Scoop: decentralized and opportunistic multicasting of information streams.

ABSTRACTWe consider the problem of delivering information streams to interested mobile users, leveraging both access to the infrastructure and device-to-device data transfers. The goal is to design practical relaying algorithms that aim at optimizing a global system objective that accounts for two important aspects: first, the user interest in content with respect to its type and delivery time; and, second, resource constraints such as storage and transmission costs. We first examine a set of real-world datasets reporting contacts between users moving in relatively restricted geographic areas (e.g. a city). These datasets provide evidence that significant performance gains can be achieved by extending the information dissemination from one to two hops, and that using longer paths only brings marginal benefits. We also show that correlation of delays through different paths is typically significant, thus asking for system design that would allow for general user mobility. We then propose a class of relaying strategies (referred to as SCOOP) that aim at optimizing a global system objective, are fully decentralized, require only locally observable states by individual devices, and allow for general user mobility. These properties characterize a practical scheme whose efficiency is evaluated using real-world mobility traces.