Researchers at the University of Washington have developed the first wide-area backscatter communication system, the LoRa Backscatter, that is not only is low-power and cost-efficient at 10 cents per unit, but also provides long-range communication of up to 2.8 km.

The team behind the new LoRa device hopes to increase the ubiquity of wireless communication between embedded systems, especially in IoT applications. This drove their focus to be on developing a solution that was energy efficient, had a long communication range, was economical to produce, and was scalable for use in embedded systems. 


The LoRa backscatter device. Image courtesy of the University of Washington.


Deficiencies in Current Wireless Communication Technology

Current wireless communication technologies tend to offer only one of two options: low-power, cheap, but short-range or high-power, long-range, but expensive. A comparison was made against Wi-Fi, SigFox, Zigbee, and LTE-M active radio technologies, which were found to be significantly more expensive ($4 to $6 per unit), and also had much higher power requirements. While all the aforementioned have long-range communication capabilities, their energy and economic requirements made them less ideal for large-scale use in embedded systems.


Supercharging the Use of Backscatter

Ambient backscatter technology uses radio frequencies already being produced by other devices to generate its own electricity and reflect a signal to other devices. These radio signals can be Wi-Fi, radio, television, or mobile device signals. This has a great advantage of not requiring or depending on a built-in or physically connected power source and is also an ultra-low-cost solution.

However, ambient backscattering also has some downsides: its range is quite limited, it can be unreliable, and in medical applications the attenuation of RF signals by the human body causes the range of medical or wearable devices to be significantly reduced. 


Hence, the addition of LoRa, a Low-Power Wide-Area-Network (LPWAN) specification, that sends smaller packets at lower power and has a longer range. This adds the required sensitivity to make the backscattering technique operational over greater distances with the addition of a small power source providing 9.25 micro-Watts. The sensitivity was brought down to -149 dBm, had a data rate of 18bps-37.5kbps, and could be powered by a button cell battery, a printed battery, or a small solar cell.


Image courtesy of the University of Washington.


Innovative Features and Potential Applications

The LoRa Backscatter device has a few claims to fame that make it notable. First, it uses the first chirp spread spectrum backscatter design as a result of the ambient backscatter device being integrated with the LoRa specification, which uses CSS. Second, the device cancels side-band harmonics and is the first backscatter harmonic cancellation mechanism.

The device has many potential applications with its long-range, low-power, and relatively high-data rate features—not to mention it can be produced at 10 cents per unit at scale. The researchers behind the device tested it out in a home and office scenario and in a precision agriculture scenario and can envision it also being used in smart cities, in medical devices, or in personal wearable devices. By reducing its power requirement, extending range, and bringing down the cost of each unit, the team hopes it will enable a more ubiquitous use of wireless communications among embedded system devices.


Featured image courtesy of the University of Washington.