<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 use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic.

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic.

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.

The aim of this work is to analyze the modern radio communication technologies and to formulate a methodology and means for implementing them in customers’ premises networks.