An ultrasonic local positioning system using four base stations

The purpose of tracking technology as it is currently used is to detect the position of a moving object. The leading position detection methods are classified as active type and passive type methods. Typical active type methods include radiofrequency identification (RFID) tags and ultrasonic waves, and passive type methods are global positioning systems (GPS) and cameras. RFID tags are being used indoors in many businesses. Though the ultrasonic wave method is advantageous because of the lower cost, there has been less research into this method than into the use of RFID tags. However, when the measurement environment changes such as the speed of sound, attenuation of the ultrasonic wave causes signal-to-noise (S/N) ratio decrease, pulse waveform is distorted by obstacles. Therefore, we propose a position detecting system using a time of arrival (ToA) method to improve the accuracy.