4.4 Synchronisation procedures

25.2243GPPPhysical layer procedures (TDD)TS

4.4.1 Cell search

During the cell search, the UE searches for a cell and determines the downlink scrambling code, basic midamble code and frame synchronisation of that cell. How cell search is typically done is described in Annex C.

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

4.4.2 Dedicated channel synchronisation

4.4.2.1 Synchronisation primitives

4.4.2.1.1 General

For the dedicated 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.

When operating HS-DSCH, the configuration of a downlink DPCH by UTRAN is optional. Subclause 4.4.2.1.2 relates to downlink synchronisation in the case that an uplink and downlink DPCH have been configured by higher layers. Subclause 4.4.2.1.2A relates to downlink synchronisation in the case that only an uplink DPCH has been configured by higher layers.

4.4.2.1.2 Downlink synchronisation primitives

Layer 1 in the UE shall check the synchronization status of each DL CCTrCH individually in every radio frame All bursts and transport channels of a CCTrCH shall be taken into account. Synchronisation status is indicated to higher layers, using the CPHY-Sync-IND or CPHY-Out-of-Sync-IND primitives. For dedicated physical channels configured with Repetition Periods [15 ] only the configured active periods shall be taken into account in the estimation. The status check shall also include detection of the Special Bursts defined in 4.5 for DTX.

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

The first phase lasts until 160 ms after the downlink CCTrCH is considered to be established by higher layers. During this time, Out-of-sync shall not be reported. In-sync shall be reported using the CPHY-Sync-IND primitive if any one of the following three criteria is fulfilled.

a) The UE estimates the burst reception quality over the previous 40 ms period to be better than a threshold Q_in. This criterion shall be assumed not to be fulfilled before 40 ms of burst reception quality measurement have been collected.

b) At least one transport block with a CRC attached is received in a TTI ending in the current frame with correct CRC.

c) The UE detects at least one Special Burst. Special Burst detection shall be successful if the burst is detected with quality above a threshold, Q_sbin, and the TFCI is decoded to be that of the Special Burst.

The second phase starts 160 ms after the downlink dedicated 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 if all three of the following criteria are fulfilled:

– the UE estimates the received dedicated channel burst quality over the last 160 ms period to be worse than a threshold Q_out. The value, Q_out is defined implicitly by the relevant tests in [2];

– no Special Burst is detected with quality above a threshold Q_sbout within the last 160 ms period. The value Q_sbout is defined implicitly by the relevant tests in [2];

– over the previous 160 ms, no transport block has been received with a correct CRC

If the UE detects the beacon channel reception level [10 dB] above the handover triggering level, the UE shall use 320 ms estimation period for the burst quality evaluation and for the Special Burst and CRC detection window.

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

– the UE estimates the received burst reception quality over the last 160 ms period to be better than a threshold Q_in. The value, Q_in is defined implicitly by the relevant tests in [2].

– the UE detects at least one Special Burst with quality above a threshold Q_sbin within the last 160 ms period. The value, Q_sbin, is defined implicitly by the relevent tests in [2].

– at least one transport block with a CRC attached is received in a TTI ending in the current frame with correct CRC.

If the UE detects the beacon channel reception level [10 dB] above the handover triggering level, the UE uses 320 ms estimation period for the burst quality evaluation and for the Special Burst detection window.

If no data are provided by higher layers for transmission during the second phase on the downlink dedicated channel then DTX shall be applied as defined in section 4.5.

How the primitives are used by higher layers is described in [15]. The above definitions may lead to radio frames where neither the In-Sync nor Out-of-Sync primitives are reported.

4.4.2.1.2A Downlink synchronisation primitives for HS-channels

In the case that an uplink DPCH has been configured by higher layers but a downlink DPCH has not been configured, the UE shall report downlink synchronisation status based upon other downlink physical channels.

The UE shall monitor the received beacon signal level within the cell and shall average the received beacon power over a period of 160ms. This averaged value is denoted P_b dBm. The UE shall also monitor and average over the same period, the ISCP on the assigned HS-SCCH resources. This value is denoted I_HS-SCCH dBm. A quality value Q_hs is formed as follows:

Q_hs = P_b – I_HS-SCCH + D_hs-sync

– where D_hs-sync is signalled by higher layers.

In-sync shall be reported using the CPHY-Sync-IND primitive each time an HS-DSCH CRC pass is detected. On this event, an indicator maintained by the UE termed "HS-DSCH_failure" shall be set to ‘false’. In-sync shall also be reported if the HS-DSCH_failure indicator is set to ‘false’ and during the last 160ms period, Q_hs > Q_hsin, where Q_hsin is a quality threshold defined implicitly by the relevant tests in [2].

Out-of-sync shall be reported using the CPHY-Out-of-Sync-IND primitive. "Out-of-sync" is generated in the event that, during the last 160ms period, Q_hs < Q_hsout, where Q_hsout is a quality threshold defined implicitly by the relevant tests in [2]. CPHY-Out-of-Sync-IND shall also be generated in the event of 16 successive HS-DSCH CRC failures. On occurrence of this event, the HS-DSCH_failure indicator shall be set to ‘true’.

How the primitives are used by higher layers is described in [15]. The above definitions may lead to radio frames where neither the In-Sync nor Out-of-Sync primitives are reported. They may also, under some circumstances, lead to radio frames in which both In-Sync and Out-of-Sync primitives are generated. In this instance, In-sync shall override Out-of-Sync and the Out-of-Sync primitive shall not be reported.

4.4.2.1.3 Uplink synchronisation primitives

Layer 1 in the Node B shall every radio frame check synchronisation status, individually for each UL CCTrCH of the radio link. 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, but could e.g. be based on received burst quality or CRC checks. One example would be to have the same criteria as for the downlink synchronisation status primitives.

4.4.2.2 Radio link monitoring

4.4.2.2.1 Downlink radio link failure

The downlink CCTrCHs are monitored by the UE, to trigger radio link failure procedures. The downlink CCTrCH 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. These primitives shall provide status for each DL CCTrCH separately.

4.4.2.2.2 Uplink radio link failure/restore

The uplink CCTrCHs are monitored by the Node B in order to trigger CCTrCH failure/restore procedures. The uplink CCTrCH 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 CCTrCH 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 which CCTrCHs are out-of-sync using the synchronization status primitives. Furthermore, the CCTrCH state shall be changed to the out-of-sync state.

When a CCTrCH is in the out-of-sync state, after receiving N_INSYNC_IND successive in-sync indications Node B shall indicate that the CCTrCH has re-established synchronisation and the CCTrCH’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].