5.7 Discontinuous Reception (DRX)
38.3213GPPMedium Access Control (MAC) protocol specificationNRRelease 17TS
The MAC entity may be configured by RRC with a DRX functionality that controls the UE’s PDCCH monitoring activity for the MAC entity’s C-RNTI, CI-RNTI, CS-RNTI, INT-RNTI, SFI-RNTI, SP-CSI-RNTI, TPC-PUCCH-RNTI, TPC-PUSCH-RNTI, TPC-SRS-RNTI, AI-RNTI, SL-RNTI, SLCS-RNTI and SL Semi-Persistent Scheduling V-RNTI. When using DRX operation, the MAC entity shall also monitor PDCCH according to requirements found in other clauses of this specification. When in RRC_CONNECTED, if DRX is configured, for all the activated Serving Cells, the MAC entity may monitor the PDCCH discontinuously using the DRX operation specified in this clause; otherwise the MAC entity shall monitor the PDCCH as specified in TS 38.213 [6].
NOTE 1: Void
RRC controls DRX operation by configuring the following parameters:
– drx-onDurationTimer: the duration at the beginning of a DRX cycle;
– drx-SlotOffset: the delay before starting the drx-onDurationTimer;
– drx-InactivityTimer: the duration after the PDCCH occasion in which a PDCCH indicates a new UL, DL or SL transmission for the MAC entity;
– drx-RetransmissionTimerDL (per DL HARQ process except for the broadcast process): the maximum duration until a DL retransmission is received;
– drx-RetransmissionTimerUL (per UL HARQ process): the maximum duration until a grant for UL retransmission is received;
– drx-LongCycleStartOffset: the Long DRX cycle and drx-StartOffset which defines the subframe where the Long and Short DRX cycle starts;
– drx-ShortCycle (optional): the Short DRX cycle;
– drx-ShortCycleTimer (optional): the duration the UE shall follow the Short DRX cycle;
– drx-HARQ-RTT-TimerDL (per DL HARQ process except for the broadcast process): the minimum duration before a DL assignment for HARQ retransmission is expected by the MAC entity;
– drx-HARQ-RTT-TimerUL (per UL HARQ process): the minimum duration before a UL HARQ retransmission grant is expected by the MAC entity;
– drx-RetransmissionTimerSL (per SL HARQ process): the maximum duration until a grant for SL retransmission is received;
– drx-HARQ-RTT-TimerSL (per SL HARQ process): the minimum duration before an SL retransmission grant is expected by the MAC entity;
– ps-Wakeup (optional): the configuration to start associated drx-onDurationTimer in case DCP is monitored but not detected;
– ps-TransmitOtherPeriodicCSI (optional): the configuration to report periodic CSI that is not L1-RSRP on PUCCH during the time duration indicated by drx-onDurationTimer in case DCP is configured but associated drx-onDurationTimer is not started;
– ps-TransmitPeriodicL1-RSRP (optional): the configuration to transmit periodic CSI that is L1-RSRP on PUCCH during the time duration indicated by drx-onDurationTimer in case DCP is configured but associated drx-onDurationTimer is not started;
– downlinkHARQ-FeedbackDisabled (optional): the configuration to enable HARQ feedback per DL HARQ process;
– uplinkHARQ-Mode (optional): the configuration to set HARQmodeA or HARQmodeB per UL HARQ process.
Serving Cells of a MAC entity may be configured by RRC in two DRX groups with separate DRX parameters. When RRC does not configure a secondary DRX group, there is only one DRX group and all Serving Cells belong to that one DRX group. When two DRX groups are configured, each Serving Cell is uniquely assigned to either of the two groups. The DRX parameters that are separately configured for each DRX group are: drx-onDurationTimer, drx-InactivityTimer. The DRX parameters that are common to the DRX groups are: drx-SlotOffset, drx-RetransmissionTimerDL, drx-RetransmissionTimerUL, drx-LongCycleStartOffset, drx-ShortCycle (optional), drx-ShortCycleTimer (optional), drx-HARQ-RTT-TimerDL, drx-HARQ-RTT-TimerUL, downlinkHARQ-FeedbackDisabled (optional) and uplinkHARQ-Mode (optional).
