WHAT ARE THE AVAILABLE TRANSPORT CHANNELS IN LTE?

In LTE an effort has been made to keep a low number of transport channels to avoid unnecessary switching between different channel types, which are found to be time consuming in other technologies such as WCDMA.

In fact, there is currently only one transport channel in downlink and one in uplink carrying user data. Therefore, channel switching is not needed.

For LTE, the following transport channels are provided by the physical layer:

DOWNLINK

Broadcast Channel (BCH): A low fixed bit rate channel broadcast in the entire coverage area of the cell.

Downlink Shared Channel (DL-SCH): This transport channel uses the possibility to use HARQ and link adaptation by varying the modulation, coding and transmit power. Using this channel, it is possible to broadcast in the entire cell. Beamforming can also be applied using this channel. UE power saving (DRX) is supported in this channel to reduce the UE power consumption. Multimedia broadcast multicast system (MBMS) transmission is also supported.

Paging Channel (PCH): This channel is broadcasted in the entire cell. DRX is supported to enable power saving.

Multicast channel (MCH): This is a separate transport channel for multicast. Multimedia broadcast multicast service (MBMS). This channel is broadcast in the entire coverage area of the cell. Combining of MBMS transmissions from multiple cells, Multimedia Broadcast Single Frequency Network (MBSFN) is supported.

UPLINK

Uplink Shared channel (UL-SCH): A channel with possibility to use HARQ and link adaptation by varying the transmit power, modulation and coding.

Random Access Channel (RACH): This transport channel is used to obtain timing synchronization (asynchronous random access), and to transmit information needed to obtain scheduling grants (synchronous random access). The transmission is typically contention based. For UEs having an RRC connection there is some limited support for contention free access.