In a bid to aid monitoring of climate and coastal change, researchers at the Massachusetts Institute of Technology (MIT) have demonstrated the first system for ultra-low-power underwater networking and communication, which can transmit signals across kilometer-scale distances.
This technique, which the researchers have been working on for a while, takes a tiny fraction of the power that other underwater communication techniques do. The researchers have improved the technology’s viability for applications including aquaculture, coastal hurricane prediction, and climate change modeling by extending the communication range of their battery-free system.
“What started as a very exciting intellectual idea a few years ago – underwater communication with a million times lower power – is now practical and realistic. There are still a few interesting technical challenges to address, but there is a clear path from where we are now to deployment,” – Fadel Adib, associate professor in the Department of Electrical Engineering and Computer Science and director of the Signal Kinetics group in the MIT Media Lab.
In two papers that will be presented at the ACM SIGCOMM and MobiCom conferences this year, the researchers revealed their findings. Adib, who is the senior author on both papers, is joined by co-lead authors Jack Rademacher, a research assistant, and Aline Eid, a former postdoc who is now an assistant professor at the University of Michigan, as well as research assistant Waleed Akbar and Purui Wang and postdoc Ahmed Allam, on the SIGCOMM paper.
Using Low-power Underwater Communication to Monitor Climate and Coastal Change
Low-power communication is made possible via underwater backscatter, which encodes data in sound waves and scatters them back toward a receiver. These developments make it possible to more precisely point reflected signals back to their source. Retrodirectivity reduces the amount of signal scattering in the wrong directions, enabling more effective and far-reaching communication.
The retrodirective device demonstrated a communication range that was more than 15 times farther than earlier devices when tested in a river and an ocean. The length of the docks the researchers had access to, however, limited the tests.
The researchers also created an analytical model to forecast the technology’s maximum range in order to comprehend the boundaries of underwater backscatter. They used experimental data to test the concept, which demonstrated that their retrodirective system could communicate over distances of a few kilometers.
Additionally, they encoded binary data in the reflected signal using a method known as cross-polarity switching. Each node has a positive and a negative terminal (much like a car battery), so the reflected signal is a bit higher when the positive and negative terminals of the two nodes are coupled.
Together with the Woods Hole Oceanographic Institution, they conducted more than 1,500 experimental tests on the array in the Atlantic Ocean off the coast of Falmouth, Massachusetts, as well as on the Charles River in Cambridge, Massachusetts. The communication range was 300 meters, which is more than 15 times longer than they had previously proven for the gadget.
