The radar, which looks like a pair of cones, transmits a radio signal that reflects off the vibrating surface and rebounds back to the radar. (That’s the band where the upcoming high-frequency 5G wireless network will operate.) Positioned in the air above the transmitter is a new type of extremely-high-frequency radar that processes signals in the millimeter wave spectrum of wireless transmission, between 30 and 300 gigahertz. This lets the researchers transmit hundreds of bits at once. To achieve high data rates, the system transmits multiple frequencies at the same time, building on a modulation scheme used in wireless communication, called orthogonal frequency-division multiplexing. When the signal hits the surface, it causes tiny ripples in the water, only a few micrometers in height, corresponding to those frequencies.
For example, when the transmitter wants to send a 0, it can transmit a wave traveling at 100 hertz for a 1, it can transmit a 200-hertz wave. The signals travel as pressure waves of different frequencies corresponding to different data bits. TARF includes an underwater acoustic transmitter that sends sonar signals using a standard acoustic speaker. Many are also required to cover large areas, making them impracticable for, say, submarine-to-surface communications. Buoys, for instance, have been designed to pick up sonar waves, process the data, and shoot radio signals to airborne receivers. Today’s technological workarounds to this wireless communication issue suffer from various drawbacks. “If it transmits a signal every once in a while, you’d be able to use the system to pick up that signal.” “Acoustic transmitting beacons can be implemented in, say, a plane’s black box,” Adib says. And underwater drones that monitor marine life wouldn’t need to constantly resurface from deep dives to send data to researchers.Īnother promising application is aiding searches for planes that go missing underwater. Using the system, military submarines, for instance, wouldn’t need to surface to communicate with airplanes, compromising their location. But it represents a “milestone,” he says, that could open new capabilities in water-air communications. The system, called “translational acoustic-RF communication” (TARF), is still in its early stages, Adib says. He co-authored the paper with his graduate student Francesco Tonolini. Our idea is to transform the obstacle itself into a medium through which to communicate,” says Fadel Adib, an assistant professor in the Media Lab, who is leading this research.
“Trying to cross the air-water boundary with wireless signals has been an obstacle. Above the surface, a highly sensitive receiver reads these minute disturbances and decodes the sonar signal. An underwater transmitter directs a sonar signal to the water’s surface, causing tiny vibrations that correspond to the 1s and 0s transmitted. In a paper being presented at this week’s SIGCOMM conference, MIT Media Lab researchers have designed a system that tackles this problem in a novel way. This causes inefficiencies and other issues for a variety of applications, such as ocean exploration and submarine-to-plane communication.
Acoustic signals, or sonar, sent by underwater devices mostly reflect off the surface without ever breaking through. Radio signals that travel through air die very rapidly in water.
Today, underwater sensors cannot share data with those on land, as both use different wireless signals that only work in their respective mediums. MIT researchers have taken a step toward solving a longstanding challenge with wireless communication: direct data transmission between underwater and airborne devices.
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