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.
Related tools
How to use the CSI-RS Configuration tool
- Choose the port count. Select the number of CSI-RS ports (1 to 32) for your antenna setup.
- Set frequency density. Pick a density (0.5, 1 or 3) compatible with that port count.
- Define periodicity and offset. Enter the slot periodicity and offset so the resource lands where you want it.
- Review the RE locations. See which subcarriers and symbols the ports occupy and how CDM groups are formed.
Frequently asked questions
- How many CSI-RS ports can be configured and how?
- NR supports 1, 2, 4, 8, 12, 16, 24 or 32 CSI-RS ports. The port count is built from a row in the TS 38.211 CSI-RS location table that fixes how the ports spread across subcarriers and symbols and how CDM groups stack them. Higher port counts feed massive-MIMO codebooks so the gNB can pick fine-grained precoders.
- What does CSI-RS frequency density mean?
- Density is the number of CSI-RS REs per port per PRB, with allowed values of 0.5, 1 or 3 depending on the port count. Density 3 (used only for 1-port) packs three REs per PRB; density 0.5 spreads the resource over alternate PRBs to cut overhead. You pick density to balance measurement accuracy against the REs taken from data.
- How do periodicity and offset work for CSI-RS?
- Periodic CSI-RS repeats every slotPeriodicity slots (e.g. 4, 5, 10, 20 … up to 640) starting at a slotOffset, both signalled by RRC. The offset staggers resources from different cells or beams so they do not collide. Semi-persistent and aperiodic CSI-RS exist too, activated by MAC CE or triggered by DCI when periodic measurement is not enough.
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