Дисертації з теми "Multi-hop routing protocol"

Hop count, i.e., the number of wireless hops a packet has to go through to reach the destination, is a fundamental metric in multi-hop wireless ad-hoc networks. Network performance, such as throughput, end-to-end delay, energy consumption, and so on, depends critically on hop count. Previous work on modeling hop count is limited in making unrealistic simplifying assumptions either at the physical or network, or both layers of the communication protocol stack. A key contribution of this thesis is to present an analytical model to derive the probability distribution of hop count under realistic assumptions at both physical and network layers. Specifically, the model considers a log-normal shadowing radio propagation capable of accommodating the random signal fading observed in most wireless communication environments, and the widely used geographic routing at the network layer. Validation of the model is achieved by a comprehensive set of simulation experiments including a trace driven simulation of a real-word vehicular ad-hoc network. The model reveals that the presence of randomness in radio propagation reduces the required number of hops to reach a given destination significantly. To demonstrate the utility of the proposed hop count model, the thesis proposes three new applications which address some of the key challenges in multi-hop wireless networks. The first application derives the per-node packet forwarding load in multi-hop wireless sensor networks and reveals that the nodes in the vicinity of the base station has a significantly less forwarding load than previously thought under simplifying radio propagation and routing assumptions. The second application demonstrates that using hop count as a measure of distance traveled by a data packet, geocasting can be achieved in multi-hop wireless networks in situations when some of the network nodes do not have access to reliable location information. Finally, the proposed hop count model is used to evaluate the performance of the third application which demonstrates that the overhead of geographic routing can be reduced significantly by embracing a position update philosophy which adapts to the mobility and communication patterns of the underlying ad-hoc network.

Multicast/Broadcast Service (MBS) in WiMAX refers to the ability of the WiMAX network to provide flexible and efficient mechanisms to send common content to multiple users who are sharing radio resources. WiMAX multi-hop relay technology is a key enabler to expand WiMAX infrastructure to eliminate blind spots in coverage and to enhance user throughput with a lower capital expenditure and operational expenditure. To support MBS in a WiMAX multi-hop relay network, one must consider several design issues such as the dynamic relay topology discovery in response to the mobility of the relay station, the dynamic group membership management, the service activation due to join/leave operations of MBS users, the radio resource allocation and the connection management to support these dynamic behaviors. This thesis studies and develops a WiMAX relay architecture, its relay protocol and the optimal multicast algorithms to solve the above issues. To resolve the above-mentioned issues, we have created a model for our multi-hop WiMAX relay architectures. This model incorporates an inter-layer protocol design that would allow the IP layer to use its IGMP/PIM snooping capability together with WiMAX MAC layer relay protocols. Among the MBS server, the WiMAX BS (Base Station) and the MS (Mobile Station), we adopted existing IETF protocols (including IGMP and PIM) to implement some common multicast procedures at the networks layer in order to provision MBS service. To support dynamic formation of a relay network topology, we have proposed and implemented a BS-oriented source-routing protocol to automatically discover the relay path. Finally, we have implemented our MBS in an OPNET simulator, and verified their operations. We have also evaluated the performance of the video and voice applications in WiMAX relay networks under different network sizes, and discussed their performances. The performance results demonstrate the Point to Multi-Point characteristic of WiMAX.

In this dissertation, routing protocols, load-balancing protocols, and efficient evaluation techniques for multi-hop mobile wireless networks are explored. With the advancements made in wireless communication and computer technologies, a new type of mobile wireless network, known as a mobile ad hoc network (MANET), has drawn constant attention. In recent years, several routing protocols for MANETs have been proposed. However, there still remains the need for mechanisms for better scalability support with respect to network size, traffic volume, and mobility. To address this issue, a new method for multi-hop routing in MANETs called Dynamic NIx-Vector Routing (DNVR) is proposed. DNVR has several distinct features compared to other existing on-demand routing protocols, which lead to more stable routes and better scalability. Currently, ad hoc routing protocols lack load-balancing capabilities. Therefore they often fail to provide good service quality, especially in the presence of a large volume of network traffic since the network load concentrates on some nodes, resulting in a highly congested environment. To address this issue, a novel load-balancing technique for ad hoc on-demand routing protocols is proposed. The new method is simple but very effective in achieving load balance and congestion alleviation. In addition, it operates in a completely distributed fashion. To evaluate and verify wireless network protocols effectively, especially to test their scalability properties, scalable and efficient network simulation methods are required. Usually simulation of such large-scale wireless networks needs a long execution time and requires a large amount of computing resources such as powerful CPUs and memory. Traditionally, to cope with this problem, parallel network simulation techniques with parallel computing capabilities have been considered. This dissertation explores a different type of method, which is efficient and can be achieved with a sequential simulation, as well as a parallel and distributed technique for large-scale mobile wireless networks.

Le réseau de capteurs sans fil (WSN) se compose d'un grand nombre de minuscules dispositifs appelés nœuds, et ces nœuds sont généralement limités en puissance et ils sont déployés de manière aléatoire dans une zone géographique à des fins de surveillance. En raison du grand nombre de nœuds dans le WSN, leur demande en ressources de fréquence devient un véritable défi en raison de la rareté du spectre. La radio cognitive (CR) a été introduite pour améliorer l'efficacité spectrale. La CR classe les utilisateurs entre l'utilisateur principal (PU) qui détient une licence sur une bande passante du spectre et l'utilisateur secondaire (SU), c'est-à-dire un utilisateur opportuniste. L'intégration de CR dans WSN se traduit par un réseau de capteurs radio cognitifs (CRSN). Dans le CRSN, les nœuds se comportent comme des SU. Cependant, l'adoption du CRSN peut être confrontée à plusieurs défis. En effet, les nœuds du réseau peuvent arrêter de transmettre pour éviter toute interférence nuisible pour PU. De plus, la contrainte de consommation d'énergie doit être respectée. D'autres fonctionnalités peuvent être affectées par l'adoption du CRSN, telles que le processus de regroupement et l'agrégation de données dans le réseau, en particulier dans un CRSN basé sur un routage multi-sauts. Dans ce manuscrit, nous abordons les défis du CRSN à différents niveaux. Premièrement, le regroupement des nœuds améliore l'efficacité du réseau. En pratique, le regroupement des nœuds du réseau permet d'économiser de l'énergie lors de la transmission des données. Ainsi, nous étudions le nombre optimal de clusters dans le réseau en fonction de la consommation d'énergie lors de la transmission de données et de la détection du spectre pour prolonger la durée de vie du réseau. Ensuite, nous présentons LIBRO, un nouveau protocole de routage multi-sauts montant basé sur les informations de localisation géographique. LIBRO assure la livraison de paquets de données rectifiés dans des réseaux denses sans connaissance de la topologie ou des nœuds de chemin. Enfin, nous avons utilisé LIBRO et la technique de récupération d'énergie pour prolonger la durée de vie du CRSN. Ainsi, en résolvant un problème d'optimisation joignant la probabilité de collision, la consommation d'énergie, le délai de livraison des paquets et le taux de livraison des paquets, les paramètres appropriés sont trouvés. [Google traduction]
The Wireless Sensor Network (WSN) consists of a large number of tiny devices called nodes, and these nodes are generally limited in power and they are randomly deployed in a geographical area for monitoring purpose. Because of the large number of nodes in the WSN, their demand on the frequency resources becomes a real challenge due to the spectrum scarcity. Cognitive Radio (CR) was introduced to enhance the spectral efficiency. The CR classifies users into the Primary User (PU) that holds a license over a spectrum bandwidth, and the Secondary User (SU), i.e., an opportunistic user. The integration of CR into WSN results in a cognitive radio sensor network (CRSN). In CRSN, the nodes behave as SUs. However,the adoption of CRSN may face several challenges. Indeed, network nodes may stop transmitting to avoid any harmful interference for PU. In addition, energy consumption constraint should be respected. Other features may be impacted by the adoption of CRSN, such as the clustering process and the in-network data aggregation, especially in a multi-hop routing based CRSN. In this manuscript, we tackle the challenges of the CRSN from different levels. Firstly, clustering nodes enhances network efficiency. In practice, grouping the network nodes saves energy during data transmission. Thus, we investigate the optimal number of clusters in the network based on energy consumption during data transmission and spectrum sensing to extend network lifespan. Then, we present LIBRO, a new uplink multi-hop routing protocol based on the geographical location information. LIBRO ensures delivery of rectified data packets in dense networks without knowledge of topology or path nodes. Finally, we used LIBRO and the energy harvesting technique to extend the CRSN's lifespan. Thus, by solving an optimization problem jointing the collision probability, energy consumption, packet delivery delay and packet delivery ratio, the appropriate parameters are found

