Mobile Computing

Research: Your Smart Phone is Still Draining Power Even When the Screen's off

• By Dian Schaffhauser
• 09/16/15

A team of researchers from Purdue University and Intel is on a mission to double the life of smartphone batteries. Recently, they came up with an energy optimizer that promises to cut certain types of battery usage by nearly 16 percent.

As explained in a paper presented at ACM MobiCom 2015 in Paris, the scientists studied the use of 2,000 Samsung Galaxy S3 and S4 phones served by 191 mobile operators in 61 countries to figure out how smartphone energy drained "in the wild." They found that apps use up almost 29 percent while the screen is off. This happens because apps "wake up" to run in the background whether or not they need to.

"During screen-off, the phone hardware should enter the sleep state, draining close to zero power," explained Y. Charlie Hu, a professor of electrical and computer engineering at Purdue. "Apps wake the phone up periodically during screen-off to do useful things, but then afterward, they should let the phone go back to sleep." What happens, he said, is that those apps aren't "letting the phone go back to sleep" because of bugs in the software called "wakelocks" and incorrect use of Android power control application programming interfaces.

In a 2012 research project, Hu and his team developed a method for automatically detecting these "no-sleep energy bugs," which also appear to affect other brands besides Samsung. That first study presented the problem as a theoretical issue. The latest research, he noted, shows that wakelock bugs are "prevalent on real users' phones."

The solution proposed in the new paper is called "HUSH." This system distinguishes background activities that need to take place (such as a Wi-Fi beacon that touches base with the access point on a regular basis) and those that aren't essential. For instance, screen-off updates to a social networking site are only useful to users who frequently check feeds and react to notifications from that site a lot. For users who don't do that, HUSH would suppress that kind of background activity during screen-off to reduce the battery drain.

In the next phase of their work, the team will tackle reduction of power through "legitimate functions" as well as faulty apps. The team also expects to release an app version of HUSH "soon."

The work has been supported by an Intel 5G research program as well as the National Science Foundation.

"Smartphone Background Activities in the Wild: Origin, Energy Drain and Optimization" is openly available on the ACM Special Interest Group on Mobility of Systems, Users, Data and Computing (SIGMOBILE).