Downlink Control Channels Operation Support
Support for DL Operation
PDCCH transmits information about Resource allocation, HARQ info, Transport format, and implicitly the RNTI for the DL
transmission. Similar to HS-SSCH functionalities in HSDPA.
In support of MIMO, there is also some additional information transmitted: 1) The codebook entry, and 2) The transmission
rank of the following DL packet.
Support for UL Operation
PDCCH can also transmit scheduling grants to the UE. In LTE there is a need to explicitly signal the UL granted resources
differently than HSPA (CDMA-based) where only Allowed Power levels are granted. Multiple UEs cannot simultaneously
access same subcarriers in an uncontrolled manner. The scheduling grants in HSUPA are managed through E-AGCH and the
E-RGCH.
PDCCH has many functionalities and not all of them are used at the same time. Hence, PDCCH requires flexibility with
regard to possible configurations. This results in a variable size of the PDCCH and requires an additional channel to inform
the UE of a specific configuration. The PCFICH signals how many OFDM symbols (0-3) are occupied by the PDCCH.
Support for UL HARQ
PHICH sends acknowledgments on DL for UL UE transmitted data. Similar functionality as E-HICH in HSPA.
Additional Physical Channels
- Physical Broadcast Channel (PBCH)
– Carrying part of BCH
- Physical Multicast Channel (PMCH)
– Carrying MCH (MBSFN multicast)
Signals
- Reference Signal (RS) (a.k.a Pilots)
- Synchronization signals
– Primary Synchronization Signal (PSC)
– Secondary Synchronization Signal (SSC)