16 HS-DSCH reception in CELL_FACH state (1.28Mcps TDD only)

25.3083GPPHigh Speed Downlink Packet Access (HSDPA)Overall descriptionRelease 17Stage 2TS

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

The HS-DSCH reception in CELL_FACH state is always linked with E-DCH transmission in CELL_FACH and Idle mode.

The HS-DSCH reception in CELL_FACH state is enabled by the UTRAN by including the parameters for HS-DSCH reception in CELL_FACH state in the system information broadcast. Parameters include HS-SCCH, HS-SICH, HS-DSCH configuration and common H-RNTI. UTRAN may also reconfigure HS-DSCH reception parameters (H-RNTI) by dedicated RRC signalling.

In a multi-frequency cell, HS-DSCH resource in CELL_FACH state can be established on primary frequency and secondary frequencies. HS-DSCH resources include HS-SCCH, HS-SICH, and HS-PDSCH. UTRAN can configure a working frequency for a particular UE. Uplink transmission and downlink HS-DSCH reception for a specific UE is on the same carrier, on which both the uplink random access resource and downlink HS-DSCH resource should be established.

When HS-DSCH reception is configured in the cell, it shall take precedence instead of reception of S-CCPCH and FACH for dedicated signalling data in CELL_FACH state.

The BCCH is mapped on HS-DSCH for transmitting system information change information to the UEs in CELL_FACH state receiving HS-DSCH. The transmission of BCCH on HS-DSCH is performed by using BCCH specific H-RNTI on specific HS-SCCH code indicated in system information broadcast. In a multi-frequency cell, the transmission of BCCH on HS-DSCH is performed on all frequencies where CELL_FACH state UEs stay and UE detects the BCCH specific H-RNTI on its working frequency.

Simultaneous reception of HS-DSCH and S-CCPCH is only required in case of reception of CTCH and MBMS ptm transmission.

The UE in CELL_FACH state receiving HS-DSCH performs normal cell reselection process. When UE enters to a new cell, it obtains the valid HS-SCCH configuration from system information broadcast and performs Cell Update procedure.

UTRAN obtains the knowledge of the UE supporting the enhanced CELL_FACH state from the RRC Connection Request message. The support of Enhanced CELL_FACH state is optional for UE.

The HSDPA reception in CELL_FACH state utilizes the enhanced L2 architecture with flexible RLC PDU size and MAC-ehs segmentation as defined in clause 6 and in [7]. The UE in CELL_FACH state receiving HS-DSCH uses E-DCH for the uplink transmission.

16.1 UE operation

When HS-DSCH reception is configured in the system information broadcast, the UE shall after sending the RRC connection request or Cell Update, while not having a dedicated H-RNTI, monitor the common H-RNTI value on the HS-SCCH.

In a multi-frequency cell, UE performs initial access on primary frequency, i.e. UE sends RRC Connection Request or CELL Update when entering a new cell after cell re-selection on primary frequency. And then UE monitors common H-RNTI on primary frequency.

When the UE detects the common H-RNTI the UE shall receive the corresponding HS-DSCH TTI;

– if after decoding the data, the CRC is correct the UE shall pass the data to MAC-ehs;

– if the UE received MAC-ehs PDU containing CCCH message, the UE passes MAC-ehs PDU to MAC-ehs reordering reassembly function. The UE identity is included in the RRC message;

– if the UE received MAC-ehs PDU containing SRB#1 message the UE passes MAC-ehs PDU to MAC-ehs reordering reassembly function. UE shall decode the U-RNTI in MAC-c header to determine if the MAC PDU is for it.

When receiving UE’s initial access request, i.e. RRC connection request or Cell Update after cell re-selection, RNC configure a dedicated H-RNTI, E-RNTI and a working frequency for the UE. When the UE has an RRC connection and a valid H-RNTI, the UE shall monitor the dedicated H-RNTI on the HS-SCCH.

When the UE detects the correct H-RNTI value the UE shall receive the corresponding HS-DSCH TTI;

– if after decoding the data, the CRC is correct the UE passes the data to MAC-ehs for reassembly and reordering;

– after MAC-ehs processing the UE passes the complete MAC-ehs SDU directly to the corresponding RLC entity.

For uplink transmission the UE uses E-DCH. Uplink transmission and downlink HS-DSCH reception for a specific UE is on a same carrier.

During the state transition from CELL_FACH to CELL_DCH, if the reconfiguration message does not include new H-RNTI the UE keeps monitoring the HS-SCCH with the H-RNTI value used in CELL_FACH state during the uplink synchronisation procedure. The UE shall continue to use the H-RNTI in CELL_DCH state after completing the state transition to CELL_DCH state.

