Performance improvement of ad hoc networks using directional antennas and power control

Au cours de la dernière décennie, un intérêt remarquable a été éprouvé en matière des réseaux ad hoc sans fil capables de s'organiser sans soutien des infrastructures. L'utilisation potentielle d'un tel réseau existe dans de nombreux scénarios, qui vont du génie civil et secours en cas de catastrophes aux réseaux de capteurs et applications militaires. La Fonction de coordination distribuée (DCF) du standard IEEE 802.11 est le protocole dominant des réseaux ad hoc sans fil. Cependant, la méthode DCF n'aide pas à profiter efficacement du canal partagé et éprouve de divers problèmes tels que le problème de terminal exposé et de terminal caché. Par conséquent, au cours des dernières années, de différentes méthodes ont été développées en vue de régler ces problèmes, ce qui a entraîné la croissance de débits d'ensemble des réseaux. Ces méthodes englobent essentiellement la mise au point de seuil de détecteur de porteuse, le remplacement des antennes omnidirectionnelles par des antennes directionnelles et le contrôle de puissance pour émettre des paquets adéquatement. Comparées avec les antennes omnidirectionnelles, les antennes directionnelles ont de nombreux avantages et peuvent améliorer la performance des réseaux ad hoc. Ces antennes ne fixent leurs énergies qu'envers la direction cible et ont une portée d'émission et de réception plus large avec la même somme de puissance. Cette particularité peut être exploitée pour ajuster la puissance d'un transmetteur en cas d'utilisation d'une antenne directionnelle. Certains protocoles de contrôle de puissance directionnel MAC ont été proposés dans les documentations. La majorité de ces suggestions prennent seulement la transmission directionnelle en considération et, dans leurs résultats de simulation, ces études ont l'habitude de supposer que la portée de transmission des antennes omnidirectionnelles et directionnelles est la même. Apparemment, cette supposition n'est pas toujours vraie dans les situations réelles. De surcroît, les recherches prenant l'hétérogénéité en compte dans les réseaux ad hoc ne sont pas suffisantes. Le présent mémoire est dédié à proposer un protocole de contrôle de puissance MAC pour les réseaux ad hoc avec des antennes directionnelles en prenant tous ces problèmes en considération. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Réseaux ad hoc, Antennes directives, Contrôle de puissance

Impact of directional antennas on routing and neighbor discovery in wireless ad-hoc networks

Wireless ad-hoc networks are data networks that are deployed without a fixed infrastructure nor central controllers such as access points or base stations. In these networks, data packets are forwarded directly to the destination node if they are within the transmission range of the sender or sent through a multi-hop path of intermediary nodes that act as relays. This paradigm where a fixed infrastructure is not needed, is tolerant to topology changes and allows a fast deployment have been considered as a promissory technology that is suitable for a large number of network implementations, such as mobile hand-held devices, wireless sensors, disaster recovery networks, etc. Recently, smart directional antennas have been identified as a robust technology that can boost the performance of wireless ad-hoc networks in terms of coverage, connectivity, and capacity. Contrary to omnidirectional antennas, which can radiate energy in all directions, directional antennas can focus the energy in a specific direction, extending the coverage range for the same power level. Longer ranges provide shorter paths to destination nodes and also improve connectivity. Moreover, directional antennas can reduce the number of collisions in a contention-based access scheme as they can steer the main lobe in the desired direction and set nulls in all the others, thereby they minimize the co-channel interference and reduce the noise level. Connections are more reliable due to the increased link stability and spatial diversity. Shorter paths, as well as alternative paths, are also available as a consequence of the use of directional antennas. All these features combined results in a higher network capacity. Most of the previous research has focused on adapting the existing medium access control and routing protocols to utilize directional communications. This research work is novel because it improves the neighbor discovery process as it allows to discover nodes in the second neighborhood of a given node using a gossip based procedure and by sharing the relative position information obtained during this stage with the routing protocol with the aim of reducing the number of hops between source and destination. We have also developed a model to evaluate the energy consumed by the nodes when smart directional antennas are used in the ad-hoc network. This study has demonstrated that by adapting the beamwidth of the antennas nodes are able to reach furthest nodes and consequently, reduce the number of hops between source and destination. This fact not only reduces the end-to-end delay and improves the network throughput but also reduces the average energy consumed by the whole network

