A Self-Organization Framework for Wireless Ad Hoc Networks as Small Worlds

Motivated by the benefits of small world networks, we propose a self-organization framework for wireless ad hoc networks. We investigate the use of directional beamforming for creating long-range short cuts between nodes. Using simulation results for randomized beamforming as a guideline, we identify crucial design issues for algorithm design. Our results show that, while significant path length reduction is achievable, this is accompanied by the problem of asymmetric paths between nodes. Subsequently, we propose a distributed algorithm for small world creation that achieves path length reduction while maintaining connectivity. We define a new centrality measure that estimates the structural importance of nodes based on traffic flow in the network, which is used to identify the optimum nodes for beamforming. We show, using simulations, that this leads to significant reduction in path length while maintaining connectivity.Comment: Submitted to IEEE Transactions on Vehicular Technolog

Connectivity of confined 3D Networks with Anisotropically Radiating Nodes

Nodes in ad hoc networks with randomly oriented directional antenna patterns typically have fewer short links and more long links which can bridge together otherwise isolated subnetworks. This network feature is known to improve overall connectivity in 2D random networks operating at low channel path loss. To this end, we advance recently established results to obtain analytic expressions for the mean degree of 3D networks for simple but practical anisotropic gain profiles, including those of patch, dipole and end-fire array antennas. Our analysis reveals that for homogeneous systems (i.e. neglecting boundary effects) directional radiation patterns are superior to the isotropic case only when the path loss exponent is less than the spatial dimension. Moreover, we establish that ad hoc networks utilizing directional transmit and isotropic receive antennas (or vice versa) are always sub-optimally connected regardless of the environment path loss. We extend our analysis to investigate boundary effects in inhomogeneous systems, and study the geometrical reasons why directional radiating nodes are at a disadvantage to isotropic ones. Finally, we discuss multi-directional gain patterns consisting of many equally spaced lobes which could be used to mitigate boundary effects and improve overall network connectivity.Comment: 12 pages, 10 figure

Energy Efficient Wireless Sensor Network Modelling Based on Complex Networks

The power consumption and energy efficiency of wireless sensor network are the significant problems in Internet of Things network. In this paper, we consider the network topology optimization based on complex network theory to solve the energy efficiency problem of WSN. We propose the energy efficient model of WSN according to the basic principle of small world from complex networks. Small world network has clustering features that are similar to that of the rules of the network but also has similarity to random networks of small average path length. It can be utilized to optimize the energy efficiency of the whole network. Optimal number of multiple sink nodes of the WSN topology is proposed for optimizing energy efficiency. Then, the hierarchical clustering analysis is applied to implement this clustering of the sensor nodes and pick up the sink nodes from the sensor nodes as the clustering head. Meanwhile, the update method is proposed to determine the sink node when the death of certain sink node happened which can cause the paralysis of network. Simulation results verify the energy efficiency of the proposed model and validate the updating of the sink nodes to ensure the normal operation of the WSN

Vers une amélioration de la diffusion des informations dans les réseaux sans-fils

