PDSCH

PDSCH is the downlink workhorse — it carries essentially all the actual content going to a UE: internet traffic, but also SIBs, paging messages, and RRC signalling. It never travels alone. A PDCCH carrying DCI always points to it first, telling the UE the resource allocation, modulation and coding scheme, and HARQ process to use, and PDSCH itself carries DMRS so the UE can estimate the channel and demodulate.

A few things shape its real-world throughput. The MCS picks modulation up to 256-QAM (1024-QAM in 5G-Advanced) and the code rate, both adapted to channel quality. The number of MIMO layers multiplies it further. NR also made the time-domain mapping flexible — PDSCH can start mid-slot and span a configurable number of symbols (Type A starts near the slot boundary, Type B is the short, mini-slot-style allocation for low latency). If a transport block fails its CRC, HARQ retransmits it and the receiver soft-combines, rather than throwing the first attempt away.