A Passive and Asynchronous Wake-up Receiver for Acoustic Underwater Communication

TL;DR

This work tackles the challenge of sustaining long-term underwater sensor deployments by eliminating idle power in acoustic communications. It introduces a passive, asynchronous wake-up receiver that harvests energy from the incoming acoustic signal to power a wake-up path and uses OOK to transmit a sensor UUID, enabling selective activation of the host system. The approach is demonstrated with a hemispherical piezoelectric transducer and a two-path hardware design that combines energy harvesting (via a NVCR rectifier and a BQ25570 harvester) with ultra-low-power demodulation and a UUID decoder, achieving wake-up at $200~\text{bps}$ up to $5~\text{m}$ and $63~\mu\text{W}$ active consumption for the wake-up task. The results indicate true energy-neutral idle operation for underwater sensor networks, reducing acoustic exposure and extending mission lifetimes in UWSNs.

Abstract

Establishing reliable data exchange in an underwater domain using energy and power-efficient communication methods is crucial and challenging. Radio frequencies are absorbed by the salty and mineral-rich water and optical signals are obstructed and scattered after short distances. In contrast, acoustic communication benefits from low absorption and enables communication over long distances. Underwater communication must match low power and energy requirements as underwater sensor systems must have a long battery lifetime and need to work reliably due to their deployment and maintenance cost. For long-term deployments, the sensors' overall power consumption is determined by the power consumption during idle state. It can be reduced by integrating asynchronous always-on wake-up circuits with nano-watt power consumption. However, this approach does reduce but not eliminate idle power consumption, leaving a margin for improvement. This paper presents a passive and asynchronous wake-up receiver for acoustic underwater communication enabling zero-power always-on listening. Zero-power listening is achieved by combining energy and information transmission using a low-power wake-up receiver that extracts energy out of the acoustic signal and eliminates radio frontend idle consumption. In-field evaluations demonstrate that the wake-up circuit requires only 63 uW to detect and compare an 8-bit UUID at a data rate of 200 bps up to a distance of 5 m and that the needed energy can directly be extracted from the acoustic signal.

Figures (5)

• Figure 1: Application scenario overview with the proposed hybrid acoustic link as a backbone for underwater IoT. The energy-neutral receiver allows a passive and asynchronous initialization of information transmission, thus increasing maritime sensor nodes' energy efficiency.
• Figure 2: (a) The communication is divided into two parts: A wake-up part (red and blue), and a part with the actual information (green). (b) Communication strategy used to power and wake individual sensor nodes. (c) A high-level overview of an underwater sensor node hosting an acoustic wake-up circuit connected to a single piezoelectric transducer.
• Figure 3: (a) High-level overview of the proposed acoustic wake-up circuit. (b) Detailed view of the OOK demodulation circuit. (c) Involved signals in the demodulation process.
• Figure 4: Demonstration of the passive wake-up receiver. The preceding preamble provides energy to power up the system and decode the UUID. The wake-up signal is activated if the received UUID matches the wake-up receiver.
• Figure 5: (a) 3D rendering of the designed UWSN which integrates the proposed wake-up receiver, the piezoelectric hemisphere for signal reception and energy extraction, and a more powerful host system. (b) Illustration of the test setup at the river site.