Dans les systèmes d'alertes publiques, l étude de la diffusion des informations dans le réseau est essentielle. Les systèmes de diffusion des messages d'alertes doivent atteindre beaucoup de nœuds en peu de temps. Dans les réseaux de communication basés sur les interactions device to device , on s'est récemment beaucoup intéressé à la diffusion des informations et le besoin d'auto-organisation a été mis en évidence. L'auto-organisation conduit à des comportements locaux et des interactions qui ont un effet sur le réseau global et présentent un avantage de scalabilité. Ces réseaux auto-organisés peuvent être autonomes et utiliser peu d'espace mémoire. On peut développer des caractères auto-organisés dans les réseaux de communication en utilisant des idées venant de phénomènes naturels. Il semble intéressant de chercher à obtenir les propriétés des small world pour améliorer la diffusion des informations dans le réseau. Dans les modèles de small world on réalise un recâblage des liens dans le réseau en changeant la taille et la direction des liens existants. Dans un environnement sans-fils autonome une organisation de ce type peut être créée en utilisant le flocking, l'inhibition latérale et le beamforming . Dans ce but, l'auteur utilise d'abord l'analogie avec l'inhibition latérale, le flocking et le beamforming pour montrer comment la diffusion des informations peut être améliorée. L'analogue de l'inhibition latérale est utilisé pour créer des régions virtuelles dans le réseau. Puis en utilisant l'analogie avec les règles du flocking, on caractérise les propriétés des faisceaux permettant aux nœuds de communiquer dans les régions. Nous prouvons que les propriétés des small world sont vérifiées en utilisant la mesure des moyennes des longueurs des chemins. Cependant l'algorithme proposé est valable pour les réseaux statiques alors que dans les cas introduisant de la mobilité, les concepts d'inhibition latérale et de flocking nécessiteraient beaucoup plus de temps. Dans le cas d'un réseau mobile la structure du réseau change fréquemment. Certaines connexions intermittentes impactent fortement la diffusion des informations. L'auteur utilise le concept de stabilité avec le beamforming pour montrer comment on peut améliorer la diffusion des informations. Dans son algorithme il prévoit d'abord la stabilité du nœud en utilisant des informations locales et il utilise ce résultat pour identifier les nœuds qui réaliseront du beamforming. Dans l'algorithme, les nœuds de stabilité faible sont autorisés à faire du beamforming vers les nœuds de forte stabilité. La frontière entre forte et faible stabilité est fixée par un seuil. Cet algorithme ne nécessite pas une connaissance globale du réseau, mais utilise des données locales. Les résultats sont validés en étudiant le temps au bout duquel plus de nœuds reçoivent l'information et en comparant avec d'autres algorithmes de la littérature. Cependant, dans les réseaux réels, les changements de structure ne sont pas dus qu'à la mobilité, mais également à des changements de la densité des nœuds à un moment donné. Pour tenir compte de l'influence de tels événements sur la diffusion des informations concernant la sécurité publique, l'auteur utilise les concepts de modèle de métapopulation, épidémiologiques, beamforming et mobilité géographique obtenu à partir de données D4D. L'auteur propose la création de trois états latents qu'il ajoute au modèle épidémiologique connu: SIR. L'auteur étudie les états transitoires en analysant l'évolution du nombre de postes ayant reçu les informations et compare les résultats concernant ce nombre dans les différents cas. L'auteur démontre ainsi que le scenario qu'il propose permet d'améliorer le processus de diffusion des informations. Il montre aussi les effets de différents paramètres comme le nombre de sources, le nombre de paquets, les paramètres de mobilité et ceux qui caractérisent les antennes sur la diffusion des informationsIn public warning message systems, information dissemination across the network is a critical aspect that has to be addressed. Dissemination of warning messages should be such that it reaches as many nodes in the network in a short time. In communication networks those based on device to device interactions, dissemination of the information has lately picked up lot of interest and the need for self organization of the network has been brought up. Self organization leads to local behaviors and interactions that have global effects and helps in addressing scaling issues. The use of self organized features allows autonomous behavior with low memory usage. Some examples of self organization phenomenon that are observed in nature are Lateral Inhibition and Flocking. In order to provide self organized features to communication networks, insights from such naturally occurring phenomenon is used. Achieving small world properties is an attractive way to enhance information dissemination across the network. In small world model rewiring of links in the network is performed by altering the length and the direction of the existing links. In an autonomous wireless environment such organization can be achieved using self organized phenomenon like Lateral inhibition and Flocking and beamforming (a concept in communication). Towards this, we first use Lateral Inhibition, analogy to Flocking behavior and beamforming to show how dissemination of information can be enhanced. Lateral Inhibition is used to create virtual regions in the network. Then using the analogy of Flocking rules, beam properties of the nodes in the regions are set. We then prove that small world properties are achieved using average path length metric. However, the proposed algorithm is applicable to static networks and Flocking and Lateral Inhibition concepts, if used in a mobile scenario, will be highly complex in terms of computation and memory. In a mobile scenario such as human mobility aided networks, the network structure changes frequently. In such conditions dissemination of information is highly impacted as new connections are made and old ones are broken. We thus use stability concept in mobile networks with beamforming to show how information dissemination process can be enhanced. In the algorithm, we first predict the stability of a node in the mobile network using locally available information and then uses it to identify beamforming nodes. In the algorithm, the low stability nodes are allowed to beamform towards the nodes with high stability. The difference between high and low stability nodes is based on threshold value. The algorithm is developed such that it does not require any global knowledge about the network and works using only local information. The results are validated using how quickly more number of nodes receive the information and different state of the art algorithms. We also show the effect of various parameters such as number of sources, number of packets, mobility parameters and antenna parameters etc. on the information dissemination process in the network. In realistic scenarios however, the dynamicity in the network is not only related to mobility. Dynamic conditions also arise due to change in density of nodes at a given time. To address effect of such scenario on the dissemination of information related to public safety in a metapopulation, we use the concepts of epidemic model, beamforming and the countrywide mobility pattern extracted from the $D4D$ dataset. Here, we also propose the addition of three latent states to the existing epidemic model ($SIR$ model). We study the transient states towards the evolution of the number of devices having the information and the difference in the number of devices having the information when compared with different cases to evaluate the results. Through the results we show that enhancements in the dissemination process can be achieved in the addressed scenarioEVRY-INT (912282302) / SudocSudocFranceF

