Underwater messaging made possible with app

The University of Washington’s ‘AquaApp’ is potentially the first mobile app for acoustic-based communication and networking underwater that can be used with existing devices, such as smartphones and smartwatches, without the need for additional hardware. 

In addition to their device, the only item a user of the app would need would be a waterproof phone case rated for the depth to which they are planning to dive, the researchers said. 

The most likely use case for the application is for activities such as diving, where professionals of the sport currently use over 200 hand signals to communicate information ranging from oxygen level to the proximity of aquatic species, to the performance of cooperative tasks.

Using this language as an inspiration, the AquaApp interface enables users to select from a list of 240 pre-set messages that correspond to divers’ hand signals. Users can also filter messages according to eight categories, including directional indicators, environmental factors and equipment status. In this way, the app enables critical communication without the need for a network connection. 

“Smartphones rely on radio signals like Wi-Fi and Bluetooth for wireless communication. Those don’t propagate well underwater, but acoustic signals do,” said co-lead author Tuochao Chen. “With AquaApp, we demonstrate underwater messaging using the speaker and microphone widely available on smartphones and watches.” 

The team tested the real-world utility of the AquaApp system in six locations offering a variety of water conditions and activity levels, including under a bridge in calm water, at a popular waterfront park with strong currents, next to the fishing dock of a busy lake and in a bay with strong waves. The researchers evaluated the app’s performance at distances of up to 113 metres and depths of up to 12 metres.

The results revealed that the ideal range for sending and receiving messages was from zero to 30 metres, which covers most recreational and professional diving scenarios.

However, while building and testing the app, the team had to overcome a variety of technical challenges that they haven’t previously encountered on dry land.

“The underwater scenario surfaces new problems compared to applications over the air,” said co-lead author Justin Chan. “For example, fluctuations in signal strength are aggravated due to reflections from the surface, floor and coastline. The motion caused by nearby humans, waves and objects can interfere with data transmission.”

To address these issues, the team created an algorithm that allows AquaApp to optimise, in real-time, the bitrate and acoustic frequencies of each transmission based on certain parameters, including distance, noise and variations in frequency response across devices.

When one user wants to send a message to another device, their app first sends a quick note, called a ‘preamble’, to the other device. AquaApp on the second device runs the algorithm to determine the best conditions to receive this preamble. It then tells the first device to use those same conditions to send the actual message.

The researchers developed a networking protocol to share access to the underwater network, akin to how Wi-Fi networks referee internet traffic, to support messaging between multiple devices. AquaApp can accommodate up to 60 unique users on its local network at one time.

“AquaApp brings underwater communication to the masses,” said senior author Shyam Gollakota, a UW professor in the Allen School. “The state of underwater networking today is similar to Arpanet, the precursor of the Internet, in the 1970s, where only a select few had access to the Internet.

“AquaApp has the potential to change that status quo by democratising underwater technology and making it as easy as downloading software on your smartphone.”

The researchers presented their paper describing AquaApp at SIGCOMM 2022.