Physical Channel Structure
Downlink physical channels and downlink physical signals are as follows. 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)
Downlink physical channel and downlink physical signal structure is shown in Figure 14
Figure 14: 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.
Uplink physical channel and uplink physical signal structure is shown in Figure 15.
Figure 15: Uplink Physical Channel Structure