39 research outputs found
Joint Routing and STDMA-based Scheduling to Minimize Delays in Grid Wireless Sensor Networks
In this report, we study the issue of delay optimization and energy
efficiency in grid wireless sensor networks (WSNs). We focus on STDMA (Spatial
Reuse TDMA)) scheduling, where a predefined cycle is repeated, and where each
node has fixed transmission opportunities during specific slots (defined by
colors). We assume a STDMA algorithm that takes advantage of the regularity of
grid topology to also provide a spatially periodic coloring ("tiling" of the
same color pattern). In this setting, the key challenges are: 1) minimizing the
average routing delay by ordering the slots in the cycle 2) being energy
efficient. Our work follows two directions: first, the baseline performance is
evaluated when nothing specific is done and the colors are randomly ordered in
the STDMA cycle. Then, we propose a solution, ORCHID that deliberately
constructs an efficient STDMA schedule. It proceeds in two steps. In the first
step, ORCHID starts form a colored grid and builds a hierarchical routing based
on these colors. In the second step, ORCHID builds a color ordering, by
considering jointly both routing and scheduling so as to ensure that any node
will reach a sink in a single STDMA cycle. We study the performance of these
solutions by means of simulations and modeling. Results show the excellent
performance of ORCHID in terms of delays and energy compared to a shortest path
routing that uses the delay as a heuristic. We also present the adaptation of
ORCHID to general networks under the SINR interference model
TRASA: TRaffic Aware Slot Assignment Algorithm in Wireless Sensor Networks
International audienceIn data gathering applications which is a typical application paradigm in wireless sensor networks, sensor nodes may have different traffic demands. Assigning equal channel access to each node may lead to congestion, inefficient use of the bandwidth and decrease of the application performance. In this paper, we prove that the time slot assignment problem is NP-complete when p-hop nodes are not assigned the same slot, with 1 <= p <= h for any strictly positive integer h. We propose TRASA, a TRaffic Aware time Slot Assignment algorithm able to allocate slots to sensors proportionally to their demand. We evaluate the performance of TRASA for different heuristics and prove that it provides an optimized spatial reuse and a minimized cycle length
OSERENA, an Optimized Coloring Algorithm for Dense or Large Scale Wireless Networks
The goal of this research report is to present OSERENA "Optimized SchEduling
RoutEr Node Activity", a distributed coloring algorithm optimized for dense
wireless networks. Network density has an extremely reduced impact on the size
of the messages exchanged to color the network. Furthermore, the number of
colors used to color the network is not impacted by this optimization. We
describe in this research report the properties of the algorithm and prove its
correctness and termination. Simulation results point out the considerable
gains in bandwidth.Comment: No. RR-7785 (2011
On the Coloring of Grid Wireless Sensor Networks: the Vector-Based Coloring Method
Graph coloring is used in wireless networks to optimize network resources:
bandwidth and energy. Nodes access the medium according to their color. It is
the responsibility of the coloring algorithm to ensure that interfering nodes
do not have the same color. In this research report, we focus on wireless
sensor networks with grid topologies. How does a coloring algorithm take
advantage of the regularity of grid topology to provide an optimal periodic
coloring, that is a coloring with the minimum number of colors? We propose the
Vector-Based Coloring Method, denoted VCM, a new method that is able to provide
an optimal periodic coloring for any radio transmission range and for any h-hop
coloring, h>=1. This method consists in determining at which grid nodes a color
can be reproduced without creating interferences between these nodes while
minimizing the number of colors used. We compare the number of colors provided
by VCM with the number of colors obtained by a distributed coloring algorithm
with line and column priority assignments. We also provide bounds on the number
of colors of optimal general colorings of the infinite grid, and show that
periodic colorings (and thus VCM) are asymptotically optimal. Finally, we
discuss the applicability of this method to a real wireless network
Node Coloring in Wireless Networks: Complexity Results and Grid Coloring
International audienceColoring is used in wireless networks to improve communication efficiency, mainly in terms of bandwidth, energy and possibly end-to-end delays. In this paper, we define the h-hop node coloring problem, with h any positive integer, adapted to two types of applications in wireless networks. We specify both general mode for general applications and strategic mode for data gathering applications.We prove that the associated decision problem is NP-complete. We then focus on grid topologies that constitute regular topologies for large or dense wireless networks. We consider various transmission ranges and identify a color pattern that can be reproduced to color the whole grid with the optimal number of colors. We obtain an optimal periodic coloring of the grid for the considered transmission range. We then present a 3-hop distributed coloring algorithm, called SERENA. Through simulation results, we highlight the impact of node priority assignment on the number of colors obtained for any network and grids in particular. We then compare these optimal results on grids with those obtained by SERENA and identify directions to improve SERENA
