CSI-RS Configuration
Configure a 5G NR CSI-RS resource — port count X, frequency density ρ, CDM type, and periodicity/offset — and see the resource element pattern inside a PRB as defined by 3GPP TS 38.211 Table 7.4.1.5.3-1.
| Row | Ports | ρ | CDM | Seed (k̄, l̄) |
|---|---|---|---|---|
| 6 | 8 | 1 | FD-CDM2 | (0,0) (2,0) (4,0) (6,0) |
| 7 | 8 | 1 | FD-CDM2 | (0,0) (4,0) (0,1) (4,1) |
| 8 | 8 | 1 | CDM4 | (0,0) (4,0) |
About CSI-RS
The Channel State Information Reference Signal (CSI-RS) is the primary downlink reference signal used by a 5G UE to measure channel quality, rank, and precoding information. It is defined in 3GPP TS 38.211 section 7.4.1.5 with the resource-element pattern selected from Table 7.4.1.5.3-1, which maps the number of antenna ports X, the density ρ (REs per PRB per port-pair) and the CDM type (no-CDM, FD-CDM2, CDM4 or CDM8) to concrete (k̄, l̄) seed locations inside one PRB.
Higher port counts (16, 24, 32) enable high-rank MIMO and beam management, but they need more REs per PRB and benefit from CDM4/CDM8 to pack port-groups into the same REs using orthogonal cover codes. ρ = 3 is typically used for TRS (tracking reference signal); ρ = 1 is standard for measurement resources, and ρ = 0.5 is a low-overhead option where a CSI-RS RE appears in every other PRB.
Periodicity and slot offset
A CSI-RS resource is transmitted in a slot when (slot − offset) mod periodicity = 0. Periodicities 4, 5, 8, 10, 16, 20, 32, 40, 64, 80, 160, 320 and 640 slots are supported; longer periodicities reduce overhead but increase the measurement stale-time visible to the UE's CSI report.
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