Free tool · 3GPP TS 38.211 §7

One slot, every signal

The PRB×slot grid with all its tenants: control region, demodulation pilots, phase tracking and CSI-RS. Toggle each layer and watch how many resource elements are actually left for your data.

Grid composition

One PRB × one 14-symbol slot — illustrative single-PRB view (PT-RS appears in PRBs it occupies; KPT-RS spaces it across PRBs)

CORESET / PDCCHDM-RS PT-RSCSI-RSPDSCH data
Under the hood

Rate-matching: data flows around everything

PDSCH is the tenant, not the landlord. The encoder doesn't pre-plan holes — it generates the coded bit stream, and the mapper writes it into every RE that isn't claimed by something with higher standing: CORESET, DM-RS, PT-RS, CSI-RS, SSB. That's rate-matching: same codeword, fewer landing spots, higher effective code rate.

PT-RS exists for phase noise — mmWave oscillators drift within a symbol, and a sparse single-subcarrier pilot tracked across symbols lets the receiver derotate it. That's why it's dense in time, sparse in frequency: phase noise is common to all subcarriers.

The overhead figure you see here is why TS 38.306 uses 14% for FR1 DL — count the colored squares across configurations and you land remarkably close to the spec's flat factor.

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FAQ

Common questions

What is resource element mapping in 5G?
Every physical channel and reference signal is assigned specific resource elements (one subcarrier × one OFDM symbol) of the grid by TS 38.211. PDSCH then rate-matches around everything else — this visualizer shows exactly who owns what in a slot.
What is PT-RS and why is it dense in time but sparse in frequency?
The phase-tracking reference signal compensates oscillator phase noise, which matters at FR2. Phase error is common to all subcarriers but changes symbol-to-symbol, so one subcarrier tracked every (1, 2 or 4) symbols is enough — the opposite shape of DM-RS.
How much 5G capacity is lost to overhead?
With 2 CORESET symbols, DM-RS pos1 and periodic CSI-RS, roughly 12–18% of REs in a scheduled slot are non-data — which is why TS 38.306 assumes a flat 14% (FR1 DL) for peak-rate math. Toggle the layers above to see the live number.
What is a CORESET?
The control resource set is the time-frequency region where PDCCH may appear (1–3 symbols here). The UE blind-decodes candidate locations inside it to find its downlink grants and uplink allocations.
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