A Scalable Ultrasonic-Based Localization System Using the Phase Accordance Method

Abstract

We introduce a localization system using ultrasonic signals. Our system adopts the Phase Accordance Method, which we proposed previously for accurate distance measurement [1, 2]. Unlike other ultrasonic-based systems, our system can locate ultrasonic transmitters with only one receiver, thanks to the high accuracy of the Phase Accordance Method. Thus our system can cover wider areas with fewer beacons than conventional systems, improving the scalability of the system. To evaluate the scalability and accuracy of our system, we developed a robot-tracking system and conducted an experiment with a moving robot. During the experiment, localization was executed both by our proposed method and by a conventional method based on trilateration. The experiment was repeated with different densities of receivers so that we could compare the accuracy and the scalability of our proposed method with those of the conventional method. We found that the position error of our method was degraded from 6.1 cm to 14.6 cm compared with the conventional method. However, our method improved the success rate of localization from 31% to 95%. We also conducted some localization experiments in which the robot stood still. This was because we wanted to investigate why the accuracy was degraded in the dynamic tracking. The results showed that the degradation of accuracy might be because of a systematic error in localization that is dependent on the geometric relationship between the transmitter and the receiver.