Logical Channels

• Control Channels

Control channels are used for transfer of control plane information only. The control channels offered by MAC are:

• Broadcast Control Channel (BCCH)
  A downlink channel for broadcasting system control information.
• Paging Control Channel (PCCH)
  A downlink channel that transfers paging information and system information change notifications. This channel is used for paging when the network does not know the location cell of the UE.
• Common Control Channel (CCCH)
  Channel for transmitting control information between UEs and network. This channel is used for UEs having no RRC connection with the network.
• Multicast Control Channel (MCCH)
  A point-to-multipoint downlink channel used for transmitting MBMS control information from the network to the UE, for one or several MTCHs. This channel is only used by UEs that receive MBMS.
• Dedicated Control Channel (DCCH)
  A point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. Used by UEs having an RRC connection.

• Traffic Channels
  
  Traffic channels are used for the transfer of user plane information only. The traffic channels offered by MAC are:

• Dedicated Traffic Channel (DTCH)
  A Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one UE, for the transfer of user information. A DTCH can exist in both uplink and downlink.
• Multicast Traffic Channel (MTCH)
  A point-to-multipoint downlink channel for transmitting traffic data from the network to the UE. This channel is only used by UEs that receive MBMS.

Transport Channels in LTE

The physical layer offers information transfer services to MAC and higher layers. The physical layer transport services are described by how and with what characteristics data are transferred over the radio interface.

Downlink transport channel types are:

1. Broadcast Channel (BCH) characterised by:

• fixed, pre-defined transport format;
• requirement to be broadcast in the entire coverage area of the cell.

2. Downlink Shared Channel (DL-SCH) characterised by:

• support for HARQ;
• support for dynamic link adaptation by varying the modulation, coding and transmit power;
• possibility to be broadcast in the entire cell;
• possibility to use beam forming;
• support for both dynamic and semi-static resource allocation;
• support for UE discontinuous reception (DRX) to enable UE power saving;

3. Paging Channel (PCH) characterised by:

• support for UE discontinuous reception (DRX) to enable UE power saving (DRX cycle is indicated by the network to the UE);
• requirement to be broadcast in the entire coverage area of the cell;
• mapped to physical resources which can be used dynamically also for traffic/other control channels.

4. Multicast Channel (MCH) characterised by:

• requirement to be broadcast in the entire coverage area of the cell;
• support for MBSFN combining of MBMS transmission on multiple cells;
• support for semi-static resource allocation e.g. with a time frame of a long cyclic prefix.

Uplink transport channel types are:

1. Uplink Shared Channel (UL-SCH) characterised by:

• possibility to use beamforming; (likely no impact on specifications)
• support for dynamic link adaptation by varying the transmit power and potentially modulation and coding;
• support for HARQ;
• support for both dynamic and semi-static resource allocation.

2. Random Access Channel(s) (RACH) characterised by:

• limited control information;
• collision risk;