Carries physical layer signaling to a single UE, such as modulation scheme (1 bit), channelization code set (7 bit), transport block size (6bit), HARQ process number (3bit), redundancy version (3bit), new data indicator (1bit), UE identity (16bit) HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channel used to carry downlink signaling related to HS-DSCH transmission
HS-SCCH High-Speed Shared Control Channel is an added channel to UMTS to increase downlink data rates. This is defined in Release 5 of the UMTS specifications. It is also part of the HSDPA.
HS-SCCH uses a SF=128 and has q time structure based on a sub-frame of length 2 ms, i.e. the same length as the HS-DSCH TTI. The timing of HS-SCCH starts two slots prior to the start of the HS-PDSCH sub frame.
The following 7 items information is carried on the HS-SCCH
- Modulation scheme(1bit) QPSK or 16QAM
- Channelization code set (7bits)
- Transport block size ( 6bits)
- HARQ process number (3bits)
- Redundancy version (3bits)
- New Data Indicator (1bit)
- UE identity (16 bits)
In each 2 ms interval corresponding to one HS-DSCH TTI, one HS-SCCH carries physical-layer signaling to a single UE.
As there should be a possibility for HS-DSCH transmission to multiple users in parallel (code multiplex), multiplex HS-SCCH may be needed in a cell. The specification allows for up to four HS-SCCHs as seen from a UE point of view .i.e. UE must be able to decode four HS-SCCH.