In LTE, different types of control information are transmitted inside the control region of physical downlink control channels. But what are these control information? and what are the corresponding channels?
Control information and corresponding channels
| Control Information | Physical Control Channel |
| Downlink Control Information (DCI) | PDCCH |
| Control Format Indicator (CFI) | PCFICH |
| Hybrid-ARQ Indicator (HI) | PHICH |
However, in 5G NR, the PHICH and the PCFICH, are not needed.
The PHICH is used in LTE to handle uplink retransmissions and is tightly coupled to the use of a synchronous hybrid-ARQ protocol, but since the NR hybrid-ARQ protocol is asynchronous in both uplink and downlink the PHICH is not needed in NR.
The PCFICH, is not necessary for NR as the size of the control resource sets does not vary dynamically and reuse of control resources for data is handled in a different way than in LTE.