Communication over water is difficult. Due to the physical properties of the medium, it is usually more difficult to communicate with submarines and sensors in the ocean than it is to send a signal to the Sea of Tranquility on the Moon.
Most underwater communication is therefore carried out via sound waves. Although acoustic signals are slower than radio or optical signals, they can travel much further underwater. However, the special hardware and software for acoustic underwater communication is expensive. Modems alone often cost more than $10,000.
To make underwater acoustic communication more accessible, researchers at the University of Padua in Italy are developing low-cost alternatives for two critical – and expensive – components of underwater communication: modems (transmitters/receivers) and transducers (antennas).
Starting in November, the researchers led by Filippo Campagnaro and Michele Zorzi plan to start selling their modem through their startup. SubSeaPulse SRLat a price about a tenth of the price of other modems on the market. The SubSeaPulse modem consists of three layers: a Raspberry Pi base, a sound card hardware connector 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 each. Their transducer converts energy into acoustic signals (and vice versa) using a modified device normally used to listen in on marine mammals, which costs about $400.
Why underwater acoustic communication is so expensive
The cost of underwater communications has largely limited the field to applications in defense and offshore oil and gas production. But SubSeaPulse’s technology could broaden its uses. For example, some researchers are using underwater sensors in coastal areas to study climate change, monitor pollution or track biodiversity. “There is a huge technology gap that needs to be filled,” says Campagnaro.
Researchers tested the underwater modem in an Italian river.University of Padua
“The main problem with underwater communications is the cost of the modem,” Zorzi says. That one component can be more expensive than the rest of a researcher’s equipment — even if the equipment includes an underwater robot, he says. Cheaper modems could allow users to deploy additional sensors and improve sampling of an environment.
Aside from the cost, current modems may not meet the specific needs of potential users. SubSeaPulse’s modem, on the other hand, is software-defined, allowing users to customize the signal modulation for their particular application. The device can also be used as an analog front end (rather than a full modem) for testing acoustic signals, and users can install their own software. Campagnaro compares the modem’s flexibility to the way amateur radio operators experiment with their equipment.
Milica StojanovicProfessor of electrical engineering at Northeastern University who develops algorithms for wireless underwater communications, 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 waveform they want.
However, the modem is only one component of a complete underwater communications system, says Stojanovic. Range and bit rate are also important factors for users and are primarily determined by the converter and the bandwidth limitations inherent in underwater communications.
“The problems of propagation and signal distortion (in an underwater acoustic channel) are not trivial,” says Stojanovic. She is pleased with the development of SubSeaPulse’s device. “The more people working on it, the better.”
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