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