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Physical Channel Structure

The following list describes LTE downlink physical channels and physical signals. Downlink physical channels carry layer 2 information but downlink physical signals are only used by the physical layer.

Downlink physical channels:

  • Physical Downlink Shared Channel (PDSCH)
    • Carries the DL-SCH and PCH. DL-SCH contains actual user data.
  • Physical Downlink Control Channel (PDCCH)
    • Informs the UE about the resource allocation of PCH and DL-SCH, and HARQ information related to DL-SCH. Carries the uplink scheduling grant.
  • Physical HARQ Indicator Channel (PHICH)
    • Carries ACK/NACKs in response to uplink transmissions.
  • Physical Control Format Indicator Channel (PCFICH)
    • Informs the UE about the number of OFDM symbols used for the PDCCHs; Transmitted in every subframe.
  • Physical Broadcast Channel (PBCH)
    • The coded BCH transport block is mapped to four subframes within a 40 ms interval.

Downlink physical signals:

  • Reference Signal
  • Synchronization Signal (P-SS and S-SS)

The figure below shows the structure of the downlink physical channel and downlink physical signals.

Figure 1 :  Downlink Physical Channel Structure

Uplink physical channels and uplink physical signals are as follows. Uplink physical channels carries layer 2 information but uplink physical signals are only used by the physical layer.

Uplink physical channels:

  • Physical Uplink Shared Channel (PUSCH)
    • Carries the UL-SCH, ACK/NACK and CQI. UL-SCH contains actual user data.
  • Physical Uplink Control Channel (PUCCH)
    • Carries ACK/NACKs in response to downlink transmission. Carries CQI (Channel Quality Indicator) report and SR (Scheduling Request).
  • Physical Random Access Channel (PRACH)
    • Carries random access preamble.

Uplink physical signals:

  • Demodulation Reference Signal (UL-RS), associated with transmission of PUSCH and PUCCH.
  • Sounding Reference Signal (SRS), not associated with transmission of PUSCH and PUCCH.

The uplink physical channel and physical signal structure is shown below.

Figure 2 :  Uplink Physical Channel Structure