A cell-phone application that logs everything the phone’s user does–from sending e-mail to playing games–may not sound so desirable. But researchers are deploying the software to see if they can determine the best ways to improve the battery life of phones and uncover network dead spots.
Working with colleagues at Microsoft Research, Hossein Falaki, a PhD candidate at UCLA’s Center for Embedded Network Sensing, has developed software that records data use, phone use, and battery-charge levels. The software is designed to run on devices that use Windows Mobile or the Android operating system. The Android version can also track the data sent and received by individual applications.
“One major problem we all experience with smart phones is that the batteries don’t last long enough,” says Falaki, who will present a paper next month at the Internet Measurement Conference in Melbourne, Australia, on more than 2,000 days of data collected from eight Windows Mobile and 35 Android users. “By studying how people use [the phones], we can find ways to match devices and networks to people.”
For example, the tracking application uncovered data suggesting that a tweak to the hardware of two phones made by the Taiwanese manufacturer HTC– could save approximately 40 percent of the power consumed by their radios. These handsets automatically switch off the radio after being idle for 17 seconds, a tactic used by all handsets and often with a similar timeout value. But that is a poor match with the very “bursty” way that smart-phone users access data, says Falaki. “People take the phone out of their pocket, interact with it for a few minutes, and then don’t use it for a relatively long time after,” he says.
Logs of data use showed that after a burst of activity, users rarely needed more data in the subsequent 17 seconds, so the radio was often left on needlessly. In fact, some 95 percent of data packets were sent or received within 4.5 seconds of the last one. Resetting the device so that the radio powered down after 4.5 seconds would consume 40 percent less power without affecting performance, says Falaki.
“These ‘tail times’ are larger than they need to be,” says Arun Venkataramani, an assistant professor at University of Massachusetts, Amherst who studies power use in mobile devices. “From an application and user perspective, there’s significant room for improvement.” The Microsoft-UCLA data agrees with results from his own experiments looking at the energy costs of cell-phone timeout periods, he says.