Battery-free wifi network inches closer to reality for IoT

Engineers at the University of Washington have further developed the short range, battery-free, wireless communication system they first showed off last year.

The continued development is interesting with respect to the Internet of Things because it is able to use ambient radio signals as a power source, laying the path for the creation of networks of battery-free wireless sensors.

The adoption of wifi backscatter could see sensors embedded in everyday objects to help monitor and track everything from the structural safety of bridges to the health of patient’s hearts.

At present however, having a way to cheaply power and connect these devices to the internet has kept this from taking off.

Wifi backscatter uses radio frequency signals as a power source and reuses existing wifi infrastructure to provide internet connectivity to battery-free devices. This latest development builds upon previous research that showed how low-powered devices such as temperature sensors or wearable technology could run without batteries or cords by harnessing energy from existing radio, TV and wireless signals in the air.

This work takes that a step further by connecting each individual device to the internet, which previously wasn’t possible. According to the engineers, the challenge in providing wifi connectivity to these devices is that conventional, low-power wifi consumes three to four orders of magnitude more power than can be harvested in these wireless signals.

The researchers instead developed an ultra-low power tag prototype with an antenna and circuitry that can talk to wifi-enabled laptops or smartphones while consuming negligible power.

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“If Internet of Things devices are going to take off, we must provide connectivity to the potentially billions of battery-free devices that will be embedded in everyday objects,” said Shyam Gollakota, a UW assistant professor of computer science and engineering.

“We now have the ability to enable wifi connectivity for devices while consuming orders of magnitude less power than what wifi typically requires.”

The researchers will publish their results at the Association for Computing Machinery’s Special Interest Group on Data Communication‘s annual conference this month in Chicago. The team also plans to start a company based on the technology, supported by patents they have filed.

So far the wifi backscatter tag has communicated with a wifi device at rates of 1kbps with about two meters between the devices. They plan to extend the range to about 20 meters.

These tags work by essentially “looking” for wifi signals moving between the router and a laptop or smartphone. They encode data by either reflecting or not reflecting the wifi router’s signals, slightly changing the wireless signal. Wifi-enabled devices like laptops and smartphones would detect these minute changes and receive data from the tag.

“You might think, how could this possibly work when you have a low-power device making such a tiny change in the wireless signal? But the point is, if you’re looking for specific patterns, you can find it among all the other wifi reflections in an environment,” said Joshua Smith, a UW associate professor of computer science and engineering and of electrical engineering.

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  1. Avatar Abbas 06/08/2014 @ 10:51 am

    Nice development, I am interested to know, if there is any effect on the quality of signal (between wireless router and laptop/smartphone) when wifi backscatter is used !

  2. Avatar John Moran 09/08/2014 @ 7:59 pm

    This sounds very much like conventional RFID communications protocol. If that is the case, then the modulation depth will be 5-10% max, so wont interfere with the normal WIFI operational unless its marginal in the first place.

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