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

Abstract

In this letter, we zoom in on the distance estimation in a chirp-based hybrid 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 4 times improvement with respect to conventional ADC-based indoor ranging techniques. The provided method can be extended to a system for indoor localisation and also opens the possibility to implement RF backscattering-based solutions for fully passive nodes.

Energy-Neutral Devices: Can Hybrid RF-Acoustic Signals Point Them Out?

“…The power consumption and turn-on time of each element in the tag's functional diagram is shown in Table I. It shows that the ultrasonic MEMS microphone has a relatively high power consumption and large turn-on time, while the amplifier 1 Microphone: Knowles SPU0410, amplifiers: TI TLV341A, comparator: TI TLV3691, multiplexer: TI TS5A3160, oscillators: Touchstone TS3001, RFswitch: AD ADG904 In accordance with the ranging strategy proposed in [10], the tag is assumed to be powered for 1 ms after start-up. The total energy consumption E tag to perform one ranging measurement using a split start-up is calculated to be 11.7 µJ, based on the component's technical datasheet information in Table I.…”

“…An overview of the ranging strategy is shown in Fig. 1 and is based on the chirp frequency demodulation technique presented in [10]. The system consists of two types of entities: a fixed beacon (B) and one or multiple mobile tags (M x ).…”

“…The system architecture of a hybrid RF-acoustic tag based on RF backscatter is presented here, further improving energy consumption with respect to the work presented in [10] which is based on an active radio transceiver. The functional diagram is shown in Fig.…”

“…Although the energy efficiency of wireless acoustic sensor nodes has progressed significantly because of the developments in MEMS microphones and low power computing power, current hybrid RF-acoustic solutions have not achieved fully passive operation. Research has shown that the RF communication is the main limiting factor to achieve this [10].…”

“…needs, the hybrid RF-acoustic tag can harvest energy from the environment. However, the power density of these ambient sources is too low in comparison to the energy requirements of the acoustic ranging system presented in [10] to serve as a useful energy source [12]. One way to overcome this problem is to steer a directional RF power beam towards the tag, significantly increasing the power density [13][14].…”