RF5G Channel Types: Logical and Transport Channels Explained
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This page provides an overview of 5G channel types, specifically focusing on logical and transport channels used in both the uplink and downlink directions, along with the mapping between them. 5G NR (New Radio) defines a well structured set of logical and transport channels to efficiently manage data flow between the user equipment (UE) and the network.
The 5G logical channels include xBCCH, xCCCH, xDCCH, xDTCH, and others. The 5G transport channels encompass xBCH, xDL-SCH, xRACH, xUL-SCH, and more. These 5G channels are utilized by the MAC layer in the 5G protocol stack to facilitate various data transfer services.
5G Logical Channels | xBCCH, xCCCH, xDCCH, xDTCH
5G logical channels are categorized based on its purpose into control channels and traffic channels. These logical channels ensure that network resources are allocated appropriately for both user traffic and control signaling.
Each 5G logical channel is defined by the type of information it transmits. Logical channels are grouped as follows:
- Control Channel: Used for transferring control plane related information (i.e. signaling pupose), Examples : BCCH, CCCH, DCCH, and PCCH.
- Traffic Channel: Used for transferring user plane related information. (i.e. user and multicast data), Examples : DTCH and MTCH.
5G Control Channels
The following table describes the 5G control channels used exclusively for transmitting control plane information. The control channels offered by 5G-MAC include 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 the network (i.e., 5G-Node B or base station). It is used for UEs that do not have an RRC connection with the network. |
| xDCCH | This channel is bi-directional and point-to-point. It carries dedicated control information between the UE and the network and is used by UEs that have an 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 dedicated to a single UE.
- It carries user information.
- It exists in both the downlink (from 5G-NB to UE) and uplink (from UE to 5G-NB).
Mapping between Logical Channels and Transport Channels
The figure above illustrates the mapping between logical channels and transport channels in both the uplink and downlink directions.
Uplink Mapping:
- xCCCH channel can be mapped to the xUL-SCH channel.
- xDCCH channel can be mapped to the xUL-SCH channel.
- xDTCH channel can be mapped to the xUL-SCH channel.
Downlink Mapping:
- xBCCH channel can be mapped to the xBCH channel.
- xCCCH channel can be mapped to the xDL-SCH channel.
- xDCCH channel can be mapped to the xDL-SCH channel.
- xDTCH channel can be mapped to the xDL-SCH channel.
5G Transport Channels | xBCH, xDL-SCH, xRACH, xUL-SCH
On the other hand, transport channels determine how data is physically transmitted over the radio interface, ensuring optimal scheduling, multiplexing and retransmission handling. The 5G transport channels are used by the 5G physical layer (layer-1) based on their functions. These are described below.
| 5G Transport Channel Type | Description |
|---|---|
| xBCH | It is the 5G broadcast channel which carries system control information of the 5G MAC layer. |
| xDL-SCH | It is the 5G Downlink Shared Channel, which carries data for all UEs in the downlink direction from the 5G Base station. |
| xUL-SCH | It is the 5G Uplink Shared Channel, which carries data from UEs to the 5G base station in the uplink direction. |
| xRACH | It is the 5G Random Access Channel, which is used by the UE in the uplink direction to establish a connection with the 5G base station. It is used to establish the 5G-RRC Connection between the UE and 5G-RAN in the RRC connection setup procedure. |
Conclusion
The separation of logical and transport channels enhances flexibility, improves resource utilization, and supports diverse 5G services, including ultra-reliable low-latency communication (URLLC), massive machine-type communication (mMTC), and enhanced mobile broadband (eMBB). By structuring data transmission through layered channel mapping, 5G NR achieves high efficiency, scalability, and reliability, ensuring seamless communication between network elements while meeting the stringent performance requirements of next-generation wireless systems.
