Using Node Combination Method in Time-expanded Networks

This study concerns the problem of finding shortest paths in time-expanded networks by repeatedly combining the source nodes nearest neighbor, time-expanded network is derived from dynamic network G= (V,A,T) and contains one copy of the node set of the underlying static network for each discrete time step (building a time layer). we use node combination (NC) method in networks which arc costs can vary with time, each arc has a transit time and parking with a corresponding time-varying cost is allowed at the nodes. The NC algorithm finds the shortest paths with three simple iterative steps: find the nearest neighbor of the source node, combine that node with the source node, and modify the costs on arcs that connect to the nearest neighbor. The NC algorithm is more comprehensible and convenient for programming as there is no need to maintain a set with the nodes distances

Finding the Shortest Path in Dynamic Network using Labeling Algorithm

Abstract This study concerns the problem of finding shortest paths from one node to all other nodes in networks for which arc costs can vary with time, each arc has a transit time and parking with a corresponding time-varying cost is allowed at the nodes. it show that this problem is equivalent to a classical shortest path problem in a timeexpanded network. The label correcting algorithm is used for finding shortest paths. Keywords: Dynamic shortest paths, time-expanded network, label correcting algorithm. Introduction In congested transportation networks, arc travel times change over time due to time-of-day variations in traffic congestion. Even if one can account for these time-of-day variations, future travel times can at best be known a priori with uncertainty due to unforeseen events, such as poor roadway conditions, vehicle breakdowns, traffic accidents, and driver behavior. In this work, we develop path search techniques that explicitly consider the inherent time-varying nature of future travel times. Recent studies have focused on time-dependent graphs Review of the shortest path proble

Shortest-path and minimumdelay algorithms in networks with time-dependent edge-length

We consider in this paper the shortest-path problem in networks in which the delay (or weight) of the edges changes with time according to arbitrary functions. We present algorithms for finding the shortest-path and minimum-delay under various waiting constraints and investigate the properties of the derived path. We show that if departure time from the source node is unrestricted then a shortest path can be found that is simple and achieves a delay as short as the most unrestricted path. In the case of restricted transit, it is shown that there exist cases where the minimum delay is finite but the path that achieves it is infinite

Distributed Shortest-Path Protocols For Time-Dependent Networks

This paper addresses algorithms for networks whose behavior changes with time according to known functions. Because the computation depends on the the same functions it attempts to compute, its execution must obey strict timing constraints. When distributed versions of such algorithms are considered, a key difficulty is how to transfer local timing functions among the participating nodes. To that end it is necessary to characterize the parameterization of the functions and accommodate this parameterization in the computation. In particular, we consider the shortest-path problem in networks in which the delay of the edges changes with time according to continuous functions. We present distributed protocols for finding the shortest and minimum delay path under various waiting constraints. We investigate and analyze protocols that exchange local time-delay functions only within limited intervals yet allow every node to calculate its representation in the shortest path in time for it to be..

Réseaux de capteurs sans fil étendus dédiés aux collectes de données environnementales

Wireless sensor networks are used in many environmental monitoring applications (e.g., to monitor forest fires or volcanoes). In such applications, sensor nodes have a limited quantity of energy, but must operate for years without having their batteries changed. The main mechanism used to allow nodes to save energy is to sequence periods of activity and inactivity. However, the design of MAC and routing protocols for applications with low duty-cycle is still a challenge. In this thesis, we proposed unsynchronized MAC and routing protocols for wireless sensor networks devoted to environmental monitoring applications. The main specificity of our protocols is that they are adapted to very low duty-cycle (less than 1 % for all nodes). Our protocols are analyzed and compared to existing protocols by simulation and experimentation on TelosB nodes. Despite this low duty-cycle for all nodes, our protocols are able to achieve good performance, unlike other protocols in the literature, which are not adapted to these extreme conditions.Les réseaux de capteurs sans fil sont utilisés dans de nombreuses applications de surveillance de l’environnement (par exemple, pour surveiller les volcans ou pour détecter les incendies de forêts). Dans de telles applications, les nœuds capteurs disposent d’une quantité limitée d’énergie, mais doivent fonctionner pendant des années sans avoir leurs batteries changées. La principale méthode utilisée pour permettre aux nœuds d’économiser leur énergie est de séquencer les périodes d’activité et d’inactivité. Cependant, la conception de protocoles MAC et de routage pour les applications avec des taux d’activité faibles est un défi. Dans cette thèse nous proposons des protocoles MAC avec de très faibles taux d’activité (moins de 1% d’activité) et des protocoles de routages adaptés pour des réseaux de capteurs sans fil dédiés aux applications de surveillance environnementale. Nos protocoles sont analysés et comparés aux protocoles existants par simulation et par expérimentation sur des nœuds TelosB. Malgré un taux d’activité très faible pour tous les nœuds, nos protocoles sont capables d’obtenir de bonnes performances, contrairement aux autres protocoles de la littérature, qui ne sont pas adaptés à opérer avec de faibles taux d’activité