5.7b Discontinuous Reception (DRX) for MBS Multicast

38.3213GPPMedium Access Control (MAC) protocol specificationNRRelease 17TS

For MBS multicast, the MAC entity may be configured by RRC with a DRX functionality per G-RNTI or per G-CS-RNTI that controls the UE’s PDCCH monitoring activity for the MAC entity’s G-RNTI(s) and G-CS-RNTI(s) as specified in TS 38.331 [5]. When in RRC_CONNECTED, if multicast DRX is configured, the MAC entity is allowed to monitor the PDCCH for this G-RNTI or G-CS-RNTI discontinuously using the multicast DRX operation specified in this clause; otherwise the MAC entity monitors the PDCCH for this G-RNTI or G-CS-RNTI as specified in TS 38.213 [6]. The multicast DRX operation specified in this clause is performed independently for each G-RNTI or G-CS-RNTI and independently from the DRX operation specified in clauses 5.7 and 5.7a.

RRC controls multicast DRX operation per G-RNTI or per G-CS-RNTI by configuring the following parameters:

– drx-onDurationTimerPTM: the duration at the beginning of a DRX cycle;

– drx-SlotOffsetPTM: the delay before starting the drx-onDurationTimerPTM;

– drx-InactivityTimerPTM: the duration after the PDCCH occasion in which a PDCCH indicates a new DL multicast transmission for the MAC entity;

– drx-LongCycleStartOffsetPTM: the long DRX cycle drx-LongCycle-PTM and drx-StartOffset-PTM which defines the subframe where the long DRX cycle starts;

– drx-RetransmissionTimerDL-PTM (per DL HARQ process for MBS multicast): the maximum duration until a DL multicast retransmission is received;

– drx-HARQ-RTT-TimerDL-PTM (per DL HARQ process for MBS multicast): the minimum duration before a DL multicast assignment for HARQ retransmission is expected by the MAC entity.

When multicast DRX is configured for a G-RNTI or G-CS-RNTI, the Active Time includes the time while:

– drx-onDurationTimerPTM or drx-InactivityTimerPTM or drx-RetransmissionTimerDL-PTM for this G-RNTI or G-CS-RNTI is running.

When multicast DRX is configured for a G-RNTI or G-CS-RNTI, the MAC entity shall for this G-RNTI or G-CS-RNTI:

1> if a MAC PDU is received in a configured downlink multicast assignment:

2> if HARQ feedback is enabled:

3> start the drx-HARQ-RTT-TimerDL-PTM for the corresponding HARQ process in the first symbol after the end of the corresponding transmission carrying the DL HARQ feedback;

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.

2> stop the drx-RetransmissionTimerDL-PTM for the corresponding HARQ process;

2> stop the drx-RetransmissionTimerDL for the corresponding HARQ process.

1> if a drx-HARQ-RTT-TimerDL-PTM expires:

2> if the data of the corresponding HARQ process was not successfully decoded:

3> start the drx-RetransmissionTimerDL-PTM for the corresponding HARQ process in the first symbol after the expiry of drx-HARQ-RTT-TimerDL-PTM.

1> if a DRX Command MAC CE with DCI scrambled with a G-RNTI is received:

2> stop drx-onDurationTimerPTM of the DRX for this G-RNTI;

2> stop drx-InactivityTimerPTM of the DRX for this G-RNTI.

1> if [(SFN × 10) + subframe number] modulo (drx-LongCycle-PTM) = drx-StartOffset-PTM:

2> start drx-onDurationTimerPTM after drx-SlotOffsetPTM from the beginning of the subframe.

1> if the MAC entity is in Active Time for this G-RNTI or G-CS-RNTI:

2> monitor the PDCCH for this G-RNTI or G-CS-RNTI as specified in TS 38.213 [6];

2> if the PDCCH indicates a DL multicast transmission:

3> if HARQ feedback is enabled:

4> start the drx-HARQ-RTT-TimerDL-PTM for the corresponding HARQ process in the first symbol after the end of the corresponding transmission carrying the DL HARQ feedback;

4> 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.

3> stop the drx-RetransmissionTimerDL-PTM for the corresponding HARQ process;

3> stop the drx-RetransmissionTimerDL for the corresponding HARQ process.

2> if the PDCCH indicates a new multicast transmission for this G-RNTI or G-CS-RNTI:

3> start or restart drx-InactivityTimerPTM in the first symbol after the end of the PDCCH reception.

NOTE: A PDCCH indicating activation of multicast SPS is considered to indicate a new transmission.

The MAC entity needs not to monitor the PDCCH for a G-RNTI or a G-CS-RNTI if it is not a complete PDCCH occasion (e.g. the Active Time for a G-RNTI or a G-CS-RNTI starts or ends in the middle of a PDCCH occasion).