4 Synchronization procedures

36.2133GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical layer proceduresRelease 17TS

4.1 Cell search

Cell search is the procedure by which a UE acquires time and frequency synchronization with a cell and detects the physical layer Cell ID of that cell. E-UTRA cell search supports a scalable overall transmission bandwidth corresponding to 6 resource blocks and upwards.

The following signals are transmitted in the downlink to facilitate cell search: the primary and secondary synchronization signals.

A UE may assume the antenna ports 0 – 3 and the antenna port for the primary/secondary synchronization signals of a serving cell are quasi co-located (as defined in [3]) with respect to Doppler shift and average delay.

For a BL/CE UE, if the UE is configured with higher layer parameter RSS-Config, the UE can use the resynchronization signal (as defined in [3]) to re-acquire time and frequency synchronization with the cell.

4.2 Timing synchronization

4.2.1 Radio link monitoring

The downlink radio link quality of the primary cell shall be monitored by the UE for the purpose of indicating out-of-sync/in-sync status to higher layers.

If the UE is configured with a SCG [11] and the parameter rlf-TimersAndConstantsSCG is provided by the higher layers and is not set to release, the downlink radio link quality of the PSCell [11] of the SCG shall be monitored by the UE for the purpose of indicating out-of-sync/in-sync status to higher layers.

In non-DRX mode operation, the physical layer in the UE shall every radio frame assess the radio link quality, evaluated over the previous time period defined in [10], against thresholds (Q_out and Q_in) defined by relevant tests in [10].

In DRX mode operation, the physical layer in the UE shall at least once every DRX period assess the radio link quality, evaluated over the previous time period defined in [10], against thresholds (Q_out and Q_in) defined by relevant tests in [10].

If higher-layer signalling indicates certain subframes for restricted radio link monitoring, the radio link quality shall not be monitored in any subframe other than those indicated.

The physical layer in the UE shall in radio frames where the radio link quality is assessed indicate out-of-sync to higher layers when the radio link quality is worse than the threshold Q_out. When the radio link quality is better than the threshold Q_in, the physical layer in the UE shall in radio frames where the radio link quality is assessed indicate in-sync to higher layers.

4.2.2 Inter-cell synchronization

No functionality is specified in this clause in this release.

4.2.3 Transmission timing adjustments

Upon reception of a timing advance command or a timing adjustment indication for a TAG containing the primary cell or PSCell, the UE shall adjust uplink transmission timing for PUCCH/PUSCH/SRS of the primary cell or PSCell based on the received timing advance command or a timing adjustment indication.

The UL transmission timing for PUSCH/SRS of a secondary cell is the same as the primary cell if the secondary cell and the primary cell belong to the same TAG. If the primary cell in a TAG has a frame structure type 1 and a secondary cell in the same TAG has a frame structure type 2 or frame structure 3, UE may assume that N_TA ≥ 624.

If the UE is configured with a SCG, the UL transmission timing for PUSCH/SRS of a secondary cell other than the PSCell is the same as the PSCell if the secondary cell and the PSCell belong to the same TAG.

Upon reception of a timing advance command or a timing adjustment indication for a TAG not containing the primary cell or PSCell, if all the serving cells in the TAG have the same frame structure type, the UE shall adjust uplink transmission timing for PUSCH/SRS of all the secondary cells in the TAG based on the received timing advance command or a timing adjustment indication where the UL transmission timing for PUSCH /SRS is the same for all the secondary cells in the TAG.

Upon reception of a timing advance command or a timing adjustment indication for a TAG not containing the primary cell or PSCell, if a serving cell in the TAG has a different frame structure type compared to the frame structure type of another serving cell in the same TAG, the UE shall adjust uplink transmission timing for PUSCH/SRS of all the secondary cells in the TAG by using N_TAoffset = 624 regardless of the frame structure type of the serving cells and based on the received timing advance command or a timing adjustment indication where the UL transmission timing for PUSCH /SRS is the same for all the secondary cells in the TAG. N_TAoffset is described in [3].

The timing adjustment indication specified in [11] indicates the initial N_TA used for a TAG.The timing advance command for a TAG indicates the change of the uplink timing relative to the current uplink timing for the TAG as multiples of 16. The start timing of the random access preamble is specified in [3].

In case of random access response, an 11-bit timing advance command [8], T_A, for a TAG indicates N_TA values by index values of T_A = 0, 1, 2, …, 256 if the UE is configured with a SCG, and T_A = 0, 1, 2, …, 1282 otherwise, where an amount of the time alignment for the TAG is given by N_TA = T_A ×16. N_TA is defined in [3].

In other cases, a 6-bit timing advance command [8] or the Timing advance adjustment field in DCI format 6-0A/B if present [4], T_A, for a TAG indicates adjustment of the current N_TA value, N_TA,old, to the new N_TA value, N_TA,new, by index values of T_A = 0, 1, 2,…, 63, where N_TA,new = N_TA,old + (T_A −31)×16. Here, adjustment of N_TA value by a positive or a negative amount indicates advancing or delaying the uplink transmission timing for the TAG by a given amount respectively.

