In a test using eight laptops and nine Nexus One Android-based smartphones on an 802.11n network, the researchers found that the scheduling technique, dubbed SleepWell, resulted in energy reductions of 38% to 51% across a variety of online applications, including YouTube, Pandora and Last.fm Internet radio, and TCP bulk data transfers. What’s more, they found that as the quality of radio links degrades (with each packet transmitted at lower bit rates, resulting in a longer transmit interval), the relative energy gains are even higher.

BACKGROUND:

"In light of these results, we believe that SleepWell may be an effective solution for the future, not only to sustain a demanding suite of [mobile] applications, but also to improve ‘immunity’ to increasingly dense WiFi environments," the researchers conclude, in a paper "Avoiding the Rush Hours: WiFi Energy Management via Traffic Isolation," presented this week at the annual MobiSys Conference in Washington, D.C. It’s authored by the principal researcher, grad student Justin Manweiler, and Romit Roy Choudhury, Assistant Professor, Dept. of Electrical & Computer Engineering and. Dept. of Computer Science, at Duke, Durham, N.C. The

In effect, as the two researchers note, SleepWell introduces a kind of distributed time division multiple access (TDMA) technique to a Wi-Fi network. TDMA is a channel access method for "shared medium" networks, for example, cellular networks. Several users can share the same frequency channel by dividing the signal into different time slots that are used by different users.

Wi-Fi radios are a major drain on a device’s battery. It’s being made worse by a change in the way mobile devices are used. Instead of intermittent, bursty data traffic, users today often are streaming media and interacting with always-on social networking applications.