This interactive tool visualizes CSI-RS (Channel State Information Reference Signal) resource-element mapping on a grid of 3 Resource Blocks (36 subcarriers) × 14 OFDM symbols per slot, according to 3GPP TS 38.211 Section 7.4.1.5.3 and Table 7.4.1.5.3-1.

NOTE : If you want to know exactly how the CSI RS position and value are calculated, check out this note. Understanding the details on this subject would require huge amount of mental work and practice of calculating the position by hands if you are really interested.

RE positions are given by k = k₀ + k̅ + k′ and l = l₀ + l̅ + l′, where (k₀, l₀) are the configured offset, (k̅, l̅) the row-dependent base, and (k′, l′) the CDM spread. Each RE carries a complex symbol from the pseudo-random sequence r(m′) and Orthogonal Cover Codes (OCC). Density ρ (3, 1, or 0.5) controls REs per RB. CDM types: No CDM, FD-CDM2, CDM4 (FD2×TD2), CDM8 (FD2×TD4). Antenna ports 3000–3031.

Usage

Use the controls to explore CSI-RS RE mapping:

1. 3GPP Row: Select row 1–18 from Table 7.4.1.5.3-1. Each row defines number of ports (1–32), density ρ (3, 1, or 0.5), and CDM type (No CDM, FD-CDM2, CDM4, CDM8).
2. k0 and l0: Subcarrier offset (k₀ in control panel, 0–11) and symbol offset (firstOFDMSymbolInTimeDomain = l₀, 0–13).
3. gNB TX / UE RX: Tabs switch between per-port transmit grids and the UE receive view. UE RX shows the superposition of all Tx ports (combined REs in cyan) and the channel matrix H (nRx×nTx) with a phase-offset slider.
4. Polar plot: Hover over an occupied RE (mini or main grid) to see the complex value: combined received signal (H × sequence × OCC) at that RE, or the Tx symbol when OCC cancels (e.g. FD-CDM2 at k′=1).
5. Resource grid: 36 subcarriers (3 RBs) × 14 OFDM symbols. REs are color-coded by CDM group. Density 0.5 uses only RB 0 and RB 2.
6. Reference table: The 3GPP table is below the grid; the selected row is highlighted.

Tip: Row 1 (Density 3) shows three vertically aligned REs per RB. Row 18 (CDM8) shows four blocks of 2×4 REs. The polar plot shows realistic complex values (sequence r(m′) and OCC); when multiple ports cancel (e.g. FD-CDM2), the Tx symbol is shown instead. Use UE Rx Antenna and Channel Phase Offset to see how the combined signal at the UE changes.

Parameters

• Mapping: k = k₀ + k̅ + k′, l = l₀ + l̅ + l′. (k̅, l̅) from table per CDM group; (k′, l′) from FD/TD spread.
• Density: ρ = 3 (3 REs per RB at 0, 4, 8); ρ = 1 (1 RE per RB); ρ = 0.5 (every second RB only).
• CDM: FD-CDM2 (k′ ∈ {0,1}, l′ = 0); CDM4 (FD2, TD2): k′ ∈ {0,1}, l′ ∈ {0,1}; CDM8 (FD2, TD4): k′ ∈ {0,1}, l′ ∈ {0,1,2,3}.
• Antenna ports: 3000–3031. Port index p = 3000 + j×N + i where j is CDM group and N is CDM size (2, 4, or 8).
• Sequence & OCC: Each RE symbol is r(m′) (pseudo-random, magnitude 1/√2) scaled by the Orthogonal Cover Code (OCC) per port. FD-CDM2 uses [+1,+1] / [+1,−1] over k′; CDM4/CDM8 use the 38.211 OCC tables.
• Grid: Vertical axis = subcarrier k (0 at top), horizontal = symbol l (0–13).