LTE tutorial[6] -LTE physical logical & transport channels

In order that data can be transported across the LTE radio interface, various "channels" are used. These are used to segregate the different types of data and allow them to be transported across the radio access network in an orderly fashion

Effectively the different channels provide interfaces to the higher layers within the LTE protocol structure and enable an orderly and defined segregation of the data.

3G LTE channel types

There are three categories into which the various data channels may be grouped.

• Physical channels: There are transmission channels that carry user data and control messages.
• Transport channels: The physical layer transport channels offer information transfer to Medium Access Control (MAC) and higher layers.
• Logical channels: Provide services for the Medium Access Control (MAC) layer with the LTE protocol structure.

3G LTE channel types

There are three categories into which the various data channels may be grouped.

• Physical channels: These are transmission channels that carry user data and control messages.
• Transport channels: The physical layer transport channels offer information transfer to Medium Access Control (MAC) and higher layers.
• Logical channels: Provide services for the Medium Access Control (MAC) layer within the LTE protocol structure.

3G LTE physical channels

The LTE physical channels vary between the uplink and the downlink as each has different requirements and operates in a different manner.

• Downlink:
  
  • Physical Broadcast Channel (PBCH): This physical channel carries system information for UEs requiring to access the network.
  • Physical Control Format Indicator Channel (PCFICH) :
  • Physical Downlink Control Channel (PDCCH) : The main purpose of this physical channel is to carry mainly scheduling information.
  • Physical Hybrid ARQ Indicator Channel (PHICH) : As the name implies, this channel is used to report the Hybrid ARQ status.
  • Physical Downlink Shared Channel (PDSCH) : This channel is used for unicast and paging functions.
  • Physical Multicast Channel (PMCH) : This physical channel carries system information for multicast purposes.
  • Physical Control Format Indicator Channel (PCFICH) : This provides information to enable the UEs to decode the PDSCH.
• Uplink:
  
  • Physical Uplink Control Channel (PUCCH) : Sends Hybrid ARQ acknowledgement
  • Physical Uplink Shared Channel (PUSCH) : This physical channel found on the LTE uplink is the Uplink counterpart of PDSCH
  • Physical Random Access Channel (PRACH) : This uplink physical channel is used for random access functions.

LTE transport channels

The LTE transport channels vary between the uplink and the downlink as each has different requirements and operates in a different manner. Physical layer transport channels offer information transfer to medium access control (MAC) and higher layers.

• Downlink:
  
  • Broadcast Channel (BCH) : The LTE transport channel maps to Broadcast Control Channel (BCCH)
  • Downlink Shared Channel (DL-SCH) : This transport channel is the main channel for downlink data transfer. It is used by many logical channels.
  • Paging Channel (PCH) : To convey the PCCH
  • Multicast Channel (MCH) : This transport channel is used to transmit MCCH information to set up multicast transmissions.


• Uplink:
  
  • Uplink Shared Channel (UL-SCH) : This transport channel is the main channel for uplink data transfer. It is used by many logical channels.
  • Random Access Channel (RACH) : This is used for random access requirements.

LTE logical channels

• Control channels:
  
  • Broadcast Control Channel (BCCH) : This control channel provides system information to all mobile terminals connected to the eNodeB.
  • Paging Control Channel (PCCH) : This control channel is used for paging information when searching a unit on a network.
  • Common Control Channel (CCCH) : This channel is used for random access information, e.g. for actions including setting up a connection.
  • Multicast Control Channel (MCCH) : This control channel is used for Information needed for multicast reception.
  • Dedicated Control Channel (DCCH) : This control channel is used for carrying user-specific control information, e.g. for controlling actions including power control, handover, etc..


• Traffic channels:
  
  • Dedicated Traffic Channel (DTCH) : This traffic channel is used for the transmission of user data.
  • Multicast Traffic Channel (MTCH) : This channel is used for the transmission of multicast data.