5G Channel Types | 5G Logical Channels, 5G Transport Channels

5G channel types viz. logical channels and transport channels used in uplink and downlink with mapping between them. The 5G logical channels include xBCCH, xCCCH, xDCCH, xDTCH etc. The 5G transport channels include xBCH, xDL-SCH, xRACH, xUL-SCH etc.

These 5G channels are used to provide different kinds of data transfer services by MAC layer in 5G protocol stack.

5G Logical Channels | XBCCH, XCCCH, XDCCH, XDTCH

The 5G logical channels are further divided into control channels and traffic channels based on their functionalities. They are described below.

Each of the 5G logical channels are defined by what information type is transferred by them. Logical channels are classified into two groups as follows.
• Control channel: It is used to transfer control plane related information.

• Traffic channel: It is used to transfer user plane related information.

5G Control Channels

Following table-1 mentions 5G control channels used to transfer control plane information only. The control channels offered by 5G-MAC are xBCCH, xCCCH and xDCCH.

5G Control Channel Type	Description
xBCCH	This channel is used in the downlink to broadcast system control information.
xCCCH	This channel is used to transmit control information between UEs and network (i.e. 5G-Node B or base station). It is used for UEs having no RRC connection with network.
xDCCH	This channel is bi-directional and point to point. It carries dedicated control information between UE and network. It is used by UEs having RRC connection.

5G Traffic Channel | XDTCH

• The 5G traffic channel is used to transfer user plane information only.
• The xDTCH is the only dedicated traffic channel used in 5G wireless technology.
• It is a point to point channel which is dedicated to single UE.
• It carries user information.
• It exists both in the downlink (From 5G-NB to UE) and uplink (From UE to 5G-NB).

Mapping Between Logical Channels And Transport Channels

The figure depicts mapping between logical channels and transport channels in the uplink and downlink.
As shown following are the mapping in uplink side.
• xCCCH channel can be mapped to channel xUL-SCH
• xDCCH channel can be mapped to channel xUL-SCH
• xDTCH channel can be mapped to channel xUL-SCH

As shown following are the mapping in downlink side.
• xBCCH channel can be mapped to channel xBCH
• xCCCH channel can be mapped to channel xDL-SCH
• xDCCH channel can be mapped to channel xDL-SCH
• xDTCH channel can be mapped to channel xDL-SCH

5G Transport Channels | XBCH, XDL-SCH, XRACH, XUL-SCH

The 5G transport channels are used by 5G physical layer (i.e. layer-1) based on their functionalities. They are described below.

5G Transport Channel Type	Description
xBCH	It is 5G broadcast channel which carries system control information of 5G MAC layer.
xDL-SCH	It is 5G Downlink Shared Channel which carries data of all the UEs in the downlink direction from 5G Base station.
xUL-SCH	It is 5G Uplink Shared Channel which carries data from UEs to 5G base station in the uplink direction.
xRACH	It is 5G Random Access Channel which is used by UE in the uplink direction to establish connection with 5G base station. It is used to establish 5G-RRC Connection between UE and 5G-RAN in RRC connection setup procedure.