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WiFi "Napping" Doubles Phone Battery Life

System eliminates competition between devices to get downloads, leaving them all bettter-rested.  

Graduate student Justin Manweiler would like to teach cell phones to take turns when sharing bandwidth.

A Duke University graduate student has
found a way to double the battery life of mobile devices -- such as smartphones
or laptop computers -- by making changes to WiFi technology.

is a popular wireless technology that helps users download information from the
Internet. Such downloads, including pictures, music and video streaming, can be
a major drain of battery.

energy drain is especially severe in the presence of other WiFi devices in the
neighborhood.  In such cases, each device
has to "stay awake" before it gets its turn to download a small piece
of the desired information. This means that the battery drainage in downloading
a movie in Manhattan is far higher than
downloading the same movie in a farmhouse in the Midwest,
the researchers said.

Duke-developed software eliminates this problem by allowing mobile devices to
sleep while a neighboring device is downloading information. This not only saves
energy for the sleeping device, but also for competing devices as well.

new system has been termed SleepWell by Justin Manweiler, a graduate student in
computer science under the direction of Romit Roy Choudhury, assistant
professor of electrical and computer engineering at Duke’s Pratt School of
Engineering. The SleepWell system was presented at the ninth Association for
Computing Machinery's International Conference on Mobile Systems, Applications
and Services (MobiSys), being held in Washington, D.C.

described the system by analogy: "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. 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."

same is true of mobile devices trying to access the Internet at the same time,"
Manweiler said. "The SleepWell-enabled WiFi access points can stagger their
activity cycles to minimally overlap with others, ultimately resulting in
promising energy gains with negligible loss of performance."

cloud computing on the horizon, mobile devices will need to access the Internet
more frequently -- however, such frequent access could be severely constrained
by the energy toll that WiFi takes on the device's battery life, according to
Roy Choudhury.

is certainly a key problem for the future of mobile devices, such as iPhones,
iPads and Android smartphones," Roy Choudhury said. "The SleepWell
system can certainly be an important upgrade to WiFi technology, especially in
the light of increasing WiFi density."

said that "the testing we conducted across a number of device types and
situations gives us confidence that SleepWell is a viable approach for the near

Choudhury's research team, known as the Systems Networking Research Group, is
supported by the National Science Foundation, as well as from industries such
as Microsoft Research, Cisco, Nokia and Verizon.