High precision hybrid RF and ultrasonic chirp-based ranging for low-power IoT nodes
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RESEARCH
Open Access
High precision hybrid RF and ultrasonic chirp-based ranging for low-power IoT nodes Bert Cox1*
, Liesbet Van der Perre1 , Stijn Wielandt2 , Geoffrey Ottoy1 and Lieven De Strycker1
*Correspondence: [email protected] 1 KU Leuven, ESAT-DRAMCO Research Group, Gebroeders De Smetstraat 1, 9000 Gent, Belgium Full list of author information is available at the end of the article
Abstract Hybrid acoustic-RF systems offer excellent ranging accuracy, yet they typically come at a power consumption that is too high to meet the energy constraints of mobile IoT nodes. We combine pulse compression and synchronized wake-ups to achieve a ranging solution that limits the active time of the nodes to 1 ms. Hence, an ultra low-power consumption of 9.015 μW for a single measurement is achieved. The operation time is estimated on 8.5 years on a CR2032 coin cell battery at a 1 Hz update rate, which is over 250 times larger than state-of-the-art RF-based positioning systems. Measurements based on a proof-of-concept hardware platform show median distance error values below 10 cm. Both simulations and measurements demonstrate that the accuracy is reduced at low signal-to-noise ratios and when reflections occur. We introduce three methods that enhance the distance measurements at a low extra processing power cost. Hence, we validate in realistic environments that the centimeter accuracy can be obtained within the energy budget of mobile devices and IoT nodes. The proposed hybrid signal ranging system can be extended to perform accurate, low-power indoor positioning. Keywords: Ranging, Hybrid signaling, Ultra low-power electronics, Pulse compression, Acoustic signal processing
1 Introduction Accurate positioning of users and devices plays a major role in the growing number of location-aware applications. In time-based localization ranging systems, acoustic signals are inherently interesting candidates for precise ranging thanks to their relatively low propagation speed. They do not require high processing speeds, nor the same level of synchronization accuracy as RF-based systems. However, they are receptive to environmental and room characteristics, such as temperature, relative air velocity, reflection, and diffraction, impacting the accuracy of the measurements [1]. Hybrid signal ranging [2, 3] combines the advantages of both wave types: an RF signal is used as timing reference and the time difference with the slower propagating (ultra)sound signal is used to calculate the distance. Two classes of hybrid RF/acoustic techniques have been proposed: indirect and self positioning. An example of the first is the Active Bat Local Positioning System [4]. The base stations are attached to the ceiling and periodically broadcast © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source,
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