Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Security and Trust in Mobile Ad-Hoc Networks
    (2015) Jain, Shalabh; Baras, John S; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Distributed ad-hoc networks have become ubiquitous in the current technological framework. Such networks have widespread applications in commercial, civil and military domains. Systems utilizing these networks are deployed in scenarios influencing critical aspects of human lives, e.g.: vehicular networks for road safety, infrastructure monitoring for smart grid or wildlife, and healthcare systems. The pervasive nature of such systems has made them a valuable target for adversarial action. The risk is compounded by the fact that typically the networks are composed of low power, unattended devices with limited protection and processing capabilities. Usage of cryptographic primitives can prove to be a significant overhead in these scenarios. Further, behavioral aspects of participants, that are critical for distributed system operation, are not effectively addressed by cryptography. In this dissertation, we explore the direction of using notions of trust and privacy to address security in these networks. In the first part of the dissertation, we consider the problems of generation, distribution and utilization of trust metrics. We adopt a cross-layer and component based view of the network protocols. We propose schemes operating at the physical layer of the communication stack, to generate trust metrics. We demonstrate that these schemes reliably detect relay adversaries in networks, and can be an effective measure of trust for the neighborhood discovery component. We propose techniques to combine trust from different detectors across multiple layers into a singular trust metric. Further, we illustrate via simulations, the advantages and disadvantages of existing techniques for propagation of local trust metrics throughout the network. We propose modifications to increase the robustness of the semiring based framework for trust propagation. Finally, we consider utilization of trust metrics to increase resilience of network protocols. We propose a distributed trust based framework, to secure routing protocols such as AODV, DSR. We highlight utility of our framework by using the proposed point-to-point link trust metrics. In the second part of the dissertation, we focus on the role of privacy in ad-hoc networks. We demonstrate that for three broad categories of systems; distributed state estimation, distributed consensus and distributed monitoring systems, privacy of context can reduce cryptographic requirements (such as the need for encryption). In fact, efficient methods to preserve privacy can significantly reduce the energy footprint of the overall security component. We define a privacy framework applicable to these scenarios, where the network can be partitioned into a hierarchical structure of critical and non-critical components. We utilize a physical layer watermarking scheme to ensure privacy guarantees in our framework. Further, for systems that lack a natural hierarchical structure, such as information fusion systems, we define an efficient framework to define a hierarchy (network partition), without leaking the structure to the adversary.
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    Efficient Spectrum Management for Mobile Ad Hoc Networks
    (2010) Jones, Leo Henry; Baecher, Gregory B; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The successful deployment of advanced wireless network applications for defense, homeland security, and public safety depends on the availability of relatively interference-free spectrum. Setup and maintenance of mobile networks for military and civilian first-response units often requires temporary allocation of spectrum resources for operations of finite, but uncertain, duration. As currently practiced, this is a very labor-intensive process with direct parallels to project management. Given the wide range of real-time local variation in propagation conditions, spatial distribution of nodes, and evolving technical and mission priorities current human-in-the loop conflict resolution approaches seem untenable. If the conventional radio regulatory structure is strictly adhered to, demand for spectrum will soon exceed supply. Software defined radio is one technology with potential to exploit local inefficiencies in spectrum usage, but questions regarding the management of such network have persisted for years. This dissertation examines a real-time spectrum distribution approach that is based on principles of economic utility and equilibrium among multiple competitors for limited goods in a free market. The spectrum distribution problem may be viewed as a special case of multi-objective optimization of a constrained resource. A computer simulation was developed to create hundreds of cases of local spectrum crowding, to which simultaneous perturbation simulated annealing (SPSA) was applied as a nominal optimization algorithm. Two control architectures were modeled for comparison, one requiring a local monitoring infrastructure and coordination ("top down") the other more market based ("bottom up"). The analysis described herein indicates that in both cases "hands-off" local spectrum management by trusted algorithms is not only feasible, but that conditions of entry for new networks may be determined a priori, with a degree of confidence described by relatively simple algebraic formulas.
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    Heterogeneous Wireless Networks: An Analysis of Network and Service Level Diversity
    (2004-04-28) Kozat, Ulas Can; Tassiulas, Leandros; Electrical Engineering
    Future wireless systems will be a collection of symbiotic and hierarchical networks that address different aspects of communication needs. This architectural heterogeneity constitutes a network level diversity, where wireless domains can benefit from each other's spare resources in terms of bandwidth and energy. The dissertation investigates the network diversity through particularly interesting scenarios that involve capacity-limited multi-hop ad hoc networks and high-bandwidth wired or wireless infrastructures. Heterogeneity and infrastructures not only exist at the level of networking technologies and architectures, but also at the level of available services in each network domain. Efficient discovery of services across the domains and allocation of service points to individual users are beneficial for facilitating the actual communication, supplying survivable services, and better utilizing the network resources. These concepts together define the service level diversity, which is the second topic studied in our dissertation. In this dissertation, we first focus on a large-scale hybrid network, where a relatively resource abundant infrastructure network overlays a multi-hop wireless network. Using a random geometric random graph model and defining appropriate connectivity constraints, we derive the overall transport capacity of this hybrid network. In the sequel, we dwell upon hybrid networks with arbitrary size and topology. We develop a Quality of Service (QoS) based framework to utilize the joint resources of the ad hoc and infrastructure tier with minimal power exposure on other symbiotic networks that operate over the same radio frequency bands. The framework requires a cross-layer approach to adequately satisfy the system objectives and individual user demands. Since the problem is proven to be intractable, we explore sub-optimal but efficient algorithms to solve it by relying on derived performance bounds. In the last part of the dissertation, we shift our attention from network level diversity to service level diversity. After investigating possible resource discovery mechanisms in conjunction with their applicability to multi-hop wireless environments, we present our own solution, namely Distributed Service Discovery Protocol (DSDP). DSDP enables a highly scalable, survivable, and fast resource discovery under a very dynamic network topology. It also provides the necessary architectural and signaling mechanisms to effectively implement resource allocation techniques.