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Van Nam N.,French Institute for Research in Computer Science and Automation | Guerin-Lassous I.,French Institute for Research in Computer Science and Automation | Moraru V.,Institute Of La Francophonie Pour Linformatique Ifi | Sarr C.,University Of Thies
MSWiM'11 - Proceedings of the 14th ACM International Conference on Modeling, Analysis, and Simulation of Wireless and Mobile Systems | Year: 2011

Estimating the available bandwidth in IEEE 802.11-based multihop wireless networks is a very difficult task due to the medium sharing among contending nodes and collisions between hidden stations. Several methods have been proposed so far for these networks to compute the available bandwidth on wireless links. If some recent solutions such as ABE and IAB now take into account collisions and their impact on the mean backoff, none considers the packet retransmissions due to collisions although these retransmissions have an impact on the available bandwidth. In this article, we propose a new available bandwidth estimation for multihop wireless networks called RABE (Retransmission-based Available Bandwidth). This method integrates the average number of retransmission attempts in the available bandwidth estimation. RABE is evaluated by simulation and the obtained results show that RABE can achieve a mean error ratio of 17% in comparison with the real measurement. Furthermore RABE is at least two times more accurate than ABE and ten times more accurate than IAB. Copyright 2011 ACM. Source


Pham Q.-D.,Catholic University of Louvain | Do P.-T.,Hanoi University of Science and Technology | Deville Y.,Catholic University of Louvain | Ho T.-V.,Institute Of La Francophonie Pour Linformatique Ifi
ACM International Conference Proceeding Series | Year: 2010

Routing problems have been considered as central problems in the fields of transportation, distribution and logistics. LS(Graph) is a generic framework allowing to model and solve constrained optimum paths problems on graphs by local search where paths are known to be elementary (i.e., edges, vertices cannot be repeated on paths). In many real-world situations, the paths to be determined are not known to be neither simple nor elementary. In this paper, we extend the LS(Graph) framework by designing and implementing abstractions that allow to model and solve constrained paths problem where edges, vertices can be repeated on paths (call non-simple paths). We also propose an instance of such problem class: the routing for network covering (RNC) problem which arises in the context of rescue after a natural disaster in which we have to route a fleet of identical vehicles with limited capacity on a transportation network in order to collect the informations of the disaster. Given an undirected weighted graph G = (V, E) representing a transportation network and a vertex v 0 ε V representing the depot, the RNC problem consists of routing a fleet of unlimited number of identical vehicles with limited capacity that cannot perform a path of length > L such that each vehicle starts from and teminates at the depot and all the edges of a given set S (S ⊆ E) must be visited. The objective of the routing plan is to minimize the number of vehicles used. This paper discusses the challenge around this problem and applies the constructed framework to the resolution of this problem. The proposed model is generic; it allows to solve some variants of the problem where side constraints are required to be added. © 2010 ACM. Source


Bui Q.T.,Institute Of La Francophonie Pour Linformatique Ifi | Pham Q.-D.,Catholic University of Louvain | Deville Y.,Catholic University of Louvain
ACM International Conference Proceeding Series | Year: 2011

Partitioning a field into parcels is one step of the project of merging and repartitioning agricultural lands which emerges in many provinces in Vietnam. Historically, this problem has been conducted based on human experiences and without using optimization technology nor computer science. In this paper, we propose a model for the problem of fields partitioning taking into account real issues. We also propose local search algorithms for solving this problem with typical shapes of fields i.e., rectangle, trapezium, triangle. Experimental results show that our local search approach gives better solutions than those realized by human experiences. © 2011 ACM. Source


Taillandier P.,Institute Of La Francophonie Pour Linformatique Ifi | Taillandier P.,Institute Geographique National IGN | Duchene C.,Institute Geographique National IGN | Drogoul A.,Institute Of La Francophonie Pour Linformatique Ifi | Drogoul A.,University Pierre and Marie Curie
International Journal of Geographical Information Science | Year: 2011

Automating the generalisation process, a major issue for national mapping agencies, is extremely complex. Several works have proposed to deal with this complexity using a trial and error strategy. The performance of systems based on such a strategy is directly dependent on the quality of the control knowledge (i.e. heuristics) used to guide the trials. Unfortunately, most of the time, the definition and updation of knowledge is a fastidious task. In this context, automatic knowledge revision can not only improve the performance of the generalisation, but also allow it to automatically adapt to various usages and evolve when new elements are introduced. In this article, an offline knowledge revision approach is proposed, based on a logging of the system and on the analysis of outcoming logs. This approach is dedicated to the revision of control knowledge expressed by production rules. We have implemented and tested this approach for the automated generalisation of groups of buildings within a generalisation model called AGENT, from initial data that reference a scale of approximately 1:15,000 compared with the target map's scale of 1:50,000. The results show that our approach improves the quality of the control knowledge and thus the performance of the system. Moreover, the approach proposed is generic and can be applied to other systems based on a trial and error strategy, dedicated to generalisation or not. © 2011 Copyright Taylor and Francis Group, LLC. Source


Van Minh L.,Hanoi University | Adam C.,RMIT University | Canal R.,Institute Of La Francophonie Pour Linformatique Ifi | Gaudou B.,Toulouse 1 University Capitole | And 3 more authors.
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2012

Nowadays, more and more emergency evacuation simulations are used to evaluate the safety level of a building during an emergency evacuation after an accident. The heart of this kind of simulations is the simulation of human behavior because simulation results depend for a big part on how this behavior is simulated. However, human behaviors in a real emergency situation are determined by a lot of cognitive mechanisms. In order to make the simulation more realistic, plenty of factors (e.g. innate characteristics, perception of the environment, internal rules, personality and even emotions) that affect human behaviors must be taken into account. This paper focuses on the influence of emotions, and more precisely on the influence of their dynamics and propagation from an agent to another. The main contribution of this work is the development of a model of emotions taking into account their dynamics and their propagation and its integration in an evacuation simulation. The first results of the simulation show the benefits of considering emotion propagation. © Springer-Verlag Berlin Heidelberg 2012. Source

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