Information propagation speed in large scale mobile and intermittently connected networks

Abstract

In this keynote, we look the fundamental limits of the information propagation speed in large scale mobile and intermittently connected networks, where end-to-end multihop paths may not exist and communication routes may only be available through time and mobility. We first introduce some analytical tools to derive generic theoretical bounds for the information propagation speed in this networks. We upper-bound the optimal performance, in terms of delay, that can be achieved using any routing algorithm. We also show how our analysis can be applied to specific mobility models to obtain specific analytical estimates. We then look at the maximum amount of data that can be transferred: (i) from a source to a destination in a given journey, (ii) overall in the network compared to the average delay. Finally we look at the particular case of multi-lane vehicle-to-vehicle networks such as roads or highways. We focus on the impact of time-varying radio ranges and of multiple lanes of vehicles, varying in speed and in density. We show the existence of a vehicle density threshold under which information propagates on average at the fastest vehicle speed and above which information propagates dramatically faster. We characterize conditions under which the phase transition occurs and we derive bounds on the corresponding threshold as a simple relationship between the vehicle density on the fastest lane and the sum of densities on the other lanes. Our results intrinsically encompass a wide range of vehicular network scenarios, including one-way and two-way roads, as well as special cases such as road side units and/or parked cars being used as relays.