Ultra-Low Power Wi-Fi Chip Can Operate on a Coin Cell Battery for Years

A new ultra-low power Wi-Fi radio developed by electrical engineers at the University of California San Diego, could enable more portable, fully wireless smart home setups with lower power wearables and battery-less smart devices. The newly developed solution was showcased at the ISSCC 2020 Conference in San Francisco last month.

The device, which is housed in a chip smaller than a grain of rice, enables Internet of Things (IoT) devices to communicate with existing Wi-Fi networks using 5,000 times less power than today’s Wi-Fi radios. It consumes just 28 microwatts of power while transmitting data at a rate of 2 megabits per second (a connection fast enough to stream music and most YouTube videos) over a range of up to 21 meters.

According to Dinesh Bharadia, a professor of electrical and computer engineering at the UC San Diego Jacobs School of Engineering and part of the research team, one can connect a phone, 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 the device. You do not need to buy anything else. And the chip could operate for years on a single coin cell battery.

Commercial Wi-Fi radios typically consume hundreds of milliwatts to connect IoT devices with Wi-Fi Access Points. As a result, Wi-Fi compatible devices need, either large batteries or frequent recharging or other external power sources to run. The new Wi-Fi radio consumes very low power levels opening up new application spaces where the IoT devices no longer need to be plugged in to a wall. This could unleash smaller, fully wireless IoT setups. 

An example would be a portable Google Home device that can be taken around the house and can last for years instead of just hours when unplugged. It could also allow connecting devices that are not currently connected - things that cannot meet the power demands of current Wi-Fi radios, like a smoke alarm.

The Wi-Fi radio runs on extremely low power by transmitting data via a technique called backscattering. It takes incoming Wi-Fi signals from a nearby device (like a smartphone) or Wi-Fi access point, modifies the signals and encodes its own data onto them, and then reflects the new signals onto a different Wi-Fi channel to another device or access point.

This work builds on low-power Wi-Fi radio technology that Bharadia helped develop as a Ph.D. student at Stanford. In this project, he teamed up with Patrick 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 a longer communication range  of up to 21 meters. This is a practical distance for operating in a smart home environment, the researchers said. According to Mercier, here they have demonstrated the first pragmatic chip design that can actually be deployed in a small, low-power device.

Details of this Wi-Fi Solution were presented in a Paper titled: “A 28µW IoT Tag that Can Communicate with Commodity WiFi Transceivers via a Single-Side-Band QPSK Backscatter Communication Technique

The student researchers include Po-Han Peter Wang, Chi Zhang, Hongsen Yang and Manideep Dunna, UC San Diego.