TWEET: an envelope detection based broadband ultrasonic ranging system

Fine-grained location information at long range can benefit many applications of embedded sensor networks and robotics. In this paper, we focus on range estimation - an important prerequisite for fine-grained localization - in the ultrasonic domain for both indoor and outdoor environments, and make three contributions. First, we evaluate the characteristics of broadband signals, and provide useful statistics in their design and engineering to achieve a good trade-off between range and accuracy. Second, to overcome the inaccuracy due to correlation sidelobes, we propose a signal detection technique that estimates the envelope of the correlated pulse using a simple least-square approximation approach, and undertake a simulation study to verify its ranging efficiency on linear chirps. Third, leveraging on the insights obtained from our initial study, we present the design and implementation of TWEET: a mote-based ultrasonic broadband ranging system based on linear chirps using the CSIRO Audio nodes, which comprises of a Fleck-3z mote along with audio codecs and a Blackfin DSP. Our evaluation results indicate that the system is precise enough to support source localization applications: a reliable operational range of 20m (outdoor) and an average accuracy of < 2 cm with a 95% confidence interval of 2 cm.