Antenna port — A channel property, not a piece of metal
Space — layers, ports, reporting
Where it sits
What it is
What it is. TS 38.211 clause 4.4.1, in one sentence:
"An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed." — TS 38.211 clause 4.4.1
Read what that does not say. It says nothing about antennas, elements, connectors or hardware. A port is defined entirely by an inference the receiver is permitted to make: two symbols share a port exactly when measuring one tells you about the other.
This is the abstraction that lets massive MIMO exist without changing the device specification. A base station with 64 physical elements can present four ports; one with four elements presents four ports. The device sees the same thing and cannot tell the difference — because what it is told is "these symbols share a channel", not "these symbols came from this metal".
And it is why PDSCH §6.4 can be an identity matrix. The precoder is folded into the port definition: the DM-RS is precoded with the data, so the channel the device measures on a port already includes whatever the transmitter did.
The numbers are ranges, one per signal (TS 38.211 clause 7.2, downlink):
| From | Used by | Where in these notes |
|---|---|---|
| 1000 | PDSCH | PDSCH §7.1 — DM-RS ports 1000–1011 and beyond |
| 2000 | PDCCH | ref-channels §1 |
| 3000 | CSI-RS | ref-signals §1 |
| 4000 | SS/PBCH block | ref-signals §5 |
| 5000 | Positioning reference signals | ref-signals §6 |
Read on
This concept was first written up in ref-mimo, which reads the whole group as one argument.
Before this concept, the hierarchy says to learn the following — the full chain, in order: