Ultra-low power Wi-Fi connectivity for IoT devices

A new Wi-Fi device runs on extremely low power by utilising backscattering.

An ultra-low power Wi-Fi radio developed by electrical engineers at the University of California San Diego, housed in a chip smaller than a grain of rice, could enable Internet of Things devices to communicate with existing Wi-Fi networks using 5000 times less power than today’s devices.

The radio consumes just 28 microwatts of power, and does so while transmitting data at a rate of 2 megabits per second over a range of up to 21 metres.

“You can connect your phone, your smart devices, even small cameras or various sensors to this chip, and it can directly send data from these devices to a Wi-Fi access point near you,” said Dinesh Bharadia, a professor of electrical and computer engineering at the UC San Diego Jacobs School of Engineering.

“And it could last for years on a single coin cell battery.”

Current commercial Wi-Fi radios typically consume hundreds of milliwatts to connect IoT devices with Wi-Fi transceivers.

“This Wi-Fi radio is low enough power that we can now start thinking about new application spaces where you no longer need to plug IoT devices into the wall. This could unleash smaller, fully wireless IoT set-ups,” said UC San Diego electrical and computer engineering professor Patrick Mercier, who co-led the work with Bharadia.

“It could also allow you to connect devices that are not currently connected — things that cannot meet the power demands of current Wi-Fi radios, like a smoke alarm — and not have a huge burden on battery replacement,” Mercier said.

UC San Diego electrical and computer engineering professor Dinesh Bharadia holds a PCB onto which the Wi-Fi radio is mounted (component underneath the black blob). Credit: David Baillot/UC San Diego Jacobs School of Engineering

The new device runs on extremely low power by transmitting using backscattering. It takes incoming Wi-Fi signals from a nearby device or Wi-Fi access point, modifies the signals and encodes its own data onto them, and then sends the new signals onto a different Wi-Fi channel to another device or access point.

The work builds on low-power Wi-Fi radio technology that Bharadia helped develop as a PhD student at Stanford. In this project, he teamed up with Mercier to develop an even lower-power Wi-Fi radio. They accomplished this by building in a component called a wake-up receiver. This ‘wakes up’ the Wi-Fi radio only when it needs to communicate with Wi-Fi signals, so it can stay in low-power sleep mode the rest of the time, during which it consumes only 3 microwatts of power.

The UC San Diego team’s improvements to the technology also feature a custom integrated circuit for backscattering data, which makes the whole system smaller and more efficient, and thus enables their Wi-Fi radio to operate over longer communication range (21 metres in this case). This is a practical distance for operating in a home or office environment, the researchers said.

“Here, we demonstrate the first pragmatic chip design that can actually be deployed in a small, low-power device,” Mercier said.

Image credit: David Baillot/UC San Diego Jacobs School of Engineering