By: Larry Greenemeier and scientific american

Photo by Pete Prodoehl via Flickr Creative Commons

No matter how fancy mobile gadgets get, they're useless when their batteries run out. With the push toward cloud computing and the always-on wireless culture gaining momentum every day, laptop, tablet and smart phone batteries are being asked to do more despite no real breakthroughs in battery technology hitting the market.

Consider: Twitter users send 200 million tweets daily, up from 65 million just a year ago. Meanwhile, Google is banking on the success of several new mobile apps to help its Google+ social network effort dethrone Facebook.

All of these services are draining enough to make any mobile device want to take a nap, which isn't such a bad idea, according to one Duke University researcher. Justin Manweiler, a computer science graduate student at Duke's Pratt School of Engineering, has developed software he calls SleepWell, which is designed to double the battery life of Internet-connected devices increasingly called on to upload and download music, images and video via WiFi.

Mobile devices today waste a lot of energy searching for a WiFi signal, and then staying connected while overtaxed wireless networks ferry data to and from them. SleepWell allows a mobile device to slip into power-saving mode while it is waiting its turn to connect. This is no small matter, particularly when scores of caffeine-craving technophiles gather at the local Starbucks to take advantage of the free wireless access. Manweiler likens the competition for WiFi to big-city traffic. When workers leave their offices en masse at the end of the day, they clog up the roads and rail lines. If these workers staggered the times they left, the transit systems would be less crowded, and it would take less time to get home. Similarly, if mobile devices took their turn accessing WiFi access points, data would move faster and these devices would use less energy.

SleepWell is installed on the devices that create a WiFi network infrastructure, including WiFi routers and access points. As such, it is designed so that any mobile device--whether it uses Apple OS X, Google Android, Windows or some other platform -- can take advantage of it.

The SleepWell software differs from the "sleep" mode already available in many devices. An operating system's version of sleep is designed to work over long time scales -- minutes, hours or days. "SleepWell is enabling short 'sleep' periods multiple times per second," says Manweiler, who works under the direction of Romit Roy Choudhury, a Pratt School assistant professor of electrical and computer engineering. "These sleep periods are so short, the user remains unaware and unaffected."

During testing, Manweiler found that SleepWell could double the battery life of mobile phones. "We ran lots of live experiments using real off-the-shelf smart phones, mostly Google Android phones," he says. "We tested with a variety of use cases, including the user watching a movie trailer on YouTube, playing music on Pandora and Last.FM Internet radio, and downloading a large file from the web."

The extent to which battery life would be prolonged of course varies depending on the situation. Still, Manweiler hopes the brief naps that SleepWell affords mobile devices will add up to significant energy conservation when WiFi networks are in high demand.

This article is reproduced with permission from Scientific American. It was first published on July 1, 2011.