Some complexity and approximation results for coupled-tasks scheduling problem according to topology

We consider the makespan minimization coupled-tasks problem in presence of compatibility constraints with a specified topology. In particular, we focus on stretched coupled-tasks, i.e. coupled-tasks having the same sub-tasks execution time and idle time duration. We study several problems in framework of classic complexity and approximation for which the compatibility graph is bipartite (star, chain,. . .). In such a context, we design some efficient polynomial-time approximation algorithms for an intractable scheduling problem according to some parameters

Completely Independent Spanning Trees in Some Regular Graphs

Let $k\ge 2$ be an integer and $T_1,\ldots, T_k$ be spanning trees of a graph $G$. If for any pair of vertices $(u,v)$ of $V(G)$, the paths from $u$ to $v$ in each $T_i$, $1\le i\le k$, do not contain common edges and common vertices, except the vertices $u$ and $v$, then $T_1,\ldots, T_k$ are completely independent spanning trees in $G$. For $2k$-regular graphs which are $2k$-connected, such as the Cartesian product of a complete graph of order $2k-1$ and a cycle and some Cartesian products of three cycles (for $k=3$), the maximum number of completely independent spanning trees contained in these graphs is determined and it turns out that this maximum is not always $k$

ADM : A Density And Priority Levels Aware Protocol For Broadcasting In Vehicular Ad-Hoc Networks

The broadcasting communication mode is widely used in Vehicular Ad~hoc Networks (VANETs). It is used for sending emergency messages, road-traffic information or to help routing protocols to determine routes. This communication mode is known to be hard to achieve efficiently since it depends on the network density. Indeed, broadcasting methods may cause network congestion if they are not well designed. This paper introduces a novel Autonomic Dissemination Method (ADM) which delivers messages in accordance with given message classes and network density levels. The proposed approach is based on two steps: an offline optimization process and an online adaptation to the network characteristics. ADM allows each node to dynamically adapt its broadcasting strategy not only with respect to the network density, but also according to the class of the message to send: emergency (high-priority), road-traffic (medium-priority) or either comfort message (low-priority). The ultimate goal of ADM is to make effective use of radio resources when there are many messages to send simultaneously. This approach increases the efficiency of the broadcast process in terms of message delivery ratio, latency and interferences reduction. The autonomic computing paradigm improves the robustness of protocols

Scheduling stretched coupled-tasks with compatibilities constraints : model, complexity and approximation results for some class of graphs

We tackle the makespan minimization coupled-tasks problem in presence of compatibility constraints. In particular, we focus on stretched coupled-tasks, {\it i.e.}coupled-tasks having the same sub-tasks execution time and idle time duration. We study severals problems in frame works of classic complexity and approximation for which the compatibility graph $G_c$ is bipartite (star, chain, $\ldots$) In such context, we design some efficient polynomial-time approximation algorithms according to difference parameters of the scheduling problem. When $G_c$ is a $k$-stage bipartite graph, we propose, among other, a $\frac{7}{6}$-approximation algorithm when $k=1$, and a $\frac{13}{9}$-approximation algorithm when $k=2$.\

A New Development Framework for Multi-Core Processor based Smart-Camera Implementations

International audienceThe exponential evolution of the smart camera processing performances is directly linked to the improvements on hardware processing elements. Nowadays, high processing performances can be reached considering hardware targets which enables a high level of task parallelism to be implemented. Highly regular tasks are good candidate for a reconfigurable logic implementation and less regular parts of the algorithm could be described on the processor. Meanwhile the prototyping time is related to the selected target and the associated development methodology. The implementation on reconfigurable logic is highly efficient in exploiting the intrinsic task parallelism nevertheless can be time consuming using traditional methodology (i.e. Hardware Language Description). Several approaches can be considered to decrease the proto-typing time and to conserve high processing performances for instance implementation based on: • heterogeneous architectures [1] that mixed reconfig-urable logic (i.e. FPGA) and embedded processor, • high-level abstraction description and the associated fast prototyping tools [2][3][4], • multi-core processor architectures such as Digital Signal Processors (DSP), Graphic Processor Units (GPU) or even Generic Purpose Processor (GPP). In this paper, we propose to focus on implementation based on GPP due to the emergence of new generation of low-cost multi-core processors which enables high processing performances to be reached and therefore to match with some constraints of complex image-processing algorithms. The key idea of this development is to be able to propose fast prototyping using a low-cost smart camera based on this kind of target. Hence, we have developed a new framework dedicated to multi-core processor associated with an image sensor. The framework aims to offer a high degree of flexibility for managing the tasks and the memory allocation. Hence, the framework enables the priority and the allocation of each task to be controlled. Each task (or binary) is independent in terms of execution nevertheless it can be linked and controlled using a higher hierarchy level binary. The image acquisition task can be completely independent from the other processing tasks. One processor's core can even be dedicated to the acquisition task to guarantee a constant input data-flow to the image processing tasks. The data exchange is defined in POSIX, each binary can be therefore coded differently (for instance in C or C++, or in another languages) and offer a relative Operating System (OS) compatibility. The memory management enables a sequence of images to be automatically stored and a simultaneous access to be granted for several processings. The framework includes an interface dedicated to the management of the tasks: the user can add or suppress a binary during the runtime, logs or processing results can be visualised for each task

