MIT researchers 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 began developing several years ago, uses about one-millionth the power that existing underwater communication methods use. By expanding their battery-free system’s communication range, the researchers have made the technology more feasible for applications such as aquaculture, coastal hurricane prediction, and climate change modeling.
“There are still a few interesting technical challenges to address, but there is a clear path from where we are now to deployment,” said Associate Professor Fadel Adib.
When tested in a river and an ocean, the retrodirective device exhibited a communication range that was more than 15 times farther than previous devices. However, the experiments were limited by the length of the docks available to the researchers.
To better understand the limits of underwater backscatter, the team also developed an analytical model to predict the technology’s maximum range. The model, which they validated using experimental data, showed that their retrodirective system could communicate across kilometer-scale distances.
The researchers then leveraged a 70-year-old radio device called a Van Atta array, in which symmetric pairs of antennas are connected in such a way that the array reflects energy back in the direction it came from.
“Both nodes are receiving and both nodes are reflecting, so it is a very interesting system. As you increase the number of elements in that system, you build an array that allows you to achieve much longer communication ranges,” said CoLead Author Aline Eid.
“Just connecting the piezoelectric nodes together is not enough. By alternating the polarities between the two nodes, we are able to transmit data back to the remote receiver,” said Research Assistant Jack Rademacher.
When building the Van Atta array, the researchers found that if the connected nodes were too close, they would block each other’s signals.
They devised a new design with staggered nodes that enables signals to reach the array from any direction. With this scalable design, the more nodes an array has, the greater its communication range.
They tested the array in more than 1,500 experimental trials; the device achieved communication ranges of 300 meters, more than 15 times longer than they previously demonstrated.
That inspired the researchers to build an analytical model to determine the theoretical and practical communication limits of this new underwater back-scatter technology.
“It is not a traditional communication technology, so you need to understand how you can quantify the reflection. What are the roles of the different components in that process?” said Research Assistant Waleed Akbar.
“We are creating a new ocean technology and propelling it into the realm of the things we have been doing for 6G cellular networks. For us, it is very rewarding because we are starting to see this now very close to reality,” Adib said.
“Limited range has been an open problem in underwater backscatter networks, preventing them from being used in real-world applications. This paper takes a significant step forward in the future of underwater communication, by enabling them to operate on minimum energy while achieving long range,” said Assistant Professor Omid Abari, who was not involved with this work.
“The paper is the first to bring Van Atta Reflector array technique into underwater backscatter settings and demonstrate its benefits in improving the communication range by orders of magnitude. This can take battery-free underwater communication one step closer to reality, enabling applications such as underwater climate change monitoring and coastal monitoring,” he said.
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