Web Simulation 

 

 

 

5G NR PDSCH DMRS Visualizer 

This interactive tool visualizes the 5G NR PDSCH DMRS (Demodulation Reference Signal) resource-element mapping in one Resource Block (RB): 12 subcarriers × 14 OFDM symbols per slot. The mapping follows 3GPP TS 38.211 Section 7.4.1.1 (RE mapping) and TS 38.212 Section 7.3.1.2.2 (antenna port mapping tables).

Spec reference: for the detailed specification on this subject, refer to this note.

Sections

DMRS types and mapping

Type 1 (Comb-2): DMRS occupies every other subcarrier. The subcarrier index k is:

k = 4n + 2k′ + Δ

where n = 0,1,2; k′ ∈ {0, 1}; and Δ depends on the CDM group (Group 0: Δ = 0, Group 1: Δ = 1). Two CDM groups allow up to 4 ports with single-symbol DMRS, or 8 ports with double-symbol (MaxLength = 2).

Type 2 (2-adjacent REs): DMRS occupies pairs of adjacent subcarriers:

k = 6n + k′ + Δ

with k′ ∈ {0, 1}; Δ ∈ {0, 2, 4} for CDM groups 0, 1, 2. Up to 6 ports (MaxLength 1) or 12 ports (MaxLength 2).

Type 1 (Comb-2)

Type 2 (2-adjacent)

RE pattern

Every other subcarrier

Pairs of adjacent subcarriers

CDM groups

2

3

Max ports (1 / 2 symbols)

4 / 8

6 / 12

Frequency density

Higher (better channel est.)

Lower (more ports / less overhead)

Time domain: DMRS symbol positions depend on PDSCH Mapping Type (A or B), Start (S) and Length (L) per 3GPP TS 38.214 Table 5.1.2.1-1, and the dmrs-AdditionalPosition setting. Type A uses slot-absolute indices; Type B uses positions relative to the PDSCH start. Positions vary with PDSCH length per 38.211 Tables 7.4.1.1.2-3/4.

CDM and OCC: Ports in the same CDM group share REs and are separated by Orthogonal Cover Codes (OCC). The grid shows + and − on each DMRS RE to indicate the combined frequency-domain (wf) and time-domain (wt) OCC sign. Different shades (light blue, blue, dark blue) indicate CDM groups 0, 1, and 2. The 38.212 table shows port mapping; the 38.211 CDM/OCC table (7.4.1.1.2-1 or 7.4.1.1.2-2) appears below with Δ, wf(k′), and wt(l′).

Simulation

The interactive simulator is below. Use the controls to explore the concepts described above.

■ Reserved (CDM Group) ■ CDM Group 0 ■ CDM Group 1 ■ CDM Group 2 ■ PDSCH REs ■ Outside PDSCH

Type 1: Comb-2. 1 CDM group = 6 REs/RB.

RE at cursor

Hover over an RE to see (k, l) and sequence info.

3GPP 38.212 Table (Type 1, MaxLength 1)
3GPP 38.211 §7.4.1.1 defines the mapping of sequence r(n) to REs (k, l), with OCC from Tables 7.4.1.1.2-1/2. 38.214 Table 5.1.2.1-1 constrains PDSCH Start and Length. Antenna ports 1000–1011 correspond to indices 0–11.

 

Usage

Use the controls to explore PDSCH DMRS mapping:

  1. MIMO: SISO (port 1000), 2×2 (1000–1001), 4×4 (1000–1003), or 8×8 (1000–1007). For 8×8, use the Codeword dropdown with tables that support two codewords (e.g. MaxLength 2 or Type 2).
  2. DMRS Type: Type 1 (Comb-2, every other subcarrier) or Type 2 (pairs of adjacent subcarriers).
  3. MaxLength: 1 symbol (single DMRS) or 2 symbols (double-symbol DMRS pairs).
  4. PDSCH Mapping Type: Type A (slot-absolute DMRS positions) or Type B (positions relative to PDSCH start).
  5. Start and Length: PDSCH allocation S and L per 38.214 Table 5.1.2.1-1. Symbols outside the allocation are shown as "Outside PDSCH".
  6. dmrs-AdditionalPosition: Options enabled/disabled based on Mapping Type, MaxLength, and Length per 38.211 Tables 7.4.1.1.2-3/4.
  7. OCC markings: Each DMRS RE displays + or − for the orthogonal cover code (wf × wt) from 38.211 Tables 7.4.1.1.2-1/2.
  8. Show PDSCH REs: When checked, non-DMRS REs are shown in a lighter shade; when unchecked, only DMRS REs are drawn for a clearer pattern.
  9. Antenna Ports: Select which ports (1000–1011) to display. Each selected port gets its own 12×14 resource grid. Up to 12 grids in a 3×4 layout.
  10. Hover: Move the cursor over a resource element to see subcarrier index k, symbol index l, and port/sequence reference in the "RE at cursor" box.
  11. Tables: 38.212 shows Value, CDM Group, Delta, and Ports (filterable). 38.211 CDM/OCC table (below) shows p, CDM, Δ, wf(k′), wt(l′) for ports 1000–1011.
Tip: Uncheck “Show PDSCH REs” to see the Comb-2 (Type 1) or 2-adjacent (Type 2) DMRS structure clearly. Compare Type 1 vs Type 2 to see how frequency density and CDM groups differ.

Parameters

  • DMRS Type: Type 1 (comb-2, k = 4n + 2k′ + Δ) or Type 2 (2-adjacent, k = 6n + k′ + Δ).
  • MaxLength: 1 or 2 DMRS symbols per slot; 2 symbols allow more antenna ports (8 for Type 1, 12 for Type 2).
  • PDSCH Mapping Type: Type A (l0 at symbol 2 or 3) or Type B (l0 at PDSCH start). Additional positions per 38.211 Tables 7.4.1.1.2-3/4 depend on length Ld.
  • Start (S), Length (L): 38.214 Table 5.1.2.1-1; S + L ≤ 14. Type A: L ≥ 3; Type B: L ≥ 2.
  • OCC: 38.211 Tables 7.4.1.1.2-1 (Type 1) and 7.4.1.1.2-2 (Type 2) define wf(k′) and wt(l′) for each port.
  • Antenna Ports: 1000–1011 (indices 0–11). Ports in the same CDM group share REs and are orthogonalized by OCC.
  • Resource Grid: One RB = 12 subcarriers × 14 symbols. Vertical = subcarrier k (0 at bottom), horizontal = symbol l (0–13). Outside PDSCH REs (outside [S, S+L)) are dark.

Limitations

  • Mapping visualizer, not a signal: the tool shows where DMRS REs land and their OCC signs per spec. It does not generate the Gold-sequence DMRS values, run channel estimation, or model the received signal.
  • Single RB, PDSCH only: one resource block of a downlink PDSCH. PUSCH DMRS, PTRS, cross-RB precoding, and CDM across multiple RBs are out of scope.
  • Config-table driven: positions follow the 38.211/38.214 tables for the chosen parameters; invalid or reserved combinations are simply disabled rather than fully validated.
  • Ideal grid: no propagation, noise, frequency offset, or actual port-to-layer precoding is applied — it is a clean spec-accurate RE map.