Time-of-Flight (ToF)

A distance measurement technique calculating signal travel time between transmitter and receiver, then converting to distance. Provides highly accurate ranging (centimeter-level) and forms the basis for trilateration positioning. Used primarily in UWB systems requiring precise time synchronization.

Time-of-Flight (ToF) is a distance measurement principle based on measuring the time required for a signal (electromagnetic or acoustic wave) to travel from transmitter to receiver, calculating distance from propagation time and known signal velocity. For electromagnetic signals, propagation velocity is the speed of light (approximately 3×10⁸ meters per second, or 30 cm per nanosecond). For ultrasonic signals, propagation velocity is the speed of sound (approximately 343 meters per second, or 34 cm per millisecond - six orders of magnitude slower than light). The basic ToF calculation is: Distance = (Propagation Time × Signal Velocity) / 2 (division by two accounts for round-trip in TWR systems, omitted for one-way ToF). To achieve 10 cm distance measurement requires measuring electromagnetic signal flight time to approximately 0.33 nanoseconds - demanding extremely precise timing circuits. UWB is particularly well-suited to ToF ranging because: ultra-short pulses provide sharp timing edges enabling precise arrival time detection, wide bandwidth (>500 MHz) allows fine time resolution, pulse characteristics enable multipath rejection (distinguishing direct signal from reflections), and low power spectral density permits operation alongside other RF systems. Comparing ToF methods across technologies: UWB ToF achieves 10-30 cm accuracy in industrial environments with nanosecond timing, laser ToF achieves millimeter to centimeter accuracy with picosecond timing but requires line-of-sight and scanning mechanisms, ultrasonic ToF achieves 1-10 cm accuracy but limited to short range (<10 meters) and sensitive to environmental conditions, and Bluetooth/Wi-Fi phase-based ranging achieves 1-3 meter accuracy.