Layer 2 Path Selection Protocol for Wireless Mesh Networks with Smart Antennas

In this thesis the possibilities of smart antenna systems in wireless mesh networks are examined. With respect to the individual smart antenna tradeoffs, a routing protocol (Modified HWMP, MHWMP) for IEEE 802.11s mesh networks is presented, that exploits the full range of benefits provided by smart antennas: MHWMP actively switches between the PHY-layer transmission/reception modes (multiplexing, beamforming and diversity) according to the wireless channel conditions. Spatial multiplexing and beamforming are used for unicast data transmissions, while antenna diversity is employed for efficient broadcasts. To adapt to the directional channel environment and to take full benefit of the PHY capabilities, a respective MAC scheme is employed. The presented protocol is tested in extensive simulation and the results are examined.:1 Introduction 2 Wireless Mesh Networks 3 IEEE 802.11s 4 Smart Antenna Concepts 5 State of the Art: Wireless Mesh Networks with Smart Antennas 6 New Concepts 7 System Model 8 Results and Discussion 9 Conclusion and Future Wor

Development of an efficient Ad Hoc broadcasting scheme for critical networking environments

Mobile ad hoc network has been widely deployed in support of the communications in hostile environment without conventional networking infrastructure, especially in the environments with critical conditions such as emergency rescue activities in burning building or earth quick evacuation. However, most of the existing ad hoc based broadcasting schemes either rely on GPS location or topology information or angle-of-arrival (AoA) calculation or combination of some or all to achieve high reachability. Therefore, these broadcasting schemes cannot be directly used in critical environments such as battlefield, sensor networks and natural disasters due to lack of node location and topology information in such critical environments. This research work first begins by analyzing the broadcast coverage problem and node displacement form ideal locations problem in ad hoc networks using theoretical analysis. Then, this research work proposes an efficient broadcast relaying scheme, called Random Directional Broadcasting Relay (RDBR), which greatly reduces the number of retransmitting nodes and end-to-end delay while achieving high reachability. This is done by selecting a subset of neighboring nodes to relay the packet using directional antennas without relying on node location, network topology and complex angle-of-arrival (AoA) calculations. To further improve the performance of the RDBR scheme in complex environments with high node density, high node mobility and high traffic rate, an improved RDBR scheme is proposed. The improved RDBR scheme utilizes the concept of gaps between neighboring sectors to minimize the overlap between selected relaying nodes in high density environments. The concept of gaps greatly reduces both contention and collision and at the same time achieves high reachability. The performance of the proposed RDBR schemes has been evaluated by comparing them against flooding and Distance-based schemes. Simulation results show that both proposed RDBR schemes achieve high reachability while reducing the number of retransmitting nodes and end-to-end delay especially in high density environments. Furthermore, the improved RDBR scheme achieves better performance than RDBR in high density and high traffic environment in terms of reachability, end-to-end delay and the number of retransmitting nodes

The 30/20 GHz communications system functional requirements

The characteristics of 30/20 GHz usage in satellite systems to be used in support of projected communication requirements of the 1990's are defined. A requirements analysis which develops projected market demand for satellite services by general and specialized carriers and an analysis of the impact of propagation and system constraints on 30/20 GHz operation are included. A set of technical performance characteristics for the 30/20 GHz systems which can serve the resulting market demand and the experimental program necessary to verify technical and operational aspects of the proposed systems is also discussed

