Zero-Crossing Chirp Frequency Demodulation for Ultra-Low-Energy Precise Hybrid RF-Acoustic Ranging of Mobile Nodes

In this letter, we zoom in on the distance estimation in a chirp-based hybrid radio-frequency (RF)-acoustic ranging system. We present an ultra-low-power solution based on zero-crossing demodulation. We have designed an experimental prototype to validate the approach and compared the power usage, accuracy, and precision of this ranging system with a conventional method. Our measurements show that an accuracy and precision below 5 cm can be obtained for a mobile sensor node that has a lifespan of over 3794 days or ∼10 years, at an update rate of 1 Hz. This constitutes a four times improvement with respect to a conventional analog-to-digital converter based indoor ranging techniques. The provided method can be extended to a system for indoor localization and opens the possibility to implement RF backscattering-based solutions for fully passive nodes.