When DRX is configured, the Active Time for Serving Cells in a DRX group includes the time while:
– drx-onDurationTimer or drx-InactivityTimer configured for the DRX group is running; or
– drx-RetransmissionTimerDL, drx-RetransmissionTimerUL or drx-RetransmissionTimerSL is running on any Serving Cell in the DRX group; or
– ra-ContentionResolutionTimer (as described in clause 5.1.5) or msgB-ResponseWindow (as described in clause 5.1.4a) is running; or
– a Scheduling Request is sent on PUCCH and is pending (as described in clause 5.4.4 or 5.22.1.5). If this Serving Cell is part of a non-terrestrial network, the Active Time is started after the Scheduling Request transmission that is performed when the SR_COUNTER is 0 for all the SR configurations with pending SR(s) plus the UE-gNB RTT; or
– a PDCCH indicating a new transmission addressed to the C-RNTI of the MAC entity has not been received after successful reception of a Random Access Response for the Random Access Preamble not selected by the MAC entity among the contention-based Random Access Preamble (as described in clauses 5.1.4 and 5.1.4a).
The following MAC timers are used for DRX operation in a non-terrestrial network:
– HARQ-RTT-TimerDL-NTN (per DL HARQ process configured with HARQ feedback enabled): the minimum duration before a DL assignment for HARQ retransmission is expected by the MAC entity;
– HARQ-RTT-TimerUL-NTN (per UL HARQ process configured with HARQModeA): the minimum duration before a UL HARQ retransmission grant is expected by the MAC entity.
When DRX is configured, the MAC entity shall:
1> if a MAC PDU is received in a configured downlink assignment for unicast:
2> if this Serving Cell is configured with downlinkHARQ-FeedbackDisabled:
3> if the corresponding HARQ process is configured with HARQ feedback enabled:
4> set HARQ-RTT-TimerDL-NTN for the corresponding HARQ process equal to drx-HARQ-RTT-TimerDL plus the latest available UE-gNB RTT value;
4> start the HARQ-RTT-TimerDL-NTN for the corresponding HARQ process in the first symbol after the end of the corresponding transmission carrying the DL HARQ feedback.
2> else:
3> start the drx-HARQ-RTT-TimerDL for the corresponding HARQ process in the first symbol after the end of the corresponding transmission carrying the DL HARQ feedback.
NOTE 1a: Void.
NOTE 1b: Void.
2> stop the drx-RetransmissionTimerDL for the corresponding HARQ process;
2> stop the drx-RetransmissionTimerDL-PTM for the corresponding HARQ process.
1> if a MAC PDU is transmitted in a configured uplink grant and LBT failure indication is not received from lower layers:
2> if this Serving Cell is configured with uplinkHARQ-Mode:
3> if the corresponding HARQ process is configured as HARQModeA:
4> set HARQ-RTT-TimerUL-NTN for the corresponding HARQ process equal to drx-HARQ-RTT-TimerUL plus the latest available UE-gNB RTT value;
4> if drx-LastTransmissionUL is configured:
5> start the HARQ-RTT-TimerUL-NTN for the corresponding HARQ process in the first symbol after the end of the last transmission (within a bundle) of the corresponding PUSCH transmission.
4> else:
5> start the HARQ-RTT-TimerUL-NTN for the corresponding HARQ process in the first symbol after the end of the first transmission (within a bundle) of the corresponding PUSCH transmission.
2> else:
3> if drx-LastTransmissionUL is configured:
4> start the drx-HARQ-RTT-TimerUL for the corresponding HARQ process in the first symbol after the end of the last transmission (within a bundle) of the corresponding PUSCH transmission.
3> else:
4> start the drx-HARQ-RTT-TimerUL for the corresponding HARQ process in the first symbol after the end of the first transmission (within a bundle) of the corresponding PUSCH transmission.
2> stop the drx-RetransmissionTimerUL for the corresponding HARQ process at the first transmission (within a bundle) of the corresponding PUSCH transmission.
1> if a MAC PDU is transmitted in a configured sidelink grant:
2> if the PUCCH resource is configured:
3> start the drx-HARQ-RTT-TimerSL for the corresponding HARQ process in the first symbol after the end of the corresponding PUCCH transmission carrying the SL HARQ feedback; or
3> start the drx-HARQ-RTT-TimerSL for the corresponding HARQ process in the first symbol after the end of the corresponding PUCCH resource for the SL HARQ feedback when the PUCCH is not transmitted;
3> stop the drx-RetransmissionTimerSL for the corresponding HARQ process.
2> else:
3> start the drx-HARQ-RTT-TimerSL for the corresponding HARQ process at the first symbol after the end of the corresponding PSSCH transmission;
3> stop the drx-RetransmissionTimerSL for the corresponding HARQ process.
