Broadcast Control Channel (BCCH) used for transmission of system control information from the network to all mobile terminals in a cell. Prior to accessing the system, a mobile terminal needs to read the information transmitted on the BCCH to find out how the system is configured, for example the bandwidth of the system.
Paging Control Channel (PCCH) used for paging of mobile terminals whose location on cell level is not known to the network and the paging message therefore needs to be transmitted in multiple cells.
Dedicated Control Channel (DCCH) used for transmission of control information to/from a mobile terminal. This channel is used for individual configuration of mobile terminals such as different handover messages.
Multicast Control Channel (MCCH) used for transmission of control information required for reception of the MTCH
Dedicated Traffic Channel (DTCH) used for transmission of user data to/from a mobile terminal. This is the logical channel type used for transmission of all uplink and non-MBMS downlink user data.
Multicast Traffic Channel (MTCH) used for downlink transmission of MBMS services.
From the physical layer, the MAC layer uses services in the form of Transport Channels. A transport channel is defined by how and with what characteristics the information is transmitted over the radio interface. Following the notation from HSPA, which has been inherited for LTE, data on a transport channel is organized into transport blocks. In each Transmission Time Interval (TTI), at most one
transport block of a certain size is transmitted over the radio interface in absenceof spatial multiplexing. In case of spatial multiplexing (‘MIMO’), there can be up to two transport blocks per TTI.
Associated with each transport block is a Transport Format (TF), specifying how the transport block is to be transmitted over the radio interface. The transport format includes information about the transport-block size, the modulation scheme, and the antenna mapping. Together with the resource assignment, the resulting code rate can be derived from the transport format. By varying the transport format, the MAC layer can thus realize different data rates. Rate control is therefore also
known as transport-format selection.
The set of transport-channel types specified for LTE includes:
Broadcast Channel (BCH) has a fixed transport format, provided by the specifications.
It is used for transmission of the information on the BCCH logical channel
Paging Channel (PCH) is used for transmission of paging information on the PCCH logical channel. The PCH supports discontinuous reception (DRX) to allow the mobile terminal to save battery power by sleeping and waking up to receive the PCH only at predefined time instants.
Downlink Shared Channel (DL-SCH) is the transport channel used for transmission of downlink data in LTE. It supports LTE features such as dynamic rate adaptation and channel-dependent scheduling in the time and frequency domains, hybrid ARQ, and spatial multiplexing.
Multicast Channel (MCH) is used to support MBMS. It is characterized by a semi-static transport format and semi-static scheduling. In case of multi-cell transmission using MBSFN, the scheduling and transport format configuration is coordinated among the cells involved in the MBSFN transmission.
Uplink Shared Channel (UL-SCH) is the uplink counterpart to the DL-SCH. Part of the MAC functionality is multiplexing of different logical channels and mapping of the logical channels to the appropriate transport channels. Unlike the MAC-hs in HSDPA,4 the MAC in LTE supports multiplexing of RLC PDUs from different radio bearers into the same transport block. As there is some relation between the type of information and the way it should be transmitted, there are certain restrictions in the mapping of logical channels to transport channels.