Delay Optimized Time Slot Assignment for Data Gathering Applications in Wireless Sensor Networks
International audienceWireless sensor networks, WSNs, are an efficient way to deal with low-rate communications in confined environments such as mines or nuclear power plants because of their simplicity of deployment and low cost. In these application domains, WSNs are used to gather data from sensor nodes towards a sink in a multi-hop convergecast structure. In this paper, we focus on a traffic-aware time slot assignment minimizing the schedule length for tree topologies and for two special deployments (i.e. linear and multi-linear) representative of unusual environments. We formalize the problem as a linear program and provide results on the optimal number of slots. We then propose a delay optimized algorithm with two heuristics that minimize on the one hand the energy consumption and on the other hand the storage capacity as secondary criteria
Network coding in military wireless ad hoc and sensor networks: Experimentation with GardiNet
International audienceNetwork coding is a communication paradigm that allows intermediate nodes to mix packets instead of simply relaying them. Motivated by applications in military tactical networks, this paper explores the use of the network coding. It has been proved that network coding has many benefits in wireless communications such as optimal capacity achievement and packet loss recovery. In this paper, we present a generic architecture for network coding for broadcast in wireless networks called GardiNet. GardiNet is generic; its design is divided into building blocks in order to enable it to adapt to different application scenarios. In this paper, we start by describing GardiNet for wireless ad hoc networks and in particular for wireless sensor networks (WSNs). Then, we present experiment results of GardiNet in FIT IoT-LAB, a real testbed of WSNs. Results show that network coding performs well under real wireless conditions. In addition, we highlight the benefit of the Sliding Encoding Window scheme of GardiNet (SEW) to allow sensors to decode packets in real time
UAV search path planning for livestock monitoring
International audienceUnmanned Aerial Vehicles (UAVs) are being extensively deployed in numerous Livestock Management applications such as cattle disease diagnosis, counting and behavioral monitoring from videos and images captured by drones.The paper focuses on one increasingly important family of applications, UAV-assisted cattle monitoring applications where the objective is to remotely acquire some health state information from IoT nodes attached to the herding cattle. Such livestock data acquisition applications have many challenges. One of these challenges, which is the focus of this paper, is the problem that the target cattle position may not be known precisely, and might be defined with a large area. To address this issue, we design a formulation of this UAV-cattle search path problem as a mathematical optimization problem and show how it can be derived from other well-known formulation and related literature. A Mixed-Integer linear Programming (MILP) formulation is introduced to minimize the expected search time while covering all the search area to efficiently locate the animal. This formulation exploits a cattle position probability distribution map. The results show that the suggested approach yields excellent results using the existing MILP solvers
Ordonnancement de l'activité des noeuds dans les réseaux ad hoc et les réseaux de capteurs sans fil
National audienceL'efficacité énergétique est une exigence majeure pour les réseaux sans fil où certains noeuds opèrent sur batterie. L'ordonnancement de l'activité des noeuds permet de distinguer périodes actives où la communication radio est possible et périodes inactives où la radio est arrêtée. Cet ordonnancement contribue largement à améliorer l'efficacité énergétique : d'une part en évitant les collisions entre transmissions conflictuelles et donc les retransmissions associées et d'autre part en permettant aux noeuds non concernés par la transmission de dormir pour économiser leur énergie. Parmi les solutions possibles, nous étudierons plus particulièrement le coloriage des noeuds. Après avoir défini le problème et ses différentes déclinaisons, nous donnerons sa complexité et proposerons SERENA, un algorithme de coloriage distribué qui s'adapte à la collecte de données. Nous présenterons OSERENA, l'optimisation de SERENA pour les réseaux denses et son utilisation dans le réseau de capteurs sans fil OCARI. Lorsque les noeuds ont des charges de trafic fortement hétérogènes, il devient plus intéressant d'effectuer une assignation de slots. Disposer d'un accès au médium multicanal et d'un puits multi-interfaces permet de gagner en nombre de slots nécessaires à la collecte de données, de réduire les interférences et d'améliorer la résistance aux perturbations. Nous présenterons une formalisation en ILP (Integer Linear Programming) du problème d'assignation de slots visant à minimiser le nombre de slots en profitant d'un environnement mono ou multicanal et d'un puits mono ou multi-interfaces. Nous donnerons des bornes théoriques sur le nombre optimal de slots dans diverses configurations et divers environnements (mono ou multicanal, puits mono ou multi-interfaces). Nous présenterons MODESA un algorithme centralisé d'allocatoion conjointe de canaux et slots temporels. Nous terminerons par quelques questions ouvertes