1> if a drx-HARQ-RTT-TimerDL expires:
2> if the data of the corresponding HARQ process was not successfully decoded:
3> start the drx-RetransmissionTimerDL for the corresponding HARQ process in the first symbol after the expiry of drx-HARQ-RTT-TimerDL.
1> if a HARQ-RTT-TimerDL-NTN expires:
2> if the data of the corresponding HARQ process was not successfully decoded:
3> start the drx-RetransmissionTimerDL for the corresponding HARQ process in the first symbol after the expiry of HARQ-RTT-TimerDL-NTN.
1> if a drx-HARQ-RTT-TimerUL expires:
2> start the drx-RetransmissionTimerUL for the corresponding HARQ process in the first symbol after the expiry of drx-HARQ-RTT-TimerUL.
1> if a HARQ-RTT-TimerUL-NTN expires:
2> start the drx-RetransmissionTimerUL for the corresponding HARQ process in the first symbol after the expiry of HARQ-RTT-TimerUL-NTN.
1> if a drx-HARQ-RTT-TimerSL expires:
2> if a HARQ NACK feedback for the corresponding HARQ process is transmitted on PUCCH; or
2> if a HARQ NACK feedback for the corresponding HARQ process is not transmitted on PUCCH; or
2> if the PUCCH resource is not configured for the SL grant:
3> start the drx-RetransmissionTimerSL for the corresponding HARQ process in the first symbol after the expiry of drx-HARQ-RTT-TimerSL.
NOTE 1c: The UE handles the drx-RetransmissionTimerSL operation when sl-PUCCH-Config is configured by RRC but PUCCH resource is not scheduled same as when sl-PUCCH-Config is not configured.
1> if a DRX Command MAC CE with DCI scrambled with C-RNTI for unicast transmission or a Long DRX Command MAC CE is received:
2> stop drx-onDurationTimer for each DRX group;
2> stop drx-InactivityTimer for each DRX group.
1> if drx-InactivityTimer for a DRX group expires:
2> if the Short DRX cycle is configured:
3> start or restart drx-ShortCycleTimer for this DRX group in the first symbol after the expiry of drx-InactivityTimer;
3> use the Short DRX cycle for this DRX group.
2> else:
3> use the Long DRX cycle for this DRX group.
1> if a DRX Command MAC CE with DCI scrambled with C-RNTI for unicast transmission is received:
2> if the Short DRX cycle is configured:
3> start or restart drx-ShortCycleTimer for each DRX group in the first symbol after the end of DRX Command MAC CE reception;
3> use the Short DRX cycle for each DRX group.
2> else:
3> use the Long DRX cycle for each DRX group.
1> if drx-ShortCycleTimer for a DRX group expires:
2> use the Long DRX cycle for this DRX group.
1> if a Long DRX Command MAC CE is received:
2> stop drx-ShortCycleTimer for each DRX group;
2> use the Long DRX cycle for each DRX group.
1> if the Short DRX cycle is used for a DRX group, and [(SFN × 10) + subframe number] modulo (drx-ShortCycle) = (drx-StartOffset) modulo (drx-ShortCycle):
2> start drx-onDurationTimer for this DRX group after drx-SlotOffset from the beginning of the subframe.
1> if the Long DRX cycle is used for a DRX group, and [(SFN × 10) + subframe number] modulo (drx-LongCycle) = drx-StartOffset:
2> if DCP monitoring is configured for the active DL BWP as specified in TS 38.213 [6], clause 10.3:
3> if DCP indication associated with the current DRX cycle received from lower layer indicated to start drx-onDurationTimer, as specified in TS 38.213 [6]; or
3> if all DCP occasion(s) in time domain, as specified in TS 38.213 [6], associated with the current DRX cycle occurred in Active Time considering grants/assignments/DRX Command MAC CE/Long DRX Command MAC CE received and Scheduling Request sent until 4 ms prior to start of the last DCP occasion, or during a measurement gap, or when the MAC entity monitors for a PDCCH transmission on the search space indicated by recoverySearchSpaceId of the SpCell identified by the C-RNTI while the ra-ResponseWindow is running (as specified in clause 5.1.4); or
3> if ps-Wakeup is configured with value true and DCP indication associated with the current DRX cycle has not been received from lower layers:
4> start drx-onDurationTimer after drx-SlotOffset from the beginning of the subframe.
2> else:
3> start drx-onDurationTimer for this DRX group after drx-SlotOffset from the beginning of the subframe.