WiseEye: A Platform to Manage and Experiment on Smart Camera Networks

International audienceEmbedded vision is probably at the edge of phenomenal expansion. The smart cameras are embedding some processing units which are more and more powerful. Last decade, high-speed image processing can be implemented on specifically designed architectures [1] nevertheless the designing time of such systems was quite high and time to market therefore as well. Since, powerful chips (i.e System On Chip) and quick prototyping methodologies are contently emerging [2],[3],[4] and enable more complex algorithms to be implemented faster. Moreover, smart cameras which are embedding flexible and powerful multi-core processors or Graphic Processors Unit (GPU) are now available and can be considered as well as a solution to implement faster some complex image processing algorithms. The smart camera can be considered as a powerful sensor which enables very complex information to be extracted in real-time from the video scene. Using several cameras simultaneously and dealing with a multi-view configuration is even more challenging but enable more information to be available. Therefore, we present in this paper a platform, named WiseEye, to manage and experiment on a smart camera network based on low-cost multi-core processors. A network of low-cost multi-core processors has been deployed. We have already developed a framework to ease application development and debugging [5]. The framework aims to offer a high degree of flexibility for managing the tasks and the memory allocation. Hence, the framework enables the priority and the allocation of each task to be controlled. The image acquisition task can be completely independent from the other processing tasks. The framework includes an interface dedicated to the management of the tasks: the user can add or suppress a task during the runtime, logs or processing results can be visualised for each task. Smart cameras use a dedicated network configuration and service providing tool named pyM2SL (python Mesh and Multicast Services for Linux) which has been developed in le2i. pyM2SL allows dynamic application management and configuration from a master node on the network, and service deployment and discovery at runtime. Services can be anything from video stream to processing resources, each allocable according to the user's requirements. pyM2SL is a free software, publicly available [6] under AGPL v3 open source license. The viewer application has been designed using multi-platform libraries only, it is based on a Qt GUI. The received video streams can be decoded with a software decoder or with hardware to reduce the CPU usage. The video streaming is based on GStreamer which offers high performances (TCP or UDP protocols available) with very low latencies. We are currently investigating on the real-time implementation of complex image processing on this kind of hardware targets to provide extra services and security to the people living in an environment equipped with a smart camera network. Different targeted applications are then finally presented such as human tracking [7] for smart building management, control access based on a multi-modal approach, real-time fall detection [4] or recent remote physiological measurements (i.e. heart rate) based on video imaging [8]

Problèmes algorithmiques et de complexité dans les réseaux sans fil

The last couple of years have seen the advent of wireless networks, doped by their ease of deployment and their use in multiple fields: personal WiFi networks, mobile telephony, ad hoc networks, sensors networks, ...The subject of this thesis relates to the study of algorithmic problems directly inspired by operating constraints which can be found in such networks. This manuscrit is divided into three parts.The first part of our work is devoted to the study of the problem of broadcasting a single source node message to all the other nodes of a network. This problem is tackled in various communication models. All the considered model suppose range-fixed omnidirectional transmissions subject to interference phenomena. It results from that, that any given node is unable to retrieve simultaneously two incoming transmissions. We study the complexity of this problem and propose some strategies in order to solve it.In a second part, We study another algorithmic problem in the same communication model, whose object is to satisfy a given set of communication requests. Our work consists in etablishing the complexity of this problem, and studying the impact of various factors on this complexity.The last part considers the problem of designing survivable radio networks . The objective is to ensure a distribution of bandwidth from source nodes to customers nodes, by minimizing the cost of the deployed infrastructure. Communications are made via directional antennas, and are not subjects to interferences. The difficulty of the problem lies in the satisfaction of deployment constraints (limited number of antennas per node, robustness against failures of nodes, ...). We study the complexity of this problem, and propose exact and approximated resolution methods to solve reasonable size instances.Ces dernières années ont connu l'avènement des réseaux sans fil, dopés par leur facilité de déploiement et par leur usage dans de multiples domaines : réseaux domestiques Wi-Fi, téléphonie mobile, réseaux ad-hoc, réseaux de capteurs, ... L'objet de cette thèse porte sur l'étude de problèmes algorithmiques directement inspirés des contraintes de fonctionnement rencontrées dans de tels réseaux, et se découpe en trois parties.La première partie de nos travaux s'intéresse à l'étude du problème de la diffusion d'un message émis depuis un noeud source unique vers l'ensemble des noeuds participant au réseau. Ce problème est abordé dans plusieurs modèles de communication, qui supposent tous des émissions omnidirectionnelles à portée fixée et l'existence de phénomènes d'interférences. Il en résulte l'incapacité pour un noeud donné de garantir la réception correcte de deux transmissions voisines simultanées. Nous étudions la complexité de ce problème et proposons des stratégies de résolution exactes ou avec garantie de performance. Dans une seconde partie, l'un des modèles de communication précédemment introduits sert de support à l'étude d'un autre problème algorithmique, dont l'objet est la satisfaction de requêtes de communications. Les travaux menés sur ce problème visent à établir sa complexité ainsi que les facteurs dont elle dépend. La dernière partie nous amène au problème de conception de réseaux sans fil. L'objectif est d'assurer une distribution de flux depuis des noeuds sources vers des noeuds clients, en minimisant le coût de l'infrastructure déployée. Les communications établies ici à l'aide d'antennes directionnelles ne sont pas sujettes aux phénomènes d'interférences. La difficulté du problème réside dans la satisfaction de contraintes de déploiement (nombre d'antennes limitées par noeud, résistance aux pannes, ...). Nous étudions la complexité de ce problème, et proposons plusieurs méthodes de résolution exactes et approchées pour des instances de taille raisonnable

Network Optimization INOC 2019: 9th International Network Optimization Conference Avignon, France, June 12–14, 2019 Proceedings

International audienc