The backscattering process creates an unwanted mirror image copy of the signal, which consumes more bandwidth as well as interferes with networks on the mirror copy Wi-Fi channel.
Interscatter communication uses the Bluetooth, Wi-Fi or ZigBee radios embedded in common mobile devices like smartphones, watches, laptops, tablets and headsets, to serve as both sources and receivers for these reflected signals.
In one example the team demonstrated, a smartwatch transmits a Bluetooth signal to a smart contact lens outfitted with an antenna. To create a blank slate on which new information can be written, the UW team developed an innovative way to transform the Bluetooth transmission into a "single tone" signal that can be further manipulated and transformed. By backscattering that single tone signal, the contact lens can encode data—such as health information it may be collecting—into a standard Wi-Fi packet that can then be read by a smartphone, tablet or laptop.
"Bluetooth devices randomise data transmissions using a process called scrambling," said lead faculty Shyam Gollakota, assistant professor of computer science and engineering. "We figured out a way to reverse engineer this scrambling process to send out a single tone signal from Bluetooth-enabled devices such as smartphones and watches using a software app."
The challenge, however, is that the backscattering process creates an unwanted mirror image copy of the signal, which consumes more bandwidth as well as interferes with networks on the mirror copy Wi-Fi channel. But the UW team developed a technique called "single sideband backscatter" to eliminate the unintended by-product.
"That means that we can use just as much bandwidth as a Wi-Fi network and you can still have other Wi-Fi networks operate without interference," said co-author and electrical engineering doctoral student Bryce Kellogg.
The researchers—who work in the UW's Networks and Mobile Systems Lab and Sensor Systems Lab—built three proof-of-concept demonstrations for previously infeasible applications, including a smart contact lens and an implantable neural recording device that can communicate directly with smartphones and watches.
Figure 1: The interscatter team includes UW electrical engineering doctoral students Bryce Kellogg (left) and Vikram Iyer (right), computer science & engineering research associate Vamsi Talla (middle), assistant professor of computer science & engineering Shyam Gollakota (not pictured) and associate professor or electrical engineering and of computer science & engineering Josh Smith (not pictured). (Source: Mark Stone/University of Washington)
"Preserving battery life is very important in implanted medical devices, since replacing the battery in a pacemaker or brain stimulator requires surgery and puts patients at potential risk from those complications," said co-author Joshua Smith, associate professor of electrical engineering and of computer science and engineering.
"Interscatter can enable Wi-Fi for these implanted devices while consuming only tens of microwatts of power."
Beyond implanted devices, the researchers have also shown that their technology can apply to other applications such as smart credit cards. The team built credit card prototypes that can communicate directly with each other by reflecting Bluetooth signals coming from a smartphone. This opens up possibilities for smart credit cards that can communicate directly with other cards and enable applications where users can split the bill by just tapping their credit cards together.
“Providing the ability for these everyday objects like credit cards—in addition to implanted devices—to communicate with mobile devices can unleash the power of ubiquitous connectivity,” Gollakota said.