A Location Routing Protocol Based on Smart Antennas for Wireless Sensor Networks

RÉSUMÉ Les réseaux de capteurs sans fil sont une technologie émergente pour la surveillance de l’environnement. Un réseau de capteurs typique se compose d'un grand nombre de capteurs miniatures (noeuds) multifonctionnels, à faible coût et à faible consommation d’énergie, équipés d’un radio émetteur-récepteur et d’un ensemble de transducteurs pour récolter et transmettre des données environnementales d'une manière autonome. Une des contraintes les plus importantes de capteurs est la nécessitée d’économiser de l’énergie puisqu’ils utilisent des batteries de duré limitée, généralement irremplaçables. En outre, ils se caractérisent également par une faible vitesse de traitement, capacité de stockage et de bande passante, qui nécessite une gestion des ressources très attentive. En raison des limitations et caractéristiques inhérentes aux capteurs, le routage dans les réseaux de capteurs sans fil suppose un vrai défi. La tâche de trouver et de maintenir des routes n'est pas triviale étant donné les restrictions d'énergie et les changements soudains dans l'état des noeuds (exemple: mal-fonctionnement) qui entrainent des changements fréquents et imprévisibles dans la structure topologique. Ce travail présente LBRA, un nouveau protocole de routage géolocalisé qui utilise des antennes intelligentes pour estimer les positions des noeuds dans le réseau, et qui base les décisions de routage sur l’état de connexion des voisins et leur position relative. L'objectif principal de LBRA est d'éliminer le trafic de contrôle du réseau autant que possible. Pour atteindre cet objectif, l'algorithme emploie la position locale pour prendre des décisions de routage, met en oeuvre un nouveau mécanisme pour recueillir les informations de localisation et utilise seulement les noeuds impliqués dans la route pour faire la synchronisation des données de positionnement. De plus, le protocole considère le niveau de la batterie au moment de prendre des décisions de routage afin de balancer la dépense d’énergie du réseau. LBRA est une version améliorée du routage de ZigBee (norme actuelle pour les réseaux à faible coût et à faible consommation d’énergie) qui se base, lui aussi, sur AODV. Afin d'évaluer dans quelle mesure LBRA représente vraiment une amélioration par rapport au routage de ZigBee, une série de simulations a été effectué à l'aide du logiciel Network Simulator (ns). Les deux protocoles ont été implantés dans le simulateur. Les performances ont été comparées dans une variété de scenarios, dans des conditions différentes tels que les charges de trafic, les tailles de réseau et les conditions de mobilité. Les résultats des expériences ont montré que LBRA réussi à réduire le trafic de contrôle et la charge de routage, tout en améliorant le taux de livraison des paquets, à la fois pour les réseaux fixes et les réseaux mobiles. L'abaissement de l'alimentation du réseau est aussi plus équilibré, puisque les décisions de routage sont prises en fonction du niveau de la batterie des noeuds.----------ABSTRACT Wireless sensor networks are an emerging technology for environmental monitoring. A typical sensor network is composed of a large number of low-cost, low-power, multi-functional miniature sensor devices (nodes) equipped with a radio transceiver and a set of transducers utilized to acquire information about the surrounding environment. One of the most important constraints of sensor nodes is the low power consumption requirement since they carry limited, generally irreplaceable, batteries. In addition, they are also characterized by scarce processing speed, storage capacity and communication bandwidth, thus requiring careful resource management. Due to the inherent characteristics and restrictions of sensor nodes, routing in WSNs is very challenging. The task of finding and maintaining routes is nontrivial since energy restrictions and sudden changes in node status (e.g. failure) cause frequent and unpredictable topological changes. This work introduces a novel location routing protocol that uses smart antennas to estimate nodes positions into the network and to deliver information basing routing decisions on neighbour’s status connection and relative position, named LBRA. The main purpose of LBRA is to eliminate network control overhead as much as possible. To achieve this goal, the algorithm employs local position for route decision, implements a novel mechanism to collect the location information and involves only route participants in the synchronization of location information. In addition, the protocol uses node battery information to make power aware routing decisions. LBRA is an enhanced version of the ZigBee routing, which is the current standard for reliable, cost-effective and low power wireless networking, and like the latter is prototyped from AODV. In order to asses to what extent LBRA truly represents an improvement with respect to the ZigBee routing, a series of simulations were designed with the help of the Network Simulator (ns). Basically, both protocols were implemented in the simulator and its performance was compared in a variety of traffic load, network size and mobility conditions. The experiment results showed that LBRA succeed in reducing the control overhead and the routing load, improving the packet delivery rate for both static and mobile networks. Additionally, network power depletion is more balanced, since routing decisions are made depending on nodes’ battery level

Adaptation of the IEEE 802.11 protocol for inter-satellite links in LEO satellite networks

