Indoor Navigation System by Combining Ultrasonic Wave TOA and Inertial Measurement

Indoor navigation plays an important role in agricultural robots working in greenhouses. The SS-sound system, where Time of Arrival (TOA) of spread spectrum modulated sound is used to localization, is one of the effective methods for indoor navigation, but there is a called near-far problem where the sound waves emitted from distant anchors are disturbed by the one emitted from nearby anchors. Transmitting the SS-sound from multiple anchors using Time Division Multiple Access (TDMA) is effective to solve the near-far problem. However, the TOA from multiple anchors cannot be obtained simultaneously, so that the localization cannot be performed. To solve the problem, we propose a method for combining the TDMA-based SS-sound system and inertial navigation system. A simple numerical example simulating the movement of a ground-moving robot was presented to clarify the effectiveness of the proposed method.