Proactive neighbor localization based on distributed geographic table

Real-time tracking of massive numbers of mobile devices, either carried by humans or embedded into vehicles, is a challenging problem whose solution may pave the way for a large set of valuable applications, ranging from social networking to ambient intelligence. A centralized approach, i.e. a server collects position data and provides it to interested consumers, is highly questionable, as performance can hardly scale up to the needs several million concurrent users. On other hand, a decentralized peer-to-peer approach, for which positioning data would flow directly among mobile devices may be very appealing, provided that messages to be routed are not too frequent and too expensive in terms of bandwidth usage. In this context we propose a peer-to-peer overlay scheme called Distributed Geographic Table (DGT), where each participant can efficiently retrieve node or resource information (data or services) located near any chosen geographic position. In particular, we describe a DGT-based localization protocol, that allows each peer for proactively discovering and tracking all the peers that are geographically near to itself. We provide a performance analysis of our protocol, referring to a simulated (although realistic) scenario where several hundred vehicles move on a real map. Our results show that the solution is efficient, scalable and highly adaptable to different application scenarios.