Smartphone Sucking Power? Blame the Ads
The study considered multiple popular smartphone apps, including Angry Birds, Facebook, and the phone's browser. The first sections of the paper discuss the eprof (energy profiler) tool the researchers built to collect data on application behavior and how the tool functions. A smartphone is an extraordinarily complex piece of hardware that hides a great deal of activity from the user by default. The smartphones used were all fairly dated; the three phones in question were the HTC Magic running Android 2.0 (released in 2009), the HTC Tytn on Windows Mobile 6.5 (released in 2006) and the HTC Passion running Android 2.3 (released in 2010).
One of the primary findings of the group is that modern smartphones exhibit "asynchronous power behavior" where "an entity's impact on the power consumption of the phone may persist long after the entity is completed." As a result, components may remain powered up after they've finished executing workloads. This can lead to considerable wasted power, as shown in the graph below.
By not powering the 3G radio down immediately following the last send, the "3G tail" burns 59.6% of the total energy used in the first example. In the second example, there's a 5 second delay inserted between the netconnect and netsend commands. The tail still drags out, accounting for 38% of total energy expenditure.
There are several take-aways from this information. First, it's evidence that in some cases, buying the ad-free version of a product can directly translate into better battery life. Second, it's something that heavy hitters are going to pay attention to. Process technologies don't produce the same level of power consumption reductions that they used to; that's why initiatives like Intel's NTV and research into all-digital radios are so important. Hardware manufacturers are well aware of these trends; they bring with them an imperative to optimize every single step of the smartphone experience. This very much includes things like bundling requests and data read/writes to ensure optimum execution efficiency and it means powering the device down every time it's possible.
The original paper is a dense piece of work, but hopefully it sparks increased research into these fields. With hardware improvements far more difficult to achieve than they've been in recent years, we suspect companies will turn to software and low-level optimizations to boost future product sales.