What are the main 5G NR physical-layer channels (PBCH, PDCCH, PDSCH, PUSCH, PUCCH), and what is the SSB?
Channelization assigns different data types to different channels: PBCH carries basic system info, PDCCH carries downlink control, PDSCH carries downlink user data, PUSCH carries uplink user data, and PUCCH carries uplink control. The SSB (Synchronization Signal Block) bundles synchronization and broadcast signals used for cell discovery and initial access.
* NR physical channels by direction, plus the SSB for cell discovery. *
The physical channels (from "channelization"):
| Channel | Direction | Carries |
|---|---|---|
| PBCH (Physical Broadcast Channel) | down | basic system information |
| PDCCH (Physical Downlink Control Channel) | down | control information |
| PDSCH (Physical Downlink Shared Channel) | down | user data |
| PUSCH (Physical Uplink Shared Channel) | up | user data |
| PUCCH (Physical Uplink Control Channel) | up | control information |
The mnemonic structure: Broadcast, Downlink Control/Shared, Uplink Shared/Control. "Shared" = user data, "Control" = signalling; the first letter after P is the direction (D/U).
SSB (Synchronization Signal Block): a block of synchronization and broadcast signals used for cell discovery and initial access — when a phone powers on, the SSB is how it finds and locks onto a 5G cell (the 5G analogue of decoding the BCCH in GSM).
Other key NR functions in this part of the protocol stack:
- Beamforming (aiming signals in a direction), Beam Management (selecting/switching beams), CSI (Channel State Information feedback)
- Power Control, Time Synchronization, Frequency Scan, Frame Structure, and Massive MIMO
Tip: Decode the channel names by their letters: P-[B/D/U]-[C/S]-CH → P(hysical), direction, Control or Shared. The SSB is "how a 5G phone finds a cell" — remember it alongside GSM's BCCH.
Go deeper:
MIMO — incl. Massive MIMO (Wikipedia) — the multi-antenna technology behind the beamforming / Beam Management / Massive MIMO listed here: spatial multiplexing, precoding and diversity, with multipath and channel-model diagrams (also the carousel's source for this card).