Contribution to the improvement of the performance of wireless mesh networks providing real time services

Nowadays, people expectations for ubiquitous connectivity is continuously growing. Cities are now moving towards the smart city paradigm. Electricity companies aims to become part of smart grids. Internet is no longer exclusive for humans, we now assume the Internet of everything. We consider that Wireless Mesh Networks (WMNs) have a set of valuable features that will make it an important part of such environments. WMNs can also be use in less favored areas thanks to their low-cost deployment. This is socially relevant since it facilitates the digital divide reduction and could help to improve the population quality of life. Research and industry have been working these years in open or proprietary mesh solutions. Standardization efforts and real deployments establish a solid starting point.We expect that WMNs will be a supporting part for an unlimited number of new applications from a variety of fields: community networking, intelligent transportation systems, health systems, public safety, disaster management, advanced metering, etc. For all these cases, the growing needs of users for real-time and multimedia information is currently evident. On this basis, this thesis proposes a set of contributions to improve the performance of an application service of such type and to promote the better use of two critical resources (memory and energy) of WMNs.For the offered service, this work focuses on a Video on Demand (VoD) system. One of the requirements of this system is the high capacity support. This is mainly achieved by distributing the video contents among various distribution points which in turn consist of several video servers. Each client request that arrives to such video server cluster must be handled by a specific server in a way that the load is balanced. For such task, this thesis proposes a mechanism to appropriately select a specific video server such that the transfer time at the cluster could be minimized.On the other hand, mesh routers that creates the mesh backbone are equipped with multiple interfaces from different technologies and channel types. An important resource is the amount of memory intended for buffers. The quality of service perceived by the users are largely affected by the size of such buffers. This is because important network performance parameters such as packet loss probability, delay, and channel utilization are highly affected by the buffer sizes. An efficient use of memory for buffering, in addition to facilitate the mesh devices scalability, also prevents the problems associated with excessively large buffers. Most of the current works associate the buffer sizing problem with the dynamics of TCP congestion control mechanism. Since this work focuses on real time services, in which the use of TCP is unfeasible, this thesis proposes a dynamic buffer sizing mechanism mainly dedicated for such real time flows. The approach is based on the maximum entropy principle and allows that each device be able to dynamically self-configure its buffers to achieve more efficient memory utilization. The proper performance of the proposal has been extensively evaluated in wired and wireless interfaces. Classical infrastructure-based wireless and multi-hop mesh interfaces have been considered. Finally, when the WMN is built by the interconnection of user hand-helds, energy is a limited and scarce resource, and therefore any approach to optimize its use is valuable. For this case, this thesis proposes a topology control mechanism based on centrality metrics. The main idea is that, instead of having all the devices executing routing functionalities, just a subset of nodes are selected for this task. We evaluate different centralities, form both centralized and distributed perspectives. In addition to the common random mobility models we include the analysis of the proposal with a socially-aware mobility model that generates