Interference Cancelation in Ultrasonic Sensor Arrays by Stochastic Coding and Adaptive Filtering

Interference between sensors is a serious problem when ultrasonic sensor arrays are used to monitor and to explore the environment. In ultrasonic sensor arrays operating in the pulse-echo mode, the transmitters usually are excited serially by time division multiplexing. The repetition rate of the entire system is limited by the time of flight (TOF) of the pulses. For in-room applications, the TOF is in the order of 10 ms up to 100 ms due to multiple reflections. Thus, the repetition rate of an array of only 4 sensors would be in the order of 40 ms to 400 ms. Interference with signals from other ultrasonic sensor systems poses additional problems, e.g., if several robots are operating in the same area. In this paper a method for interference cancelation is presented and experimentally verified. Ultrasonic sensors are excited simultaneously in order to accelerate the repetition. We use stochastic coding of the transmitted signals and adaptive filtering of the received signal to avoid both, interference of the sensors in the array and interference with other ultrasonic sensor systems.