channel during the ON duration of the DRX cycle.

17. The apparatus of claim 1 included in a user equipment (UE).

18. An apparatus for wireless communications, comprising:

a processor;

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

output a first downlink control information (DCI) message indicating a non-numeric value for a data-to-feedback timing indicator, wherein the first DCI message schedules a downlink data message and the data-to-feedback timing indicator is associated with feedback timing for the downlink data message, and wherein the non-numeric value is associated with a postponement of feedback transmission for the downlink data message;

determine an active time for a user equipment (UE) to monitor a downlink control channel based at least in part on a timer, wherein the timer is activated in a first symbol after the scheduled downlink data message based at least in part on the first DCI message and on the data-to-feedback timing indicator being the non-numeric value; and

output a second DCI message different from the first DCI message, the second DCI message indicating the feedback timing for the downlink data message based at least in part on the determined active time for the UE to monitor the downlink control channel.

19. The apparatus of claim 18 , wherein:

the timer comprises a retransmission timer for downlink retransmissions and is associated with a hybrid automatic repeat request (HARD) process corresponding to the downlink data message.

20. The apparatus of claim 18 , wherein the instructions are further executable by the processor to cause the apparatus to:

output a radio resource control (RRC) message indicating an active duration of the timer.

21. The apparatus of claim 20 , wherein:

the active duration comprises a first active duration of the timer specific to obtaining DCI messages indicating non-numeric values; and

the RRC message further indicates a second active duration of the timer.

22. The apparatus of claim 18 , wherein the instructions are further executable by the processor to cause the apparatus to:

output the downlink data message based at least in part on the first DCI message.

23. A method for wireless communications at an apparatus of a user equipment (UE), comprising:

receiving a first downlink control information (DCI) message indicating a non-numeric value for a data-to-feedback timing indicator, wherein the first DCI message schedules a downlink data message and the data-to-feedback timing indicator is associated with feedback timing for the downlink data message, and wherein the non-numeric value is associated with a postponement of feedback transmission for the downlink data message;

activating a timer in a first symbol after the scheduled downlink data message based at least in part on the first DCI message and on the data-to-feedback timing indicator being the non-numeric value;

monitoring a downlink control channel while the timer is active; and

receiving a second DCI message different from the first DCI message, the second DCI message indicating the feedback timing for the downlink data message based at least in part on monitoring the downlink control channel.

24. The method of claim 23 , wherein:

the timer comprises a retransmission timer for downlink retransmissions and is associated with a hybrid automatic repeat request (HARD) process corresponding to the downlink data message.

25. The method of claim 23 , further comprising:

transmitting a feedback message for the downlink data message according to the feedback timing indicated by the second DCI message; and

activating a round-trip time timer in a first symbol after transmitting the feedback message.

26. The method of claim 25 , further comprising:

activating a retransmission timer in a first symbol after expiration of the round-trip time timer based at least in part on the feedback message comprising a negative acknowledgment (NACK) for the downlink data message; and

monitoring the downlink control channel while the retransmission timer is active.

27. A method for wireless communications at an apparatus of a base station, comprising:

transmitting, to a user equipment (UE) on a downlink control channel, a first downlink control information (DCI) message indicating a non-numeric value for a data-to-feedback timing indicator, wherein the first DCI message schedules a downlink data message and the data-to-feedback timing indicator is associated with feedback timing for the downlink data message, and wherein the non-numeric value is associated with a postponement of feedback transmission for the downlink data message;

determining an active time for the UE to monitor the downlink control channel based at least in part on a timer, wherein the timer is activated in a first symbol after the scheduled downlink data message based at least in part on the first DCI message and on the data-to-feedback timing indicator being the non-numeric value; and

transmitting, to the UE on the downlink control channel, a second DCI message different from the first DCI message, the second DCI message indicating the feedback timing for the downlink data message based at least in part on the determined active time for the UE to monitor the downlink control channel.

28. The method of claim 27 , wherein:

the timer comprises a retransmission timer for downlink retransmissions and is associated with a hybrid automatic repeat request (HARD) process corresponding to the downlink data message.