23 Further Enhancements to CELL_FACH state (FDD only)

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

The following sub-features related to downlink improvements are included as part of Further Enhancements to CELL_FACH:

– NodeB triggered HS-DPCCH transmission;

– HS-DSCH DRX operation with second DRX cycle in CELL_FACH (see subclause 14.4.2).

23.1 NodeB triggered HS-DPCCH transmission

The sub-feature of NodeB triggered HS-DPCCH transmission enables the network to request the UE to obtain a common E-DCH resource and provide HS-DPCCH feedback in CELL_FACH state.

The network may request the UE to obtain a common E-DCH resource and provide HS-DPCCH feedback by means of an HS-SCCH order. An ACK is not transmitted on the uplink in response to the HS-SCCH order and instead, the UE begins the random access procedure to obtain a common E-DCH resource to be used. The UE selects the next available uplink access slot upon initiation of the physical random access procedure for the access. In the presence of uplink data, E-DCH can also be transmitted on the obtained common E-DCH resource provided there is sufficient grant. In the absence of uplink data, the UE sends an SI in the MAC-i PDU and its E-RNTI in MAC-i Header 0 for collision resolution purposes. The HS-DPCCH transmissions also begin during collision resolution at the allowed start time for E-DCH transmissions. The network may configure an implicit resource release timer. If configured, the timer is started at the allowed start time of the E-DCH transmission. Thereon, legacy implicit and explicit common E-DCH resource release procedures are used to terminate the HS-DPCCH transmission. If the timer is not configured by the network, legacy procedures to release the common E-DCH resources apply.

In CELL_PCH state, when the HS-DSCH reception is enabled and the UE has stored dedicated H-RNTI and E-RNTI, the network can transmit an HS-SCCH order for NodeB triggered HS-DPCCH transmission to the UE.

Upon reception of an HS-SCCH order for NodeB triggered HS-DPCCH transmission, if random access procedure fails and there is no uplink data in the UE buffer, the UE does not re-initiate the random access procedure unless another HS-SCCH order is received.

On the interaction between NodeB triggered HS-DPCCH transmission and Fallback to R99 PRACH sub-features:-

– For NodeB triggered HS-DPCCH transmission, if an indication to fallback to R99 PRACH is received, the UE ignores the received fallback indication and does not fallback to R99 PRACH.

– If an HS-SCCH order for NodeB triggered HS-DPCCH transmission is received during the time from when the UE has already started the PRACH preamble procedure for uplink data but before receiving indication to fallback to R99 PRACH, the UE ignores the received HS-SCCH order and will continue with the fallback to R99 PRACH procedure.

– If the HS-SCCH order for NodeB triggered HS-DPCCH transmission is received during the time from when the UE receives an indication to fallback to R99 PRACH to the time of successful completion of the RACH transmission procedure, the UE ignores the received HS-SCCH order.