Description
Time-of-Flight uses the round-trip propagation delay between transmitter and receiver to estimate range. In Wi-Fi this surfaces as the 802.11mc Fine Timing Measurement (FTM) protocol, which exposes nanosecond-resolution timestamps useful for ranging. ToF is the alternative to AoA / fingerprinting for distance-based localisation and is increasingly viable on commodity APs.
When it's used
- Ranging-based indoor positioning on FTM-capable APs
- Combining ToF distances with AoA bearings for 2D fixes
- BLE 5.1 channel-sounding range estimation
Limitations
- NLOS bias inflates the distance estimate
- Hardware must support FTM (or equivalent) — limited deployment
- Sub-metre accuracy needs careful calibration of fixed processing delays