Underwater messaging app for smartphones — ScienceDaily

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For millions of people who participate in activities such as snorkeling and scuba diving each year, hand signals are the only option for communicating safety and direction information underwater. While recreational divers may use around 20 signals, the vocabulary of professional divers may exceed 200 signals on topics ranging from oxygen levels to proximity to aquatic species to performing cooperative tasks.

The visual nature of these hand signals limits their effectiveness at a distance and in low visibility. Two-way text messaging is a potential alternative, but one that requires expensive custom hardware that is not widely available.

Researchers from the University of Washington show how to achieve underwater messaging on billions of existing smartphones and smartwatches using only software. The team developed AquaApp, the first mobile app for underwater acoustic communication and networking that can be used with existing devices such as smartphones and smartwatches.

The researchers presented their paper describing AquaApp on August 25 at SIGCOMM 2022.

“Smartphones rely on radio signals like WiFi and Bluetooth for wireless communication. These don’t propagate well underwater, but acoustic signals do,” said co-lead author Tuochao Chen, a UW PhD candidate at the Paul G. Allen School of Computer Science. & Engineering. “With AquaApp, we’re demonstrating underwater messaging using the speaker and microphone widely available on smartphones and watches. Other than downloading an app to their phone, the only thing people will need is a waterproof phone case rated for the depth of their dive.”

The AquaApp interface allows users to select from a list of 240 predefined messages that match the hand signals used by professional divers, with the 20 most common signals displayed prominently for easy access. Users can also filter messages by eight categories, including directional indicators, environmental factors, and equipment status.

While creating the app, the team had to overcome a variety of technical challenges that they had never encountered before on dry land.

“The underwater scenario raises new issues compared to aerial applications,” said co-lead author Justin Chan, a doctoral student at the Allen School. “For example, fluctuations in signal strength are compounded due to surface, ground, and shoreline reflections. Movement caused by humans, waves, and nearby objects can interfere with data transmission. Plus, microphones and speakers have different characteristics in different smartphone models. We had to adapt in real time to these and other factors to make sure AquaApp would work in real-world conditions.”

Other challenges include the tendency of devices to change position and proximity quickly in the current, as well as the different noise profiles the app might encounter due to the presence of ships, animals and even low-flying aircraft.

The team created an algorithm that allows AquaApp to optimize, in real time, the bit rate and acoustic frequencies of each transmission based on certain parameters, including distance, noise, and frequency response variations between devices.

Here’s how it works: When a 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 the preamble. Then it 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, similar to how WiFi networks arbitrate Internet traffic, to support messaging between multiple devices. AquaApp can accommodate up to 60 unique users on its local network at the same time.

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 riverside park with strong currents, at side of the fishing pier of a lake and in a bay with strong waves. The researchers evaluated the application’s performance at distances of up to 113 meters and at depths of up to 12 meters.

“Based on our experiences, up to 30 meters is the ideal range for sending and receiving messages underwater, and 100 meters for transmitting SoS beacons,” Chen said. “These capabilities should be sufficient for most recreational and professional scenarios.”

Researchers also measured AquaApp’s impact on battery life by running the system continuously on two Samsung Galaxy S9 smartphones at maximum volume and with screens turned on. The app reduced the devices battery power by just 32% in four hours, which is the maximum recommended dive time for recreational scuba diving.

“AquaApp brings underwater communication to the masses,” said lead author Shyam Gollakota, a UW professor at the Allen School. “The state of undersea networks today is similar to ARPANET, the precursor to the Internet, in the 1970s, when only a privileged few had access to the Internet. AquaApp has the potential to change this status quo by democratizing the technology underwater and making it as easy as downloading software to your smartphone.”

Team data and open source Android code are available on the AquaApp website.

The researchers are supported by the Moore Inventor Fellowship and the National Science Foundation.


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