The researchers have used backscatter radio which uses existing RF signals as the power source which is then used to modify and reflect the signal with encoded data. This is the principle behind passive RFID tags but it has until now been used for communications over a few feet or meters and usually much closer, data rates of the order of kbits per second and small data payloads such as an identity code.
Active radio technologies including Wi-Fi, ZigBee, SigFox , LoRa and LTE-M provide reliable coverage and long ranges but consume power and cost $4 to $6 in volume, according to the research team.
The University of Washington’s has now proposed long-range backscatter radio system in a paper a paper to be presented Sept. 13 at UbiComp 2017. The system provides reliable long-range communication at up to 2.8km with sensors that consume 1000 times less power than existing technologies capable of transmitting data over similar distances.
The LoRa Backscatter device prototyped by the research team consumes 9.25 microwatts, operates at 100s of meters and can be powered by printed batteries and button cells. The RF source transmits a single tone, for the purposes of this paper in the 900MHz ISM band, that the backscatter device uses to synthesize chirp spread spectrum (CSS) signals. The challenge that the team has faced is to make sure at the receiver that the backscatter signal is not drowned by noise and does not suffer interference from the RF source.
The University of Washington’s contribution to the state of the art was the addition of CSS. Spreading the reflected signals across multiple frequencies allowed the team to achieve much greater sensitivities and decode backscattered signals across greater distances even when it’s below the noise.
Next: Urban and agricultural
The University of Washington’s long-range backscatter system achieved reliable coverage throughout 4800-square-foot house, an office area covering 41 rooms and a one-acre vegetable farm. This could clearly be a major boon to the Internet of Things.
The system has three components: a source that emits a radio signal, sensors that encode information in reflections of that signal and an inexpensive off-the-shelf receiver that decodes the information, in this reported case a Sx1276 receiver from Semtech. When the sensor is placed between the source and receiver, the system can transmit data at distances up to 475 meters. When the sensor is placed next to the signal source, the receiver can decode information from as far as 2.8 kilometers away.
“Until now, devices that can communicate over long distances have consumed a lot of power. The trade-off in a low-power device that consumes microwatts of power is that its communication range is short,” said Shyam Gollakota, lead faculty and associate professor in the Paul G. Allen School of Computer Science & Engineering at the University of Washington. “Now we’ve shown that we can offer both, which will be pretty game-changing for a lot of different industries and applications.”
The long-range backscatter system will be commercialized by Jeeva Wireless, a spin-out company founded by the UW team of computer scientists and electrical engineers, which expects to begin selling it within six months.
“People have been talking about embedding connectivity into everyday objects such as laundry detergent, paper towels and coffee cups for years, but the problem is the cost and power consumption to achieve this,” said Vamsi Talla, CTO of Jeeva Wireless, who was an Allen School postdoctoral researcher and received a doctorate in electrical engineering from the UW. “This is the first wireless system that can inject connectivity into any device with very minimal cost.”
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