Initial access — From nothing to connected

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Procedures over time

Where it sits

Sits atLevel 9 of the hierarchy · Procedures over time · explained
Learn firstPRACH · SS/PBCH block · RNTI · PBCH — 14 concepts in the full chain, see the paths
UnlocksRegistration
Primary clauseTS 38.213 §4, §8
Used inref-channels 4 · nr-frame-structure 2 · index 1 · ref-stack 1 · ref-ue-mobility 1 · ref-ue-state 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 procedure from knowing nothing to being addressable. It is not one clause but a sequence, told as a story in frame structure §9.1 and summarised here as the dependency chain it really is.

Figure 1: Initial access as a dependency chain. Each step is impossible until the one before it has succeeded, which is why the order is fixed and why every step uses a different channel. The device is listening for the first four and transmits for the first time only at the fifth. Clauses are TS 38.211 clause 7.4.2 for the synchronisation signals, 7.4.3 for the SS/PBCH block, TS 38.213 clause 13 for CORESET 0, and TS 38.321 clause 5.1 for random access.

The asymmetry is the point. Four steps of listening before one transmission — because a device must know the timing, the identity, the grid origin and the preamble configuration before it can say anything at all without interfering. It is the same asymmetry the SRS note finds inside the handset, seen at the level of a procedure.

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 Initial access (level 9) you first need 14 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 Cyclic prefix · Resource element
4 PRACH · Physical layer · Resource block
5 SS/PBCH block · Transport block
6 CRC
7 Polar coding · RNTI
8 PBCH
Immediately before Initial access: SS/PBCH block, PBCH, PRACH, RNTI.
Keep going — where this sits on the route
◀AI/ML in the RANstep 94 · level 9
Step 95 of 118level 9 · Procedures over time
Search spacestep 96 · level 9▶
Level 9 → 10 · this unlocks
Registration level 11
↳ all 6 concepts at level 10 · level 9 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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