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Long range transmission, almost zero power consumption

University of Washington researchers say they have demonstrated that devices consuming almost no power can transmit data over 2.8km. The demonstration, said to break a long-held barrier, could enable a range of interconnected devices.

The university’s long range backscatter system uses reflected radio signals to transmit data at extremely low power and low cost. “Until now, devices that can communicate over long distances have consumed a lot of power,” said associate professor Shyam Gollakota. “The tradeoff in a low-power device that consumes microwatts of power is that its communication range is short. Now, we’ve shown that we can offer both.”

The system has three components: a source that emits a radio signal; sensors that encode information in reflections of that signal; and an inexpensive receiver to decode the information. When the sensor is placed between the source and receiver, the system can transmit data at distances up to 475m. When the sensor is placed next to the signal source, the receiver can decode information over distances of up to 2.8km.

As an example, the research team built a contact lens prototype and a flexible epidermal patch that attaches to human skin. Long-range backscatter transmitted data across a 3300ft2 atrium, compared to the 3ft range said to be offered by smart contact lens designs.

The advantage of backscattered radio signals is that a sensor can be powered by flexible printed batteries or by energy harvested from ambient sources. However, it’s difficult for a receiver to distinguish extremely weak reflections from the original signal and other noise. Using chirp spread spectrum allowed reflected signals to be spread across multiple frequencies, bringing greater sensitivity and the ability to decode backscattered signals across greater distances.

The long-range backscatter system will be commercialised by UW spin off Jeeva Wireless, which expects to begin selling it within six months.

Graham Pitcher

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