Information Dissemination in Vehicular Networks in an Urban Hyperfractal Topology
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The goal of this paper is to increase our understanding of the fundamental performance limits of urban vehicle networks by exploiting the self-similarity and hierarchical organization of modern cities. We use an innovative model called "hyperfractal" that captures the self-similarity of the topology and vehicle locations while avoiding the extremes of regularity and randomness. We use analytical tools to derive matching theoretical upper and lower bounds for the information propagation speed of a broadcast in an urban delay tolerant network which is disconnected at all time, i.e., where end-to-end multihop paths may not exist (requiring a store-carry-and-forward routing model). We prove that the average broadcast time in a hyperfractal setup is in Θ(n^1-δ) where n is the number of mobile nodes and where δ depends on the precise hyperfractal dimension. Furthermore, we show that the performance is due in part to an interesting self-similar phenomenon, that we denote as information teleportation, that arises as a consequence of the topology and allows an acceleration of the broadcast time. We show how our model can be validated with real cities using a fitting procedure applied to open data sets, and also how it can be extended to cities that do not follow a regular hierarchical pattern. The study also presents simulations that confirm the validity of the bounds in multiple realistic settings, including scenarios with variable speed.
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