Algorithm for Term Linearizations of Aggregate Queries with Comparisons

International audienceWe consider the problem of rewriting queries based exclusively on views. Both queries and views can contain aggregate functions and include arithmetic comparisons. To study the equivalence of a query with its rewriting query, the so called "linearizations of a query" need to be computed. To find the linearizations of a query, the linearizations of terms from the query need to be generated. We propose an algorithm to find these term linearizations and give a bound for its time-complexity

Management of Real Time Constraints in Sensor Networks

International audienceThe scope of this paper is to compare existing techniques proposed to manage real time (RT) communications in wireless sensor networks. MAC, network or cross layer solutions are presented and discussed in order to draw up a global view of system designs. Identifying drawbacks of existing works allows drawing future directions concerning QoS guaranteeing data delivery under time constraints

Energy-Efficient {WSN} Infrastructure

International audienceEnergy conserving communication is one of the main challenges of wireless sensor networks. A number of studies and research are focused on saving energy and on extending the lifetime of these networks. Architectural approaches, like hierarchical structures, tend to organize network nodes in order to save energy. Most of these protocols need background information on the network in order to be efficient. In this paper, we describe a new approach for organizing large sensor networks into zones, based on the number of hops. This network architecture enables a hierarchical network view, with the purpose of offering efficient routing protocols based on zone partitioning. Simulations undertaken demonstrate that our approach is energy-efficient; this is highlighted by the reduction of traffic overhead

Wireless Sensor Networks Routing over Zones

International audienceIn this paper, we propose a routing protocol for wireless sensor networks based on a two-level, zone-based architecture. DV is applied in both intra-zone and inter-zone routing, based on the hop metric. Our solution is original because it is instrumentation-free (sensors are both localization and energy unaware) and completely distributed. We show performances of the proposed algorithm evaluating the overhead generated by the construction of the infrastructure needed in routing. Simulations for MICA2 sensors have given us indications on the energy consumption - almost 4*10$^{-4}$% of the total battery capacity, on the scalability property of the algorithm and on the memory size of the data structure used for routing - almost 13% of the RAM memory. Moreover, memory constraints allow us to determine a lower bound for the number of zones

WSN Hierarchical Routing Protocol Taxonomy

International audienceRouting protocols in wireless sensor networks are generally focused on hierarchical infrastructures, for energy saving reasons. In this paper, we intend to give a taxonomy of these approaches identifying three criteria of classification: the assumptions, the algorithms and their evaluation. We classify projects based on these parameters and we also draw a uniform view over them, which may provide a basis of comparison for different routing protocols built atop hierarchical WSN infrastructures

Wireless Sensor Network Infrastructure: Construction and Evaluation

International audienceLarge area wireless sensor deployments rely on multi-hop communications. Efficient packet transmissions and virtual topologies, which structure sensor networks, are two main features for efficient energy management in wireless sensor networks. This paper aims to present a distributed and low-cost topology construction algorithm for wireless sensor networks, addressing the following issues: large-scale, random network deployment, energy efficiency and small overhead. We propose structuring nodes in zones, meant to reduce the global view of the network to a local one. This zone-based architecture is the infrastructure used by our hierarchical routing protocol. The experimental results show that the proposed algorithm has low overhead and is scalable

Wireless sensor network system helping navigation of the visually impaired

International audienceNavigation aids for the pedestrians are considered new research challenges. The visually impaired are particularly concerned, because of their need to detect and avoid obstacles, as well as to orient themselves in unknown environments. In this paper, we discuss some existing projects in this domain and we propose a novel aid system formed of wireless sensors, meant to help navigation of the visually impaired, which addresses both orientation and obstacle negotiation. The proposed system is GPS-free and does not need external assistance in navigation

A dynamic clustering construction for wireless sensor networks

International audienceResearch in sensor networks has focused on development of energy efficient and secure infrastructures. In this article, we introduce a new approach to organize sensor networks in clusters in order to reduce energy dissipation. Our contribution is an heuristic to define the number of clusters and also an efficient manner to choose cluster heads by minimizing the distance between the cluster heads and its cluster nodes. Inspired from LEACH, a well-known TDMA cluster-based sensor network architecture, we introduce a new method for building and maintaining clusters using the paradigm of a soccer team. In this work, a new algorithm called OH-Kmeans, based on the Kmeans algorithm, is used to find dynamically the number of clusters and form them guaranteeing direct transmission between the cluster heads and cluster nodes

A SAW wireless sensor network platform for industrial predictive maintenance

Predictive Maintenance (PM) predicts the system health, based on the current condition, and defines the needed maintenance activities accordingly. This way, the system is only taken out of service if direct evidence exists that deterioration has actually taken place. This increases maintenance efficiency and productivity on one hand, and decreases maintenance support costs and logistics footprints on the other. We propose a system based on wireless sensor network to monitor industrial systems in order to prevent faults and damages. The sensors use the Surface Acoustic Wave (SAW) technology with an architecture composed of an electronic interrogation device and a passive sensor (without energy at the transducer) which is powered by the radio frequency transmitted by the interrogation unit. The radio frequency link transfers energy to the sensor to perform its measurement and to transmit the result to the interrogation unit - or in a description closer to the implemented, characterize the cooperative target cross-section characteristics to recover the physical quantity defining the transducer material properties. We use this sensing architecture to measure the temperature of industrial machine components and we evaluate the robustness of the method. This technology can be applied to other physical parameters to be monitored. Captured information is transmitted to the base station through multi-hop communications. We also treat interferences involved in both interrogator to interrogator and sensor to interrogator communications

Une approche parallèle et distribuée pour la complétion d'automates d'arbre

National audienceLa technique dite de complétion sur les automates d'arbre permet, à partir d'un automate d'arbre et d'un système de réécriture, de calculer une sur-approximation de l'ensemble des termes accessibles. Cette technique a été utilisée avec succès pour la vérification de protocoles de sécurité et, plus récemment, pour l'analyse des programmes Java. Comme dans toute approche de vérification par model-cheking, nous sommes confrontés à des problèmes d'explosion combinatoire lorsque les exemples deviennent plus conséquents. Dans cet article nous montrons comment faire face à cette situation en parallélisant et distribuant les calculs. Nous présentons aussi quelques résultats expérimentaux qui montrent que l'approche permet d'obtenir de meilleures performances en temps d'exécution