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ACPS > Research > Ongoing Research > Acoustic Modem

Acoustic Modem

ahoi: Open-Source, Inexpensive, Low-Power Underwater Acoustic Modem

Contact Prof. Dr.-Ing. Bernd-Christian Renner
Financing Hamburg University of Technology (TUHH)

 

Project Description

The recent development of small, cheap AUVs enables a plethora of underwater near- and inshore applications. Among these are monitoring of wind parks, detection of pollution sources, water-quality inspection, and the support of divers during disaster management. These tasks profit from online reporting, control, and AUV swarm interaction; yet they require underwater communication. Unfortunately, commercial devices are prohibitively expensive and typically closed-source, hampering their application in affordable products and research. Therefore, we developed the open-source ahoi acoustic modem. It is:

  • small enough to be carried by micro AUVs,
  • consumes little enough energy to not diminish operation times of its host,
  • comes at an attractive unit cost below 600 euros,
  • can reliably communicate at distances of 300 meters and more, and
  • supports ranging (distance measurements) without additional hardware.

Due to its modular build, the modem can be customized and is suitable as research platform to analyze, e.g., MAC and routing protocols. We conducted extensive real-world studies. Our results of communication range, packet reception rate, ranging accuracy, and efficient and reliable self-localization are available (see below).

 

ahoi – Overview

The ahoi acoustic modem is an open-source device comprising both hardware and software. Please refer to the section Open Source Access on details how to obtain all sources.

The hardware comprises a stack of three boards: a mainboard with a microcontroller, a receiver with analog filtering and amplification, and a transmitter. All boards follow a trade-off between high integration to achieve a small overall footprint and easy assembly by hand. We rely on COTS components only that were easily sourceable at the time of development. Component lists are provided along with schematics. In order to simplify programming and make the device open to further development, we used a microcontroller. However, the open-source nature of the device enables all users to develop and provide application-specific boards.

The firmware is written in the C language to combine performance and understandability. A modular software stack with a hardware abstraction layer has been devised to allow extensibility of the firmware. The current firmware is a proof-of-concept reference implementation useable for both academia and industry that we plan to improve and extend subsequently. Even though we consider it a starting point for future advances and research, it is ready to use for many purposes and applications.

Along with hardware and firmware, we distribute a set of tools to access and control our ahoi modem from a PC or similar device; e.g., a Raspberry Pi. These tools allow to send and receive packets and configure the modems. Moreover, they encompass a proof-of-concept image transmission application and tools to run experiments; e.g., assess the channel quality by sending and tracing a sequence of packets.

 

Key Facts

Price PCBs, ICs, and components: € 200, Hydrophone: € 400
License BSD (permissive)
Processing STM32 F4 @ 180 MHz
Availability Send us an e-mail
Dimension (wlh) 50 mm x 50 mm x 25 mm
Casing Tube-type 100 m depth rated
Weight 150 g
Modulation FSK, OFDM, FSCM (implementation pending)
Frequency Band 25 - 87.5 kHz, depending on configuration
Bandwidth 25 - 37.5 kHz, depending on configuration
Data Rate 260 - 4700 bit per second
Transmit Power up to 5 W (down to 0.75 W)
Receive Powere ca. 300 mW
Range 300 m with AS-1 hydrophone, more than 1 km with different transducer and frequency band

Open Source Access

All sources of the ahoi acoustic modem are currently available via the GitLab hosted by TUHH. Different components are available in separate repositories for a better overview and development tracking. All sources are released under a permissive open source license. Please refer to the repositories for information on licensing.
We are currently assembling a proper documentation, that will be released subsequently. At the moment, you will find basic information in the README files of all repositories. Please do not hesitate to contact us at ahoi@ahoi-modem.de

Hardware

URL: https://collaborating.tuhh.de/e-24/public/ahoi/hardware
Description Schematics, bills of material (BOM), and assembly diagrams of all PCBs.

Firmware

URL: https://collaborating.tuhh.de/e-24/public/ahoi/firmware
Description Firmware for the ahoi modem. Sources found in the master branch have been tested and are considered stable.

Python Library

URL: https://collaborating.tuhh.de/e-24/public/ahoi/pylib
Description Python tools to interface with the ahoi modem from a PC or similar device (e.g, Raspberry Pi).

Documentation

URL: http://docs.ahoi-modem.de
Description Contains the modem documentation.

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TU Hamburg
Institute for Autonomous Cyber-Physical Systems
Prof. Dr.-Ing. Bernd-Christian Renner
Harburger Schloßstr. 28
21079 Hamburg
E-mail : acps-sekretariat@tuhh.de
Phone : (Office) +49 40 42878-4800
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