As tecnologias de redes sem fio passaram a atender não só às aplicações corporativas mais sofisticadas como também àquelas envolvendo desde o rastreamento de animais, monitoramento de estruturas e automação industrial até o gerenciamento de utilidades urbanas. Este projeto de pesquisa aborda o desenvolvimento de um protocolo de rede mesh multi-hop segundo a especificação IEEE 802.15.4, com o uso de coordenadas geográficas de cada nó para o roteamento de dados em aplicações de iluminação pública. Para o desenvolvimento do protocolo de rede, é considerada a biblioteca de rotinas de interface de rede denominada Simple MAC (SMAC). Tal biblioteca pode ser utilizada para a elaboração do protocolo de roteamento geográfico destinado à rede mesh multi-hop. Paralelamente, propõe-se a descrição de um método a ser adotado para a inserção do protocolo de roteamento geográfico no SMAC. Os códigos, desenvolvidos em linguagem de programação C, são portados para a plataforma de desenvolvimento dos nós de comunicação de um toolkit específico e submetidos a ensaios experimentais. Os resultados englobam a geração de conhecimento teórico e prático a respeito das redes de sensores sem fio, bem como o desenvolvimento de um software aberto para este tipo de rede. As propriedades de auto-organização da rede, robustez e baixa latência são comprovadas nos ensaios experimentais.
The technologies of wireless networks have to serve not only the most sophisticated business applications but also those that involve the tracking of animals, monitoring of structures, industrial automation and the management of urban utilities. This research project addresses the development of a protocol for multi-hop mesh network according to IEEE 802.15.4, with the use of geographical coordinates of each node for routing data in applications such as street lighting. In order to develop the network protocol, the routines library of the network interface, called Simple MAC (SMAC), is considered. This library can be used for establishing the geographic routing protocol destined for the multi-hop mesh network. In parallel it is proposed to describe a method to be adopted for the inclusion of geographic routing protocol in SMAC. The codes, developed in C programming language, are ported to the development platform of communication nodes of a specific toolkit and subjected to experimental tests. The results include the generation of theoretical and practical knowledge regarding the wireless sensor networks, as well as the development of open software for this type of network. The properties of self-organization of the network, robustness and low latency are proven in experimental tests.

In der vorliegenden Arbeit werden praktische Protokolle für spontane drahtlose Multi-Hop Maschennetze vorgestellt, diese betrachten das drahtlose System ganzheitlich und berücksichtigen damit die Besonderheiten des drahtlosen Mediums, wie Fading, Interferenz sowie starke Signaldämpfung aufgrund von Entfernung bzw. Hindernissen. Interferenz ist eine Hauptursache für Paketverlust, Durchsatz und Latenz können durch die gleichzeitige Verwendung mehrerer interferenzfreier Kanäle verbessert werden. In Sensor- bzw. Community-Netzen kommt preiswerte und energiesparende Hardware zum Einsatz, die Verwendung zusätzlicher Antennen bzw. Radios ist deshalb nicht möglich. Andererseits werden aber zukünftige drahtlose Netze eine 100-mal höhere Knotendichte, verglichen mit heutigen Netzen, zeigen. Durch die Ausnutzung der im System inhärent vorliegenden Ressource Nutzer (Multi-User Diversität) werden durch Kooperation virtuelle Multi-Antennen und Multi-Radiosysteme aufgebaut. Aufgrund des großen Abstands zwischen den Knoten erreicht man erstens eine hohe räumliche Diversität und zweitens lassen sich damit auch negative Effekte, wie Interferenz zwischen benachbarten Kanälen, minimieren. Es werden Algorithmen sowohl für die Mediumzugriff- als auch die Routing-Schicht vorgestellt. Da keine spezielle physikalische Schicht notwendig ist, kann IEEE 802.11 verwendet werden. Schließlich kann auch auf die bereits heute verfügbare IEEE 802.11 Hardware, die nur eine Kanalumschaltzeit im Millisekundenbereich erlaubt, zurückgegriffen werden. Die zwei vorgestellten Protokolle eignen sich für Umgebungen mit hoher bzw. geringer Interferenz durch fremde WiFi-Netze. Bezüglich Durchsatz werden moderne Protokolle, wie DSR auf Basis von IEEE 802.11 und ETX-Metrik, um ein Vielfaches übertroffen, außerdem ist die Latenz klein und das TCP/IP-Protokoll kann unverändert verwendet werden.
In this work practical protocols are introduced for spontaneous wireless multi-hop mesh networks which contemplate the wireless system integrally and therefore take into account particular features of the wireless medium, like fading, interference as well as strong signal attenuation due to distance or obstacles. Interference is one of the main causes for packet loss. Throughput and latency can be improved by the simultaneous use of several non-interfering channels. In sensor or community networks inexpensive and energy-saving hardware is used. Additional antennas or radios are impossible therefore; on the other hand future wireless networks will show a 100 times higher node density in comparison with today''s networks, however. By the usage of the resource user (multi-user diversity), that is inherently present in the system virtual multi-antennas and multi-radio systems can be built up by cooperation. Firstly, a high spatial diversity can be achieved due to the large distance between the nodes and secondly, negative effects like interference can be minimized between neighboring channels. Algorithms are introduced both for medium access and routing layer. Since a special physical layer is not required IEEE 802.11 can be used. These days already available 802.11 hardware, which allows a channel switching time in milliseconds, is finally usable. The two protocols introduced here are suitable for environments with a high or low interference caused by foreign WiFi networks. Regarding their performance modern protocols like DSR based on 802.11 and ETX metric are surpassed by far. Moreover, the latency is small and the TCP/IP protocol can be used in its unchanged form.

