Quasi-co-location — Two ports sharing the channel's large-scale properties

5G Systems Notes · Concept map · Quasi-co-location Route · Hierarchy · Index · All concepts · Hub

Space — layers, ports, reporting

Where it sits

Sits atLevel 5 of the hierarchy · Space — layers, ports, reporting · explained
Also writtenQCL · quasi co-located
Learn firstAntenna port — 5 concepts in the full chain, see the paths
UnlocksNothing else depends on it directly.
Primary clauseTS 38.211 §4.4.1, TS 38.214 §5.1.5
Used inref-mimo 4 · index 1 · nr-frame-structure 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 same idea as a port, weakened to the large-scale properties only. Clause 4.4.1 again:

"Two antenna ports are said to be quasi co-located if the large-scale properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. The large-scale properties include one or more of delay spread, Doppler spread, Doppler shift, average gain, average delay, and spatial Rx parameters." — TS 38.211 clause 4.4.1

Why it is needed. A device cannot estimate everything from a DM-RS that lasts one symbol. It can get the fine channel, but not the Doppler spread or the right receive beam. QCL is the network saying: "this new port behaves like that one you already measured" — so the device can reuse the slow-moving estimates and only measure what is fast.

Four types, and the fourth is the one that matters most (TS 38.214 clause 5.1.5):

TypeProperties sharedWhat it lets the device reuse
typeADoppler shift, Doppler spread, average delay, delay spreadEverything slow — the full channel statistics
typeBDoppler shift, Doppler spreadTime-variation only
typeCDoppler shift, average delayA coarse pair, for initial tracking
typeDSpatial Rx parameterWhich receive beam to use. Not a statistic — an instruction.
Table 1: The QCL types of TS 38.214 clause 5.1.5, quoted exactly. Type D is different in kind from the other three: it is not a channel statistic but an instruction about which receive beam to point, and at FR2 a device that gets it wrong hears nothing at all.

Type D is beam management in disguise. At FR2 a device receives with a narrow beam and must point it before it can hear anything. Telling it "this PDSCH is QCL type D with that SS/PBCH block" means "use the beam you used to hear that block". The whole TCI-state machinery — dl-OrJointTCI-StateList-r17 in PDSCH §13 — exists to keep that pointer up to date.

Read on

This concept was first written up in ref-mimo, 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 Quasi-co-location (level 5) you first need 5 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 Antenna port
Immediately before Quasi-co-location: Antenna port.
Keep going — where this sits on the route
◀Layerstep 52 · level 5
Step 53 of 118level 5 · Space
TDD and FDDstep 54 · level 5▶
Nothing depends on this one directly
It is a leaf of the graph — follow the route rather than the branch.
↳ all 11 concepts at level 6 · level 5 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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