A 3D position estimating system based on acoustic signals is described. Although the method for position sensing based on acoustic signals, among many techniques, is characterized by low accuracy and short measurement range, still this is the most economical method in the case of not demanding highly precise measurements. Unlike the conventional ultrasound system, a 3D locator using audible sound is developed. This system is applicable to determine the coordinates of a sound receiver placed at an arbitrary position in a small-size room, especially an anechoic chamber. Low resolution in TOF (time-of-flight) estimation owing to the use of low frequency acoustic signals could be compensated by using phase information of the two signals between the transmitter and the receiver. Linear-phase-slope of cross-spectrum estimation is recommended to estimate TOF to reasonable accuracy for the system using wide band signals from a multi set of speakers.
In 3D localization process, the linearized spherical equation can be implemented to incorporate various sets of TOF measurement to produce the unknown position of the target object in Cartesian coordinate. TOF estimation based on phase must be calibrated to obtain the correct distance between the transmitter and the receiver, which is varying with the speed of sound. Experiment results of the system performance in an anechoic chamber are presented.
