More and more these days, mobile apps are “free” to download, and supported by advertising that is shown at the beginning and throughout the app.

But a recent study shows that in fact these in-app ads consume a lot of energy, and can be a serious drain on the already limited battery life of a mobile device.


Looking at the top 15 free Windows Phone apps, researchers found that the energy consumed by in-app advertising was very nearly one quarter of the total energy used by the app – an amazingly high percentage!

Prashanth Mohan is a graduate student at University of California at Berkeley. Working together with Suman Nath and Oriana Riva of Microsoft Research, they have published a research paper titled: “Prefetching mobile ads: Can advertising systems afford it?”.
[see download link below]

This paper looks at the actual energy that is used up by today’s standard in-app mobile advertising, and discusses an approach to cut down this battery drain.

The reason that it takes so much energy to download a few quite small files has to do with the fundamental way a phone is designed. Basically, most of the time when the app wants to download an ad, it must first “wake up” the radio communications part of the phone. And as the communications remains on for some time, it requires quite a bit of energy.

One possible way to reduce the amount of energy required for in-app advertising would be to “pre-fetch” ads. In other words, an app could download several ads at the same time. This way the app could display a series of ads over a period of time without having to wake up the radio communications part of the mobile.

Unfortunately, this doesn’t fit very well with the real-time nature of today’s mobile ad networks. Usually, each time a client wants to display an ad there is a real-time auction of the ad space. This is shown in the diagram below which is from the paper.

Pre-fetching ads can cause problems in this system. For example, the ads may be fetched and charged for, but not be actually shown to the client. On the other hand, the ad may be seen by the client, but not at the appropriate time. Or in fact the total number of times an ad is shown may go over the advertiser’s budgeted amount.

The full paper goes into a more detailed view of this, and concludes that pre-fetching could in fact save half the energy while causing very few real problems.