PUSCH Resource Mapping

What is a resource element?

Before any "mapping", you need the canvas. 5G's air interface is a grid. The smallest cell is a resource element (RE) = one subcarrier × one OFDM symbol. Stack 12 subcarriers = one resource block (RB) in frequency. Lay 14 symbols side by side = one slot in time. So one RB across one slot is a 12 × 14 = 168-RE tile — and the whole job of "resource mapping" is deciding which of those REs carry your data.

From transport block to antenna

Your data doesn't jump straight onto the grid. It walks a precise chain — each block doing one job. Hover the idea: the transport block gets a CRC, is split into LDPC code blocks, rate-matched to fit the available REs, scrambled, turned into QAM symbols, optionally transform-precoded (the uplink-only DFT spread), mapped to layers, precoded onto antenna ports, and finally — the subject of this lab — mapped to resource elements.

Placing it in the slot — mapping type & SLIV

First decision: which OFDM symbols? The DCI gives a start symbol S and a length L, packed into one number — the SLIV. Type A is slot-based (DM-RS anchored early); Type B is a mini-slot that starts anywhere for low latency. Drag the sliders and read the live SLIV; the formula below is exactly what the gNB computes.

Which resource blocks — Type 0 & Type 1

Second decision: which RBs? Type 1 is one contiguous run, compressed into a single RIV (the only option under transform precoding). Type 0 is an RBG bitmap for non-contiguous CP-OFDM grants. Both shown live.

CP-OFDM or DFT-s-OFDM?

The uplink alone can swap waveform. CP-OFDM = flexible, MIMO, higher peak. DFT-s-OFDM = a DFT pre-spread that lowers PAPR for coverage, but single-layer and contiguous only. This choice changes the DM-RS pattern in the grid below, so set it here.

Live RE mapping — data, DM-RS, PT-RS

Now it all lands. PUSCH fills its time-frequency allocation except the REs taken by DM-RS (channel estimation pilots) and PT-RS (phase tracking). Under DFT-s-OFDM the DM-RS takes whole symbols; under CP-OFDM it shares symbols comb-style. The available-RE count feeds the TBS below.

Frequency hopping

A narrowband grant stuck in a fade fails. Hopping splits the transmission across the band so no single dip is fatal. Intra-slot moves the second half by an offset; inter-slot alternates by slot number.

Sizing the transport block

Available REs × code rate × modulation order × layers → quantise → the transport block size, exactly per TS 38.214 §5.1.3.2 (shared UL/DL). Pick an MCS row and resources; every step is shown.

One grant, end to end

Let's schedule a real PUSCH and trace every number, so the whole chapter clicks into one picture.

Test yourself