The PBCH (Physical Broadcast Channel) carries
the periodic downlink broadcast of the RRC MasterInformationBlock
message. Note that system information from BCCH (Broadcast Control Channel)
is scheduled for transmission in the PDSCH (Physical Downlink Shared Channel).
The PDCCH (Physical Downlink Control Channel)
carries no higher layer information and is used for scheduling uplink and
downlink resources. Scheduling decisions, however, are the responsibility of
the MAC layer, therefore the scheduling information carried in the PDCCH is
provided by MAC. Similarly the PUCCH (Physical Uplink Control Channel) is used
to carry resource requests from UEs that will need to be processed by MAC.
The PHICH (Physical Hybrid ARQ Indicator
Channel) is used for downlink
ACK/NACK of uplink transmissions from UEs in the PUSCH (Physical Uplink
Shared Channel). It is a shared channel and uses a form of code multiplexing to
provide multiple ACK/NACK responses.
The PCFICH (Physical Control Format Indicator
Channel) is used to indicate how much resource in a subframe is reserved for
the downlink control channels. It may be either one, two or three of the first
symbols in the first slot in the subframe.
The PRACH (Physical Random Access Channel) is
used for the uplink transmission of preambles as part of the random access
procedure.
The PDSCH and the PUSCH are the main
scheduled resource on the cell. They are used for the transport of all
higher-layer information including RRC signalling, service-related signalling
and user traffic. The only exception is the system information in PBCH.
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