Free apps kill smartphone battery life

Those free apps like Angry Birds, Instagram and Tiny Wings may be loads of fun, but they suck the battery life out of your smartphone by tracking your geographical location, sending information about you to advertisers and downloading ads.

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That was the major conclusion of research done by Y. Charlie Hu, a Purdue University professor of electrical and computer engineering, who said, "It turns out the free apps aren't really free because they contain the hidden cost of reduced battery life." Hu and other researchers on his team authored a paper, "Where is the energy spent inside my app?" which will be presented during the EuroSys 2012 conference on April 10-13 in Bern, Switzerland.

The researchers findings show that 65% to 75% of the energy used to run free apps is spent for advertising-related functions. The free Angry Birds app, for example, was shown to consume about 75% of its power running "advertisement modules" in the software code and only about 25% for actually playing the game. The modules perform marketing functions such as sharing user information and downloading ads, according to the researchers.

Games and applications that heavily use built-in phone features like GPS, the camera, compass and "proximity sensor" are the main culprits of inefficient power consumption, the researchers said.

"A particular source of power inefficiency is a phenomenon called 'tails.' In principle, after an application sends information to the Internet, the 'networking unit' that allows the phone to connect to the Internet should go to a lower power state within a fraction of a second. However, researchers found that after the advertising-related modules finish using the network, the networking unit continues draining power for about seven seconds. The tails are a phenomenon of several smartphone hardware components, including 3G, or third-generation wireless systems, GPS and Wi-Fi, not flaws within the app software itself. However, software developers could sidestep the problem by modifying apps to minimize the effect of tails," Hu said.

"Any time you use the 3G network, there will be a tail after the usage," Hu said. "The ad module in Angry Birds obviously uses 3G for network uploading and downloading, while the game itself did not, which is why we blame the ad module for the tail."

The ultimate goal is to develop an "energy debugger" that automatically pinpoints flaws in software and fixes them without the intervention of a human software developer, Hu said.

The researchers have developed a tool known as "Eprof" that maps how much energy comes from each software component, giving researchers or developers a way to see smartphone energy consumption without using a power meter, an expensive and cumbersome piece of laboratory equipment.

"We've seen around 1 million apps written since smartphones emerged roughly five years ago, but there has been no systematic way for the developer to see how much energy the different components consume. Using this tool, you can see what should be changed to improve energy efficiency," the researchers said.

The power problem is palpable when it comes to smartphones.

"Despite the incredible market penetration of smartphones and exponential growth of app market, their utility has been and will remain severely limited by the battery life. Today, energy is the single most important factor plaguing smartphones. Modern smartphones come with faster processors, latest sensors, incredible screen resolutions, faster network connectivity, and as such these factors together contribute to the ability of the smartphone to consume energy at much faster rate than the ability to produce/store energy, i.e., the battery capacity. For example, the CPU performance over the last 15 years has grown by 246 times while the battery energy density has only doubled during the same period," wrote Abhinav Pathak, a Purdue doctoral student who was part of the research team.

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