Handling missed hybrid automatic repeat request (HARQ) opportunities, multiple HARQ opportunities, or both for discontinuous reception (DRX)
This disclosure provides systems, methods, and apparatus, including computer programs encoded on computer storage media, for handling hybrid automatic repeat request (HARQ) processes with discontinuous reception (DRX) operations. A user equipment (UE) may use timers to maintain an ON duration in DRX. The UE may receive, via downlink control information (DCI), an indication of a feedback transmission opportunity (TxOP) for a HARQ process. The UE may activate a timer at the end of the TxOP regardless of whether the UE transmits feedback in the TxOP to ensure that the UE remains active. In some implementations, a base station may provide the UE with multiple opportunities to transmit a feedback message. The UE may reactivate a timer after each feedback TxOP for the same HARQ process or may activate the timer after the first feedback TxOP and may refrain from activating the timer after subsequent feedback TxOPs for the HARQ process.
1. A user equipment (UE), comprising:
a processing system that includes one or more processors and one or more memories that store code, the processing system configured to cause the UE to:
obtain monitoring information for a physical downlink control channel (PDCCH) while operating in an active time for discontinuous reception (DRX) operation);
obtain, via the PDCCH and in accordance with the monitoring information, a first indication of a scheduled downlink transmission and a second indication of a feedback transmission opportunity (TxOP) for a corresponding hybrid automatic repeat request (HARQ) process;
start a round-trip time (RTT) timer for the corresponding HARQ process in a first symbol after an end of the feedback TxOP; and
start a retransmission timer for the corresponding HARQ process after expiry of the RTT timer, wherein the UE remains in the active time for the DRX operation while the retransmission timer is running.
2. The UE of claim 1 , wherein, to start the RTT timer, the processing system is configured to cause the UE to:
start the RTT timer for the corresponding HARQ process in the first symbol after the end of the feedback TxOP regardless of the UE failing a listen-before-transmit (LBT) procedure for the feedback TxOP.
3. The UE of claim 1 , wherein the processing system is further configured to cause the UE to:
obtain, via the PDCCH and in accordance with the monitoring information, a third indication of an additional feedback TxOP for the corresponding HARQ process.
4. The UE of claim 3 , wherein the processing system is further configured to cause the UE to:
restart the RTT timer for the corresponding HARQ process in accordance with a second end of the additional feedback TxOP; and
restart the retransmission timer for the corresponding HARQ process after expiry of the restarted RTT timer.
5. The UE of claim 4 , wherein the processing system is further configured to cause the UE to:
stop the retransmission timer subsequent to the additional feedback TxOP; and
reset the retransmission timer to a timer duration in accordance with the expiry of the restarted RTT timer, wherein restarting the retransmission timer is in accordance with the resetting.
6. The UE of claim 1 , wherein the processing system is further configured to cause the UE to:
refrain from outputting a feedback message for the scheduled downlink transmission in the feedback TxOP in accordance with the UE failing a listen-before-transmit (LBT) procedure for the feedback TxOP.
7. The UE of claim 1 , wherein:
the RTT timer comprises a drx-HARQ-RTT-TimerDL; and
the retransmission timer comprises a drx-Retransmission TimerDL.
8. The UE of claim 1 , wherein the processing system is further configured to cause the UE to:
determine feedback information for the scheduled downlink transmission; and
perform a listen-before-transmit (LBT) procedure for the feedback TxOP in accordance with the feedback information.
9. The UE of claim 1 , wherein the processing system is further configured to cause the UE to:
determine an expiration of a last timer maintaining the active time for the DRX operation;
enter an inactive time for the DRX operation in accordance with the expiration of the last timer; and
refrain from monitoring the PDCCH while in the inactive time for the DRX operation.
10. A network device, comprising:
a processing system that includes one or more processors and one or more memories that store code, the processing system configured to cause the network device to:
output, via a physical downlink control channel (PDCCH), a first indication of a scheduled downlink transmission and a second indication of a feedback transmission opportunity (TxOP) for a corresponding hybrid automatic repeat request (HARQ) process; and
output, via the PDCCH, a third indication of an additional feedback TxOP for the corresponding HARQ process subsequent to the feedback TxOP according to an active time for discontinuous reception (DRX) operation for a user equipment (UE) to monitor the PDCCH in accordance with a round-trip time (RTT) timer and a retransmission timer, wherein the RTT timer is started in a first symbol after an end of the feedback TxOP and the retransmission timer is started after expiry of the RTT timer.
11. The network device of claim 10 , wherein:
the RTT timer comprises a drx-HARQ-RTT-TimerDL; and
the retransmission timer comprises a drx-RetransmissionTimerDL.
12. The network device of claim 10 , wherein the processing system is further configured to cause the network device to:
output the scheduled downlink transmission in accordance with the first indication of the scheduled downlink transmission.
13. The network device of claim 12 , wherein the processing system is further configured to cause the network device to:
obtain a feedback message for the scheduled downlink transmission in the additional feedback TxOP; and
output the scheduled downlink transmission in accordance with the feedback message.
14. The network device of claim 13 , wherein the feedback message comprises an indication of a negative acknowledgment (NACK) for the scheduled downlink transmission.
15. A method for wireless communications at a user equipment (UE), comprising:
monitoring a physical downlink control channel (PDCCH) while operating in an active time for discontinuous reception (DRX) operation;
receiving, via the PDCCH and in accordance with the monitoring, a first indication of a scheduled downlink transmission and a second indication of a feedback transmission opportunity (TxOP) for a corresponding hybrid automatic repeat request (HARQ) process;
starting a round-trip time (RTT) timer for the corresponding HARQ process in a first symbol after an end of the feedback TxOP; and
starting a retransmission timer for the corresponding HARQ process after expiry of the RTT timer, wherein the UE remains in the active time for the DRX operation while the retransmission timer is running.
16. The method of claim 15 , wherein starting the RTT timer comprises:
starting the RTT timer for the corresponding HARQ process in the first symbol after the end of the feedback TxOP regardless of the UE failing a listen-before-transmit (LBT) procedure for the feedback TxOP.
17. The method of claim 15 , further comprising:
receiving, via the PDCCH and in accordance with the monitoring, a third indication of an additional feedback TxOP for the corresponding HARQ process.
18. The method of claim 17 , further comprising:
restarting the RTT timer for the corresponding HARQ process in accordance with a second end of the additional feedback TxOP; and
restarting the retransmission timer for the corresponding HARQ process after expiry of the restarted RTT timer.
19. The method of claim 18 , further comprising:
stopping the retransmission timer subsequent to the additional feedback TxOP; and
resetting the retransmission timer to a timer duration in accordance with the expiry of the restarted RTT timer, wherein restarting the retransmission timer is in accordance with the resetting.
20. The method of claim 15 , wherein:
the RTT timer comprises a drx-HARQ-RTT-TimerDL; and
the retransmission timer comprises a drx-RetransmissionTimerDL.