'It is not a lack of spectrum. It is an issue of efficient use of the available spectrum"--conclusions of the FCC Spectrum Policy Task Force. There is growing interest towards providing broadband communication with high bit rates and throughput, especially in the ISM band, as it was an ignition of innovation triggered by the FCC to provide, to some extent, a regulation-free band that anyone can use. But with such freedom comes the risk of interference and more responsibility to avoid causing it. Therefore, the need for accurate interference detection and identification, along with good blind detection capabilities are inevitable. Since cognitive radio is being adopted widely as more researchers consider it the ultimate solution for efficient spectrum sharing [1], it is reasonable to study the cognitive radio in the ISM band [2]. Many indications show that the ISM band will have less regulation in the future, and some even predict that the ISM may be completely regulation free [3]. In the dawn of cognitive radio, more knowledge about possible interfering signals should play a major role in determining optimal transmitter configurations. Since signal identification and interference will be the core concerns [4], [5], we will describe a novel approach for a cognitive radio spectrum sensing engine, which will be essential to design more efficient ISM band transceivers. In this thesis we propose a novel spectrum awareness engine to be integrated in the cognitive radios. Furthermore, the proposed engine is specialized for the ISM band, assuming that it can be one of the most challenging bands due to its free-to-use approach. It is shown that characterization of the interfering signals will help with overcoming their effects. This knowledge is invaluable to help choose the best configuration for the transceivers and will help to support the efforts of the coexistence attempts between wireless devices in such bands.

This thesis is concerned with the development of new mathematical models for the IEEE 802.11??s access mechanisms, with a particular focus on DCF and EDCA. Accurate mathematical models for the DCF and EDCA access mechanisms provide many benefits, such as improved performance analysis, easier network capacity planning, and robust network design. A feature that permeates the work presented in this thesis is the application of our new models to network environments where both saturated and non-saturated traffic sources are present. The scenario in which multiple traffic sources are present is more technically challenging, but provides for a more realistic setting. Our first contribution is the development of a new Markov model for non-saturated DCF in order to predict the network throughput. This model takes into account several details of the protocol that have been hitherto neglected. In addition, we apply a novel treatment of the packet service time within our model. We show how the inclusion of these effects provides more accurate predictions of network throughput than earlier works. Our second contribution is the development of a new analytical model for EDCA, again in order to predict network throughput. Our new EDCA model is based on a replacement of the normal AIFS parameter of EDCA with a new parameter more closely associated with DCF. This novel procedure allows EDCA to be viewed as a modified multi-mode version of DCF. Our third contribution is the simultaneous application of our new Markov models to both the non-saturated and the saturated regime. Hitherto, network throughput predictions for these regimes have required completely separate mathematical models. The convergence property of our model in the two regimes provides a new method to estimate the network capacity of the network. Our fourth contribution relates to predictions for the multimedia capacity of 802.11 networks. Our multimedia capacity analysis, which is based on modifications to our Markov model, is new in that it can be applied to a broad range of quality of service requirements. Finally, we highlight the use of our analysis in the context of emerging location-enabled networks.

