Interscatter enables medical implant data transfer

The so-called "interscatter communication" works by converting Bluetooth signals into Wi-Fi transmissions. Using only reflections, an interscatter device such as a smart contact lens converts Bluetooth signals from a smartwatch into Wi-Fi transmissions that can be picked up by a smartphone.

The new technique is described in a paper to be presented on August 22 at the annual conference of the Association for Computing Machinery's Special Interest Group on Data Communication in Brazil.

"Wireless connectivity for implanted devices can transform how we manage chronic diseases," said co-author Vikram Iyer, a UW electrical engineering doctoral student. "For example, a contact lens could monitor a diabetics blood sugar level in tears and send notifications to the phone when the blood sugar level goes down."

Due to their size and location within the body, these smart contact lenses are too constrained by power demands to send data using conventional wireless transmissions to mobile devices.

The team has demonstrated for the first time that these types of power-limited devices can communicate using standard Wi-Fi communication. Their system requires no specialised equipment, relying on mobile devices commonly found with users to generate Wi-Fi signals using 10,000 times less energy than conventional methods.

"Instead of generating Wi-Fi signals on your own, our technology creates Wi-Fi by using Bluetooth transmissions from nearby mobile devices such as smartwatches," said co-author Vamsi Talla.

The team's process is said to rely on backscatter, which allows devices to exchange information by reflecting existing signals. Because the new technique enables inter-technology communication by using Bluetooth signals to create Wi-Fi transmissions, the team has dubbed the process ‘interscattering’.

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 sources and receivers for these reflected signals.

The team has demonstrated how 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 a way to transform the Bluetooth transmission into a 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…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 backscattering process does, however, create an unwanted mirror image copy of the signal, which consumes more bandwidth and 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, including a smart contact lens and an implantable neural recording device that can communicate directly with smartphones and watches.

"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."