NOTE 2: In case of unaligned SFN across carriers in a cell group, the SFN of the SpCell is used to calculate the DRX duration.
1> if a DRX group is in Active Time:
2> monitor the PDCCH on the Serving Cells in this DRX group as specified in TS 38.213 [6];
2> if the PDCCH indicates a DL transmission; or
2> if the PDCCH indicates a one-shot HARQ feedback as specified in clause 9.1.4 of TS 38.213 [6]; or
2> if the PDCCH indicates a retransmission of HARQ feedback as specified in clause 9.1.5 of TS 38.213 [6]:
3> if this Serving Cell is configured with downlinkHARQ-FeedbackDisabled:
4> if the corresponding HARQ process is configured with HARQ feedback enabled:
5> set HARQ-RTT-TimerDL-NTN for the corresponding HARQ process equal to drx-HARQ-RTT-TimerDL plus the latest available UE-gNB RTT value;
5> start the HARQ-RTT-TimerDL-NTN for the corresponding HARQ process in the first symbol after the end of the corresponding transmission carrying the DL HARQ feedback.
3> else:
4> start or restart the drx-HARQ-RTT-TimerDL for the corresponding HARQ process(es) whose HARQ feedback is reported in the first symbol after the end of the corresponding transmission carrying the DL HARQ feedback.
NOTE 3: When HARQ feedback is postponed by PDSCH-to-HARQ_feedback timing indicating an inapplicable k1 value, as specified in TS 38.213 [6], the corresponding transmission opportunity to send the DL HARQ feedback is indicated in a later PDCCH requesting the HARQ-ACK feedback.
3> stop the drx-RetransmissionTimerDL for the corresponding HARQ process(es) whose HARQ feedback is reported;
3> stop the drx-RetransmissionTimerDL-PTM for the corresponding HARQ process;
3> if the PDSCH-to-HARQ_feedback timing indicate an inapplicable k1 value as specified in TS 38.213 [6]:
4> start the drx-RetransmissionTimerDL in the first symbol after the (end of the last) PDSCH transmission (within a bundle) for the corresponding HARQ process.
2> if the PDCCH indicates a UL transmission:
3> if this Serving Cell is configured with uplinkHARQ-Mode:
4> if the corresponding HARQ process is configured as HARQModeA:
5> set HARQ-RTT-TimerUL-NTN for the corresponding HARQ process equal to drx-HARQ-RTT-TimerUL plus the latest available UE-gNB RTT value;
5> if drx-LastTransmissionUL is configured:
6> start the HARQ-RTT-TimerUL-NTN for the corresponding HARQ process in the first symbol after the end of the last transmission (within a bundle) of the corresponding PUSCH transmission.
5> else:
6> start the HARQ-RTT-TimerUL-NTN for the corresponding HARQ process in the first symbol after the end of the first transmission (within a bundle) of the corresponding PUSCH transmission.
3> else:
4> if drx-LastTransmissionUL is configured:
5> start the drx-HARQ-RTT-TimerUL for the corresponding HARQ process in the first symbol after the end of the last transmission (within a bundle) of the corresponding PUSCH transmission.
4> else:
5> start the drx-HARQ-RTT-TimerUL for the corresponding HARQ process in the first symbol after the end of the first transmission (within a bundle) of the corresponding PUSCH transmission.
3> stop the drx-RetransmissionTimerUL for the corresponding HARQ process.
2> if the PDCCH indicates an SL transmission:
3> if the PUCCH resource is configured:
4> start the drx-HARQ-RTT-TimerSL for the corresponding HARQ process in the first symbol after the end of the corresponding PUCCH transmission carrying the SL HARQ feedback; or
4> start the drx-HARQ-RTT-TimerSL for the corresponding HARQ process in the first symbol after the end of the corresponding PUCCH resource for the SL HARQ feedback when the PUCCH is not transmitted;
4> stop the drx-RetransmissionTimerSL for the corresponding HARQ process.
3> else:
4> start the drx-HARQ-RTT-TimerSL for the corresponding HARQ process at the first symbol after end of PDCCH occasion;
4> stop the drx-RetransmissionTimerSL for the corresponding HARQ process.
2> if the PDCCH indicates a new transmission (DL, UL or SL) on a Serving Cell in this DRX group:
3> start or restart drx-InactivityTimer for this DRX group in the first symbol after the end of the PDCCH reception.
NOTE 3a: A PDCCH indicating activation of SPS, configured grant type 2, or configured sidelink grant of configured grant Type 2 is considered to indicate a new transmission.