In Intelligent Transportation Systems (ITS), disseminating warning messages in a timely and efficient way through wireless short-range communications can save many lives and reduce traffic congestion. A geographical broadcast protocol provides data delivery to specified geographical areas, using multi-hop communications if needed. Among the main challenges for such protocols are forwarder selection and the reduction of the number of hops required to reach and cover the destination area.  In this thesis we propose an efficient geographical broadcast protocol called Preferred and Contention Based Forwarding (PCBF) and evaluate it through simulations. PCBF uses a combination of contention-based forwarding and selecting preferred forwarders also found in other protocols like Emergency Message Dissemination for Vehicular Environments (EMDV). Since the preferred forwarder is allowed to immediately forward the packet (evading contention among other potential forwarders), this approach reduces end-to-end delays. Notable extensions of PCBF compared to EMDV are the use of direct negative acknowledgements in case of unnecessary rebroadcasts and the use of forwarders outside the target region.  Our simulation results show that the PCBF protocol outperforms selected other protocols in terms of end-to-end delay, re-broadcast overhead and reliability in both sparse and dense networks.

Récemment, les comportements malveillants dans les réseaux sans fil multi-sauts ont attiré l’attention de la communauté scientifique. La prolifération rapide du nombre de dispositifs sans fil ainsi que la diversification des applications basées sur ces réseaux ont grandement contribué à l’amélioration de la qualité de vie ainsi que la modernisation de la société. Cependant, la nécessité de sécuri ser ces réseaux et de garantir la robustesse de leurs services est devenue une préoccupation majeure. En effet, les caractéristiques spécifiques de ces réseaux, telles que l’absence d’infrastructure et l’absence d’une entité centrale de confiance, font que les réponses à leurs problèmes de sécurité sont tout à fait différentes de celles des réseaux filaires. De plus, le manque de confiance entre les nœuds rend ces problèmes encore plus critiques. L’objectif de cette thèse vise à contribuer au renforcement de la sécurité dans les réseaux sans fil multi-sauts. Elle se focalise sur l’étude des comportements malveillants au niveau des couches MAC et réseau. Nous nous intéressons au développement de nouvelles solutions pour faire face à l’attaque du trou noir ”Black hole” dans le contexte du protocole OLSR, ainsi qu’analyser le comportement des nœuds cupides ”Greedy” au niveau de la couche MAC, dans toutes ses versions.Une attaque de trou noir peut être menée suivant deux scénarios. Le premier scénario consiste à lancer l’attaque, exclusivement, au niveau de la couche réseau. Le second scénario consiste en une attaque multi-couches. Dans le cadre de cette thèse, nous analysons l’impact de ces deux types d’attaques et proposons des contre-mesures appropriées. Au niveau de la couche MAC, nous étudions particulièrement le comportement cupide adaptatif dans le cadre des réseaux sans fil maillés et nous proposons une solution originale baptisée, FLSAC, afin de prévenir ce type de menace. Dans le cadre des réseaux mobiles ad hoc (MANETs), nous définissons un nouveau modèle de comportement des nœuds cupides. Nous développons aussi un nouvel algorithme de backoff, dont l’avantage principal est d’assurer une détection rapide des nœuds cupides non conformes aux spécifications du protocole IEEE802.11. Cet algorithme offre un mécanisme de réaction qui incite un nœud cupide à se comporter correctement en lui donnant la chance de se repentir après détection
While the rapid proliferation of mobile devices along with the tremendous growth of various applications using wireless multi-hop networks have significantly facilitate our human life, securing and ensuring high quality services of these networks are still a primary concern. In particular, anomalous protocol operation in wireless multi-hop networks has recently received considerable attention in the research community. These relevant security issues are fundamentally different from those of wireline networks due to the special characteristics of wireless multi-hop networks, such as the limited energy resources and the lack of centralized control. These issues are extremely hard to cope with due to the absence of trust relationships between the nodes.To enhance security in wireless multi-hop networks, this dissertation addresses both MAC and routing layers misbehaviors issues, with main focuses on thwarting black hole attack in proactive routing protocols like OLSR, and greedy behavior in IEEE 802.11 MAC protocol. Our contributions are briefly summarized as follows. As for black hole attack, we analyze two types of attack scenarios: one is launched at routing layer, and the other is cross layer. We then provide comprehensive analysis on the consequences of this attack and propose effective countermeasures. As for MAC layer misbehavior, we particularly study the adaptive greedy behavior in the context of Wireless Mesh Networks (WMNs) and propose FLSAC (Fuzzy Logic based scheme to Struggle against Adaptive Cheaters) to cope with it. A new characterization of the greedy behavior in Mobile Ad Hoc Networks (MANETs) is also introduced. Finally, we design a new backoff scheme to quickly detect the greedy nodes that do not comply with IEEE 802.11 MAC protocol, together with a reaction scheme that encourages the greedy nodes to become honest rather than punishing them

Nowadays, Opportunistic Routing (OR) is widely considered to be the most important paradigm for Multi-hop wireless networks (MWNs). It exploits the broadcast nature of wireless medium to propagate information from one point to another within the network. In OR scheme, when a node has new information to share, it rst needs to set its forwarding list which include the IDs and/or any relevant information to its best suited neighboring nodes. This operation is supported by the use of appropriate metrics. Then, it executes a coordination algorithm allowing transmission reliability and high throughput among the next-hop forwarders. In this paper, we provide a comprehensive guide to understand the characteristics and challenges faced in the area of opportunistic routing protocols in MWNs. Moreover, since the planet we live on is largely covered by water, OR protocols have gained much attention during the last decade in real-time aquatic applications, such as oil/chemical spill monitoring, ocean resource management, anti-submarine missions and so on. One of the major problems in Underwater Wireless Sensor Network (UWSNs) is determining an e cient and reliable routing methodology between the source node and the destination node. Therefore, designing e cient and robust routing protocols for UWSNs became an attractive topic for researchers. This paper seeks to address in detail the key factors of underwater sensor network. Furthermore, it calls into question 5 state-of-the-art routing protocols proposed for UWSN: The Depth-Based Routing protocol (DBR), the Energy-E cient Depth-Based Routing protocol (EEDBR), the Hydraulic-pressure-based anycast routing protocol (Hydrocast), the Geographic and opportunistic routing protocol with Depth Adjustment for mobile underwater sensor networks (GEDAR), and the Void- Aware Pressure Routing for underwater sensor networks (VAPR). Finally, it covers the performance of those protocol through the use of the R programming language.

The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiver’s feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics based rate adaptation solution uses an on-demand incremental strategy for selecting a rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the route discovery process. The 802.11 mandates the use of different transmission rates for broadcast and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as ‘reachable neighbours’ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority queue are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result these factors are not considered which result in severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end delay and throughput.

