Using Wi-Fi can rapidly drain a smartphone or laptop battery, but a student at Duke University has discovered a simple way to double the battery life of mobile devices.
Currently, routers take turns moving data around when usage is high, whether that's in a Starbucks, a dorm or at a concert. Downloading is not continuous. Rather, data is sent in tiny packets where each interval is an opportunity for a packet to be inserted from another device.
In neighborhoods where multiple Wi-Fi devices are being used, each one must wait its turn to download data from the Internet. Waiting means draining the battery.
"The battery drainage in downloading a movie in Manhattan is far higher than downloading the same movie in a farmhouse in the Midwest," Justin Manweiler, a graduate student in computer science at Duke's Pratt School of Engineering, writes in a recent study that details the new Wi-Fi changing system called SleepWell.
SleepWell forces devices to "catnap" many times per second between sending bursts of data. Microsecond gains turned out to be huge energy savers, particularly in crowded cities where thousands of devices could be in the queue on a Wi-Fi network.
Manweiler compared the Wi-Fi problem to traffic congestion where a data packet is like a car.
"Big cities face heavy rush hours as workers come and leave their jobs at similar times. If work schedules were more flexible, different companies could stagger their office hours to reduce the rush," he said. "With less of a rush, there would be more free time for all, and yet, the total number of working hours would remain the same."
"The same is true of mobile devices trying to access the Internet at the same time," he said. "The SleepWell-enabled Wi-Fi access points can stagger their activity cycles to minimally overlap with others, ultimately resulting in promising energy gains with negligible loss of performance."
For the tests, SleepWell was installed on eight laptops and nine Android Nexus One phones, Wi-Fi routers and Wi-Fi access points. To simulate typical usage, the team downloaded videos from YouTube, streamed music from Pandora, and moved large graphics files from FTP sites.
Results indicated that battery life could at least be doubled when Wi-Fi connections were strong and gains were even higher when links were weak and network density high.
The team concluded that SleepWell is a desirable upgrade to Wi-Fi systems, especially in light of increasing Wi-Fi density.
Manweiler is part of the Systems Networking Research Group at Duke funded in part by Microsoft, Cisco, Nokia and Verizon, all stakeholders in the Wi-Fi ecosystem.
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