LDPC — Low-density parity-check coding — NR's data code

5G Systems Notes · Concept map · LDPC Route · Hierarchy · Index · All concepts · Hub

Bits into a codeword

Where it sits

Sits atLevel 8 of the hierarchy · Bits into a codeword · explained
The 2 of them
BG1 — base graph 1 — large blocks and high code rates
BG2 — base graph 2 — small blocks and low code rates
Learn firstCode block — 8 concepts in the full chain, see the paths
UnlocksRate matching
Primary clauseTS 38.212 §5.3.2, §7.2.2
Used innr-pdsch 36 · index 4
Scanned from the notes at page load and joined with terms.json; nothing on this card is typed by hand.

What it is

LDPC — low-density parity-check coding — is the code NR uses for data. Not one code but two base graphs, chosen by payload size and target rate.

BG2 if the payload is at most 292 bits, or at most 3824 bits at rate ≤ 0.67, or at any size with rate ≤ 0.25. BG1 otherwise (TS 38.212 clause 7.2.2).

Two codes because one cannot be efficient at both ends. A code is punctured upward from its mother rate to reach a high rate and repeated downward to reach a low one, and both cost performance. BG1 is 46×68 with mother rate ≈ 0.32, for throughput; BG2 is 42×52 at ≈ 0.19, for coverage, and its smaller matrix is cheaper to decode — which matters because the coverage case is also the far-away, low-power one.

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.

Widget not found: sim_status

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

To understand LDPC (level 8) you first need 8 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
7 Code block
Immediately before LDPC: Code block.
Keep going — where this sits on the route
◀PBCHstep 85 · level 8
Step 86 of 118level 8 · Bits into a codeword
Scramblingstep 87 · level 8▶
Level 8 → 9 · this unlocks
Rate matching
↳ 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.
5G Systems Notes · Concept map · LDPC Top · Concept map · Hub