Knowledge of the coefficient of thermal expansion (CTE) of a ceramic material is important in many application areas. Whilst the CTE can be measured, it would be useful to be able to predict the expansion behaviour of multiphase materials.. There are several models for the CTE, however, most require a knowledge of the elastic properties of the constituent phases and do not take account ofthe microstructural features of the material. If the CTE could be predicted on the basis of microstructural information, this would then lead to the ability to engineer the microstructure of multiphase ceramic materials to produce acceptable thermal expansion behaviour. To investigate this possibility, magnesia-magnesium aluminate sp~el (MMAS) composites, consisting of a magnesia matrix and magnesium aluminate s~ne'l (MAS) particles, were studied. Having determined a procedure to produce MAS fr alumina and magnesia, via solid state sintering, magnesia-rich compositions wit ~ various magnesia contents were prepared to make the MMAS composites. Further, the l\.1MAS composites prepared from different powders (i.e. from an alumina-magnesia mixture ahd from a magnesia-spinel powder) were compared. Com starch was added into the powder mixtures before sintering to make porous microstructures. Microstructural development and thermal expansion behaviour ofthe MMAS composites were investigated. Microstructures of the MAS and the MMAS composites as well as their porous bodies were quaritified from backscattered electron micrographs in terms of the connectivity of solids i.e. solid contiguity by means of linear intercept counting. Solid contiguity decreased with increasing pore content and varied with pore size, pore shape and pore distribution whereas the phase contiguity depended strongly on the chemical composition and was less influenced by porosity. ' The thermal expansion behaviour of the MAS and the MMAS composites between 100 and 1000 °C was determined experimentally. Variation in the CTE ofthe MAS relates to the degree of spinel formation while the thermal expansion of the MMAS composites depends strongly on phase content. However, the MMAS composites with similar phase compositions but made from different manufacturing processes showed differences in microstructural features and thermal expansion behaviour. Predictions of the CTE values for composites based on a simple rule-of-mixtures (ROM) using volume fraction were compared with the measured data. A conventional ROM accurately predicted the effective CTE of a range of dense alumina-silicon carbide particulate composites but was not very accurate for porous multiphase structures. It provided an upper bound prediction as all experimental values were lower. Hence, the conventional ROM was modified to take account of quantitative microstructural parameters obtained from solid contiguity. The modified ROM predicted lower values and gave a good agreement with the experimental data. Thus, it has been shown that quantitative microstructural information can be used to predict the CTE of multiphase ceramic materials with complex microstructures.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Improving the performance of wireless sensor networks using directional antennas

