Space — ports, layers, and the reports that steer them
PDSCH §11.3 ends on a number: four layers of 256QAM reach 23.4 bit/s/Hz against a 30 bit/s/Hz target, and the missing factor is spatial, not modulational. This note defines the machinery that supplies it.
In one line. Space is the only dimension left. Bandwidth is allocated, time is scheduled and modulation is near its ceiling — but a channel with many antennas at both ends carries several independent streams over the same time and frequency, and everything here is about knowing the channel well enough to separate them.
Concepts defined here. Antenna port · Quasi-co-location · MIMO · Precoding · Beamforming · The CSI framework · RI · PMI
Already explained elsewhere. Layers and codewords in PDSCH §6.3; CQI in PDSCH §10; reciprocity in SRS §1.3.
The concepts this note covers
Each concept now has a page of its own. This note is the narrative — the group read as one argument, with the connective tissue that a page-per-concept cannot carry. The pages are the definitions, and each one shows what to learn before it.
| Concept | What it is | Needs | Primary clause |
|---|---|---|---|
| Antenna port | A channel property, not a piece of metal | 1 | TS 38.211 §4.4.1 |
| Beamforming | Aiming energy rather than spraying it | 1 | TS 38.214 §5.1.6.1.2 |
| CSI | Channel state information — what the device reports back | 2 | TS 38.214 §5.2 |
| MIMO | Many antennas at both ends | 1 | TS 38.214 §5.1.1, §5.2.2 |
| PMI | Precoding matrix indicator | 2 | TS 38.214 §5.2.2.2 |
| Precoding | The matrix the transmitter applies — and why NR hides it | 1 | TS 38.211 §7.3.1.4, TS 38.214 §5.2.2.2 |
| Quasi-co-location | Two ports sharing the channel's large-scale properties | 1 | TS 38.211 §4.4.1, TS 38.214 §5.1.5 |
| RI | Rank indicator — how many layers the link can carry | 2 | TS 38.214 §5.2.2 |
Which to read. Come here to see how these ideas hang together; go to a term page when you want one definition, its prerequisites, and everything that depends on it. The concept map indexes all 118, and its hierarchy puts them in learning order.
Sources
| Document | Clause | What it gives |
|---|---|---|
| TS 38.211 | 4.4.1 | The definitions of antenna port and quasi-co-location, quoted here in full |
| 7.2, 6.2 | The downlink and uplink antenna port number ranges | |
| 7.3.1.3–.4 | Layer mapping; the antenna port mapping that is an identity | |
| TS 38.214 | 5.2.1 | The CSI framework — resource settings, reporting settings, triggering, processing criteria |
| 5.2.2.2 | All the PMI codebooks of Table 1 | |
| 5.1.5 | The four QCL types | |
| 5.1.6.1.2 | CSI-RS for L1-RSRP — the measurement beam management runs on | |
| TS 36.211 | 6.3.4 | LTE's precoding clause, including the codebook NR's downlink abandoned |
On MIMO itself, the standard reference is Tse and Viswanath, Fundamentals of Wireless Communication (Cambridge, 2005; free PDF) — chapters 7 to 9 cover capacity, rank and the conditioning argument in §7. On massive MIMO, Marzetta's 2010 paper is the usual starting point, as SRS §11.2 already notes. Neither checked against a copy here.