"We proposed a novel spectrum allocation approach for distributed cognitive radio networks. Cognitive radio systems are capable of sensing the prevailing environmental conditions and automatically adapting its operating parameters in order to enhance system and network performance. Using this technology, our proposed approach optimizes each individual wireless device and its single-hop communication links using the partial operating parameter and environmental information from adjacent devices within the wireless network. Assuming stationary wireless nodes, all wireless communication links employ non-contiguous orthogonal frequency division multiplexing (NC-OFDM) in order to enable dynamic spectrum access (DSA). The proposed approach will attempt to simultaneously minimize the bit error rate, minimize out-of-band (OOB) interference, and maximize overall throughput using a multi-objective fitness function. Without loss in generality, genetic algorithms are employed to perform the actual optimization. Two generic optimization approaches, subcarrier-wise approach and block-wise approach, were proposed to access spectrum. We also proposed and analyzed several approaches implemented via genetic algorithms (GA), such as quantizing variables, using adaptive variable ranges, and Multi-Objective Genetic Algorithms, for increasing the speed and improving the results of combined spectrum utilization/cross-layer optimization approaches proposed, together with several assisting processes and modifications devised to make the optimization to improve efficiency and execution time."

Wireless clients are vulnerable to exploitation by evil twins due to flaws in the authentication process of 802.11 Wi-Fi networks. Current certificate-based wireless authentication protocols present a potential solution, but are limited in their ability to provide a secure and usable platform for certificate validation. Our work seeks to mitigate these limitations by exploring a client-side strategy for utilizing alternative trust models in wireless network authentication. We compile a taxonomy of various trust models for conducting certificate-based authentication of wireless networks and methodically evaluate each model according to desirable properties of security, usability, and deployability. We then build a platform for leveraging alternative certificate-based trust models in wireless networks, present a proof-of-concept using one of the most promising alternative validation models identified--a whitelisting and pinning hybrid--and examine its effectiveness at defending against evil twin attacks in 802.11 networks.

Wireless sensor networks allow us to instrument our world in novel ways providing detailed insight that had not been possible earlier. Since these networks provide an interface to the physical world, it is necessary for each sensor node to learn its location in the physical space. The availability of location information at individual sensor nodes allows the network to provide higher layer services such as location stamped event reporting, geographic routing, in-network processing etc. A wide range of these sensor network protocols do not require absolute node coordinates and can work with relative node positions. This motivates for the need of anchor free localization algorithms that localize the individual sensor nodes with respect to each other in a local coordinate system. Such algorithms allow the sensor networks to be decoupled from external infrastructure and become truly place and play systems. The primary contributions of this thesis include two anchor free localization algorithms and one location refinement algorithm for ad-hoc wireless sensor networks. Our distributed anchor free localization algorithms do not require any external infrastructure in the form of landmark or manually initialized anchor nodes. These algorithms use measured inter-node distances among some node pairs and localize the entire network in a local coordinate system up to a global translation, rotation and reflection. The relative or virtual coordinates assigned by these algorithms can be readily used with a range of sensor network services like geographic routing, data aggregation, topology control etc. Our first localization algorithm is based on a distributed collaborative approach where all of the nodes in the network collaborate with each other to select a set of nodes. These nodes are localized and then used as reference nodes for the remaining sensor nodes. The novelty of this approach is that instead of solving the localization problem for the entire network upfront, first a small well-formed localization problem is solved and then these results are used to solve the localization problem for the remaining nodes in the network. Our second localization algorithm borrows ideas from the data visualization field and exploits the general undirected graph drawing theory to solve the sensor network localization problem. This algorithm divides the network into a large number of small overlapping clusters and creates local coordinate systems for each of the clusters. These clusters are then merged together in a single coordinate system using a novel distributed algorithm that seeks to minimize the error during this merge process. Our final contribution is a distributed location refinement algorithm that can be used with any of the range based localization algorithms to refine the sensor node coordinates to conform to the measured inter-node distances. We model this coordinate refinement problem as an unconstrained non-linear optimization problem and then transform this optimization problem into an aggregate computation problem. We propose two different approaches to solve this aggregate computation problem in a distributed manner. We evaluate our algorithms with detailed simulations using both Matlab and TinyOS simulator TOSSIM. We also validate our simulation results with experimentation carried out on a real network of MIT Cricket motes. We conclude this thesis with lessons learned during this research and discuss some future directions which can be explored to advance the research in sensor network localization.