Les réseaux véhiculaires sont passés du stade de simple curiosité pour revêtir aujourd'hui un intérêt certain aussi bien du point de vue de l'industrie automobile que des opérateurs de réseaux et services. Ces réseaux sont en effet une classe émergente de réseaux sans fil permettant des échanges de données entre véhicules ou encore entre véhicules et infrastructure. Ils suscitent un intérêt certain aussi bien en Europe qu’au Japon et en Amérique du Nord, dans le but de fournir de nouvelles technologies capables d'améliorer la sécurité et l'efficacité des transports routiers. Suivant cette même vision, nous nous intéressons dans cette thèse aux communications inter-véhicules dans un environnement urbain. Notre objectif est de proposer des solutions de routage ad hoc et de dissémination géolocalisée, adaptées à un environnement ville, répondant à la fois aux exigences et besoins technologiques des cas d'utilisation envisagés (principalement des services d'information et de confort), mais aussi et surtout aux contraintes des communications inter-véhiculaires ad hoc (fragmentation fréquente du réseau, connectivité intermittente, etc…). Notre démarche consiste à prendre en compte un paramètre clé qui influence le bon fonctionnement du réseau ad hoc de véhicules, à savoir la densité du réseau. Dans un premier temps, nous proposons un mécanisme distribué qui permet de caractériser de manière plus fine la densité de trafic d'un tronçon de route entre deux intersections, en fournissant une distribution spatiale des véhicules mobiles sur la voie de circulation. Ensuite, nous proposons un nouveau protocole de routage géographique, qui tire partie des caractéristiques des voies urbaines et qui intègre le mécanisme d'estimation de densité de trafic pour le routage des paquets. Pour finir, et afin de compléter les mécanismes de communication véhiculaire ad hoc (couche réseau) proposés, nous nous intéressons à la dissémination des données. Nous proposons un nouveau mécanisme distribué et ad hoc qui permet d'émuler le fonctionnement d'une infrastructure classique destinée à diffuser localement (au niveau d'une intersection) des paquets de données de manière périodique. Certains aspects de nos solutions sont évalués analytiquement alors que leurs performances sont évaluées par simulation à l'aide de l'outil QNAP, du simulateur QualNet et du modèle de mobilité réaliste VanetMobiSim
Inter-Vehicle Communication (IVC) is attracting considerable attention from the research community and the automotive industry, where it is beneficial in providing Intelligent Transportation System (ITS) as well as assistant services for drivers and passengers. In this context, Vehicular Networks are emerging as a novel category of wireless networks, spontaneously formed between moving vehicles equipped with wireless interfaces that could have similar or different radio interface technologies, employing short-range to medium-range communication systems. The distinguished characteristics of vehicular networks such as high mobility, potentially large scale, and network partitioning introduce several challenges, which can greatly impact the future deployment of these networks. In this thesis, we focus on inter-vehicle communication in urban environments. Our main goal is to propose new routing and dissemination algorithms, which efficiently adapts to the vehicular networks characteristics and applications. Temporary disconnection in vehicular network is unavoidable. It is thereby of imminent practical interest to consider the vehicular traffic density. Therefore, at first, we propose a completely distributed and infrastructure–free mechanism for city road density estimation. Then, and based on such traffic information system, we propose a novel intersection-based geographical routing protocol, capable to find robust and optimal routes within urban environments. Finally, in order to help the efficient support of dissemination-based applications, a self-organizing mechanism to emulate a geo-localized virtual infrastructure is proposed, which can be deployed in intersections with an acceptable level of vehicular density. The advocated techniques are evaluated by a combination of network simulation and a microscopic vehicular traffic model

Wireless communication has seen a tremendous growth in the last decades. Continuing on this trend, wireless multi-hop networks  are nowadays used or planned for use in a multitude of contexts, spanning from Internet access at home to emergency situations. The Transmission Control Protocol (TCP) provides reliable and ordered delivery of a data and is used by major Internet applications such as web browsers, email clients and file transfer programs. TCP traffic is also the dominating traffic type on the Internet. However, TCP performs less than optimal in wireless multi-hop networks due to packet reordering, low link capacity, packet loss and variable delay. In this thesis, we develop novel proposals for enhancing the network and transport layer to improve TCP performance in wireless multi-hop networks. As initial studies, we experimentally evaluate the performance of different TCP variants, with and without mobile nodes. We further evaluate the impact of multi-path routing on TCP performance and propose packet aggregation combined with aggregation aware multi-path forwarding as a means to better utilize the available bandwidth. The last contribution is a novel extension to multi-path TCP to  enable single-homed hosts to fully utilize the network capacity.

Opponent changed. Prof. C. Lindeman from the University of Leipzig was substituted by Prof. Zhang.

Due to the high availability of cheap hardware, wireless multi-hop networks and in particular Wireless Mesh Networks (WMNs) are becoming popular in more and more contexts. For instance, IEEE 802.11 based WMNs have already started to be deployed as means to provide Internet access to rural areas in the developing world. To lower the cost and increase the coverage in such deployments, the wired network is extended with a wireless backbone of fixed mesh routers. With advances in technology and reduction in price comes also the possibility for more powerful wireless nodes, having multiple radios that allow transmitting on different channels in parallel. To be a successful platform for providing general Internet access, wireless multi-hop networks must provide support for common Internet applications. As most of the applications in the Internet today use the Transmission Control Protocol (TCP), TCP performance is crucial. Unfortunately, the design of TCP’s congestion control that made it successful in today’s Internet makes it perform less than optimal in wireless multi-hop networks. This is due to, among others, TCP’s inability to distinguish wireless losses from congestion losses. The current trend for operating system designers is also to focus TCP development on high-speed fixed networks, rather than on wireless multi-hop networks. To enable wireless multi hop networks as a successful platform there is therefore a need to provide good performance using TCP variants commonly deployed in the Internet. In this thesis, we develop novel proposals for the network layer in wireless multi-hop networks to support TCP traffic more efficiently. As an initial study, we experimentally evaluate different TCP variants, with and without mobile nodes, in a MANET context. Our results show that TCP Vegas, which does not provoke packet loss to determine available bandwidth, reduces the stress on the network while still providing the same or slightly increased performance, compared to TCP Newreno. We further propose and evaluate packet aggregation combined with aggregation aware multi-path forwarding to better utilize the available bandwidth. IP layer packet aggregation, where small packets are combined to larger ones before sent to the link layer, has been shown to improve the performance in wireless multi-hop networks for UDP and small packet transfers. Only few studies have been made on the impact of packet aggregation on TCP traffic, despite the fact that TCP traffic constitutes the majority of the Internet traffic. We propose a novel aggregation algorithm that is specifically addressing TCP relevant issues like packet reordering, fairness and TCP timeouts. In a typical WMN scenario, the aggregation algorithm increases TCP performance by up to 70 % and decreases round trip time (RTT) by up to 40 %. A detailed evaluation of packet aggregation in a multi radio setting has shown that a naive combination of multi path routing and packet aggregation can cause valuable aggregation opportunities to be lost. Therefore, we propose a novel combined packet aggregation and aggregation aware forwarding strategy that can reduce delay, packet loss and increase TCP performance by around 30 %.

