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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.

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PDSCH data
DMRS
PTRS
CSI-RS
Total REs
168
PDSCH REs
162
DMRS REs
6
PTRS REs
0
CSI-RS REs
0

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

  1. Set the slot layout. Confirm the PRB grid (12 subcarriers × 14 symbols) for normal CP.
  2. Enable the signals. Toggle DMRS, PTRS and CSI-RS on or off to layer them onto the grid.
  3. Adjust densities. Change DMRS positions and PTRS time/frequency density to see the reserved REs shift.
  4. 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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