Mobile Wi-Fi Offload

In the course of researching my upcoming Heavy Reading report on Wi-Fi Offload for Mobile Operators, I came across an interesting academic paper that estimates 65 percent of smartphone traffic is already (or can be) offloaded to Wi-Fi under normal usage conditions.
The paper, "Mobile Data Offloading: How Much Can WiFi Deliver?," attempts to quantify how much traffic is, or can be, offloaded from cellular networks to Wi-Fi by analyzing users' actual physical movements throughout the day and mapping that to a data consumption model.
To achieve this, researchers developed custom handset software that tracked 100 iPhone users in South Korea to determine how often, and for how long, people are within range of Wi-Fi connectivity to the Internet, and what the data rates were at any given point. This data was then combined with a traffic model to simulate how much mobile data could be offloaded to Wi-Fi over a one-month period.
The study demonstrates with a degree of academic rigor what we know intuitively: that many people spend a good deal of their time within range of an accessible Wi-Fi connection. The simulation assumed 7GB of data consumption per month, as predicted by the Cisco Visual Network Index for 2014, adapted to approximate a real-world consumption pattern (i.e., a mix of small and large files).
The key takeaways from this project -- at least, as I see them -- include the following:

• Users are in Wi-Fi coverage 63 percent of the time during the day (70 percent over 24 hours); each stay in a Wi-Fi zone lasts about two hours.
• 65 percent of traffic can be offloaded to Wi-Fi under typical usage conditions using on-the-spot offload (i.e., using Wi-Fi on demand when available)
• Greater offload performance can be achieved if the user is prepared to accept delayed offload (e.g., sync your videos or photos when you get home)
• This means that out of the 7GB usage per month, 4.5GB would travel by Wi-Fi and 2.5GB by cellular. Therefore a 2GB-3GB per month cellular data plan is probably enough for most users.
• Offload performance depends, obviously, on the pattern of Wi-Fi coverage as well as user mobility. South Korea probably has denser Wi-Fi than some other markets, but still many of us have Wi-Fi at home or at work.
• Wi-Fi provides connections of 2 Mbit/s on average, which is skewed to 2.76 Mbit/s at night, (probably home Wi-Fi) and 1.26 Mbit/s during the day (probably shared Wi-Fi).
• Because Wi-Fi is faster than 3G, offload also generates a 55 percent improvement in battery life. However, the simulation only considered the energy used during transmission and did not take into account the battery drain from scanning for, and attaching to, Wi-Fi access points.

The assumptions and methodology of a study will inevitably have an impact on the output of the simulation, but the data does appear to show, pretty conclusively, that Wi-Fi is already taking much of the burden of smartphone traffic growth.
A logical question from this finding is then: How useful would it be for operators to more actively manage Wi-Fi offload? Would that generate an even greater performance gain? Or are operators getting most of the offload benefit without having to do anything?
— Gabriel Brown, Senior Analyst, Heavy Reading