Dans cette thèse, nous nous sommes intéressés aux réseaux urbains considérés par le projet ANR ARESA2 qui sont principalement des réseaux de capteurs et actionneurs hétérogènes : l’hétérogénéité est causée par la coexistence des noeuds capteurs à faibles ressources et des noeuds actionneurs riches en ressources. Ces derniers devraient être utilisés de manière différenciée par le réseau. C’est dans ce contexte que se déroule cette thèse dans laquelle nous avons étudié des algorithmes d’auto-organisations et de routage s’appuyant sur l’hétérogénéité. Au début, nous nous sommes intéressés à l’auto-organisation dans un contexte hétérogène. Se basant sur l’idée que les ressources au niveau des noeuds actionneurs doivent être exploitées afin de réduire la charge de communication au niveau des noeuds capteurs, nous avons proposé un protocole d’auto-organisation appelée Far-Legos. Far-Legos permet de profiter de la puissance d’émission des actionneurs pour apporter une information de gradient au niveau des capteurs. Les actionneurs initient et construisent une topologie logique. Cette dernière sera utilisée pour faciliter la phase de collecte de données à partir des noeuds capteurs vers les noeuds actionneurs. Ensuite, nous nous sommes intéressés aux liens asymétriques causés par la présence de différents types de noeuds avec différentes portées de transmission. Ces liens asymétriques, causés par l’hétérogénéité au niveau des noeuds constituant le réseau, peuvent détériorer les performances des protocoles de routage qui ne tiennent pas compte de ce type de liens. Pour éviter la dégradation de ces protocoles de routage, nous introduisons une nouvelle métrique de calcul de gradient ou de rang. Celle-ci sera utile pour détecter et éviter les liens asymétriques au niveau de la couche réseau pour le protocole de routage RPL. Nous présentons aussi une adaptation du protocole de collecte de données basé sur Legos pour détecter et éviter ces liens asymétriques. Enfin, nous nous sommes intéressés à l’exploitation de ces liens asymétriques. Nous proposons ainsi un protocole de collecte de données dédiés aux réseaux hétérogènes contenant des liens asymétriques appelé AsymRP. AsymRP est un protocole de routage dédié au trafic de collecte de données basé sur une connaissance de voisinage à 2-sauts combinée avec l’utilisation des messages d’acquittements (ACKs) implicites et une technique de routage de messages ACKs explicites. Cette proposition tire profit des liens asymétriques afin d’assurer une collecte de données fiable
In this thesis, we focused on urban wireless networks considered by the ANR project ARESA2. The networks considered by this project are heterogeneous networks. This heterogeneity is caused by the coexistence of sensor nodes with limited resources and actuator nodes with higher resources. Actuators nodes should be used differentially by the network. Hence designed protocols for WSANs should exploit resource-rich devices to reduce the communication burden on low power nodes. It is in this context that this thesis takes place in which we studied self-organizing and routing algorithms based on the heterogeneity. First, we are interested in self-organization protocols in a heterogeneous network. Based on the idea that resource-rich nodes must be exploited to reduce the communication load level on low-power nodes, we proposed self-organizing protocol called Far-Legos. Far-Legos uses the large transmit power of actuators to provide gradient information to sensor nodes. Actuators initiate and construct a logical topology. The nature of this logical topology is different inside and outside the transmission range of these resourceful nodes. This logical topology will be used to facilitate the data collection from sensor to actuator nodes. Second, we investigated the asymmetric links caused by the presence of heterogeneous nodes with different transmission ranges. The apparition of asymmetric links can dramatically decrease the performance of routing protocols that are not designed to support them. To prevent performance degradation of these routing protocols, we introduce a new metric for rank calculation. This metric will be useful to detect and avoid asymmetric links for RPL routing protocol. We also present an adaptation of data collection protocol based on Legos to detect and avoid these asymmetric links. Finally, we are interested in exploiting the asymmetric links present in the network. We proposed a new routing protocol for data collection in heterogeneous networks, called AsymRP. AsymRP, a convergecast routing protocol, assumes 2-hop neighborhood knowledge and uses implicit and explicit acknowledgment. It takes advantage of asymmetric links to ensure reliable data collection

Les accidents routiers et leurs dommages représentent un problème croissant dans le monde entier. Dans ce contexte, les réseaux véhiculaires (VANETs) peuvent être déployés pour réduire les risques et pour améliorer le confort. Ils permettent aux véhicules d'échanger différents types de données qui vont des applications de sécurité et de gestion du trafic aux applications de confort. De nos jours, les applications de sécurité sont l’objet de beaucoup d'attention des chercheurs ainsi que des fabricants d'automobiles. Dans cette thèse, nous étudierons les applications critiques pour la sécurité routière visant à fournir une assistance dans des situations dangereuses ou difficiles. Notre objectif principal sera de proposer de nouveaux protocoles de contrôle d'accès au support de transmission (MAC) et de routage, qui peuvent s’adapter dynamiquement aux changements fréquents de topologies des VANETs. Après un aperçu des protocoles d’accès sans contention dans les VANETs, nous proposons des solutions basées sur la technique de division du temps: Time Division Multiple Access (TDMA). D’abord, nous nous concentrons sur le développement d’un nouveau protocole distribué (DTMAC), qui ne repose pas sur l’utilisation d’infrastructure. DTMAC utilise les informations de localisation et un mécanisme de réutilisation des slots pour assurer que les véhicules accèdent au canal efficacement et sans collision. Les résultats obtenus ont confirmé l’efficacité de notre protocole, DTMAC se comporte très significativement mieux que VeMAC (protocole MAC basé sur TDMA.) Ensuite nous proposons TRPM, un protocole de routage basé sur une approche cross-layer. Dans TRPM, l’ordonnancement des slots TDMA construit par DTMAC et la position de la destination sont utilisés pour choisir le meilleur relais. Les résultats montrent que TRPM offre de meilleures performances, du nombre moyen de relais et de la fiabilité de livraison des messages comparé à d’autres protocoles. Dans la deuxième partie de cette thèse, nous nous focaliserons sur les mécanismes centralisés d’allocation de slots qui utilisent des coordinateurs. D’abord, nous proposons CTMAC, un protocole basé sur TDMA centralisé utilisant les RSUs (RoadSide Units) pour créer et maintenir les ordonnancements. CTMAC met en œuvre un mécanisme qui permet d’empêcher les “Access Collisions” de se produire plus que deux fois entre les véhicules qui tentent d’acquérir un même slot disponible. Les résultats ont montré que CTMAC permet de mieux minimiser les collisions, ainsi que le surcoût généré pour créer et maintenir les ordonnancements par rapport aux protocoles MAC, basés sur TDMA distribué. Cependant, dans CTMAC, les véhicules roulant vite devront acquérir des nouveaux slots après une courte période de temps à chaque fois qu’ils quittent les zones de leurs RSUs courants. Cette situation rend les protocoles centralisés inefficaces et couteux dans les réseaux à grande vitesse. Afin de pallier à ce problème inhérent à l’utilisation des RSUs, nous adaptons un algorithme d’ordonnancement basé sur le clustering dans lequel certains véhicules sont élus pour gérer l'accès au canal. Ceci permet aux véhicules de rester attachés à leurs clusters plus longtemps. Pour ce faire, nous proposons 1- un protocole de clustering nommé AWCP afin de former des clusters stables avec une longue durée de vie. AWCP est basé sur l’algorithme de clustering pour les réseaux mobiles WCA dans lequel les têtes des clusters sont élues en se basant sur une fonction de poids. 2- Nous formulons le réglage des paramètres de protocole AWCP comme un problème d’optimisation multi-objective et nous proposons un outil d’optimisation qui combine la version multi-objective de l’algorithme génétique appelé NSGA-II avec le simulateur de réseau ns-2 pour trouver les meilleurs paramètres du protocole AWCP. 3- Nous proposons ASAS, une stratégie adaptative pour l’attribution des slots temporels basée sur une approche cross-layer entre TDMA et AWCP
Road crashes and their damages represent a serious issue and are one of the main causes of people death. In this context, Vehicular Ad hoc NETworks (VANETs) are deployed to reduce the risk of road accident as well as to improve passengers’ comfort by allowing vehicles to exchange different kinds of data which ranges widely from road safety and traffic management to infotainment. Nowadays, safety applications are receiving a great deal of attention from researchers as well as from automobile manufacturers. In this thesis, we particularly focus on safety-critical applications, designed to provide drivers assistance in dangerous situations and to avoid accidents in highway environments. Such applications must guarantee to the vehicles access to the medium and have strict requirements regarding end-to-end delay and packet loss ratio. Therefore, our main goal is to propose new medium access control and routing protocols, which can efficiently adapt to frequent changing VANET network topologies. After a comprehensive overview of free-contention MAC protocols, we propose several solutions, based on Time Division Multiple Access Technique (TDMA). We have designed DTMAC, a fully distributed TDMA-based MAC protocol, which does not rely on an expensive infrastructure. DTMAC uses vehicles’ locations and a slot reuse concept to ensure that vehicles in adjacent areas have collision-free schedule. Using simulations, we prove that DTMAC provides a lower rate of access and merging collisions than VeMAC, a well-known TDMA based MAC protocol in VANET. Then, in order to ensure that event-driven safety messages can be sent over a long distance, we propose TRPM, a TDMA aware Routing Protocol for Multi-hop communication. Our routing scheme is based on a cross layer approach between the MAC and the routing layers, in which the intermediate vehicles are selected using TDMA scheduling information. Simulation results show that TRPM provides better performances in terms of average end-to-end delay, average number of hops and average delivery ratio. In the second part, we focus on coordinator-based TDMA scheduling mechanisms. First, we propose the Centralized TDMA based MAC protocol (CTMAC) which uses Road Side Units (RSUs) as a central coordinator to create and maintain the TDMA schedules. CTMAC implements an Access Collision Avoidance mechanism that can prevent the access collision problem occurring more than twice between the same vehicles that are trying to access the channel at the same time. Using simulation we show an improvement in terms of access and merging collisions as well as the overhead required to create and maintain the TDMA schedules compared to distributed scheduling mechanisms. However, in the CTMAC protocol, fast moving vehicles will need to compete for new slots after a short period of time when they leave their current RSU area, which makes a centralized scheduling approach very expensive. In order to further improve the performance of coordinator-based TDMA scheduling mechanisms, we focus on cluster-based TDMA MAC protocols in which some vehicles in the network are elected to coordinate the channel access, allowing the vehicles to remain connected with their channel coordinator for a longer period of time. To this end, first we propose an adaptive weighted clustering protocol, named AWCP, which is road map dependent and uses road IDs and vehicle directions to make the clusters’ structure as stable as possible. Then, we formulate the AWCP parameter tuning as a multi-objective problem and we propose an optimization tool to find the optimal parameters of AWCP to ensure its QoS. Next, we propose ASAS, an adaptive slot assignment strategy for a cluster-based TDMA MAC protocol. This strategy is based on a cross layer approach involving TDMA and AWCP. The objective is to overcome the inter-cluster interference issue in overlapping areas by taking into account vehicles’ locations and directions when the cluster head assign slots

