How a new method could help stream video without draining batteries

NC State engineers develop a method to stream video and wirelessly charge devices with one signal


How a new method could help stream video without draining batteries

October 17, 2017

Streaming video rules. 

The fact that we can watch "Game of Thrones," a live football game or a story about how broadcasters put the first down line on the screen, anytime, anywhere, with nothing but a phone, is as mind-blowing as it is fun.

Young Man on a TabletThere’s just one problem. Invariably just as the Hail Mary pass goes into the air or the dragons show up to save the day, that pesky “10 percent battery remaining” message pops up, sending you scrambling for a power cord and any outlet you can find, hoping beyond hope you can find one quickly enough to finish your show.

Melodrama aside, streaming video does tend to chew up one’s battery. It would be nice if that weren't the case, so we could save that battery life for other important things like games and Instagram. By 2020, 80 percent of all Internet traffic will be devoted to video, according to a report by Cisco, which is a recipe for a lot of time attached to the charging cord.

Now, North Carolina State University electrical engineers have taken the first major steps toward video streaming that won’t drain your battery. They developed a way to transmit both data and power with one signal.

The technology combines wireless phone chargers with a standard data signal to make a single beam that does both. Further, the mobile device does not need to be actually touching the signal source, like you see on many wireless chargers. And adding the data to the wireless charging signal only reduces the efficiency of the charging by less than five percent. 

David Ricketts, NC State electrical and computer engineering professor and lead author of the study, says the system is capable of simultaneously transferring both the data required to watch Netflix and the power to keep that phone’s battery from draining.

The secret to the perpetual streaming machine lies in the fact that both data and wireless charging signals rely on oscillating magnetic fields. Data signals are microwaves—low-energy electromagnetic radiation in which electric and magnetic fields feed into each other. Wireless charging relies on the electromagnetic induction, a process in which moving magnetic fields create electric current, which can power up a phone battery.

Woman Using a Smart PhoneA match made in heaven, one would think. The problem is that data is broadcast over a wide range of frequencies—where the word “broadband” comes from—to communicate a large amount of data at one time. Wireless charging, on the other hand, makes use of signals with an extremely narrow bandwidth that the device can tune into. The narrow band minimizes the amount of power the charging source has to put out for the device to key in on. Many devices that have a wireless charger actually use two separate antennae to get their data and power signals to keep those waves of different bandwidth separate.

Ricketts and the other researchers had the idea to package both power and data into one broadband signal with narrow, high-energy components. Using that broad signal with narrow pieces, the researchers were effectively able to transmit power at two or three watts, plenty to keep a tablet charged. Adding 3.39 megabytes of data per second to that signal—streaming HD video requires 0.83 megabytes per second according to Netflix—only dropped the efficiency of charging by less than two percent for the two watt signal and less than three percent for the three watt signal.

The short version: streaming forever!

Before you start dreaming of whiling away a long road trip with a "Pretty Little Liars" marathon, there are some caveats to consider. First, there is a reason why most of the wireless chargers you see advertised require the phone to be touching the charging pad. The technology for wireless charging has a long way to go before we can throw our power cords away. Ricketts got his experimental results when the device was about six inches away from the signal transmitter, so it will be a while before cell towers are beaming a chargeable signal to every phone.

Second, even when the technology is ready, both phones and broadcast towers will need updating before mass data and charging signals go national, if research even proves that to be possible.

Still, the tantalizing concept of wirelessly charging up your phone or tablet while catching up on "Stranger Things" (or if you’re a nerd like me, while putting David Attenborough nature documentaries on to help you fall asleep) is a major step closer to being a reality.

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.

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