Code division positioning by continuous signals using spread spectrum ultrasonic waves

Indoor real-time positioning is required in order to realize self-localization for autonomous mobile robots. In particular, accurate control in plural mobile robots requires 3-D coordinate information. This paper presents the positioning accuracy and response time for a 3-D real-time indoor positioning system which uses continuous spread spectrum ultrasonic signals that are generated and detected using inexpensive all-purpose transducers, and a Code Division Multiple Access (CDMA) communication system. For application with moving targets, we propose signal acquisition and tracking using continuous signals in analogy to the already effective Global Navigation Satellite System (GNSS). The proposed calculation algorithm for coordinate acquisition is based on the Newton-Raphson method for continuous signals. The calculation time and accuracy of this method is verified by conducting a positioning experiment. The results show that the positioning error is less than 50 mm in a 4000 mm by 4000 mm experimental space with 4 transmitters. Moreover, the maximum response time to update a result is 80 ms, displaying the efficacy of this system for robot navigation.