Un réseau sans fil multi-saut est un ensemble d'entités mobiles et/ou fixes formant un réseau dynamique temporaire avec ou sans l'aide de toute administration centralisée. Cette particularité rend le routage problématique en cas d'instabilité des éléments qui composent les communications non directes. Afin de palier ces problèmes, de nouvelles formes de routage sont utilisées comme le routage multi-chemin (MC). Le routage MC permet d'envoyer les données sur des chemins multiples et semble être une solution efficace pour ces réseaux. Le but de cette thèse est d'étudier les techniques de routage MC dans un contexte sans fil multi-saut en vue d'obtenir de meilleures performances. Nous avons choisi pour notre étude une extension MC du protocole OLSR, appelée MP-OLSR. Nous évaluons ses performances sous divers scénarios sous NS-2. Ces tests d'évaluation nous ont amenés à mettre en 'evidence deux problèmes dans MP-OLSR : la réactivité du protocole de routage MC suite à des ruptures de route et la stratégie de répartition des données sur les chemins multiples. Nous avons étudié la réactivité de tels mécanismes dans MP-OLSR. Nous avons proposé trois nouvelles techniques de réparation de pannes qui diminuent les temps de rétablissement d'une route et réduisent le taux de perte des flux transmis. Nous proposons aussi un mécanisme qui détecte la dégradation de la qualité des liens durant le transfert d'un trafic de données. Les informations déduites de ce mécanisme servent à adapter la proportion de trafic à affecter à chaque chemin selon les conditions réseaux. Cette nouvelle variante du protocole MP-OLSR est évaluée par simulation.

