WLAN-Opp: Ad-hoc-less opportunistic networking on smartphones

Opportunistic networking enables many appealing applications including local social-networking, communication in emergency situations, and circumventing censorship. The increasing penetration of smartphones should, in theory, foster opportunistic networking. In practice, current candidate technologies for opportunistic networking, such as Wi-Fi ad-hoc, Bluetooth, and Wi-Fi Direct, are either not available on current smartphones, or require undesired user interaction to establish connectivity.To overcome these shortcomings, we propose WLAN-Opp for smartphones. This IEEE 802.11-based technology leverages the tethering mode of smartphones, a feature originally used to share Internet access, which allows smartphones to become WLAN-based access points that provide networks for other smartphones operating as stations. The transitions between WLAN-Opp access point and station mode are randomized as a function of the number of other co-located networks and stations, and depend on duty cycling intervals. We optimize the probabilistic operations in a simulation study and provide a parametrized implementation of WLAN-Opp for out of the box smartphones. By replaying real contact traces in simulation, we find that WLAN-Opp can utilize up to 80% of the contact time while saving up to 90% of the energy Wi-Fi ad-hoc would consume. Finally, we demonstrate in a field trial with 34 users over 5 days that WLAN-Opp can provide a practical solution in a realistic setting.