Les réseaux sans fil connaissent aujourd'hui un essor important. Le<br />nombre croissant d'offres commerciales basées sur la norme IEEE 802.11<br />(Wi-Fi) et ses déclinaisons en atteste. Ces réseaux nécessitent<br />actuellement la présence d'une station de base pour assurer les<br />communications entre mobiles. Les réseaux ad hoc sont des<br />réseaux sans fil spontanés, mobiles et totalement autonome. Les mobiles<br />communiquent directement entre eux, relayant les communications des<br />autres mobiles lorsque les correspondants sont hors de portée radio. Il<br />est dès lors possible de créer un réseau par la simple présence de<br />terminaux équipés de cartes d'interfaces adéquates. Ces réseaux mobiles<br />et dynamiques peuvent être utilisés pour étendre la portée de stations<br />de base, offrant ainsi un accès à l'Internet sur une zone géographique<br />étendue à moindre coût. Ils peuvent être déployés rapidement et être<br />utilisés par exemple dans des situations d'urgence.<br /><br />Les caractéristiques particulières du médium radio, telle que la portée<br />de communication limitée ou le mode de partage du canal radio ainsi que<br />la mobilité des terminaux rendent souvent les mécanismes et protocoles<br />issus du monde filaire peu performants. À l'heure actuelle, de nombreux<br />travaux ont été effectués afin de concevoir des protocoles de routage<br />adaptés à ces réseaux. Le groupe de travail MANET de l'IETF est en passe<br />de standardiser une ou plusieurs solutions de routage. De nombreuses<br />problématiques restent cependant ouvertes telles que la sécurité, le<br /> multicast ou encore la qualité de service. Ces différents<br />sujets ont fait couler beaucoup d'encre durant ces dernières années.<br />Toutes les solutions issues du monde filaire ont été ré-examinées et<br />adaptées mais peu de propositions réellement adaptées aux spécificités<br />de ces réseaux ont vu le jour.<br /><br />Le travail effectué durant ma thèse se situe autour de la problématique<br />de la réservation de bande passante dans les réseaux ad hoc.<br />Ce travail a débuté par la proposition d'un protocole de réservation de<br />bande passante prenant en compte les interférences pouvant survenir<br />entre émetteurs hors de portée de communication. En effet, deux mobiles<br />ne pouvant communiquer directement peuvent avoir à se partager la bande<br />passante du canal radio. Mettre en oeuvre un protocole de réservation de<br />bande passante nécessite d'apporter suffisamment d'informations aux<br />routeurs en charge d'accepter ou de refuser les requêtes formulées par<br />les applications afin de leur permettre d'effectuer un contrôle<br />d'admission réaliste.<br /><br />Ce travail nous a conduit à nous intéresser à l'étude du protocole<br />d'accès au médium de la norme IEEE 802.11 afin d'évaluer sa capacité.<br />L'intégralité des études théoriques des performances de ce protocole<br />concernaient jusqu'à présent des réseaux dans lesquels tous les mobiles<br />sont à portée de communication les uns des autres. Or, dans certaines<br />situations, la présence de communications distantes a un impact très<br />marqué sur les performances et sur l'équité de ce protocole d'accès au<br />médium. Nous avons modélisé plusieurs scénarios présentant une forte<br />inégalité dans l'accès au médium, phénomène pouvant avoir un impact<br />important sur l'estimation des ressources disponibles.<br /><br /><br />Le protocole d'accès au médium n'étant pas équitable dans un contexte<br />multi-sauts, nous avons proposé un algorithme distribué d'allocation de<br />bande passante dans de tels réseaux permettant de préserver une certaine<br />équité tout en conservant une utilisation globale du réseau correcte.<br />Dans de tels réseaux, il y a en effet souvent opposition entre<br />performance globale et partage équitable des ressources. La solution que<br />nous proposons permet dans un contexte statique ainsi que dans un<br />contexte mobile de réaliser un compromis entre ces deux objectifs<br />antinomiques, et ce de façon totalement distribuée.<br /><br />Enfin, dans le cadre de réseaux hybrides composés d'un réseau d'accès<br />sans fil offrant un accès à l'Internet à un réseau ad hoc<br />sous-jacent, nous avons étudié l'impact du trafic de contrôle sur les<br />performances du réseau. Cette problématique nécessite souvent de faire<br />un compromis entre transmission rapide et fiable des informations de<br />gestion du réseau telles que la localisation des différents mobiles<br />permettant de construire l'arbre de routage et utilisation du réseau. En<br />effet, une transmission fréquente d'informations de contrôle permet<br />d'aboutir à une vision précise du réseau mais a un coût important. Nous<br />avons montré, par simulation, que le gain obtenu par la précision de la<br />vision du réseau apportée à chaque routeur était rapidement compensé par<br />l'occupation des ressources engendrée à cette fin.<br /><br />Concevoir une solution de qualité de service pour de tels réseaux n'est<br />pas une problématique simple et beaucoup reste à faire. L'importance<br />d'une évaluation précise de la capacité du médium a été démontrée mais<br />ce processus reste coûteux à mettre en oeuvre et il est impossible de<br />prévoir toutes les situations pouvant survenir dans des réseaux radio<br />mobiles. Les protocoles de qualité de service devront donc s'efforcer<br />d'évaluer au mieux l'état du réseau afin de ne pas sur ou sous-évaluer<br />sa capacité mais devront aussi être adaptatif afin de réagir rapidement<br />et efficacement à la versatilité de ces réseaux.

<p>Communicating over a wireless channel poses many unique challenges not found in wired communication because of the special characteristics of the wireless channel. The capacity in a wireless network is typically scarce as a result of the limited bandwidth and many distinct phenomenons, like attenuation and interference, that work destructively on the received signals.</p><p>The Medium Access Control (MAC) layer is responsible for sharing this limited resource among the users. This allocation problem should be handled by considering the Quality of Service (QoS) requirements of each user as to maximize the utility. Efficient MAC algorithms are crucial in minimizing collisions between transmissions and thus achieving high utilization of the channel.</p><p>This thesis focuses on conflict resolution and service differentiation algorithms for wireless local area networks, where there is no central control of the channel and each sender independently contends for access.</p><p>In part I, we study three approaches to improve the IEEE 802.11(e) standards with focus on QoS. In the first approach, utility functions are considered, that model application preferences, to achieve service differentiation and maximize the aggregated utility. We provide algorithms for two subsidiary problems that arise from the maximization problem, and show that a near--optimal solution is found. In the second approach a collision detection algorithm for multicast transmissions is proposed, that increases the reliability for multicast compared to the protected unicast traffic. The third approach is an improved MAC algorithm for the QoS standard IEEE 802.11e. The improved algorithm outperforms the standard and achieves close to optimal performance for large number of scenarios, which significantly reduces the need of adjusting the contention parameters.</p><p>In part II, we focus on channel bursting protocols that use noise bursts to resolve channel conflicts. These protocols is capable of achieving very low collision probability. We propose two new bursting protocols, that achieve very high channel utilization, and show that the bursting technique has good fairness properties and provides efficient support for service differentiation. We also show that it is possible to reduce the number of bursts without loosing performance.</p><p>In part III, the optimal backoff distribution that minimizes the collision probability is derived. We then propose a heuristic backoff distribution with similar properties that yields high channel utilization. An extension for service differentiation is provided where the sizes of the backoff windows are adjusted.</p>

