5.2 Maintenance of Uplink Time Alignment

38.3213GPPMedium Access Control (MAC) protocol specificationNRRelease 17TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

RRC configures the following parameters for the maintenance of UL time alignment:

– timeAlignmentTimer (per TAG) which controls how long the MAC entity considers the Serving Cells belonging to the associated TAG to be uplink time aligned;

– inactivePosSRS-TimeAlignmentTimer which controls how long the MAC entity considers the Positioning SRS transmission in RRC_INACTIVE in clause 5.26 to be uplink time aligned;

– cg-SDT-TimeAlignmentTimer which controls how long the MAC entity considers the uplink transmission for CG-SDT to be uplink time aligned.

The MAC entity shall:

1> when a Timing Advance Command MAC CE is received, and if an N_TA (as defined in TS 38.211 [8]) has been maintained with the indicated TAG:

2> apply the Timing Advance Command for the indicated TAG;

2> if inactivePosSRS-TimeAlignmentTimer is configured and there is ongoing Positioning SRS Transmission in RRC_INACTIVE as in clause 5.26:

3> start or restart the inactivePosSRS-TimeAlignmentTimer associated with the indicated TAG.

2> if CG-SDT procedure triggered as in clause 5.27 is ongoing:

3> start or restart the cg-SDT-TimeAlignmentTimer associated with the indicated TAG.

2> else:

3> start or restart the timeAlignmentTimer associated with the indicated TAG.

1> when a Timing Advance Command is received in a Random Access Response message for a Serving Cell belonging to a TAG or in a MSGB for an SpCell:

2> if the Random Access Preamble was not selected by the MAC entity among the contention-based Random Access Preamble:

3> apply the Timing Advance Command for this TAG;

3> start or restart the timeAlignmentTimer associated with this TAG.

2> else if the timeAlignmentTimer associated with this TAG is not running:

3> apply the Timing Advance Command for this TAG;

3> start the timeAlignmentTimer associated with this TAG;

3> when the Contention Resolution is considered not successful as described in clause 5.1.5; or

3> when the Contention Resolution is considered successful for SI request as described in clause 5.1.5, after transmitting HARQ feedback for MAC PDU including UE Contention Resolution Identity MAC CE:

4> stop timeAlignmentTimer associated with this TAG.

3> when the Contention Resolution is considered not successful as described in clause 5.1.5:

4> if CG-SDT procedure triggered as in clause 5.27 is ongoing:

5> set the N_TA value to the value before applying the received Timing Advance Command as in TS 38.211 [8].

3> when the Contention Resolution is considered successful for Random Access procedure while the CG-SDT procedure is ongoing:

4> stop timeAlignmentTimer associated with this TAG;

4> start or restart the cg-SDT-TimeAlignmentTimer associated with this TAG.

3> when the Contention Resolution is considered successful for Random Access procedure while SRS transmission in RRC_INACTIVE is ongoing:

4> start or restart the inactivePosSRS-TimeAlignmentTimer associated with this TAG.

2> else:

3> ignore the received Timing Advance Command.

1> when an Absolute Timing Advance Command is received in response to a MSGA transmission including C-RNTI MAC CE as specified in clause 5.1.4a:

2> apply the Timing Advance Command for PTAG;

2> if CG-SDT procedure is ongoing:

3> start or restart the cg-SDT-TimeAlignmentTimer associated with PTAG.

2> else:

3> start or restart the timeAlignmentTimer associated with PTAG.

1> when the indication is received from upper layer for stopping the inactivePosSRS-TimeAlignmentTimer:

2> stop the inactivePosSRS-TimeAlignmentTimer.

1> when the indication is received from upper layer for starting the inactivePosSRS-TimeAlignmentTimer:

2> start or restart the inactivePosSRS-TimeAlignmentTimer.

1> when instruction from the upper layer has been received for starting the cg-SDT-TimeAlignmentTimer:

2> start the cg-SDT-TimeAlignmentTimer.

1> when instruction from the upper layer has been received for stopping the cg-SDT-TimeAlignmentTimer:

2> consider the cg-SDT-TimeAlignmentTimer as expired.

1> when instruction from the upper layer has been received for starting the TimeAlignmentTimer associated with PTAG:

2> start the TimeAlignmentTimer associated with PTAG.

1> when a timeAlignmentTimer expires:

2> if the timeAlignmentTimer is associated with the PTAG:

3> flush all HARQ buffers for all Serving Cells;

3> notify RRC to release PUCCH for all Serving Cells, if configured;

3> notify RRC to release SRS for all Serving Cells, if configured;

3> clear any configured downlink assignments and configured uplink grants;

3> clear any PUSCH resource for semi-persistent CSI reporting;

3> consider all running timeAlignmentTimers as expired;

3> maintain N_TA (defined in TS 38.211 [8]) of all TAGs.

2> else if the timeAlignmentTimer is associated with an STAG, then for all Serving Cells belonging to this TAG:

3> flush all HARQ buffers;

3> notify RRC to release PUCCH, if configured;

3> notify RRC to release SRS, if configured;

3> clear any configured downlink assignments and configured uplink grants;

3> clear any PUSCH resource for semi-persistent CSI reporting;

3> maintain N_TA (defined in TS 38.211 [8]) of this TAG.

1> when the inactivePosSRS-TimeAlignmentTimer expires:

2> notify RRC to release Positioning SRS for RRC_INACTIVE configuration(s).

1> when the cg-SDT-TimeAlignmentTimer expires:

2> clear any configured uplink grants;

2> if a PDCCH addressed to the MAC entity’s C-RNTI after initial transmission for the CG-SDT with CCCH message has not been received:

3> consider ongoing CG-SDT procedure as terminated;

3> indicate the expiry of cg-SDT-TimeAlignmentTimer to the upper layer.

2> flush all HARQ buffers;

2> maintain N_TA (defined in TS 38.211 [8]) of this TAG.

When the MAC entity stops uplink transmissions for an SCell due to the fact that the maximum uplink transmission timing difference between TAGs of the MAC entity or the maximum uplink transmission timing difference between TAGs of any MAC entity of the UE is exceeded, the MAC entity considers the timeAlignmentTimer associated with the SCell as expired.

The MAC entity shall not perform any uplink transmission on a Serving Cell except the Random Access Preamble and MSGA transmission when the timeAlignmentTimer associated with the TAG to which this Serving Cell belongs is not running, CG-SDT procedure is not ongoing or SRS transmission in RRC_INACTIVE as in clause 5.26 is not on-going. Furthermore, when the timeAlignmentTimer associated with the PTAG is not running, CG-SDT procedure is not ongoing and SRS transmission in RRC_INACTIVE as in clause 5.26 is not ongoing, the MAC entity shall not perform any uplink transmission on any Serving Cell except the Random Access Preamble and MSGA transmission on the SpCell. The MAC entity shall not perform any uplink transmission except the Random Access Preamble and MSGA transmission when the cg-SDT-TimeAlignmentTimer is not running during the ongoing CG-SDT procedure as triggered in clause 5.27. The MAC entity shall not perform any uplink transmission except the Random Access Preamble and MSGA transmission when inactivePosSRS-TimeAlignmentTimer is not running during the procedure for SRS transmission in RRC_INACTIVE as in clause 5.26.