PBCH — Physical broadcast channel — how to join a cell

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Channels — what carries what

Where it sits

Sits atLevel 8 of the hierarchy · Channels — what carries what · explained
Learn firstSS/PBCH block · Polar coding — 10 concepts in the full chain, see the paths
UnlocksInitial access
Primary clauseTS 38.211 §7.3.3, §7.4.3
Used innr-pdsch 10 · ref-signals 6 · nr-frame-structure 5 · ref-channels 5 · index 2 · ref-ue-mobility 1
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

What it is. The channel carrying the master information block, the first thing a device can read. TS 38.211 clause 7.3.3, and it lives inside the SS/PBCH block (clause 7.4.3).

It is tiny and fixed on purpose. The payload is the MIB plus eight timing bits added at layer 1 (TS 38.212 clause 7.1.1), encoded with a polar code to exactly 864 bits (clause 7.1.5). No MCS, no scheduling, no configuration — because a device that has just switched on has none of those things.

Its content is the bootstrap minimum: whether the cell is barred, the subcarrier spacing to use next, where CORESET 0 is, and offsetToPointA — the origin of all frequency numbering (frame structure §7).

Everything else moved to PDSCH. SIB1 and every later system information block are ordinary PDSCH transmissions addressed to SI-RNTI (PDSCH §2.3). PBCH carries only what is needed to reach them.

Read on

This concept was first written up in ref-channels, which reads the whole group as one argument.

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Before this concept, the hierarchy says to learn the following — the full chain, in order:

To understand PBCH (level 8) you first need 10 other concepts. Read them in this order — everything on one line can be read in any order, but no line before the one above it:
Level Learn these
0 Subcarrier
1 OFDM
2 OFDM symbol
3 Resource element
4 Physical layer · Resource block
5 SS/PBCH block · Transport block
6 CRC
7 Polar coding
Immediately before PBCH: SS/PBCH block, Polar coding.
Keep going — where this sits on the route
◀PDCCHstep 84 · level 8
Step 85 of 118level 8 · Channels
LDPCstep 86 · level 8▶
Level 8 → 9 · this unlocks
Initial access
↳ all 8 concepts at level 9 · level 8 in full · the whole route
The route is every concept in the folder ordered by level, so nothing here needs anything after it. Computed at page load from terms.json; the same numbering as the route page.
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