Why there is no PHICH (Physical channel HybridARQ Indicator Channel) in 5G?
Instead of PHICH we have DCI formats in which all the above information transmitted.
We have separate bits for CBG transmission itself.
Yes, we have PDCCH instead of PHICH to send ack/nack for UL packets.
PHICH is present in LTE but is not required in NR.
PHICH channel is used in LTE to handle uplink re-transmissions and are tightly coupled to use of synchronous hybrid-ARQ protocol, but as the HARQ protocol is asynchronous in NR in both downlink as well as uplink.
Hence the PHICH is not required in NR.