For a non-BL/CE UE, for a timing advance command received on

– subframe n, the corresponding adjustment of the uplink transmission timing shall apply from the beginning of subframe n+5 if the UE is configured with higher layer parameter shortProcessingTime and the corresponding PDCCH with CRC scrambled by C-RNTI is in the UE-specific search space, n+6 otherwise.

– slot n, the corresponding adjustment of the uplink transmission timing shall apply from the first subframe boundary no earlier than slot [n+8].

– subslot n, the corresponding adjustment of the uplink transmission timing shall apply from the first subframe boundary no earlier than

– subslot [n+16] if higher layer parameter proc-TimeAdv-r15= ‘nplus4set1‘.

– subslot [n+18] if higher layer parameter proc-TimeAdv-r15= ‘nplus6set1‘or ‘nplus6set2‘.

– subslot [n+20] if higher layer parameter proc-TimeAdv-r15= ‘nplus8set2‘.

For serving cells in the same TAG, when the UE’s uplink PUCCH/PUSCH/SRS transmissions in subframe n and subframe n+1 are overlapped due to the timing adjustment, the UE shall complete transmission of subframe n and not transmit the overlapped part of subframe n+1.

For a BL/CE UE, for a timing advance command received on subframe n, the corresponding adjustment of the uplink transmission timing shall apply for the uplink PUCCH/PUSCH/SRS transmissions in subframe n+6+K_offset. When the BL/CE UE’s uplink PUCCH/PUSCH/SRS transmissions in subframe n and subframe n+1 are on the same narrowband and are overlapped due to the timing adjustment, the UE shall complete transmission of subframe n and is not required to transmit in subframe n+1 until the first available symbol that has no overlapping portion with subframe n. When the BL/CE UE’s uplink PUCCH/PUSCH/SRS transmissions in subframe n and subframe n+1 are on different narrowbands, and the timing adjustment occurs in the guard period for narrowband retuning, the UE is not required to transmit in subframe n+1 until the first available symbol that has no overlapping portion with subframe n and which does not reduce the guard period. The value of is given by,

– if the UE is configured with the higher layer parameter CellSpecificKoffset,

– where

is the parameter CellSpecificKoffset provided by higher layers, and

is the parameter UESpecificKoffset provided by higher layers, otherwise

– otherwise,

– .

If the received downlink timing changes and is not compensated or is only partly compensated by the uplink timing adjustment without timing advance command as specified in [10], the UE changes N_TA accordingly.

For a BL/CE UE in a NTN serving cell, using serving satellite higher-layer ephemeris parameters, if configured, the BL/CE UE determines  (defined in [3]) using the serving satellite position and its own position to pre-compensate the two-way transmission delay on the service link. To pre-compensate the two-way transmission delay between the uplink time synchronization reference point and the serving satellite, the BL/CE UE determines (defined in [3]) based on one-way propagation delay which can be obtained as:

where , , and are given by the higher layer parameters nta-Common, nta-CommonDrift, and nta-CommonDriftVariation respectively, and is the epoch time given by the higher layer parameter epochTime. provides a distance at time between the serving satellite and the uplink time synchronization reference point divided by the speed of light. The uplink time synchronization reference point is the point where DL and UL are frame aligned with an offset given by .

For a BL/CE UE communicating over NTN, time and frequency pre-compensation is adjusted per uplink segment with a transmission duration of time units, where the quantity is provided by system information, as specified in 3GPP TS 36.331.

4.3 Timing for Secondary Cell Activation / Deactivation

When a UE receives an activation command [8] for a secondary cell in subframe n, the corresponding actions in [8] shall be applied no later than the minimum requirement defined in [10] and no earlier than subframe n+8, except for the following:

– the actions related to CSI reporting on a serving cell which is active in subframe n+8

– the actions related to the sCellDeactivationTimer associated with the secondary cell [8]

which shall be applied in subframe n+8.

– the actions related to CSI reporting on a serving cell which is not active in subframe n+8

which shall be applied in the earliest subframe after n+8 in which the serving cell is active.

When a UE receives an RRC configuration which configures secondary cell as activated [11] in subframe n, the corresponding actions in [8] shall be applied no later than the minimum requirement defined in [10] and no earlier than subframe n+20, except for the following:

– the actions related to CSI reporting on a serving cell which is active in subframe n+20

– the actions related to the sCellDeactivationTimer associated with the secondary cell [8]

which shall be applied in subframe n+20.

– the actions related to CSI reporting on a serving cell which is not active in subframe n+20

which shall be applied in the earliest subframe after n+20 in which the serving cell is active.

If a UE has been configured with cqi-ShortPeriodicSCell for a secondary cell, parameters cqi-pmi-ConfigIndex and ri-ConfigIndex in clause 7.2 are given by cqi-ShortPeriodicSCell from subframe n+8 until subframe n+34.

When a UE receives a deactivation command [8] for a secondary cell or the sCellDeactivationTimer associated with the secondary cell expires in subframe n, the corresponding actions in [8] shall apply no later than the minimum requirement defined in [10], except for the actions related to CSI reporting on a serving cell which is active which shall be applied in subframe n+8.