10 Ways To Fight Email Overload

Advertising is supposed to provide a way for app publishers to provide free content to consumers, but it doesn't quite work that way.

Advertising has a hidden cost. Beyond time, attention and network data usage, ads consume power, which is not a trivial consideration on mobile devices.

The advertisements in a typical mobile app consume almost a quarter of the app's energy, according to research paper published by scientists at University of California, Berkeley, and Microsoft Research.

The study, "Prefetching mobile ads: Can advertising systems afford it?" states that among popular Windows Phone apps "on average, ads consume 65% of an app's total communication energy, or 23% of an app's total energy."

[ Want to know about updates in Apple's upcoming mobile OS? Read iOS 7 Beta 2 Lands On iPad. ]

The study authors, Prashanth Mohan, U.C. Berkeley graduate student; Suman Nath, senior researcher at Microsoft Research; and Oriana Riva, researcher at Microsoft Research, examine the issue with an eye toward making mobile ad delivery more energy efficient.

About two-thirds of the Android apps in the Google Play app store are free, according to the paper, and the majority of those (about 80%) are ad-supported.

They propose a scheme known as "prefetching," which as the term suggests, involves fetching online ads in bulk before they're needed, to minimize "tail time," a period of several seconds that the mobile phone's data connection is kept open as a means of improving network performance for any network requests that immediately follow. Prefetching is problematic for mobile ad networks, however, since just-in-time delivery matters and delayed ads can violate service level agreements (SLAs).

The researchers demonstrate that downloading 10 mobile ads of 1 KB as a group over an AT&T 3G network is more energy efficient than downloading one every minute. Prefetching, they assert, "is capable of reducing the energy consumed by an average client by 50%, while maintaining SLA violation rates below 3%."

The study's findings underscore the fact that developers need better tools to understand the relationship between application code and power consumption. As it turns out, Microsoft Research last year developed one, Eprof, a smartphone app energy profiler. The profiler shows, for example, that the third-party Flurry module consumes 45% of the energy in the Angry Birds app.

Till Faida, co-founder and managing director of Adblock Plus, sees the research as further evidence that ads need to be moderated. "The use of in-app advertising has enabled an ecosystem of free apps for many people's enjoyment, but we have to consider the impact this is having on battery drain," he said in an emailed statement. "... Many consumers are blaming their phone for poor battery performance when it is the advertising that is at fault."

Google, the leading mobile ad provider, doesn't see ads as a problem. It's more concerned about ensuring that people do see ads. Earlier this year, it removed removed AdBlock Plus from Google Play, citing the app's interference with other applications.