6G Topics › Integrated Sensing & Communication
6G Topic 05 — ISAC

The network that sees

A radio signal that bounces off a wall, a car, or a hand already carries information about that object — radar has exploited this for a century. ISAC's idea is to let the same 6G waveform that carries your data also act as radar, so the network senses range, velocity and presence as a built-in service. Sensing as a use case is agreed; how the radio does it is still being designed.

IMT-2030 — ISAC TR 22.870
Status. ISAC is an agreed 6G usage scenario (requirement). The radio realisation — waveform reuse, sensing modes, architecture — is a candidate under study; no normative 6G sensing design exists.

Foundation: range from delay, velocity from Doppler

The physics is old and exact. Transmit a pulse; if it reflects off an object at distance R, the echo returns after a round-trip delay τ = 2R/c. Measure the delay, recover the range. If the object is moving, the echo's frequency is shifted by the Doppler effect, proportional to its radial velocity. A radio that can measure delay and frequency precisely — which a wideband OFDM system can — is already a radar.

foundationR = c·τ/2; velocity from Doppler shift

Range comes from round-trip time-of-flight; radial velocity from the Doppler frequency shift of the echo. Range resolution improves with bandwidth, which is one reason sensing pairs naturally with 6G's wide upper-mid-band and sub-THz channels. This is established radar theory, reused — not invented for 6G.

arxiv.org — ISAC architecture 2025-08 secondary
Interactive — monostatic sensing (range from echo delay) illustrative physics — drag the target
Drag the target. The base station transmits and listens for the echo on the same site (monostatic). Delay τ = 2R/c gives range. Numbers are real physics (c = 3×10⁸ m/s) used illustratively, not a 6G performance claim.

Where it stops being simple

requirementISAC is an agreed 6G usage scenario

Both the ITU-R IMT-2030 framework and 3GPP's Stage-1 study (TR 22.870) name integrated sensing and communication as a target 6G capability — covering use cases from intrusion detection and traffic monitoring to gesture and environment mapping.

3gpp.org — TR 22.870 2026-03-13
candidateSensing mode and waveform are still under study

Open design questions: monostatic (transmit and receive at one node) vs bistatic/multistatic (separate nodes) sensing; whether to reuse the communication waveform unchanged or add sensing-friendly shaping; how to schedule sensing without starving data; and how results flow through the architecture. Early study work leans toward reusing OFDM with a monostatic option, but nothing is decided.

arxiv.org 2025-08 secondary
foundationOFDM is already a good radar waveform

Wideband OFDM — 6G's baseline — supports accurate delay and Doppler estimation, which is exactly why "reuse the comms waveform for sensing" is plausible rather than fanciful. The continuity argument from the radio page applies here too.

ranbits — 6G radio physical layer 2026
ISAC sensing architectures — monostatic vs bistatic vs multistatic arxiv.org 2025-08 (secondary) · TR 22.870
Mode TX and RX at Self-interference Sync requirement Typical use cases 6G study direction
Monostatic Same node High — TX leaks into RX, needs isolation None (co-located) Vehicle detection, intrusion, presence sensing candidate leading early direction
Bistatic Separate TX, RX nodes None Tight time/phase sync over backhaul Cooperative environment mapping, NLoS sensing candidate under study
Multistatic Multiple distributed RX None Tight sync across multiple nodes High-accuracy 3D localisation, gesture candidate under study
ISAC sensing physics — range resolution vs signal bandwidth Established radar theory (δR = c / 2B) — physical relationship, not a 6G spec value
Signal bandwidth B Range resolution δR = c / (2B) Representative 6G band Sensing capability
100 MHz 1.5 m Lower FR3 / cmWave Large object / vehicle detection
500 MHz 0.30 m cmWave / mid FR3 Person detection, parking
1 GHz 0.15 m Upper FR3 Fine object discrimination
4 GHz 0.038 m ≈ 3.8 cm sub-THz Gesture, high-precision mapping
Tracker — what 3GPP / ITU-R is doing here full tracker ↗
ISAC (6G) candidate
Integrated Sensing and Communication
ISAC is one of the six IMT-2030 usage scenarios (requirement) and appears in TR 22.870. The RAN realization — waveform reuse, monostatic/bistatic modes, architecture — is a candidate still under study.
arxiv.org 2025-08 secondary
Use case agreed (IMT-2030/TR 22.870); RAN design under studyno % published

Where this connects

ISAC depends on the waveform (it senses with it) and the spectrum (wide bandwidth = fine range resolution), and leans on ML to interpret cluttered echoes. It is one of the three genuinely new IMT-2030 scenarios.

Foundations The correlation and timing machinery sensing relies on is the same maths a 5G UE uses to detect PSS — taught with worked numbers in Foundations. 5G PSS detection →
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