Layer 2
This section introduces transport channels, Layer 2 structure, and logical channels in LTE.
Downlink transport channels:
- 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 or 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 channels:
- 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