Getting closer to no-battery devices

Combining wake-up receivers with the parasitic use of ambient radio waves could drastically slash IoT power consumption.


IoT sensors that don't require power sources could be coming soon. Researchers from University of California, San Diego, claim they've figured out how to optimize lab-based modules to such an extent that a Wi-Fi radio, used in IoT for communications with a network, could soon be using 5,000-times less energy and yet still feature enough bandwidth to send video.

The technique being exploited takes advantage of backscattering. That's a way of parasitically using radio signals inherent in everyday environments. In this case, the chip piggybacks on existing Wi-Fi transmissions to send its data. This method of sending data is power-light, because the carrier needed for the radio transmission is already created—it doesn’t need new energy for the message to be sent.

Interestingly, two principal scientists involved in this backscattering project, which was announced by UC San Diego's Jacobs School of Engineering, have also been heavily involved in the development of "wake-up" radios.

Wake-up is when a Wi-Fi or other radio comes alive to communicate only when it has something to transmit or receive. The technology uses two radios. One radio is for the wake-up signaling; that radio's only purpose is to listen for a signature. The second is a more heavy-duty radio for the data send. Power is saved because the main radio isn't on all the time.

Dinesh Bharadia, now a professor of electrical and computer engineering at UC San Diego, was at Stanford University working on a wake-up radio that I’ve written about. I also wrote about Patrick Mercier's work on dual radio wake-up; Mercier is also a professor electrical and computer engineering at UC San Diego. Stanford has been involved in other backscatter-related research, too.

The intermingling of these scientists means we might someday see backscattering—the harnessing of ambient radio signals—combined commercially with a power-sipping wake-up radio in a single commercial package.

What the UC San Diego researchers are doing is grabbing Wi-Fi signals from devices found nearby, like smartphones and laptops, and then layering encoded data in the existing transmissions. The chip reflects the new, modified signal onto a different Wi-Fi channel, which a regular, commodity Wi-Fi receiver then picks up. The incumbent's data isn't affected.

The microprocessor that the team has been working on uses 28 microwatts of power and is a speck— it's only 1.5 square millimeters in area. For comparison, normal radios can use hundreds of milliwatts. The scientists say their chip can send data at 2 megabits per second over 21 meters.

All this is heading towards a kind of duo processor: A processor that grabs power out of the air (backscattering) and only sends messages when needed (wake-up) could reduce power consumption to such a significant degree that power use would ultimately become almost nothing, if not zero.

"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 setups," Mercier said, referring to the backscattering part.

In the big picture, the significance of the UC San Diego research goes beyond reducing IoT power requirements. What it really means is that if one could remove all power requirements, then absolutely everything, one day, could get connected to the Internet.

"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.

Copyright © 2020 IDG Communications, Inc.

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