RE Mapping Visualizer
Overlay PDSCH, DMRS, PTRS and CSI-RS on a 12 × 14 PRB resource element grid. Toggle any reference signal on or off, click a cell to inspect it, and watch the remaining PDSCH RE count — the starting point of a 5G NR Transport Block Size (TBS) calculation.
One PT-RS subcarrier per PRB that carries it, and only every K-th PRB does. This grid is one such PRB.
About RE mapping
A 5G NR PRB carries 12 subcarriers × 14 OFDM symbols = 168 resource elements per slot. Before PDSCH data can occupy the grid, the gNB must first reserve REs for reference signals: DMRS for channel estimation, PTRS to track high-frequency phase noise in FR2, and CSI-RS for beam / channel-state measurement. Everything not reserved becomes available PDSCH RE.
The available PDSCH RE count feeds directly into the TBS (Transport Block Size) determination in TS 38.214 §5.1.3: NRE = min(156, N'RE) × nPRB, then Ninfo = NRE · R · Qm · ν, quantised to a TBS entry. Use this tool to build intuition for how much overhead each reference signal actually costs you.
Related tools
How to use the RE Mapping Visualizer
- Set the slot layout. Confirm the PRB grid (12 subcarriers × 14 symbols) for normal CP.
- Enable the signals. Toggle DMRS, PTRS and CSI-RS on or off to layer them onto the grid.
- Adjust densities. Change DMRS positions and PTRS time/frequency density to see the reserved REs shift.
- Read the data fill. Observe how PDSCH rate-matches around every reserved RE and count the usable data REs.
Frequently asked questions
- How are resource elements mapped in a 5G NR PDSCH PRB?
- A PRB is 12 subcarriers by 14 OFDM symbols in a normal-CP slot, giving 168 resource elements. The mapping rules in TS 38.211 reserve REs for DMRS first, then PTRS and any CSI-RS, and PDSCH fills everything left over with the rate-matching pattern skipping the reserved positions. The visualizer colour-codes each RE so you can see what is data and what is reference signal.
- What is PTRS and when does it appear?
- PTRS (phase-tracking reference signal) tracks oscillator phase noise and is mostly used in FR2 and with high modulation orders where phase error degrades the constellation. It rides on a sparse set of subcarriers with a configurable time and frequency density and is associated with a DMRS port. At low SCS and low MCS it is often disabled, so it may not show on the grid.
- Why does CSI-RS punch holes in the PDSCH allocation?
- CSI-RS occupies its own REs for channel measurement, and PDSCH must rate-match around them so no data lands on those positions. If the UE did not know the CSI-RS REs were reserved, it would try to decode noise there. The visualizer shows these reserved REs so you can confirm the data mapping skips them cleanly.
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