Code block — A piece of a transport block, sized for the decoder

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Bits into a codeword

Where it sits

Sits atLevel 7 of the hierarchy · Bits into a codeword · explained
Learn firstTransport block · CRC — 7 concepts in the full chain, see the paths
UnlocksLDPC
Primary clauseTS 38.212 §5.2.2
Used innr-pdsch 16
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

A code block is a piece of a transport block, sized so a decoder can manage it. A block that fits is left whole; one that does not is cut up, each piece getting its own 24-bit CRC.

The maximum is 8448 bits for LDPC base graph 1 and 3840 for base graph 2 (TS 38.212 clause 5.2.2).

8448 is not a round number, and that is the clue: it is $22 \times 384$, where 384 is the largest lifting size in the standard's table. The limit is not a design target — it is whatever the largest permitted expansion of the base graph happens to hold.

The cost is 24 bits per block, and it buys parallelism — a decoder works on all blocks at once, and a block that decoded correctly need never be sent again.

Read on

The full treatment is in nr-pdsch — this page is the definition and the map reference; that note is where the subject is actually developed.

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

To understand Code block (level 7) you first need 7 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
5 Transport block
6 CRC
Immediately before Code block: Transport block, CRC.
Keep going — where this sits on the route
◀SRSstep 73 · level 7
Step 74 of 118level 7 · Bits into a codeword
Polar codingstep 75 · level 7▶
Level 7 → 8 · this unlocks
LDPC
↳ all 8 concepts at level 8 · level 7 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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