Smartphone app transmits underwater messages between scuba divers
When it comes to communicating with one another while underwater, scuba divers typically use either hand signals or writing boards … both of which have limitations. Soon, however, they could be utilizing an app on their existing smartphone.
One of the problems with hand signals and boards lies in the fact that they can't always be clearly seen from a distance – or in murky water – plus the diver who is sending the initial message has to make sure that the recipient is already looking in their direction.
Unfortunately radio communications aren't an option, as radio waves don't travel well through the water. There are acoustic voice communications systems, but they require both divers to be using expensive transceivers.
Seeking a simpler and more affordable alternative, a team at the University of Washington developed an app that can be used on a smartphone in an underwater housing. Named AquaApp, it allows users to choose between 240 preprogrammed messages which correspond to hand signals used by divers.
In order to keep things simple, messages conveying the 20 most commonly used signals are prominently displayed for quick access. Additionally, the messages can be sorted into eight subject categories, such as those relating to environmental factors or equipment status.
Once a message has been selected, the phone's speakers send it through the water as a series of acoustic pulses. These pulses are detected by the mic of the recipient's phone, where the app converts them back into a visual on-screen message. The app also alerts the recipient to the fact that a message has been received.
And thanks to a special networking protocol, up to 60 divers can communicate with one another at once, at one location. Based on field tests conducted in a variety of outdoor settings, the app is claimed to work well up to a distance of 30 m (98 ft), and can transmit/receive an SOS beacon as far as 100 m (328 ft).
There are complicating factors to consider, including acoustic reflections off the seafloor, surface or underwater objects; background noises from sources such as boat engines; variations in the speakers and mics of different phones; and the physical orientation of the divers relative to one another.
For this reason, each "conversation" begins with the first phone sending a short acoustic signal known as a preamble. The app on the second phone analyzes that signal and uses it to determine the best way in which the actual message should be sent – such as the optimum bitrate and acoustic frequency – given the present conditions. That information is transmitted back to the first phone, which then sends the message accordingly.
"AquaApp brings underwater communication to the masses,” said Prof. Shyam Gollakota, who led the research along with PhD students Tuochao Chen and Justin Chan. "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 democratizing underwater technology and making it as easy as downloading software on your smartphone."
The app is demonstrated in the following video.
Source: University of Washington