NOTE 3b: If the PDCCH reception includes two PDCCH candidates from corresponding search spaces, as described in clause 10.1 in 38.213, start or restart drx-InactivityTimer for this DRX group in the first symbol after the end of the PDCCH candidate that ends later in time.
2> if a HARQ process receives downlink feedback information and acknowledgement is indicated:
3> stop the drx-RetransmissionTimerUL for the corresponding HARQ process.
1> if DCP monitoring is configured for the active DL BWP as specified in TS 38.213 [6], clause 10.3; and
1> if the current symbol n occurs within drx-onDurationTimer duration; and
1> if drx-onDurationTimer associated with the current DRX cycle is not started as specified in this clause:
2> if the MAC entity would not be in Active Time considering grants/assignments/DRX Command MAC CE/Long DRX Command MAC CE received and Scheduling Request sent until 4 ms prior to symbol n when evaluating all DRX Active Time conditions as specified in this clause; and
2> if allowCSI-SRS-Tx-MulticastDRX-Active is not configured or, if all multicast DRXes would not be in Active Time considering multicast assignments/DRX Command MAC CE for MBS multicast received until 4 ms prior to symbol n when evaluating all DRX Active Time conditions as specified in Clause 5.7b and all multicast sessions are configured with multicast DRX:
3> not transmit periodic SRS and semi-persistent SRS defined in TS 38.214 [7];
3> not report semi-persistent CSI configured on PUSCH;
3> if ps-TransmitPeriodicL1-RSRP is not configured with value true:
4> not report periodic CSI that is L1-RSRP on PUCCH.
3> if ps-TransmitOtherPeriodicCSI is not configured with value true:
4> not report periodic CSI that is not L1-RSRP on PUCCH.
1> else:
2> in current symbol n, if a DRX group would not be in Active Time considering grants/assignments scheduled on Serving Cell(s) in this DRX group and DRX Command MAC CE/Long DRX Command MAC CE received and Scheduling Request sent until 4 ms prior to symbol n when evaluating all DRX Active Time conditions as specified in this clause; and
2> if allowCSI-SRS-Tx-MulticastDRX-Active is not configured or, in current symbol n, if all multicast DRXes corresponding to the DRX group would not be in Active Time considering multicast assignments/DRX Command MAC CE for MBS multicast received until 4 ms prior to symbol n when evaluating all DRX Active Time conditions as specified in Clause 5.7b and all multicast sessions corresponding to the DRX group are configured with multicast DRX:
3> not transmit periodic SRS and semi-persistent SRS defined in TS 38.214 [7] in this DRX group;
3> not report CSI on PUCCH and semi-persistent CSI configured on PUSCH in this DRX group.
2> if CSI masking (csi-Mask) is setup by upper layers:
3> in current symbol n, if drx-onDurationTimer of a DRX group would not be running considering grants/assignments scheduled on Serving Cell(s) in this DRX group and DRX Command MAC CE/Long DRX Command MAC CE received until 4 ms prior to symbol n when evaluating all DRX Active Time conditions as specified in this clause; and
3> if allowCSI-SRS-Tx-MulticastDRX-Active is not configured or, in current symbol n, if drx-onDurationTimerPTM(s) of all multicast DRXes corresponding to the DRX group would not be running considering multicast assignments and DRX Command MAC CE for MBS multicast received until 4 ms prior to symbol n when evaluating all DRX Active Time conditions as specified in Clause 5.7b and all multicast sessions corresponding to the DRX group are configured with multicast DRX:
4> not report CSI on PUCCH in this DRX group.
NOTE 4: If a UE multiplexes a CSI configured on PUCCH with other overlapping UCI(s) according to the procedure specified in TS 38.213 [6] clause 9.2.5 and this CSI multiplexed with other UCI(s) would be reported on a PUCCH resource either outside DRX Active Time of the DRX group in which this PUCCH is configured or outside the on-duration period of the DRX group in which this PUCCH is configured if CSI masking is setup by upper layers, it is up to UE implementation whether to report this CSI multiplexed with other UCI(s).
Regardless of whether the MAC entity is monitoring PDCCH or not on the Serving Cells in a DRX group, the MAC entity transmits HARQ feedback, aperiodic CSI on PUSCH, and aperiodic SRS defined in TS 38.214 [7] on the Serving Cells in the DRX group when such is expected.
The MAC entity needs not to monitor the PDCCH if it is not a complete PDCCH occasion (e.g. the Active Time starts or ends in the middle of a PDCCH occasion).