- HS - SCCH Less Operation, is a mechanism whereby the First transmission of small MAC - hs / ehs TBs on predefined HS-DSCH is done with out accompanying HS-SCCH.
- HARQ re-transmission of the first HS-DSCH transmission is accompanied by HS-SCCH.
- HS - SCCH less operation is used only in Cell_DCH State and when F-DPCH is configured without DCH in UL and DL. i.e. HS-SCCH less operation can be used only with E-DCH in UL and HS-DSCH in DL.
- HS-SCCH Less Operation can be configured together with DTX_DRX operation
HS - SCCH Less Operation characteristics:
- The Modulation used is restricted to QPSK.
- Only 4 pre-defined TBs for MAC-hs / ehs PDUs are allowed
- The HS-PDSCH CRC is 24 bit long and its generation is same as current HS-SCCH, by using 16 bit UE specific H-RNTI
- Only 2 HS-PDSCH ovsf codes are assigned per UE:
- UE can receive data on any of the assigned HS-SCCH less HS-PDSCH channels
- UE needs to perform Blind TF detection using the 4 pre-defined TBs
- In order to perform Blind TF detection UE needs to maintain a cyclic soft buffer storing 13 contiguous TTIs
- The UE does not transmit negative acknowledgements (NACK) in the first transmission when decoding the chosen formats. It transmits ACK or NACKs for the retransmissions.
- HARQ is limited to:
- 2 retransmissions.
- The redundancy version is pre-defined and not configurable.
- The HARQ retransmissions of an HS-SCCH-less HS-DSCH transmission are accompanied by an HS-SCCH, which is sent with the same channel coding and decoding as the Release 5/6 HS-SCCH. Some of the bits of the HS-SCCH are reinterpreted in order to signal the UE the following information.
- That the HS-SCCH is intended for HS-SCCH-less operation
- Whether the retransmission is the first retransmission or the second retransmission
- The channelization code and the transport block size used by the HARQ process
- The HARQ combining information – in the form of an offset from the current TTI indicating where the previous transmission was sent
- In addition, the UE continues to attempt reception of the legacy HS-SCCH in the configured HS-SCCH set.
- For a UE configured for HS-SCCH-less operation, the serving HS-DSCH cell can deactivate and reactivate HS-SCCH less operation by transmitting an HS-SCCH order to the UE.
