Get ready to send a thank-you note to students at the University of Washington, where a group of electrical engineers is trying to solve the eternal struggle of Wi-Fi battery drain. It’s a problem that’s rapidly getting worse as more and more devices require access to the cloud, not to mention the constant strain of searching for a good signal or boosting a weak one.
The student researchers invented a new type of hardware that uses 10,000 times less power than traditional Wi-Fi networking equipment. It’s called Passive Wi-Fi, (you can read their paper here) and it works just like a home router, just more efficiently. To give some perspective, the state of the art in low power Wi-Fi transmissions today consume 100s of milliwatts of power, whereas the technology the student researchers developed consume only 10-50 microwatts—10,000 times lower power.
Wi-Fi typically requires two radios to communicate back and forth, and it takes a lot of energy to discern the signal from the noise because there may be several devices using the same frequency (2.4 GHz or 5 GHz). Each device has an RF transmitter that creates a radio wave and a baseband chip that encodes that radio wave with data. With Passive Wi-Fi, instead of each device using an analog radio frequency to receive and transmit a signal, just one produces a radio frequency. That frequency is relayed to your Wi-Fi-enabled device via separate, passive sensors that have only the baseband chip and an antenna and require almost no power. Those sensors pick up the signal and mirror it in a way that sends readable Wi-Fi to any device that has a Wi-Fi chipset in it.
This may sound a lot like a mesh network, with the signal bouncing from antenna point to antenna point, but it’s not. A mesh network uses multiple routers, with full analog RF transmitters and digital baseband chips to receive and rebroadcast a signal.
“The low power passive device isn’t transmitting anything at all. It’s creating Wi-Fi packets just by reflection,” says Vamsi Talla, another student working on the project. “It’s a transmission technique that’s ultra low-powered, as opposed to a network device.”
That “reflection” happens via a process called “backscatter,” and the students at UW have created Wi-Fi equipment that sends out a signal via backscatter instead of using a full radio signal.
Right now most devices do not have the backscatter hardware inside of them to send Wi-Fi packets back to the Internet-connected router. But if this technology takes off, it could increase the amount of devices that are connected to the Internet because it nearly nullifies previous energy constraints of making a device Wi-Fi compatible.
To be clear, Passive Wi-Fi still requires running one Wi-Fi router, and Wi-Fi routers aren’t super energy efficient. The Environmental Projection Agency even created an Energy Star certification for home networking devices in 2013 to try to encourage the manufacture of less energy intensive devices. According to the EPA’s website, “If all small network equipment sold in the United States were ENERGY STAR certified, the energy cost savings would grow to more than $590 million each year and more than 7 billion pounds of annual greenhouse gas emissions would be prevented.” The energy savings with Passive Wi-Fi come from the Wi-Fi transmission chipset in devices that communicate via wireless Internet, not the router connected to the initial uplink.
It’s hard to say what this will do for your battery life, because there are so many components in a device that impact that—like the screen, for example. “But using Passive Wi-Fi would improve battery life by about as much as turning your Wi-Fi off would,” said Bryce Kellog, an electrical engineering graduate student at UW who co-developed Passive Wi-Fi.
In the future, these passive sensors may even end up in our devices themselves, reflecting packets to send back to the router instead of broadcasting new transmitter waves. For now, using the hardware can reduce the energy used to spread Wi-Fi to devices.
“Our passive Wi-Fi devices now talk up to 11 megabits per second,” said Kellog. For comparison’s sake, that’s 11 times faster than Bluetooth. One of the main selling points of devices communicating via Bluetooth rather than Wi-Fi has been Bluetooth’s comparatively low energy consumption. But Passive Wi-Fi is 1,000 times more energy efficient than Bluetooth, and the network can be secured like any Wi-Fi signal can, unlike Bluetooth.
11 megabits per second might be faster than Bluetooth, but it’s slower than most home broadband connections. “While backscatter radio technology typically has less range and reliability and lower data rates than active radios, you wouldn’t use this type of communication to watch a YouTube video,” Chris Valenta, an engineer at the Georgia Tech Research Institute told WIRED. “For many Internet of Things applications, however, this technology is perfect. Radios typically account for the largest power draw of any cell phone.”
Wi-Fi hasn’t always been the best choice for connecting our Internet-ready smart devices because of its power constraints. “Communication tends to be a big portion of smart home devices’ power budget,” said Kellog.
For now, Passive Wi-Fi is a laboratory-controlled research project, but in the future, these passive sensors may end up as part of the ubiquitous hardware construction of Wi-Fi connected devices. That would mean that our electronics would be reflecting packets to send back to the router instead of always broadcasting new transmitter waves to communicate via Wi-Fi. But even now, using the students’ hardware can reduce the energy used to spread Wi-Fi to devices.
“Passive Wi-Fi uses only a few simple components, so it would be very cheap and easy to integrate into existing devices like smartphones or tablets. Additionally, it could even reuse the antenna already inside those devices,” Kellog added.
“This type of technology is really meant to reduce the power consumption of the transmitter to enable IoT devices to send small amounts of data back and forth,” says Valenta. As more and more of our smart devices rely on batteries instead of needing to be plugged directly into the wall, conserving battery power will continue to be an important issue with how we use our electronics. And according to the student researchers, companies are already tapping them on the shoulder to see if their vision of a less energy consumptive, increasingly networked world might one day be a reality.