4 Services offered to higher layers
25.2213GPPPhysical channels and mapping of transport channels onto physical channels (TDD)Release 17TS
4.1 Transport channels
Transport channels are the services offered by layer 1 to the higher layers. A transport channel is defined by how and with what characteristics data is transferred over the air interface. A general classification of transport channels is into two groups:
– Dedicated Channels, using inherent addressing of UE
– Common Channels, using explicit addressing of UE if addressing is needed
General concepts about transport channels are described in [12].
4.1.1 Dedicated transport channels
There exists two types of dedicated transport channel, the Dedicated Channel (DCH) and the Enhanced Dedicated Channel (E-DCH).
4.1.1.1 DCH – Dedicated Channel
The Dedicated Channel (DCH) is an up- or downlink transport channel that is used to carry user or control information between the UTRAN and a UE.
4.1.1.2 E-DCH – Enhanced Dedicated Channel
The Enhanced Dedicated Channel (E-DCH) is an uplink transport channel.
For 1.28Mcps TDD multi-carrier E-DCH transmission, a UE in CELL_DCH state shall have only one E-DCH per carrier. There would be one or more E-DCHs to be transmitted from a UE in CELL_DCH state in a TTI.
4.1.2 Common transport channels
There are seven types of common transport channels for 3.84Mcps and 7.68Mcps TDD: BCH, FACH, PCH, RACH, USCH, DSCH, HS-DSCH.
There are eight types of common transport channels for 1.28Mcps TDD: BCH, FACH, PCH, RACH, USCH, DSCH, HS-DSCH, E-DCH.
4.1.2.1 BCH – Broadcast Channel
The Broadcast Channel (BCH) is a downlink transport channel that is used to broadcast system- and cell-specific information.
4.1.2.2 FACH – Forward Access Channel
The Forward Access Channel (FACH) is a downlink transport channel that is used to carry control information to a mobile station when the system knows the location cell of the mobile station. The FACH may also carry short user packets.
4.1.2.3 PCH – Paging Channel
The Paging Channel (PCH) is a downlink transport channel that is used to carry control information to a mobile station when the system does not know the location cell of the mobile station.
4.1.2.4 RACH – Random Access Channel
The Random Access Channel (RACH) is an up link transport channel that is used to carry control information from mobile station. The RACH may also carry short user packets.
4.1.2.5 USCH – Uplink Shared Channel
The uplink shared channel (USCH) is an uplink transport channel shared by several UEs carrying dedicated control or traffic data.
4.1.2.6 DSCH – Downlink Shared Channel
The downlink shared channel (DSCH) is a downlink transport channel shared by several UEs carrying dedicated control or traffic data.
4.1.2.7 HS-DSCH – High Speed Downlink Shared Channel
The High Speed Downlink Shared Channel (HS-DSCH) is a downlink transport channel shared by several UEs. The HS-DSCH is associated with one or several Shared Control Channels (HS-SCCH). The HS-DSCH is transmitted over the entire cell or over only part of the cell using e.g. beam-forming antennas.
For 1.28Mcps TDD, in a multi-frequency HS-DSCH cell, the HS-DSCH may be transmitted to a UE on one or more carriers in CELL_DCH state and on only one carrier in CELL_FACH, CELL_PCH and URA_PCH state in a TTI. The term ‘multi-carrier HS-DSCH reception’ refers to the HS-DSCH reception on multiple carriers in a TTI for a UE.
4.1.2.8 E-DCH – Enhanced Dedicated Channel
The Enhanced Dedicated Channel (E-DCH) is an uplink transport channel in CELL_FACH and IDLE mode for 1.28Mcps TDD only.
4.2 Indicators
Indicators are means of fast low-level signalling entities which are transmitted without using information blocks sent over transport channels. The meaning of indicators is implicit to the receiver.
The indicator(s) defined in the current version of the specifications are: Paging Indicator (PI) and MBMS Notification Indicator (NI).