New tool reduces smartphone battery drain by intelligently suppressing background activities

September 10, 2015  

WEST LAFAYETTE, Ind. – The first large-scale study of smartphones in everyday use by consumers has revealed that apps drain 28.9 percent of battery power while the screen is off. To address the problem, researchers have created a software tool that reduces the energy drain by about 16 percent.

Researchers at Purdue University, Intel Corp. and startup company Mobile Enerlytics studied the use of 2,000 Samsung Galaxy S3 and S4 phones served by 191 mobile operators in 61 countries.

"This was the first large-scale study of smartphone energy drain 'in the wild,' or in everyday use by consumers," said Y. Charlie Hu, a Purdue professor of electrical and computer engineering.

Out of the 45.9 percent of daily battery drain where the screen is off, 28.9 percent is due to apps that frequently wake up and run in the background. Out of this 28.9 percent, researchers have shown how to save 15.7 percent with a new system called HUSH, which is available for free at

"During screen-off, the phone hardware should enter the sleep state, draining close to zero power," Hu said. "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. They are not letting the phone go back to sleep because of software bugs and, specifically, due to the incorrect use of Android power control application programming interfaces called wakelocks."

Researchers presented findings this week at the ACM MobiCom 2015 conference in Paris. The ACM is the Association for Computing Machinery Inc. The research paper was authored by Purdue graduate students Xiaomeng Chen, Abhilash Jindal and Ning Ding; Hu; and Intel researchers Maruti Gupta and Rath Vannithamby.

"We presented the first study a few years back showing wakelock bugs could cause significant energy drain," Hu, said. "But this is the first study showing that wakelock bugs appear prevalent on real users' phones."

The "in-the-wild" battery drain study also was detailed in a paper presented in June that included data from the use of about 1,500 phones. The work was described in a Scientific American podcast.

"Being able to reduce the total daily energy drain by about 16 percent is rather significant because you can extend the battery charge by one-sixth," Hu said.

The key insight behind the proposed solution, HUSH, is that background activities of individual apps are not equally important to individual smartphone users. For example, frequent Facebook updates during screen-off may be useful to a user who checks Facebook feeds and reacts to notifications often, but they are much less useful to another user who rarely checks such updates. The HUSH system dynamically identifies app background activities that are not useful to the user experience on a per-app basis and suppresses such background app activities during screen-off to reduce the battery drain.

When the phone is in screen-off, it also continues draining power for various legitimate maintenance purposes: for example, A WiFi beacon, when the phone's WiFi system sends a periodic signal to the access point once every 200 milliseconds, and a "cellular paging" function, when the phone talks to the base station every 1.28 seconds to check for incoming calls or data.

In efforts to extend battery life, researchers will work to reduce energy drain from these legitimate functions as well as faulty apps.

"The big picture is that we want to double the battery life for smartphones," Hu said. "This is going to be a non-trivial journey because much of the battery drain is caused by various apps when the screen is on and also legitimate maintenance functions."

The research is ongoing, with implications to the 5G wireless network design.

The research has been funded by the Intel 5G Research Program and the National Science Foundation. 

Writer: Emil Venere, 765-494-4709,  

Source:  Y. Charlie Hu, 765 494-9143,  

Note to Journalists: An electronic copy of the research paper is available by contacting Emil Venere, at 765-494-4709,           


Smartphone Background Activities in the Wild: Origin, Energy Drain, and Optimization

Xiaomeng Chen†∧ Abhilash Jindal†∧ Ning Ding†∧ Y. Charlie Hu†∧ Maruti Gupta* Rath Vannithamby*

†Purdue University ∧Mobile Enerlytics *Intel Corporation

As new iterations of more powerful and better connected smart- phones emerge, their limited battery life remains a leading factor adversely affecting the mobile experience of millions of smart- phone users. While it is well-known that many apps can drain battery even while running in background, there has not been any study that quantifies the extent and severity of such background energy drain for users in the wild. To extend battery life, various new features are being incorporated within the phone, one of them being preventing applications from running in background, i.e., when the screen is off, but their impact is largely unknown. This paper makes several contributions. First, we present a large- scale measurement study that performs an in-depth analysis of the activities of various apps running in background on thousands of phones in the wild. Second, we quantify the amount of battery drain by all such background activities and possible energy saving. Third, we develop a metric to measure the usefulness of background activities that is personalized to each user. Finally, we present a system called HUSH (screen-off optimizer) that monitors the metric online and automatically identifies and suppresses back- ground activities during screen-off periods that are not useful to the user experience. In doing so, our proposed HUSH saves screen-off energy of smartphones by 15.7% on average while incurring mini- mal impact on the user experience with the apps. 

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