Luk, Chun Pong.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2008.
Includes bibliographical references (leaves 122-125).
Abstracts in English and Chinese.
Abstract --- p.i
Acknowledgement --- p.iv
Chapter 1 --- Introduction / Motivation --- p.1
Chapter 1.1 --- Background and Motivation --- p.1
Chapter 1.2 --- Performance Analysis of Opportunistic Routing in Multi-hop Wireless Network --- p.3
Chapter 1.3 --- Opportunistic Routing Protocol Design --- p.5
Chapter 1.4 --- Chapter Summary --- p.6
Chapter 2 --- Literature Review --- p.8
Chapter 2.1 --- Introduction --- p.8
Chapter 2.2 --- Opportunistic Routing Protocols --- p.9
Chapter 2.2.1 --- Challenges of the Opportunistic Routing Protocol Design --- p.9
Chapter 2.2.2 --- Overview of Existing Opportunistic Routing Protocols --- p.11
Chapter 2.2.3 --- Forwarding Set Selection Algorithms --- p.12
Chapter 2.2.4 --- Actual Forwarder Determination --- p.13
Chapter 2.2.5 --- Duplicate Suppression Strategies --- p.14
Chapter 2.2.6 --- Variations of Opportunistic Routing Protocols --- p.16
Chapter 2.3 --- Performance Evaluation and Analysis of Opportunistic Routing --- p.16
Chapter 2.4 --- Routing in Networks with Directional Antennas --- p.19
Chapter 2.4.1 --- Performance Analysis of the use of Directional Antenna in Routing --- p.20
Chapter 2.4.2 --- Existing Routing and MAC protocols for Networks with Directional Antennas --- p.21
Chapter 2.5 --- Chapter Summary --- p.22
Chapter 3 --- Performance Analysis of Opportunistic Routing in Multi-hop Wireless Network --- p.24
Chapter 3.1 --- Introduction --- p.24
Chapter 3.2 --- Analytical Derivation of the Expected Progress per Transmission of Opportunistic Routing --- p.25
Chapter 3.2.1 --- Problem Formulations and Assumptions --- p.26
Chapter 3.2.2 --- Reception Probability of a Node in a Given Region --- p.28
Chapter 3.2.3 --- Radio Channel Models --- p.30
Chapter 3.2.4 --- Average Progress per Transmission --- p.32
Chapter 3.3 --- Validation and Analytical Results --- p.34
Chapter 3.3.1 --- Results Validation --- p.34
Chapter 3.3.2 --- Baseline Models --- p.35
Chapter 3.3.3 --- Results and Analysis --- p.36
Chapter 3.4 --- Further Extension of the Model --- p.40
Chapter 3.5 --- Chapter Summary --- p.42
Chapter 4 --- Opportunistic Routing in Multi-hop Wireless Networks with Directional Antennas --- p.44
Chapter 4.1 --- Introduction --- p.44
Chapter 4.2 --- Performance Analysis of Opportunistic Routing in Networks with Directional Antennas --- p.46
Chapter 4.2.1 --- Network Model --- p.46
Chapter 4.2.2 --- Radio Channel Models --- p.47
Chapter 4.2.3 --- Antenna Models --- p.49
Chapter 4.2.4 --- Expected Progress per Transmission with Directional Antenna --- p.51
Chapter 4.2.5 --- Simulation Setup --- p.52
Chapter 4.2.6 --- Results and Analysis --- p.54
Chapter 4.3 --- Maximizing the Gain of Opportunistic Routing by Adjusting Antenna Beamwidth and Direction --- p.60
Chapter 4.3.1 --- Introduction and Motivation --- p.60
Chapter 4.3.2 --- Network Models --- p.61
Chapter 4.3.3 --- Algorithms --- p.61
Chapter 4.3.4 --- Results and Discussions --- p.66
Chapter 4.3.5 --- Section Summary --- p.71
Chapter 4.4 --- Chapter Summary --- p.72
Chapter 5 --- Impact of Interference on Opportunistic Routing --- p.74
Chapter 5.1 --- Introduction --- p.74
Chapter 5.2 --- Interference Model --- p.75
Chapter 5.3 --- MAC Protocols --- p.76
Chapter 5.4 --- Simulation Results and Discussions --- p.78
Chapter 5.4.1 --- Simulation Setup --- p.78
Chapter 5.4.2 --- Baseline Models --- p.78
Chapter 5.4.3 --- Results and Analysis --- p.79
Chapter 5.5 --- Chapter Summary --- p.84
Chapter 6 --- Threshold-based Opportunistic Routing Protocol --- p.86
Chapter 6.1 --- Introduction --- p.86
Chapter 6.2 --- Limitations of Existing Opportunistic Routing Protocols --- p.87
Chapter 6.3 --- System Model --- p.89
Chapter 6.4 --- Operating Principles of TORP --- p.91
Chapter 6.5 --- Protocol Details --- p.93
Chapter 6.5.1 --- Forwarding Set Computation --- p.93
Chapter 6.5.2 --- Update of Forwarding Set and Remaining Transmission Counts --- p.97
Chapter 6.5.3 --- Forwarding Threshold Computation and Details of the Packet Forwarding Process --- p.100
Chapter 6.5.4 --- Node State --- p.101
Chapter 6.5.5 --- Packet Format --- p.101
Chapter 6.5.6 --- Batched Acknowledgement --- p.102
Chapter 6.6 --- Advantages of TORP --- p.102
Chapter 6.6.1 --- Distributed Forwarding Set Computation --- p.102
Chapter 6.6.2 --- Threshold-based Forwarding --- p.103
Chapter 6.6.3 --- MAC-Independence --- p.104
Chapter 6.7 --- Protocol Extensions --- p.104
Chapter 6.7.1 --- Implicit ACK --- p.104
Chapter 6.7.2 --- Progress Recovery --- p.105
Chapter 6.7.3 --- Modification of TORP for Large Networks --- p.106
Chapter 6.8 --- Results and Discussions --- p.106
Chapter 6.8.1 --- Simulation Setup --- p.106
Chapter 6.8.2 --- Baseline Models --- p.107
Chapter 6.8.3 --- Performance Evaluations and Analysis --- p.108
Chapter 6.9 --- Chapter Summary --- p.116
Chapter 7 --- Conclusion and Future Works --- p.118
Chapter 7.1 --- Conclusion --- p.118
Chapter 7.2 --- Future Work --- p.120
Bibliography --- p.122

博士
淡江大學
資訊工程學系
91
A multi-hop mobile ad hoc network (MANET) is formed with several independent mobile hosts (MHs) or devices in a limited communication range. Some form of routing protocol is in general necessary in such an environment, since two MHs that may wish to exchange packets might not be able to communicate directly. Therefore, how to design an efficient routing protocol is an important issue in such multi-hop MANET. Many ad hoc routing protocols exchange and update their routing information by using broadcast scheme. However, in current wireless communications such as IEEE 802.11 wireless local area network (WLAN), there is no acknowledgment reply mechanism for broadcast and multicast frames. This shortcoming leads to an uncertain broadcast/multicast problem in MANET and will degrade the performance of routing protocols. Recently, adaptive transmission techniques have been extensively investigated for improvement of transmission performance in wireless communications. One of these techniques is the variable-rate quadrature amplitude modulation (QAM) scheme. With the characteristics of modulation schemes, the data rate of wireless communication is inversely proportional with the transmission distance (range). Therefore, how to design an efficient medium access control (MAC) and routing protocol for supporting multi-rate/multi-range transmission in multi-hop MANET environment is another important issue. According to above-mentioned problems, we propose a reliable broadcast mechanism to solve the uncertain broadcast/multicast problem in MANET, and then propose a multi-rate/multi-range routing protocol (M2RP) for multi-rate transmissions (e.g., 1/2/5.5/11 Mb/sec) in this dissertation. With the characteristics of these issues, the conventional shortest path of minimum-hops approach will be no longer suitable for the multi-rate/multi-range multi-hop ad hoc networks (M3AN). Thus, by analyzing the MAC delay of the IEEE 802.11 MAC protocol, the proposed M2RP is capable of predicting the transfer delay of a routing path and finding the best one, which has the minimum transfer delay from source to destination. The proposed M2RP can maximize the channel utilization as well as to minimize the network transfer delay from source to destination. Simulation results show that M2RP performs the load balancing and fast routing very well, and its call blocking probability is obviously lower than that of conventional minimum-hops approach with fixed transmission rate.

碩士
國立成功大學
電腦與通信工程研究所
100
Wireless transmission suffers from channel fading. An efficient solution is to utilize cooperative diversity. In wireless ad hoc networks, cooperative diversity can be achieved by sharing antennas between nodes, and for this reason, many transmission schemes has been proposed. However, rare of these transmission schemes can provide quality-of-service (QoS). In this article, we propose a time division multiple access (TDMA)-based QoS routing protocol. For each data flow with QoS requirement, the proposed QoS routing protocol not only discovers a route, but allocates TDMA slot, transmission rate and transmission power for each link on this route. Nodes can obtain diversity by receiving multiple members’ transmissions. Since many parameters of the proposed QoS routing protocol can affect the system performance, we develop computer simulations to give a design overview.

