Layer 2
Transport channels, Layer2 structure, Logical channels, and the procedures are introduced in this section.
Transport Channels
Downlink transport channel types are:
- Broadcast Channel (BCH) characterized by:
- fixed, pre-defined transport format
- requirement to be broadcast in the entire coverage area of the cell.
- Downlink Shared Channel (DL-SCH) characterized 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 beamforming
- support for both dynamic and semi-static resource allocation
- support for UE discontinuous reception (DRX) to enable UE power saving.
- Paging Channel (PCH) characterized 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.
- Multicast Channel (MCH) (from Release 9) characterized 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:
- Uplink Shared Channel (UL-SCH) characterized 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.
- Random Access Channel(s) (RACH) characterized by:
- limited control information
- collision risk
| 