New devices can transmit information with almost zero power

UW"s new devices

For the first time, researchers demonstrated devices that run on zero power and transmit data across distances of up to 2.8 kilometers.

The UW"s long-range backscatter system reflect radio signals to transmit data at extremely low power and low cost, achieved reliable coverage throughout 4800-square-foot house, an office area covering 41 rooms and a one-acre vegetable farm.

"Until now, devices that can communicate over long distances have consumed a lot of power. The tradeoff in a low-power device consumes microwatts of power is that its communication range is short," said Shyam Gollakota.

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The latest long-range backscatter system provides reliable long-range communication with sensors that consume 1000 times less power than existing technologies.



Also, the sensors monitor pollution, noise or traffic in cities. This is the first wireless system that can inject connectivity into any device with very minimal cost.

On research, the researchers built a contact lens prototype and a flexible epidermal patch that attaches to human skin, which successfully used long-range backscatter to transmit information across a 3300-square-foot atrium. That"s orders of magnitude larger than the 3-foot range achieved by prior smart contact lens designs.

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The long-range backscatter system uses a source that emits a radio signal, low-power sensors that encode information in reflected signals, and an off-the-shelf receiver. When the sensor placed between the source and receiver, the system can transmit data at distances up to 475 meters. When the sensor placed next to the signal source, the receiver decodes information from as far as 2.8 kilometers away. It"s difficult for a receiver to distinguish extremely weak reflections from the original signal and other noise.

chirp spread spectrum

To overcome the problem, the team introduced a new type of modulation called chirp spread spectrum into its backscatter design. Spreading the reflected signals across multiple frequencies allowed the team to achieve much greater sensitivities and decode backscattered signals across greater distances even below the noise.

The sensors are so cheap, with an expected bulk cost of 10 to 20 cents each. Farmers can measure soil temperature or moisture could affordably blanket an entire field to determine how to efficiently plant seeds or water.

"We basically started with a clean slate and said if what we really need to enable smart applications is long-range communication, how could we design the system from the ground up to achieve that goal?" said Bryce Kellogg, a UW electrical engineering student.

More information: [long-range backscatter system]

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