In multi-hop wireless network (MWN), the mobile nodes relay others’ packets for enabling new applications and enhancing the network deployment and performance. However, the selfish nodes drop the packets because packet relay consumes their resources without benefits, and the malicious nodes drop the packets to launch Denial-of-Service attacks. Packet drop attacks adversely degrade the network fairness and performance in terms of throughput, delay, and packet delivery ratio. Moreover, due to the nature of wireless transmission and multi-hop packet relay, the attackers can analyze the network traffic in undetectable way to learn the users’ locations in number of hops and their communication activities causing a serious threat to the users’ privacy. In this thesis, we propose efficient security protocols for thwarting packet drop attacks and preserving users’ privacy in multi-hop wireless networks. First, we design a fair and efficient cooperation incentive protocol to stimulate the selfish nodes to relay others’ packets. The source and the destination nodes pay credits (or micropayment) to the intermediate nodes for relaying their packets. In addition to cooperation stimulation, the incentive protocol enforces fairness by rewarding credits to compensate the nodes for the consumed resources in relaying others’ packets. The protocol also discourages launching Resource-Exhaustion attacks by sending bogus packets to exhaust the intermediate nodes’ resources because the nodes pay for relaying their packets. For fair charging policy, both the source and the destination nodes are charged when the two nodes benefit from the communication. Since micropayment protocols have been originally proposed for web-based applications, we propose a practical payment model specifically designed for MWNs to consider the significant differences between web-based applications and cooperation stimulation. Although the non-repudiation property of the public-key cryptography is essential for securing the incentive protocol, the public-key cryptography requires too complicated computations and has a long signature tag. For efficient implementation, we use the public-key cryptography only for the first packet in a series and use the efficient hashing operations for the next packets, so that the overhead of the packet series converges to that of the hashing operations. Since a trusted party is not involved in the communication sessions, the nodes usually submit undeniable digital receipts (proofs of packet relay) to a centralized trusted party for updating their credit accounts. Instead of submitting large-size payment receipts, the nodes submit brief reports containing the alleged charges and rewards and store undeniable security evidences. The payment of the fair reports can be cleared with almost no processing overhead. For the cheating reports, the evidences are requested to identify and evict the cheating nodes. Since the cheating actions are exceptional, the proposed protocol can significantly reduce the required bandwidth and energy for submitting the payment data and clear the payment with almost no processing overhead while achieving the same security strength as the receipt-based protocols. Second, the payment reports are processed to extract financial information to reward the cooperative nodes, and contextual information such as the broken links to build up a trust system to measure the nodes’ packet-relay success ratios in terms of trust values. A node’s trust value is degraded whenever it does not relay a packet and improved whenever it does. A node is identified as malicious and excluded from the network once its trust value reaches to a threshold. Using trust system is necessary to keep track of the nodes’ long-term behaviors because the network packets may be dropped normally, e.g., due to mobility, or temporarily, e.g., due to network congestion, but the high frequency of packet drop is an obvious misbehavior. Then, we propose a trust-based and energy-aware routing protocol to route traffics through the highly trusted nodes having sufficient residual energy in order to establish stable routes and thus minimize the probability of route breakage. A node’s trust value is a real and live measurement to the node’s failure probability and mobility level, i.e., the low-mobility nodes having large hardware resources can perform packet relay more efficiently. In this way, the proposed protocol stimulates the nodes not only to cooperate but also to improve their packet-relay success ratio and tell the truth about their residual energy to improve their trust values and thus raise their chances to participate in future routes. Finally, we propose a privacy-preserving routing and incentive protocol for hybrid ad hoc wireless network. Micropayment is used to stimulate the nodes’ cooperation without submitting payment receipts. We only use the lightweight hashing and symmetric-key-cryptography operations to preserve the users’ privacy. The nodes’ pseudonyms are efficiently computed using hashing operations. Only trusted parties can link these pseudonyms to the real identities for charging and rewarding operations. Moreover, our protocol protects the location privacy of the anonymous source and destination nodes. Extensive analysis and simulations demonstrate that our protocols can secure the payment and trust calculation, preserve the users’ privacy with acceptable overhead, and precisely identify the malicious and the cheating nodes. Moreover, the simulation and measurement results demonstrate that our routing protocols can significantly improve route stability and thus the packet delivery ratio due to stimulating the selfish nodes’ cooperation, evicting the malicious nodes, and making informed decisions regarding route selection. In addition, the processing and submitting overheads of the payment-reports are incomparable with those of the receipts in the receipt-based incentive protocols. Our protocol also requires incomparable overhead to the signature-based protocols because the lightweight hashing operations dominate the nodes’ operations.

Thesis (M. S.)--Florida State University, 2005.
Advisor: Dr. Kartik Gopalan, Florida State University, College of Arts and Sciences, Dept. of Computer Science. Title and description from dissertation home page (viewed Sept. 19, 2005). Document formatted into pages; contains xi, 61 pages. Includes bibliographical references.

碩士
國立臺灣大學
電機工程學研究所
95
ABSTRACT Vehicular Ad Hoc Network (VANET) is the technique for overcoming the limit of transmission range in wireless vehicular communication. Traditional ad hoc multi-hop routing protocols may not achieve optimal performance in VANET, because specified mobility pattern affects the packets transmission. However, the effect of road conditions on performance of routing protocols is seldom discussed in current related work. Hence, this thesis proposes a route lifetime predicting mechanism with road parameters of vehicular environment to improve the performance of ad-hoc routing protocols under VANET environment. Because mobility pattern of vehicles is limited by road conditions, such as numbers of lanes and waiting time of traffic light, we first discuss the relationship between routing performance and these different road conditions. After study and analysis, it is concluded that the main problem is shorter route lifetime because of route failure which is caused by inter-vehicle mobility. Turning or stopping at the intersections of the vehicles which participate in the route would cause the route failure. Based on mobility pattern, we propose a route lifetime predicting model that can predict the inter-vehicle lifetime with inter-vehicle geographical information. Based on this predicted route lifetime model, we also propose a distributed route lifetime priority mechanism that can help to select the route with longer route lifetime to increase the delivery ratio of packet transmission. After simulation under topology with different road conditions, the proposed route lifetime mechanism can increase about 20\% performance. The proposed route lifetime mechanism can optimally improve the performance of routing protocol under vehicular environment.

This MSc thesis is focused in the study, solution proposal and experimental evaluation of security solutions for Wireless Sensor Networks (WSNs). The objectives are centered on intrusion tolerant routing services, adapted for the characteristics and requirements of WSN nodes and operation behavior. The main contribution addresses the establishment of pro-active intrusion tolerance properties at the network level, as security mechanisms for the proposal of a reliable and secure routing protocol. Those properties and mechanisms will augment a secure communication base layer supported by light-weigh cryptography methods, to improve the global network resilience capabilities against possible intrusion-attacks on the WSN nodes. Adapting to WSN characteristics, the design of the intended security services also pushes complexity away from resource-poor sensor nodes towards resource-rich and trustable base stations. The devised solution will construct, securely and efficiently, a secure tree-structured routing service for data-dissemination in large scale deployed WSNs. The purpose is to tolerate the damage caused by adversaries modeled according with the Dolev-Yao threat model and ISO X.800 attack typology and framework, or intruders that can compromise maliciously the deployed sensor nodes, injecting, modifying, or blocking packets, jeopardizing the correct behavior of internal network routing processing and topology management. The proposed enhanced mechanisms, as well as the design and implementation of a new intrusiontolerant routing protocol for a large scale WSN are evaluated by simulation. For this purpose, the evaluation is based on a rich simulation environment, modeling networks from hundreds to tens of thousands of wireless sensors, analyzing different dimensions: connectivity conditions, degree-distribution patterns, latency and average short-paths, clustering, reliability metrics and energy cost.