Communicating over a wireless channel poses many unique challenges not found in wired communication because of the special characteristics of the wireless channel. The capacity in a wireless network is typically scarce as a result of the limited bandwidth and many distinct phenomenons, like attenuation and interference, that work destructively on the received signals. The Medium Access Control (MAC) layer is responsible for sharing this limited resource among the users. This allocation problem should be handled by considering the Quality of Service (QoS) requirements of each user as to maximize the utility. Efficient MAC algorithms are crucial in minimizing collisions between transmissions and thus achieving high utilization of the channel. This thesis focuses on conflict resolution and service differentiation algorithms for wireless local area networks, where there is no central control of the channel and each sender independently contends for access. In part I, we study three approaches to improve the IEEE 802.11(e) standards with focus on QoS. In the first approach, utility functions are considered, that model application preferences, to achieve service differentiation and maximize the aggregated utility. We provide algorithms for two subsidiary problems that arise from the maximization problem, and show that a near--optimal solution is found. In the second approach a collision detection algorithm for multicast transmissions is proposed, that increases the reliability for multicast compared to the protected unicast traffic. The third approach is an improved MAC algorithm for the QoS standard IEEE 802.11e. The improved algorithm outperforms the standard and achieves close to optimal performance for large number of scenarios, which significantly reduces the need of adjusting the contention parameters. In part II, we focus on channel bursting protocols that use noise bursts to resolve channel conflicts. These protocols is capable of achieving very low collision probability. We propose two new bursting protocols, that achieve very high channel utilization, and show that the bursting technique has good fairness properties and provides efficient support for service differentiation. We also show that it is possible to reduce the number of bursts without loosing performance. In part III, the optimal backoff distribution that minimizes the collision probability is derived. We then propose a heuristic backoff distribution with similar properties that yields high channel utilization. An extension for service differentiation is provided where the sizes of the backoff windows are adjusted.

Aujourd'hui, les utilisateurs mobiles intègrent plusieurs interfaces sans fil dans leurs dispositifs mobiles, tels que IEEE 802.11, des technologies cellulaires 2G/3G/4G, WiMAX ou Bluetooth, car ces technologies hétérogènes peuvent fournir un accès Internet dans les zones urbaines. Dans ce contexte, il existe un potentiel pour les utilisateurs mobiles d'exploiter la diversité des interfaces sans fil, afin d'être connectés aux réseaux de la meilleure manière possible, à tout moment et partout. Cependant, afin de profiter de cette diversité des réseaux il est nécessaire d'avoir une gestion efficace de la mobilité et de la multi-domiciliation. En ce qui concerne la mobilité, les utilisateurs mobiles ont besoin de découvrir les réseaux sans fil et basculer entre des points d'accès d'une façon transparente et sans coupures. Afin de supporter la multi-domiciliation et de permettre l'utilisation de plusieurs réseaux sans fil simultanément, il est nécessaire de définir des mécanismes de sélection des réseaux visant à attribuer les flux d'applications aux différentes inter- faces sans fil d'une manière optimale. Dans cette thèse, nous avons d'abord caractérisé la diversité des réseaux en explorant et en analysant les performances des déploiements sans fil actuelles dans les zones urbaines, en particulier les réseaux cellulaires et les réseaux communautaires basés sur IEEE 802.11. Ensuite, nous avons étudié la mobilité dans les réseaux IEEE 802.11, particulièrement le processus de découverte des points d'accès, en fournissant deux algorithmes adaptatifs qui visent à utiliser les paramètres de découverte les plus appropriés dans chaque scénario. Nous évaluons ces algorithmes par l'expérimentation et nous comparons leurs performances par rapport aux stratégies utilisant des paramètres par défaut. Enfin, nous étudions la sélection des réseaux dans un scénario multi-domicilié et nous proposons un algorithme de prise de décision pour trouver l'attribution optimale des flux aux différentes interfaces, en prenant en compte des critères de qualité de service et de consommation d'énergie. Cet algorithme de décision est modélisé par un problème d'optimisation multi-objectif et est résolu avec des algorithmes génétiques. Nous évaluons, par le biais de simulations, les performances de notre approche contre des algorithmes de décision basés sur des préférences.

