Logical / transport / physical channel mappingV15.9.0

  1. Logical channels transfer data (RLC PDU) between the RLC and MAC layers.
  2. Transport channels transfer data (MAC PDU, also known as Transport Blocks) between the MAC and Physical layers.
  3. Physical channels transfer data across the air-interface.
  4. Physical signals are used by the physical layer for synchronization, channel quality measurements and channel estimation.

Uplink channel mapping

ul_channels
Mapping of uplink logical channels to transport channels and physical channels

  • Common Control Channel (CCCH) and Dedicated Control Channel (DCCH) are used to transfer RRC signaling messages, i.e. data belonging to the set of Signaling Radio Bearers (SRB).
  • Dedicated Traffic Channel (DTCH) is used to transfer application data.
  • CCCH, DCCCH, DTCH all map to UL-SCH and PUSCH.
  • Physical Uplink Control Channel (PUCCH) transfers Uplink Control Information (UCI), including Scheduling Requests, HARQ Acknowledgements and Channel State Information (CSI). It is not used to transfer higher layer information.
  • Random Access Channel (RACH) is used to transfer the index of the preamble sequence.
  • Demodulation Reference Signals (DM-RS) are sequences which are known to the base station. They are needed for base station to estimate the channel properties for PUCCH and PUSCH.
  • Sounding Reference Signal (SRS) is used by the base station for channel aware packet scheduling and link adaptation.
  • Phase Tracking Reference Signal (PT-RS) is used to compensate for phase noise generated by the local oscillators at both the transmitter and receiver.

Downlink channel mapping

dl_channels
Mapping of downlink logical channels to transport channels and physical channels

  • Broadcast Control Channel (BCCH) is used to transfer both the Master Information Block (MIB) and System Information Blocks (SIB). MIB is mapped to BCH and PBCH; SIBs are mapped to DL-SCH and PDSCH.
  • Common Control Channel (CCCH) and Dedicated Control Channel (DCCH) are used to tranfer RRC signaling messages.
  • Dedicated Traffic Channel (DTCH) is used to transfer application data.
  • CCCH, DCCCH, DTCH all map to DL-SCH and PDSCH.
  • Physical Downlink Control Channel (PDCCH) transfers Downlink Control Information (DCI), which is used by the base station to allocate uplink and downlink resources. DCI can also be used to provide uplink power control commands, config slot format, and indicate that pre-emption has occured. It is not used to transfer higher layer information.
  • Demodulation Reference Signals (DM-RS) are sequences which are known to the UE. They are needed for UE to estimate the channel properties for PBCH, PDCCH, and PDSCH.
  • Phase Tracking Reference Signal (PT-RS) is used to compensate for phase noise generated by the local oscillators at both the transmitter and receiver.
  • Channel State Informationo Reference Signal (CSI-RS) is used by the UE to measure and report channel quality. This information can be used by the link adaptation algorithm at the Base Station. It can also be used for beaem management and connected mode mobility procedures.
  • Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS) are used during the cell search procedure and beam management procedure. SSS is used for Reference Signal Received Power (RSRP) and Reference Signal Received Quality (RSRQ) measurements.