networks with a community structure.Actualmente las expectativas de las personas de una conectividad ubicua están creciendo. Las ciudades están trabajando para alcanzar el paradigma de ciudades inteligentes. Internet ha dejado de ser exclusivo de las personas y ahora se asume el Internet de todo. Las redes inalámbricas de malla (WMNs) poseen un valioso conjunto de características que las harán parte importante de tales entornos. Las WMNs pueden utilizarse en zonas menos favorecidas debido a su despliegue económico. Esto es socialmente relevante ya que facilita la reducción de la brecha digital y puede ayudar a mejorar la calidad de vida de la población. Los esfuerzos de estandarización y los despliegues de redes reales establecen un punto de partida sólido.Se espera entonces, que las WMNs den soporte a un número importante de nuevas aplicaciones y servicios, de una variedad de campos: redes comunitarias, sistemas de transporte inteligente, sistemas de salud y seguridad, operaciones de rescate y de emergencia, etc. En todos estos casos, es evidente la necesidad de disponer de información multimedia y en tiempo real. En base a estos precedentes, esta tesis propone un conjunto de contribuciones para mejorar el funcionamiento de un servicio de este tipo y promover un uso eficiente de dos recursos críticos (memoria y energía) de las WMNs.Para el servicio ofrecido, este trabajo se centra en un sistema de video bajo demanda. Uno de los requisitos de estos sistemas es el de soportar capacidades elevadas. Esto se consigue principalmente distribuyendo los contenidos de video entre diferentes puntos de distribución, los cuales a su vez están formados por varios servidores. Cada solicitud de un cliente que llega a dicho conjunto de servidores debe ser manejada por un servidor específico, de tal forma que la carga sea balanceada. Para esta tarea, esta tesis propone un mecanismo que selecciona apropiadamente un servidor de tal manera que el tiempo de transferencia del sistema sea minimizado.Por su parte, los enrutadores de malla que crean la red troncal están equipados con múltiples interfaces de diferentes tecnologías y tipos de canal. Un recurso muy importante para éstos es la memoria destinada a sus colas. La calidad de servicio percibida por los usuarios está altamente influenciada por el tamaño de las colas. Esto porque parámetros importantes del rendimiento de la red como la probabilidad de pérdida de paquetes, el retardo, y la utilización del canal se ven afectados por dicho tamaño. Un uso eficiente de tal memoria, a más de facilitar la escalabilidad de los equipos, también evita los problemas asociados a colas muy largas. La mayoría de los trabajos actuales asocian el problema de dimensionamiento de las colas con la dinámica del mecanismo de control de congestión de TCP. Debido a que este trabajo se enfoca en servicios en tiempo real, en los cuales no es factible usar TCP, esta tesis propone un mecanismo de dimensionamiento dinámico de colas dedicado principalmente a flujos en tiempo real. La propuesta está basada en el principio de máxima entropía y permite que los dispositivos sean capaces de auto-configurar sus colas y así lograr un uso más eficiente de la memoria. Finalmente, cuando la WMN se construye a través de la interconexión de los dispositivos portátiles, la energía es un recurso limitado y escaso, y cualquier propuesta para optimizar su uso es muy valorada. Para esto, esta tesis propone un mecanismo de control de topología basado en métricas de centralidad. La idea principal es que en lugar de que todos los dispositivos realicen funciones de enrutamiento, solo un subconjunto de nodos es seleccionado para esta tarea. Se evalúan diferentes métricas, desde una perspectiva centralizada y otra distribuida. A más de los modelos aleatorios clásicos de movilidad, se incluye el análisis de la propuesta con modelos de movilidad basados en información social que toman en cuenta el comportamiento humano y generan redes con una clara estructura de comunidade