Multilateration
A positioning technique determining location by measuring time differences of signal arrival at multiple receivers. Also called TDOA (Time Difference of Arrival). Tag transmits a signal received by multiple anchors at slightly different times. Differences reveal distances enabling position calculation. Commonly used in UWB and other RF-based RTLS.
Positioning technique calculating location by measuring distances from object to multiple reference points (anchors) with known positions, then solving geometric equations to determine position. Multilateration (also called trilateration in 2D) requires: minimum 3 anchors for 2D positioning, 4 anchors for 3D positioning (though 3D systems often use >4 for accuracy through redundancy). Distance measurements obtained through: Time of Flight (ToF) - measuring signal travel time and converting to distance using propagation speed (UWB primary method, achieving 10-30 cm accuracy), Received Signal Strength (RSSI) - estimating distance from signal attenuation (BLE/Wi-Fi, 1-15 meter accuracy), or Two-Way Ranging (TWR) - bidirectional time measurements eliminating clock synchronization requirements. Multilateration mathematics: each distance measurement defines sphere (3D) or circle (2D) centered on anchor with radius equal to measured distance. Tag position is intersection of these spheres/circles. Example: 10 cm ranging error with GDOP of 2 produces 20 cm position error, but same error with GDOP of 8 produces 80 cm position error. Industrial multilateration considerations: (1) Anchor placement optimization - ensuring good geometry throughout coverage area (avoiding collinear arrangements, maximizing spatial separation). (2) Over-determination - using >4 anchors (6-10 typical) providing redundancy and accuracy improvement. (3) Outlier rejection - identifying and excluding anomalous distance measurements (NLoS paths, interference). (4) Kalman filtering - combining current multilateration result with movement model and previous positions for smoothing. Multilateration accuracy varies by technology: UWB achieving 10-30 cm (90th percentile) in industrial environments with proper anchor placement, Wi-Fi/BLE RSSI achieving 3-15 meters, GPS achieving 3-10 meters outdoors.