16.2 Initial link adaptation

If UE has no dedicated H-RNTI, the UE includes available, i.e. UE does not delay reporting due to performing measurements, measurement results on RACH to uplink RRC messages based on configuration parameters set in SIB11/12. The UE includes the measurement results on RACH in Cell Update message when performing Cell update procedure.

The HS-DSCH data frame header includes a "Measured Results on RACH" field to which the RNC can include the received measurement results on RACH. The Node B HS-DSCH scheduler can use this information to determine the MCS, retransmission times and DL transmit power for the HS-SCCH and HS-PDSCH transmissions.

Figure 16.2-1: Link adaptation based on measurement results on RACH

16.3 Link adaptation when H-RNTI is allocated

If UE has valid H-RNTI the UE sends ACK/NACK feedback and CQI report on the related HS-SICH. The Node B HS-DSCH scheduler can use this information to determine the MCS, retransmission and DL transmit power for the HS-SCCH and HS-PDSCH transmissions.

Maintaining of Uplink synchronization is not needed in CELL_FACH state, UE could be out of synchronization after a period of transmission pause. When DL transmission is recommenced following a transmission pause, Node B shall order UE to establish the UL synchronization via HS-SCCH in case it detects the UE is out of UL synchronization. The synchronization detection in Node B is based on timer mechanism. Response to the synchronization establishment command, UE then initiates the UL synchronization procedure. When it accomplishes the UL synchronization establishment, UE sends E-RUCCH to Node B. During the procedure, no HS-SICH is sent. If Node B receives E-RUCCH from the UE, the Node B can then resume the HS-DSCH transmission for the UE.

16.4 Discontinuous reception

In CELL_FACH state, the UE performs continuous reception of the HS-SCCH (expect measurement occasion frames) if DRX operation in CELL_FACH is not configured. The discontinuous reception is enabled for the UE by the UTRAN by the following methods:

– Moving the UE to CELL/URA_PCH state by means of dedicated RRC reconfiguration procedure.

– Configuring the UE with a DRX Cycle configuration for usage in CELL_FACH state. The DRX configuration is CELL specific. Details of the DRX operation are described in 16.4.1.

In the reconfiguration procedure to CELL_PCH or URA_PCH states, the UTRAN may indicate two DRX cycles and inactivity time. The UE shall use the first DRX cycle and start the inactivity timer after completing the state transition. If the inactivity timer expires in CELL/URA_PCH state the UE shall start using second DRX cycles.

16.4.1 HS-DSCH DRX operation in CELL_FACH state

For the HS-DSCH DRX operation in CELL_FACH, the UTRAN indicates an inactivity timer, a DRX cycle length and a RX burst length. This information is stored by the UE for use when in CELL_FACH state. The HS-DSCH DRX operation in CELL_FACH state is only possible when the UE has a dedicated H-RNTI configured.

The HS-DSCH DRX operation in CELL_FACH state is initialized when the inactivity timer expires. The inactivity timer is triggered whenever no data transmission activities are on-going. At this point, the UE shall continuously receive HS-DSCH for the length of the inactivity timer configured. Once the inactivity timer has expired, the UE may choose not to receive HS-DSCH for a given time within the period of the configured DRX Cycle. The UE shall receive HS-DSCH for the RX burst length of the DRX Cycle configured.

The UE shall interrupt DRX operation in CELL_FACH state and continuously receive HS-DSCH, if data transmission activity is initiated.

UE with dedicated H-RNTI, after state transition from CELL_PCH to CELL_FACH, shall not initiate discontinuously reception until it has detected its dedicated H-RNTI on HS-SCCH indicating HS-DSCH reception.

16.5 Measurement Occasion

When HS-SCCH(s) in TS0 is configured for HS-DSCH transmission in CELL_FACH state in a certain frequency, the Node B HS-DSCH scheduling shall ensure that the HS-SCCH(s) in the TS0 is not received by the UE in its measurement period. To achieve this, the measurement period N is set to a fixed value, and the measurement occasion cycle length coefficient is signalled to the UE and to the Node B by a corresponding IE in RRC and NBAP signalling protocol(s). The Node B uses the dedicated H-RNTI, measurement period N and the cycle length coefficient to calculate the UE’s measurement period and considers it accordingly in the scheduling of HS-DSCH transmissions on that frequency.

When DRX is configured, Measurement Occasion is still used for interfrequency and interRAT measurements. In the case of the overlapping of RX burst and Measurement Occasion, the UE perform interfrequency and interRAT measurements according to Measurement Occasion.