DMRS Pattern Visualizer
Visualize 5G NR Demodulation Reference Signal (DMRS) mapping for PDSCH or PUSCH on the 12 × 14 PRB resource element grid. Configure DMRS type, single / double symbol, additional positions and mapping type per 3GPP TS 38.211 §7.4.1.1.
About DMRS
The Demodulation Reference Signal (DMRS) is a UE-specific pilot used by the receiver for channel estimation before it demodulates PDSCH or PUSCH data REs. 5G NR supports two configuration types: Type 1 puts 6 DMRS subcarriers per PRB in a comb-like pattern (2 CDM groups of 6), while Type 2 uses 4 DMRS subcarriers per PRB organised into 3 CDM groups of 4. Type 1 gives higher frequency-domain density; Type 2 supports more orthogonal ports for MU-MIMO.
Mapping type A places the first DMRS at symbol l0 ∈ {2, 3} (signalled in SIB1 / dedicated RRC) and is used for full-slot PDSCH. Mapping type B places DMRS at l0 = 0 and is used for mini-slot / low-latency transmissions. Additional DMRS positions (0–3) are added later in the slot to track fast-changing channels and are specified in TS 38.211 Table 7.4.1.1.2-3.
Related tools
How to use the DMRS Pattern Visualizer
- Choose the channel. Select PDSCH or PUSCH, since the mapping type affects DMRS symbol positions.
- Pick the DMRS type. Switch between configuration Type 1 and Type 2 to see the comb versus adjacent-pair layout.
- Set additional positions. Add 0 to 3 extra DMRS symbols to model channel tracking at higher speeds.
- Select ports / CDM groups. Choose the antenna ports and watch how they share REs within each CDM group.
- Inspect the RE grid. Read the highlighted grid to see which REs hold DMRS versus data.
Frequently asked questions
- What is the difference between DMRS Type 1 and Type 2?
- Type 1 (configuration type 1) places DMRS on every other subcarrier in a comb pattern and supports up to 8 ports across 2 CDM groups. Type 2 uses pairs of adjacent subcarriers and supports up to 12 ports across 3 CDM groups, trading a denser frequency footprint for more orthogonal layers. Type 2 suits high-rank MU-MIMO; Type 1 is the common default.
- What are DMRS additional positions?
- Additional positions are extra DMRS symbols added later in the slot beyond the front-loaded symbol(s). More positions (1 to 3 extra) let the receiver track fast channel variation at high speed, but each one consumes OFDM symbols that could have carried data. You scale them to the Doppler: few at pedestrian speed, more on high-speed rail.
- Why does DMRS reduce throughput?
- DMRS symbols occupy resource elements that would otherwise carry the data payload, so denser DMRS or extra additional positions leave fewer REs for PDSCH/PUSCH. This is exactly why the 38.306 peak-rate formula applies an overhead factor. The trade-off is deliberate: enough pilots for reliable channel estimation without starving the data.
- What are CDM groups and why do they matter?
- A CDM (code-division multiplexing) group is a set of DMRS ports that share the same REs but are separated by orthogonal cover codes in frequency and time. Ports in the same group must stay orthogonal; ports in different groups sit on different REs. The number of CDM groups without data also tells the receiver which REs are reserved for DMRS and not for PDSCH.
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