Indoor positioning for moving objects using a hardware device with spread spectrum ultrasonic waves

Moving objects, especially autonomous mobile robots, require information of indoor self-location with high accuracy to reach their destination safely and correctly. In this study, we aimed to measure the indoor position of a moving object using SS (spread spectrum) ultrasonic waves, and we discussed the accuracy of the moving distance measured using a newly developed hardware device. In the case of static object, we showed that because of the noise tolerance of SS waves, a distance up to 20 [m] could be measured between a transmitter and a receiver on cm-order. To detect the SS ultrasonic signals, correlation calculations were carried out between a range of received waves and same range of replica signals; the replica signals were the same as the transmitted SS signals. Popular positioning systems using SS electrical waves employ signal acquisition to calculate coordinates of objects from correlation values and signal tracking to measure the relative shift of distances of moving objects. It is difficult for the system using SS ultrasonic waves to continue tracking because of the decrease in the self-correlation value due to the Doppler effect that acted on a moving object. To solve this problem, we proposed a tracking method for keeping correlation values by limited range of correlation calculations. In this study, for obtaining real-time updates of positional information from the relative shift, an experiment of distance measurement was also conducted using a newly developed hardware device that was used to carry out signal acquisition and the proposed tracking method. The results show that real-time signal tracking with our method could be realized, same as existing software between +/- 0.5 [m/s]. This paper reports that we can expect self-localization of robots using this system.