Cocktail Party on the Mobile

We present the architecture, user interface and prototype implementation of fluid voice, a proximity based mobile group communication system for opportunistic social exchanges. It is designed for coordinating people in outdoor settings, spreading news during emergency responses and supporting impromptu social exchanges by exploiting the inherent broadcast nature of wireless and mobility of people. It supports diverse media: live audio, asynchronous audio, text messages, audio messages, audio polls and wish lists. In this paper, we focus on the audio support and the design for intermittent connectivity characteristics of mobile systems with limited range. Users can transition from live to asynchronous audio communication in a fluid manner depending on the wireless environment. When every node is able to hear each other, the receiver mixes all sources and provides the user with a "push to listen" interface to "tune in" to who they want to listen to. When the wireless channel is congested, it transitions to a "push to talk" interface (without taking over the whole channel) to reduce collisions while allowing people to barge in. When nodes cannot hear each other, Fluid Voice caches content for future delivery using a dynamic multi-stream mixer with time shifting (Tivo) functionality. The system was prototyped on the Nokia N810\´s for real world testing and we discuss its technical and social limitations.