The AquaApp allows divers and others to communicate underwater via smartphone messenger. Researchers at the University of Washington have developed a method that allows any of the billions of smartphones around the world to act as an acoustic-based messenger and networking device for use underwater.

The software can be used on any existing smartphone or smartwatch. It beats the hundreds of hand signals that professional divers need to learn and use to communicate, or the 20 or so hand-signs recreational divers use. This technology uses acoustics through a speaker and microphone, to transfer message signals that the receiving smartphone then interprets.

The paper describing AquaApp was presented on August 25th, 2022 at SIGCOMM 2022.

“Smartphones rely on radio signals like Wi-Fi and Bluetooth for wireless communication. Those signals don’t propagate well underwater, but acoustic signals do,” Co-lead author Tuochao Chen, a University of Washington doctoral student, said in a statement. Chen attends the Paul G Allen School of Computer Science and Engineering.

“With AquaApp, we demonstrate underwater messaging using the speaker and microphone widely available on smartphones and smartwatches,” Chen said. “Other than downloading an app on their phone, the only thing people will need is a waterproof phone case rated for the depth of their dive.”

To make the system functional, the AquaApp interface enables users to select from a list of 240 pre-set messages that correspond to hand signals. This creates a platform that professional divers are already familiar with, but to enhance this even more, the 20 most common signals are prominently displayed on the screen and easily accessible.

Messages can be filtered according to eight categories, including environmental aspects, direction factors, and status of the equipment.

With all the positives of the app, there are some basic, technical issues that affect the sending and receiving of messages underwater.

Compared to over-the-air transmission, underwater communication presents its own challenges. There are fluctuations in signal strength, exacerbated by reflections from the coastline, the floor of the body of water, and the surface. Motion, caused by humans, waves, or other objects such as fish, can interfere with data transmission. In order for real-world use of AquaApp, scientists had to allow for the differing characteristics of speakers and microphones across different smartphone models.

There was the challenge of shifting positions and proximity of smartphones in moving currents. There was also noise from surrounding vessels, animals, and even low-flying aircraft. To address all these issues an algorithm was developed that could account for variations in distance, noise, and frequency response between devices, optimizing the bitrate and acoustic frequencies of each transmission.

The process works in a certain way, to prevent interference. When one user intends to send a message to another user, AquaApp sends a quick note (sound) to the other device. On the second device, AquaApp runs the algorithm to determine the best parameters for what researchers term the preamble (note).

There is an underwater network capability, where 60 unique users can be in the same network at one time. This is similar to a Wi-Fi network, but beneath the water. The last aspect to AquaApp is the range, up 30 meters seems to be the ideal distance between devices. But tests measured ranges up to 113 meters and at depths of 12 meters.

There seems to be a consensus that AquaApp is akin to the early forms of the internet, called ARPANET. The research team claimed that this technology can bring underwater communication to the masses.

AquaApp is open source code and will be available to everyone to download and use on their smartphones and smartwatches. For further information, review the website at the UW website AquaApp.

Read the paper's abstract below:

"Since its inception, underwater digital acoustic communication has required custom hardware that neither has the economies of scale nor is pervasive. We present the first acoustic system that brings underwater messaging capabilities to existing mobile devices like smartphones and smart watches. Our software-only solution leverages audio sensors, i.e., microphones and speakers, ubiquitous in today's devices to enable acoustic underwater communication between mobile devices. To achieve this, we design a communication system that in real-time adapts to differences in frequency responses across mobile devices, changes in multipath and noise levels at different locations and dynamic channel changes due to mobility. We evaluate our system in six different real-world underwater environments with depths of 2--15 m in the presence of boats, ships and people fishing and kayaking. Our results show that our system can in real-time adapt its frequency band and achieve bit rates of 100 bps to 1.8 kbps and a range of 30 m. By using a lower bit rate of 10--20 bps, we can further increase the range to 100 m. As smartphones and watches are increasingly being used in underwater scenarios, our software-based approach has the potential to make underwater messaging capabilities widely available to anyone with a mobile device.

Project page with open-source code and data can be found here: https://underwatermessaging.cs.washington.edu/"