Physical layer — Layer 1 — what turns a transport block into radio
The protocol stack
Where it sits
What it is
What it is. Layer 1 — everything that turns a transport block into radio and back. TS 38.202 is the short specification that defines it as a service rather than as machinery: clause 4.1 says the physical layer offers data transport to higher layers, accessed through transport channels via the MAC sublayer.
The functions, from TS 38.202 clause 4.2 — this is the whole job, in eleven lines:
Error detection on the transport channel and indication to higher layers · FEC encoding/decoding · hybrid ARQ soft-combining · rate matching of the coded transport channel to physical channels · mapping onto physical channels · power weighting · modulation and demodulation · frequency and time synchronisation · radio characteristics measurements and indication to higher layers · MIMO antenna processing · RF processing.
Every one of those is a section of another note in this folder. Error detection is PDSCH §4.1; FEC and rate matching are §4.2–§5; modulation is ref-modulation §1; soft-combining is PDSCH §12; synchronisation is the SSB story in frame structure §9.1.
The boundary is the interesting part. The physical layer never learns what a transport block contains — see PDSCH §2.2. Add a new service above and layer 1 needs no change, because it never looked inside. That opacity is what makes the whole stack extensible, and it is why this reference note can describe five sublayers without any of them re-describing the radio.
Read on
This concept was first written up in ref-stack, which reads the whole group as one argument.
Before this concept, the hierarchy says to learn the following — the full chain, in order: