Logical channels define ‘WHAT’ type of information is being transferred and transport channel defines ‘HOW’ the information is being transferred.
Logical channels reside between Radio Link Control (RLC) and Medium Access Control (MAC) layer. There are broadly two categories of logical channels available.
- Control Channels
- Traffic Channels
Control channels are used to carry control plane information e.g. information from Radio Resource Control (RRC) Protocol.
Types of control channels
- Broadcast Control Channel (BCCH)
- Paging Control Channel
- Dedicated Control Channel
- Common Control Channel
- Shared Channel Control Channel
Broadcast Control Channel
BCCH is a downlink channel and are used for broadcasting system information.
Paging Control Channel
PCCH is a downlink channel. This is used for carrying downlink paging information from UTRAN and Core Network.
Dedicated Control Channel
DCCH is a point to point bi-directional logical channel used to transmit dedicated control information between network and UE. This channel is commonly established through RRC connection establishment procedure.
Common Control Channel
CCCH is a bi-directional channel used to transfer control information between the UE and the network. CCCH is used when UEs have no RRC connection available.
Shared Control Channel
Bi-directional channel that transmits control information for uplink and downlink shared channels between network and UEs. This channel is for TDD only.
MBMS point-to-multipoint Control Channel (MCCH)
A point-to-multipoint downlink channel used for transmitting control information from the network to the UE. This channel is only used by UEs that receive MBMS.
MBMS point-to-multipoint Scheduling Channel (MSCH)
A point-to-multipoint downlink channel used for transmitting scheduling control information, from the network to the UE, for one or several MTCHs carried on a CCTrCH. This channel is only used by UEs that receive MBMS.
Dedicated Traffic Channel
DTCH is a point to pint bi-directional channel dedicated to one UE, for transfer of user information.
Common Traffic Channel
A point to multipoint unidirectional channel to carry user information for all or a group of specified UEs.
MBMS point-to-multipoint Traffic Channel (MTCH)
A point-to-multipoint downlink channel used for transmitting traffic data from the network to the UE. This channel is only used for MBMS.
There are broadly two types of transport channels available.
- Common Transport Channel
- Dedicated Transport Channel
Common Transport Channel
Random Access Channel (RACH)
A contention based uplink channel used for transmission of relatively small amounts of data, e.g. for initial access or non-real-time dedicated control or traffic data.
Forward Access Channel (FACH)
Common downlink channel without closed-loop power control used for transmission of relatively small amount of data. In addition FACH is used to carry broadcast and multicast data.
Downlink Shared Channel (DSCH)
A downlink channel shared by several UEs carrying dedicated control or traffic data, used in TDD mode only.
Uplink Shared Channel (USCH)
An uplink channel shared by several UEs carrying dedicated control or traffic data, used in TDD mode only.
Broadcast Channel (BCH)
A downlink channel used for broadcast of system information into an entire cell.
Paging Channel (PCH)
A downlink channel used for broadcast of control information into an entire cell allowing efficient UE sleep mode procedures. Currently identified information types are paging and notification. Another use could be UTRAN notification of change of BCCH information.
High Speed Downlink Shared Channel (HS-DSCH)
A downlink channel shared between UEs by allocation of individual codes, from a common pool of codes assigned for the channel.
Dedicated Transport Channel
Dedicated Channel (DCH)
A channel dedicated to one UE used in uplink or downlink.
Enhanced Dedicated Channel (E-DCH)
A channel dedicated to one UE used in uplink only. The E-DCH is subject to Node-B controlled scheduling and HARQ.
Logical Channels and Transport Channels mapping
Mapping in Uplink
NOTE: The color green indicates a logical channel can be mapped on a transport channel.