The increasing popularity of wireless networks over the last years indicates that there will be a demand for communicating devices providing high capacity communication together with QoS requirements. There are two types of wireless networks, infrastructure and Ad Hoc networks. The variation of topology caused by the mobility of hosts in the Ad Hoc networks results in a long latency, large jitter and low throughput. In infrastructure wireless networks, a base station (BS) or an Access Point (AP) is in charge of the data transmission. Therefore, the wireless hop can be considered as another hop of the transmission path. With the rapid growth of wireless traffics, the future wireless network is expected to provide services for heterogeneous data traffics with different quality of service requirements. Most proposed schemes do not have mechanisms to adapt to environment changes. In real situation, bandwidths, error rates, and loss rates of wireless links vary frequently. The QoS issues are very important in modern networks. There are many proposed service models and mechanisms to support QoS in wireline networks. Most of these QoS mechanisms are not suitable for direct application to the wireless network because of the characteristics of wireless communication which includes: 1) high error rates and bursty errors, 2) location-dependent and time-varying wireless channel capacity, 3) scarce bandwidth, 4) user mobility, and 5) power constraints of the mobile hosts. All of these above characteristics make the development of QoS in wireless networks very difficult and challenging. We try to cope with the bandwidth variations caused by the high error rate and bursty errors in wireless links, and the location-dependent and time-varying natures of wireless channel capacity. Furthermore, we expect to utilize the scarce wireless bandwidth more efficiently. In our proposed scheme, the higher priority flow is capable of broadcasting a message to inform the lower priority flows to change their priorities to adapt to environment variations. We will base on the differentiated service model and propose a Wireless Differentiation (WD) scheme for UDP flows and a Wireless Differentiation with Prioritized ACK (WDPA) scheme for connections with TCP flows which provide QoS support for IEEE 802.11b and do not change the basic access mechanism of IEEE 802.11b.

<p>This Master’s thesis is a pilot study that investigates different systems to drive autonomous and non-autonomous vehicles simultaneously on test tracks. The thesis includes studies of communication, positioning, collision avoidance, and techniques for surveillance of vehicles which are suitable for implementation. The investigation results in a suggested system outline.</p><p>Differential GPS combined with laser scanner vision is used for vehicle state estimation (position, heading, velocity, etc.). The state information is transmitted with IEEE 802.11 to all surrounding vehicles and surveillance center. With this information a Kalman prediction of the future position for all vehicles can be estimated and used for collision avoidance.</p>

Information systems and their services (referred to as cyberspace) are ubiquitous and touch all aspects of our life. With the exponential growth in cyberspace activities, the number and complexity of cyber-attacks have increased significantly due to an increase in the number of applications with vulnerabilities and the number of attackers. Consequently, it becomes extremely critical to develop efficient network Intrusion Detection Systems (IDS) that can mitigate and protect cyberspace resources and services against cyber-attacks. On the other hand, since each network system and application has its own specification as defined in its protocol, it is hard to develop a single IDS which works properly for all network protocols. The keener approach is to design customized detection engines for each protocol and then aggregate the reports from these engines to define the final security state of the system. In this dissertation, we developed a general methodology based on data mining, statistical analysis and protocol semantics to perform anomaly behavior analysis and detection for network-centric systems and their protocols. In our approach, we develop runtime models of protocol's state transitions during a time interval ΔΤ. We consider any n consecutive messages in a session during the time interval ΔΤ as an n-transition pattern called n-gram. By applying statistical analysis over these n-gram patterns we can accurately model the normal behavior of any protocol. Then we use the amount of the deviation from this normal model to quantify the anomaly score of the protocol activities. If this anomaly score is higher than a well-defined threshold the system marks that activity as a malicious activity. To validate our methodology, we have applied it to two different protocols: DNS (Domain Name System) at the application layer and the IEEE 802.11(WiFi) at the data link layer, where we have achieved good detection results (>95%) with low detection errors (<0.1%).

This Master’s thesis is a pilot study that investigates different systems to drive autonomous and non-autonomous vehicles simultaneously on test tracks. The thesis includes studies of communication, positioning, collision avoidance, and techniques for surveillance of vehicles which are suitable for implementation. The investigation results in a suggested system outline. Differential GPS combined with laser scanner vision is used for vehicle state estimation (position, heading, velocity, etc.). The state information is transmitted with IEEE 802.11 to all surrounding vehicles and surveillance center. With this information a Kalman prediction of the future position for all vehicles can be estimated and used for collision avoidance.