Glossary · Industrial wireless and positioning
Time-of-flight ranging
Also known as: ToF ranging, Time-of-flight measurement, Two-way ranging
German: Laufzeitmessung
In wireless positioning, time-of-flight ranging is the determination of the distance between two devices from the propagation time of a radio signal between them. With several distance measurements to known reference points, a position can be calculated.
- Industrial wireless
In one sentence
Time-of-flight ranging measures the distance between two devices from the radio signal's travel time to calculate positions.
Example
A UWB tag exchanges ranging messages with four anchors; from the measured travel times, the system calculates the tag's position in the hall.
How it applies
- Engineering: Radio signals travel about 30 cm per nanosecond, so accurate ranging needs precise timestamps and wide bandwidth. Ultra-wideband (UWB) is well suited; Bluetooth and Wi-Fi also offer ranging features with varying accuracy.
- Methods: Two-way ranging exchanges messages and cancels out clock offsets; time difference of arrival (TDoA) uses synchronized anchors and one-way transmissions.
- Operation: Obstacles and reflections (non-line-of-sight conditions) add errors. Accuracy claims must refer to stated conditions.
- Documentation: The documentation team states the ranging method, accuracy under specified conditions and known limitations, and explains how anchors must be placed.
Radio time-of-flight vs. optical time-of-flight
The principle is the same, but optical time-of-flight sensors (for example ToF cameras or laser distance sensors) measure light reflected from objects, while radio ranging measures signals between two active devices. The German "Laufzeitmessung" covers both.