Signals from the Crowd

The ever increasing ubiquitousness of WiFi access points, cou- pled with the diffusion of smartphones, suggest that Internet every time and everywhere will soon (if not already has) become a re- ality. Even in presence of 3G connectivity, our devices are built to switch automatically to WiFi networks so to improve user ex- perience. Most of the times, this is achieved by recurrently broad- casting automatic connectivity requests (known as Probe Requests) to known access points (APs), like, e.g., “Home WiFi”, “Campus WiFi”, and so on. In a large gathering of people, the number of these probes can be very high. This scenario rises a natural ques- tion: “Can significant information on the social structure of a large crowd and on its socioeconomic status be inferred by looking at smartphone probes?”.

In this work we give a positive answer to this question. We or- ganized a 3-months long campaign, through which we collected around 11M probes sent by more than 160K different devices. Dur- ing the campaign we targeted national and international events that attracted large crowds as well as other gatherings of people. Then, we present a simple and automatic methodology to build the un- derlying social graph of the smartphone users, starting from their probes. We do so for each of our target events, and find that they all feature social-network properties. In addition, we show that, by looking at the probes in an event, we can learn important sociolog- ical aspects of its participants—language, vendor adoption, and so on.