Water-Air Communications Barrier Broken by MIT Researchers

Vibrations for sending underwater signals

MIT has developed a solution for this problem using a novel approach. The new system being presented by its creators at the Association for Computing Machinery's Special Interest Group on Data Communications annual SIGCOMM conference. 

It involves using an underwater transmitter that directs a signal to the water's surface that then causes small vibrations on the surface that correspond to the 1s and 0s codes. Above the water surface, a highly sensitive receiver reads and decodes these subtle messages. 

“Trying to cross the air-water boundary with wireless signals has been an obstacle. Our idea is to transform the obstacle itself into a medium through which to communicate,” said Fadel Adib, an assistant professor in the Media Lab, who is leading this research. 

Connecting submarines to airplanes

Adib co-authored the paper with his graduate student Francesco Tonolini. The system, currently dubbed “translational acoustic-RF communication” (TARF), is far from a final solution to the communication problem but Adib believes this latest work represents a significant “milestone,” in water-air communications. 

Once the system is further refined it could mean that military submarines wouldn’t need to compromise their location by surfacing to communicate with airplanes. In addition, underwater drones that monitor and research marine life could send communications to their researchers, not the surface without having to continually resurface. 

Another use for the system may be to help in the search for missing planes that disappear underwater. “Acoustic transmitting beacons can be implemented in, say, a plane’s black box,” Adib said.

“If it transmits a signal every once in a while, you’d be able to use the system to pick up that signal.” There have been other systems in the past that have attempted to fix this underwater to air communication problem but they all have their drawbacks. 

One popular method was to use buoys that pick up sonar signals and translate them into radio waves to airborne receivers. However, these buoys were easily lost, damaged or needed to cover too large an area for accurate communications. 

So far the TARF system has been extensively tested in a water tank and in two different swimming pools on MIT’s campus. In these tests the researchers also had swimmers upsetting the water surface with other waves that rose to about 16 centimeters. 

In both settings, TARF accurately decoded various data, including the sentence, “Hello! from underwater” at hundreds of bits per second, similar to standard data rates for underwater communications. “Even while there were swimmers swimming around and causing disturbances and water currents, we were able to decode these signals quickly and accurately,” Adib said.