Faculté Informatique et Communication

The supercritical regime of a percolation model refers to the range of probabilities (discrete) or densities (continuous) above a critical value for which there exists a unique unbounded cluster almost surely. In this paper, we provide an upper bound to the linear distance from the origin to this giant connected component for both the discrete and the continuous (Boolean) model in two-dimensions. By modeling a dense wireless sensor network with a supercritical Boolean model, our result bounds the distance traveled by a target moving in a straight line before it is detected by a node who can relay the alert through a multihop path to the sink. This result incorporates a solidified definition of detection requiring that the intrusion alert successfully reach the central authority.

Abstract—Vehicular Ad Hoc Networks (VANETs) are a pecu-liar subclass of mobile ad hoc networks that raise a number of technical challenges, notably from the point of view of their mobility models. In this paper, we provide a thorough analysis of the connectivity of such networks ...

Wireless networks are fundamentally limited by the intensity of the received signals and by their interference. Since both of these quantities depend on the spatial location of the nodes, mathematical techniques have been developed in the last decade to provide communication-theoretic results accounting for the network's geometrical configuration. Often, the location of the nodes in the network can be modeled as random, following for example a Poisson point process. In this case, different techniques based on stochastic geometry and the theory of random geometric graphs -including point process theory, percolation theory, and probabilistic combinatorics -have led to results on the connectivity, the capacity, the outage probability, and other fundamental limits of wireless networks. This tutorial article surveys some of these techniques, discusses their application to model wireless networks, and presents some of the main results that have appeared in the literature. It also serves as an introduction to the field for the other papers in this special issue.

We conduct an experiment where ten attendees of an open-air music festival are acting as Bluetooth probes. We then construct a parametric statistical model to estimate the total number of visible Bluetooth devices in the festival area. By comparing our estimate with ground truth information provided by probes at the entrances of the festival, we show that the total population can be estimated with a surprisingly low error (1.26% in our experiment), given the small number of agents compared to the area of the festival and the fact that they are regular attendees who move randomly. Also, our statistical model can easily be adapted to obtain more detailed estimates, such as the evolution of the population size over time.

Previous work on the coverage of mobile sensor networks focuses on algorithms to reposition sensors in order to achieve a static configuration with an enlarged covered area. In this paper, we study the dynamic aspects of the coverage of a mobile sensor network that depend on the process of sensor movement. As time goes by, a position is more likely to be covered; targets that might never be detected in a stationary sensor network can now be detected by moving sensors. We characterize the area coverage at specific time instants and during time intervals, as well as the time it takes to detect a randomly located stationary target. Our results show that sensor mobility can be exploited to compensate for the lack of sensors and improve network coverage. For mobile targets, we take a game theoretic approach and derive optimal mobility strategies for sensors and targets from their own perspectives.

Constructing sensor barriers to detect intruders crossing a randomly-deployed sensor network is an important problem. Early results have shown how to construct sensor barriers to detect intruders moving along restricted crossing paths in rectangular areas. We present a complete solution to this problem for sensors that are distributed according to a Poisson point process. In particular, we present an efficient distributed algorithm to construct sensor barriers on long strip areas of irregular shape without any constraint on crossing paths. Our approach is as follows: We first show that in a rectangular area of width w and length with w = Ω(log ), if the sensor density reaches a certain value, then there exist, with high probability, multiple disjoint sensor barriers across the entire length of the area such that intruders cannot cross the area undetected. On the other hand, if w = o(log ), then with high probability there is a crossing path not covered by any sensor regardless of the sensor density. We then devise, based on this result, an efficient distributed algorithm to construct multiple disjoint barriers in a large sensor network to cover a long boundary area of an irregular shape. Our algorithm approximates the area by dividing it into horizontal rectangular segments interleaved by vertical thin strips. Each segment and vertical strip independently computes the barriers in its own area. Constructing "horizontal" barriers in each segment connected by "vertical" barriers in neighboring vertical strips, we achieve continuous barrier coverage for the whole region. Our approach significantly reduces delay, communication overhead, and computation costs compared to centralized approaches. Finally, we implement our algorithm and carry out a number of experiments to demonstrate the effectiveness of constructing barrier coverage.

... With the use of parallel programming for the EAs, asynchronous evolution has appeared. ... However the kind of information to exchange in order to have an efficient EA depends on the problem consi-dered. ... 3. Hierarchical ingredients 3.1. Further description levels ...

Le but de l'alignement des textes est la mise en correspondance des sous-parties similaires de deux ou plusieurs traductions ou versions d'un même écrit. La plupart des méthodes utilisées dans la technique d'alignement reposent sur l'analyse statistique des fréquences de mots ou de caractères, ou sur la cooccurrence des chaînes que ceux-ci constituent. Afin d'en améliorer l'efficacité, d'autres approches incluent certaines propriétés linguistiques (morpho-syntaxiques et lexico-sémantiques) et structurelles (marques de chapitres, de sections, etc.) des documents. Cet article expose les résultats d'une adaptation de la technique d'alignement aux états parallèles des anciens textes à partir d'une approche multicritère qui tient compte de la similitude au niveau lexical, morpho-syntaxique et lexicosémantique du français de la période médiévale.