A New Wave of Underwater Comms Is Coming

Communicating through water is hard. The physics of the medium means it’s usually more difficult to communicate with submarines and sensors in the ocean than it is to send a signal to the moon’s Sea of Tranquility.

Most underwater communication is thus sent with sound waves. Acoustic signals, while slower than radio or optical signals, can travel much farther underwater. But the specialized hardware and software for acoustic underwater communication are expensive. Modems alone often cost more than US $10,000.

To make underwater acoustic communication more accessible, researchers at the University of Padova in Italy are developing low-cost alternatives for two critical—and costly—components of underwater communication: modems (the transmitter/receiver) and transducers (the antenna).

By November, the researchers, led by Filippo Campagnaro and Michele Zorzi, aim to begin selling their modem through their startup, SubSeaPulse SRL, at a price roughly one-tenth that of other modems on the market. The SubSeaPulse modem consists of three layers: a Raspberry Pi base; a sound card hardware attachment responsible for generating and recording audio signals; and a front end.

The team is also working on a cheaper version of traditional transducers, which can cost more than $2,000 a piece. Their transducer will convert energy into acoustic signals (and vice versa) using a modified device that’s typically used to listen to marine mammals and costs about $400.

Why underwater acoustic communications is so expensive

The expense of underwater communication has largely limited the field to applications in defense and offshore oil and gas. But SubSeaPulse’s technology could expand its uses. Some researchers, for example, use underwater sensors in coastal areas to study climate change, monitor pollution, or track biodiversity. “There’s a huge technology gap that needs to be filled,” says Campagnaro.

Researchers tested the underwater modem in an Italian river.University of Padova

“The main issue of underwater communication is the cost of the modem,” says Zorzi. That one component can be more expensive than the rest of a researcher’s setup—even if the setup includes an underwater robot, he says. Cheaper modems could allow users to deploy additional sensors and improve sampling of an environment.

In addition to the cost, current modems might not fit the specific needs of potential users. SubSeaPulse’s modem, by contrast, is software-defined, so users can modify the signal modulation for their particular application. The device can also be used as an analog front-end (rather than a complete modem) to test acoustic signals, and users can install their own software. Campagnaro likens the modem’s flexibility to how ham radio operators experiment with their equipment.

Milica Stojanovic, a professor of electrical engineering at Northeastern University who develops algorithms for underwater wireless communication, believes SubSeaPulse’s modem could be useful for researchers who don’t have access to expensive equipment or who want a software-defined unit to transmit any type of waveform they desire.

But the modem is only one component of a full underwater communication system, Stojanovic says. Range and bit rate are also important factors for users, and they are primarily determined by the transducer and the bandwidth limitations inherent to underwater communication.

“The problems of propagation and signal distortions [in an underwater acoustic channel] are not trivial,” Stojanovic says. She’s glad to see the development of SubSeaPulse’s device. “The more people work on this, the better.”