<p>Internet has gained much popularity among the public since the mid 1990's and is now an integrated part of our society. A large range of high-speedbroadband providers and the development of new and more efficient Internet applications increase the possibilities to watch movies and live TV, use IP-telephony and share files over the Internet. Such applications demand high data transmission rates, which in turn consume network bandwidth. Since several users must share the common bandwidth capacity on the Internet, there will be locations in the network where the demand is higher than the capacity. This causes network congestion, which has negative impact on both the data transmission rate and transmission quality.</p><p>This thesis is about methods for measuring the available bandwidth of a network path between two computers. The available bandwidth can be interpreted as the maximum transfer rate possible without causing congestion. By deploying the methods studied in this thesis the available bandwidth can be measured without previous knowledge of the network topology. When an estimate of the available bandwidth is obtained, the transfer rate when sending messages between computers can be set to the measured value in order to avoid congestion.</p><p>In the thesis an active end-to-end available bandwidth measurement method called "Bandwidth Available in Real Time" (BART for short) is evaluated. BART measures the available bandwidth by injecting probe packets into the network at a given rate and then analysing how this rate has changed on the receiving side. A Kalman filter is used to update the current estimate of the available bandwidth using the new measurement sample.</p><p>The focus of the thesis is on how methods, such as BART, function in wireless 802.11 networks, which are very popular in work as well as in home environments. Wireless networks have a different construction compared to many other types of networks and this can affect the accuracy of the measurement methods discussed in this thesis. The effects must be analyzed and understood in order to obtain accurate available bandwidth estimates. Since wireless links are often parts of the network path between a sender and a receiver on the Internet, it is important to study how these links affect the estimates of the available bandwidth.</p>

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Internet has gained much popularity among the public since the mid 1990's and is now an integrated part of our society. A large range of high-speedbroadband providers and the development of new and more efficient Internet applications increase the possibilities to watch movies and live TV, use IP-telephony and share files over the Internet. Such applications demand high data transmission rates, which in turn consume network bandwidth. Since several users must share the common bandwidth capacity on the Internet, there will be locations in the network where the demand is higher than the capacity. This causes network congestion, which has negative impact on both the data transmission rate and transmission quality. This thesis is about methods for measuring the available bandwidth of a network path between two computers. The available bandwidth can be interpreted as the maximum transfer rate possible without causing congestion. By deploying the methods studied in this thesis the available bandwidth can be measured without previous knowledge of the network topology. When an estimate of the available bandwidth is obtained, the transfer rate when sending messages between computers can be set to the measured value in order to avoid congestion. In the thesis an active end-to-end available bandwidth measurement method called "Bandwidth Available in Real Time" (BART for short) is evaluated. BART measures the available bandwidth by injecting probe packets into the network at a given rate and then analysing how this rate has changed on the receiving side. A Kalman filter is used to update the current estimate of the available bandwidth using the new measurement sample. The focus of the thesis is on how methods, such as BART, function in wireless 802.11 networks, which are very popular in work as well as in home environments. Wireless networks have a different construction compared to many other types of networks and this can affect the accuracy of the measurement methods discussed in this thesis. The effects must be analyzed and understood in order to obtain accurate available bandwidth estimates. Since wireless links are often parts of the network path between a sender and a receiver on the Internet, it is important to study how these links affect the estimates of the available bandwidth.

In wireless ad hoc networks, the resources such as bandwidth, power, computing ability, etc., for end users are limited by the environments and hardware. In addition, the mobility of each user is different. Furthermore, the varied wireless networks with different properties such as transmission rate, coverage, power and protocols make it rarely difficult to establish and maintain the communications through the multiple intermediate nodes which are mobile devices. This dissertation will focus on the following three issues: 1. Most homogeneous wireless networks only considering one or less resources of the mobile device can not select and distribute the routes. In addition, it can cause the load of the intermediate nodes to increase. 2. The various wireless networks have different characteristics of resources. The route selection and distribution algorithms proposed before in homogeneous wireless networks are not adapted for the heterogeneous wireless networks. 3. Most route selection and distribution algorithms are designed for specific type of wireless environments (such as only for proactive type or reactive type). For different environment and different mobility, its cost will be different. To allow an environment-aware based adaptive management for heterogeneous wireless networks with different characteristics of resources becomes an important issue. In homogeneous wireless ad hoc networks, the resources of the mobile devices such as bandwidth, power, computing ability, etc., are limited and different by the environments and hardware. To evaluate the individual resource of each mobile device, the route distribution and selection algorithm considering the multiple resource variations in wireless ad hoc networks is proposed. First, the evaluation and management for individual resource of each mobile device such as bandwidth, power, and computing ability, are proposed. Second, according to the proposed algorithm, a mobile device can be estimated whether it supports the QoS or not. In addition, these resources evaluation results are transformed as the bottleneck resource information. At last, according to the bottleneck resource information of all the found routes, the route distributed through different intermediate nodes with most resources is selected for load distribution and balance. Considering the wireless network infrastructure today including 3G wireless communication, IEEE 802.11 wireless local area network, and wireless ad hoc networks, the characteristics such as transmission rates, bandwidth, power consumption, and transmission range of these wireless structures are not the same. In other words, the routing selection algorithm for homogeneous wireless networks may not be flexible for another wireless network. In this thesis, these different wireless network structures are integrated into one heterogeneous wireless network. Individual characteristics such as transmission rates, bandwidth, power consumption, and transmission range of these wireless structures are evaluated. According to the adaptive resource evaluation and route selection algorithm for the heterogeneous wireless networks, the route with the lowest cost and most resources is selected based on the integrated information of each resource estimation and the bottleneck information of each route found. Besides considering the characteristic of the heterogeneous wireless networks, the module (type) of the route selection and distribution algorithms also induces different costs and performance. The existing algorithms can be defined and divided into two typical types: proactive (table-driven) protocol and reactive (source initiated) protocol. The proactive type protocol pays the memory and periodical update (bandwidth consumption) costs for selecting the routing directly. In opposite, the reactive type protocol saves the costs but may increase the overhead for finding a routing path to the destination. To decrease the total costs of finding and maintaining routing paths, the environment-aware based adaptive management for heterogeneous wireless networks is proposed in this thesis. Corresponding to the movement of the users, the appropriate type of the routing algorithm should be selected for reducing the total costs of finding routing paths. In the adaptive management, we propose the type selection process to individually evaluate the cost of the two type protocols (proactive and reactive) via considering the protocols and the mobility of the users. According to the evaluation results, the appropriate protocol with less cost will be selected for finding and maintaining the routes in the heterogeneous wireless networks. According to the simulation, the routing selection and distribution algorithm proposed in this dissertation can not only effectively distribute the routing paths but also balance the load within homogeneous or heterogeneous wireless networks. Corresponding to the mobility of the users, the suitable type of routing protocol can be selected. Furthermore, the cost for routing paths searching, selection and maintenance is decreased. The block rate of these routing paths is reduced. Overall, according to the simulation, this dissertation makes the major contributions as follows: 1. The individual resource evaluations and managements for the mobile devices in the homogeneous wireless networks are proposed. The routes which satisfy the QoS can be selected and distributed according to the proposed algorithm. 2. The various wireless networks with different are integrated into a heterogeneous wireless network. The route search, selection, and maintenance algorithm for the hybrid properties heterogeneous wireless networks is proposed. 3. The classification to separate and classify the route search and selection algorithms is proposed. Corresponding to the mobility of the users, the environment-aware based adaptive management for heterogeneous wireless networks is proposed to reduce the costs caused by route search, selection, and maintenance.