Over the last decades, lots of new applications have emerged thanks to the availability of small devices capable of wireless communications that form Wireless Sensor Networks (WSNs). These devices allow sensing, processing, and communication of multiple physical variables while keeping a low power consumption. During the last years, most of the research efforts were spent on the development and optimization of wireless communication protocols, aiming to maximize the reliability of the network while achieving the lowest possible power consumption. In this thesis, we study how to improve the performance of these WSNs by using directional antennas. Directional antennas can provide a higher gain and reduce the interference with other nodes by concentrating the radiated power in a certain direction. We present the different kinds of directional antennas available for WSNs, and we select the 6-element SPIDA antenna as a case of study. We present an electromagnetic model of this antenna, and we incorporate it into the COOJA network simulator. We report the first complete characterization of this antenna, including the radiation pattern and S11 parameters. The characterization shows that the antenna has a maximum gain of 6.8 dBi, a Half-Power Beamwidth (HPBW) of 113° and a module of S11 parameter of -7.5 dB at the central frequency (fc = 2.4525 GHz). We also present a novel way to optimize the antenna without changing its design by isolating multiple director elements. We show that with this technique, the performance of the antenna can be improved in terms of maximum gain, narrower HPBW, and a lower module of the S11 parameter without making any changes in the antenna itself. We evaluate the impact of supporting directional communications in the different layers of the network stack. We analyze the different challenges that arise and propose optimizations to overcome them in order to take advantage of the benefits of directional communication. We present an analysis of the state-of-the-art in neighbor discovery protocols for WSNs with directional antennas, and we propose, implement end evaluate two novel fully directional protocols: Q-SAND and DANDi. We compare both of them with SAND, a fully directional neighbor discovery protocol. DANDi is a fully directional asynchronous and dynamic neighbor discovery protocol where the contention resolution relies on a collision detection mechanism. To the best of our knowledge, DANDi is the fastest neighbor discovery protocol for WSN with directional antennas, with the additional advantage of being able to discover every reliable communication link in a network without requiring any prior information of the network topology. We combine the directional neighbor discovery protocol with MAC and routing optimizations in order fully take advantage of the benefits of using directional antennas. We focus on convergecast, a typical data collection application where every node sends packets periodically to a sink node. We present DirMAC, a novel MAC protocol that fully supports directional communication, together with four different heuristics to optimize the performance of the protocols. One of these heuristics has the added major benefit of being completely distributed and with no need for offline processing. Our evaluation shows that optimizations at both the MAC and routing layers are needed in order to reap the benefits of using directional antennas for convergecast. Our results show that the performance of the network can be greatly improved in terms of packet delivery rate, energy consumption, and energy per received packet, and that we obtain the largest performance improvements in networks with dense traffic. Simulations with different node densities show that when using directional antennas the PDR increases up to 29%, while energy consumption and energy per received packet decreases by up to 55% and 46% respectively. Experiments with real nodes validate these results showing a significant performance increase when using directional antennas in our scenarios, with a reduction in the RDC and EPRP of 25% and 15% respectively, while maintaining a PDR of 100%.Durante las últimas décadas, la disponibilidad de pequeños dispositivos con comunicación inalámbrica ha permitido el desarrollo de muchas nuevas aplicaciones. Estos dispositivos forman Redes de Sensores Inalámbricos (RSI, o WSN por sus siglas en inglés) que permiten sensar, procesar y comunicar datos provenientes de variables físicas, mientras que mantienen un bajo consumo energético. En los últimos años, la mayor parte de los esfuerzos de la comunidad científica estuvieron concentrados en el desarrollo y optimización de los protocolos de comunicación inalámbricos, buscando maximizar la confiabilidad de la red y minimizar el consumo energético. En esta tesis estudiamos cómo mejorar el rendimiento de las RSI usando antenas direccionales. Las antenas direccionales pueden proporcionar una mayor ganancia y reducir la interferencia con otros nodos al concentrar la potencia radiada en una cierta dirección. Comenzamos presentando los distintos tipos de antenas direccionales disponibles para las RSI, y seleccionamos la antena SPIDA de 6 elementos como caso de estudio. Luego presentamos un modelo electromagnético de la antena, que incorporamos al simulador de red COOJA. Construimos un primer prototipo con el que realizamos la primera caracterización completa de ésta antena, incluyendo el patrón de radiación y el parámetro S11. La caracterización muestra que la antena tiene una ganancia máxima de 6,8 dBi, un ancho de haz a mitad de potencia (HPBW por sus siglas en inglés) de 113° y un módulo del parámetro S11 de -7,5 dB en la frecuencia central (fc = 2,4525 GHz). También mostramos una forma innovadora de optimizar la antena sin cambiar su diseño utilizando varios elementos directores al mismo tiempo. Mostramos que con esta técnica se puede mejorar el rendimiento de la antena en términos de ganancia máxima, ancho de haz a mitad de potencia, y módulo del parámetro S11. Luego evaluamos el impacto de usar comunicaciones direccionales en las diferentes capas del stack de red. Analizamos los diferentes desafíos que surgen y proponemos optimizaciones para sortearlos. Presentamos un análisis del estado del arte en protocolos de descubrimiento de vecinos en RSI con antenas direccionales, y proponemos, implementamos y evaluamos dos protocolos direccionales : Q-SAND y DANDi. DANDi es un protocolo de descubrimiento de vecinos direccional, asíncrono y dinámico, donde la contienda por el canal se resuelve con un mecanismo basado en la detección de colisiones. Hasta donde sabemos, DANDi es el protocolo de descubrimiento de vecinos más rápido para RSI con antenas direccionales, con la ventaja adicional de que permite descubrir todos los enlaces de comunicación confiables de una red sin requerir ningún conocimiento previo de la topología. Luego combinamos los protocolos de descubrimiento de vecinos con optimizaciones en las capas de ruteo y acceso al medio para construir una aplicación de recolección de datos, donde cada nodo envía paquetes periódicamente a un nodo centralizador. Presentamos DirMAC, un protocolo de acceso al medio innovador que soporta comunicaciones direccionales, junto con cuatro heurísticas que permiten optimizar el rendimiento de los protocolos (una de ellas con la ventaja adicional que es totalmente distribuida). Los resultados muestran que usar antenas direccionales en este tipo de aplicaciones permite mejorar sustancialmente el rendimiento de la red, mostrando las mayores mejoras en redes con alto tráfico. Las simulaciones con diferentes densidades de nodos muestran que al usar antenas direccionales se puede aumentar el ratio de entrega de paquetes en hasta 29%, mientras que el consumo energético y la energía por paquete recibido bajan en hasta 55% y 46% respectivamente. Los experimentos en nodos reales validan estos resultados, mostrando una reducción en el consumo energético y en la energía por paquete recibido de 25% y 15% respectivamente, mientras que mantienen un ratio de entrega de paquetes de 100%