5.3 Synchronisation procedures

25.2243GPPPhysical layer procedures (TDD)TS

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

5.3.1 Cell search

During the initial cell search, the UE searches for a cell. It then determines the DwPTS synchronisation, scrambling code and basic midamble code, control multi-frame synchronisation and then reads the BCH. How cell search is typically done is described in Annex CA.

For MBSFN FACH, the downlink scrambling codes and basic midamble codes to be used for non-beacon timeslots are signalled by higher layers.

5.3.2 DCH synchronization

The DPCH synchronisation is the same as that of 3.84 Mcps TDD, cf. [4.4.2 Dedicated channel synchronisation].

5.3.2A Shared physical channel synchronization

For HS-DSCH and E-PUCH operation without DPCH, the synchronisation procedure is defined in the subclause.

5.3.2A.1 Synchronisation primitives

5.3.2A.1.1 General

For the shared physical channels, synchronisation primitives are used to indicate the synchronisation status of radio links, both in uplink and downlink. The definition of the primitives is given in the following subclauses.

5.3.2A.1.2 Downlink synchronisation primitives

The UE shall measure any of the following downlink physical channels on any carrier to estimate downlink quality.

a) HS-PDSCH

b) HS-SCCH

c) E-AGCH

Layer 1 in the UE shall check the synchronization status of downlink physical channels on all carriers. Synchronisation status is indicated to higher layers, using the CPHY-Sync-IND or CPHY-Out-of-Sync-IND primitives.

The criteria for reporting synchronization status are defined in two different phases.

The first phase lasts until the downlink shared channel is considered to be established by higher layers. During this phase, out-of-sync shall not be reported.in-sync shall be reported using the CPHY-Sync-IND primitive if the following criterion is fulfilled.

– At least one downlink physical channel with a CRC attached is received in the current subframe with correct CRC.

The second phase starts after the downlink shared channel is considered established by higher layers. During this phase, both out-of-sync and in-sync are reported as follows.

Out-of-sync shall be reported using the CPHY-Out-of-Sync-IND primitive based on the synchronization status in an out-of-sync detection window if the following criterion is fulfilled.The out-of-sync detection window (out-of-sync window) is configured by higher layers.

– No downlink physical channel has been received with a correct CRC in the out-of-sync detection window period.

In the second phase, the first out-of-sync detection window starts when the second phase starts; after this, the next out-of-sync detection window starts right after the previous out-of-sync detection window.

In-sync shall be reported using the CPHY-Sync-IND primitive if the following criteria is fulfilled:

– At least one downlink physical channel with a CRC attached is received in the current subframe with correct CRC.

5.3.2A.1.3 Uplink synchronisation primitives

Layer 1 in the Node B shall check synchronisation status of uplink physical channels. Synchronisation status is indicated to the RL Failure/Restored triggering function using either the CPHY-Sync-IND or CPHY-Out-of-Sync-IND primitive.The exact criteria for indicating in-sync/out-of-sync is not subject to specification.

5.3.2A.2 Radio link monitoring

5.3.2A.2.1 Downlink radio link failure

The downlink shared physical channels are monitored by the UE, to trigger radio link failure procedures. The downlink radio link failure status is specified in [15], and is based on the synchronisation status primitives CPHY-Sync-IND and CPHY-Out-of-Sync-IND, indicating in-sync and out-of-sync respectively.

5.3.2A.2.2 Uplink radio link failure/restore

The uplink shared physical channels are monitored by the Node B in order to trigger uplink radio link failure/restore procedures. The uplink radio link failure/restore status is reported using the synchronisation status primitives CPHY-Sync-IND and CPHY-Out-of-Sync-IND, indicating in-sync and out-of-sync respectively.

When the uplink shared physical channel is in the in-sync state, Node B shall start timer T_RLFAILURE after receiving N_OUTSYNC_IND consecutive out-of-sync indications. Node B shall stop and reset timer T_RLFAILURE upon receiving successive N_INSYNC_IND in-sync indications. If T_RLFAILURE expires, Node B shall indicate to higher layers the uplink shared physical channel is out-of-sync using the synchronization status primitives. Furthermore, the uplink shared physical channel state shall be changed to the out-of-sync state.

When the uplink shared physical channel is in the out-of-sync state, after receiving N_INSYNC_IND successive in-sync indications Node B shall indicate that the uplink shared physical channel has re-established synchronisation and the uplink shared physical channel’s state shall be changed to the in-sync-state. The specific parameter settings (values of T_RLFAILURE, N_OUTSYNC_IND, and N_INSYNC_IND) are configurable, see [16].

5.3.3 Synchronization procedure in CELL_FACH state

5.3.3.1 Uplink synchronization status detection

Maintaining of uplink synchronization is not needed in CELL_FACH state, UE could be out of synchronization after a period of transmission pause.

The uplink synchronization status detection is under control of Node B, which determines UE’s synchronization status according to a timer T-sync. The timer is UE specific and the parameter is configured by higher layers. Node B determines the UE out of synchronization when the T-sync timer expires and in synchronization otherwise. The details of the timer T-sync operation are shown as below:

– Initially starting the timer

When Node B receives the UE’s uplink E-RUCCH transmission correctly, it will initially start the timer.

– Restarting the timer

When Node B receives the UE’s any uplink transmission (e.g. E-RUCCH, E-DCH or HS-SICH) correctly, it will restart the timer.

5.3.3.2 Establishment of uplink synchronization

Node B shall order UE to establish the uplink synchronization via HS-SCCH order in case that it detects the UE is out of uplink synchronization. Response to this synchronization establishment command, UE then initiates the random access procedure, cf [subclause 5.6 Random Access Procedure], which only involves the UpPCH and the E-RUCCH.

Node B will limit the synchronization delay based on a timer T-protect. If Node B doesn’t receive the E-RUCCH in the synchronization procedure before T-protect expires, Node B will restart another uplink synchroniztion procedure via HS-SCCH order. After N-protect successive uplink synchronization attempts, Node B shall terminate the synchroniztion procedure and indicate an uplink synchronization failure to higher layers. The specific parameter settings (values of T-protect and N-protect) are configured by higher layers.