With the rapid development in the areas of mobile manufacturing and multimedia communications, there is an increasing demand for Networked Virtual Environment (NVE) applications, such as Augmented Reality (AR), virtual walk-throughs, and massively multiplayer online games (MMOGs), on hand-held devices. Unfortunately, downloading and rendering a complex 3D scene is very computationally intensive and is not compatible with current mobile hardware specifications nor with available wireless bandwidth. Existing NVE applications deploy client/server based 3D streaming over thin mobile devices, which suffer from single point of failure, latency, and scalability issues. To address these issues, image-based rendering (IBR) and cloud-based 3D streaming have been introduced. The former introduces visual artifacts that reduce, and usually cancel, the realistic behaviors of the Virtual Environment (VE) application, while the latter is considered very expensive to implement. Peer-to-peer (P2P) 3D streaming is promising and affordable, but it has to tackle issues in object discovery and selection as well as content provider strategies. Distributing VE content over a mobile ad-hoc network (MANET) makes the system difficult to update due to the dynamic nature of the mobile clients. In order to tackle these issues, we came up with a novel protocol that combines the pros of both central and distributed approaches. Our proposed hybrid protocol, called OCTET, enables 3D scene streaming over thin devices in a way that can cope with current mobile hardware capabilities and mitigate the challenges of client/server and P2P 3D streaming. In fact, OCTET provides strategies that select, prioritize, and deliver only those objects that contribute to the user’s visible scene. OCTET is implemented using the "ns-2" simulation environment, and extensive experiments have clearly demonstrated significant achievements in mobile resource utilization, throughput, and system scalability.

This thesis presents the establishment of a covert-channel in wireless networks in the form of frames with intentionally corrupted Frame Check Sequences (FCSs). Previous works had alluded to the possibility of using this kind of covert-channel as an attack vector. We modify a simulation tool, called Sinalgo, which is used as a test bed for generating hypothetical scenarios for establishing a covert-channel. Single and Multi-Agent systems have been proposed as behaviour-based intrusion detection mechanisms, which utilize statistical information about network traffic. This utilized statistical information is used to detect covert-channel communications. This work highlights the potential impact of having this attack perpetrated in communications equipment with a low chance of being detected, if properly crafted. / UOIT

In order to improve the Quality of Service in wireless networks it is crucial to design and optimize the communication algorithms based on the underlying Physical and Link Layers. In this thesis we show that if instead of the link abstraction used in traditional wireless networking we rely on the much broader definition of a link, used in the context of cooperative communication, we can improve the performance of relay transmission systems operating over the wireless medium. From a networking perspective there are a whole host of layering and cross-layer design issues that enable one to propose optimal cooperative algorithms for wireless communication. Most of the research in this area has been concentrated on the physical layer issues. In this thesis, we consider the interaction of the physical layer cooperative link with the higher layers, in particular the Medium Access Control Layer, and show that by appropriate protocol design we can improve the performance of wireless networks by using cooperation. Enabling cooperation among nodes in an optimal manner can lead to significant increase in the throughput for multi-hop wireless networks. We study and design cooperative protocols that lead to this throughput increase and quantify the appropriate level of cooperation among the users which leads to improving QoS.