This thesis presents a new family of converters for high power interconnection of dc buses with different voltage levels. Proposed converters achieve high voltage dc-dc conversion without an intermediate ac conversion stage. This function is implemented without series connection of active switches, or the use of isolation transformers. The salient features of proposed converters are (i) design and construction simplicity, (ii) low switching losses through soft turn-on and soft turn-off, (iii) single stage dc-dc conversion without high-current chopping, (iv) modular structure, (v) equal voltage sharing among the converter modules. Three converter circuits are investigated. The first performs unidirectional power transfer from a dc bus with higher voltage to a dc bus with lower voltage. The second performs unidirectional power transfer from a dc bus with lower voltage to a dc bus with higher voltage. Both converters are suitable for interconnecting single pole dc buses with same polarity, or double pole dc buses. A third converter is also presented which performs the function of either the first or the second converter with polarity reversal. The third converter is suitable for interconnecting single pole dc buses with different polarities, or double pole dc buses. By hybrid integration of the proposed three converters, the thesis also investigates other topologies for bidirectional power transfer between two dc buses. Proposed converters operate only in discontinuous conduction mode and exhibit soft switching operation for the active and passive switches. A common feature between the proposed converters is the self current turn-off for the active switches at zero voltage. This allows the use of thyristors as active switches alleviating their reverse recovery losses. For each converter topology, the structure is presented, its operation principle is explained and a complete set of design equations are derived. Comparisons are performed on high-power and high-voltage design examples. The merits and limitations of each converter are concluded. Practical considerations regarding components selection, loss analysis, filter design and the non-idealities of the circuits are studied. Experimental implementation of scaled-down laboratory prototypes is presented to provide a proof of concept and validate the operation principle of the proposed converter topologies.

Deployments of city-wide multi-hop 802.11 networks introduce challenges for maintaining client performance at vehicular speeds. In this thesis, we experimentally demonstrate that current network interfaces employ policies that result in long outage durations, even when clients are always in range of at least one access point. Consequently, we design and evaluate a family of client-driven handoff techniques that target vehicular mobility in multi-tier multi-hop wireless mesh networks. Our key technique is for clients to invoke an association change based on (i) joint use of channel quality measurements and AP quality scores that reflect long-term differences in AP performance and (ii) controlled measurement and hand-off time scales to balance the need for the instantaneously best association against performance penalties incurred from spurious handoffs due to channel fluctuations and marginally improved i associations. We utilize a 4,000 user urban deployment to evaluate the performance of a broad class of hand-off policies.

Multi-tier wireless mesh network deployments are a popular, cost-effective means to provide wireless broadband connectivity to neighborhoods and cities. Client devices within the coverage area of a mesh network connect wirelessly to fixed mesh nodes, which then forward traffic directly or via multi-hop paths to capacity injection points. The small number of capacity points act as Internet gateways and reduce overall network cost by limiting the amount of costly wired infrastructure needed. Non-uniform wireless signal propagation and the contention caused by multi-hop traffic contribute the challenge of deploying mesh networks with both high performance and low cost. This dissertation presents and evaluates cost-efficient algorithms for deployment planning and measurement-based assessment of wireless mesh networks. The mesh node placement problem requires mesh nodes to provide ubiquitous network coverage to clients, as well as connectivity amongst mesh nodes. The first contribution of this thesis is to present a graph-theoretic formulation of the NP-hard mesh node placement problem. This is the first formulation which considers the case in outdoor networks where signal propagation is non-uniform and enables the design of graph-theoretic approximation algorithms in order to minimize the deployment size or average contention. Secondly, deployment planning must select locations for the placement of capacity points, as their locations determine the path lengths in the networks and the resulting capacity available to transmit data to and from the Internet. To choose capacity point locations, I first present a technique to efficiently calculate network capacity and then two local search algorithms adapted from solutions to the facility location problem. Third, this thesis presents a framework for the measurement-based verification of a deployed network's performance. To avoid relying on expensive and exhaustive measurement studies, I consider the assessment problem with a limited number of measurements. The framework uses terrain-informed estimation, per-node virtual sectorization, and measurement refinement to accurately predict the network's performance at any given location. I evaluate the presented algorithms on realistic network topologies and with a large-scale measurement study of two currently deployed mesh networks: the TFA network and GoogleWiFi network. The thesis results demonstrate the essential nature of incorporating measurements, realistic propagation, and wireless contention into mesh network planning and assessment techniques.

This work addresses the problem of building a macromodel from frequency response measurements by means of a stable and passive linear dynamical system in state-space representation. The proposed algorithms are based on a system-theoretic tool, the matrix pencil of the shifted Loewner and Loewner matrices. Their performance is compared with that of the widely-used vector fitting in terms of the computational time required to build such a model and the accuracy of the interpolating system, when the same order model is constructed, and it is shown that our algorithms render better models in less time. Even though the main application we have in mind is modeling the scattering parameters of an electromagnetic device, no modifications are needed when the admittance parameters are provided instead. Last, our algorithms are especially suited for devices with a large number of ports because the data matrices are collapsed into vectors.

Spectrum sharing is an opportunistic strategy to improve the efficient usage of the frequency spectrum. Much of the research to quantify these gains are under the premise that the spectrum is being used inefficiently. Our main result will be that even in what appears to be a spectrally efficient network, users can exploit the network topology to render additional gains. We propose a Device-to-Device (D2D) mode where cellular users can communicate directly with each other rather than using the base station. The purpose of this mode would be to provide cellular users with ad-hoc multihop access to each other on the same frequency resources that are simultaneously in use by other cellular users communicating with the base station. We will provide both analytical and simulation results showing that this D2D scheme could be a feasible option in the rollout of next generation cellular networks.

Physically unclonable functions (PUFs) provide a basis for many security, and digital rights management protocols. PUFs exploit the unclonable and unique manufacturing variability of silicon devices to establish a secret. However, as we will demonstrate in this work, the classic delay-based PUF structures have a number of drawbacks including susceptibility to prediction, reverse engineering, man-in-the-middle and emulation attacks, as well as sensitivity to operational and environmental variations. To address these limitations, we have developed a new set of techniques for design and implementation of PUF. We design a secure PUF architecture and show how to predict response errors as well as to compress the challenge/responses in database. We further demonstrate applications where PUFs on reconfigurable FPGA platforms can be exploited for privacy protection. The effectiveness of the proposed techniques is validated using extensive implementations, simulations, and statistical analysis.

Increasing demand for wireless services is putting major pressure on network resources, which demands a new paradigm with a more efficient design. Recently, cooperative communications has emerged as a viable option for future wireless devices. Major improvements have been made in the theoretical analysis of cooperative communications and relay channels in recent years. But, most of the analyses have some simplifying assumptions that may not be valid in practice. These assumptions include using infinite-length block codes, zero processing delay, etc. This thesis considers cooperative communications from a practical point of view and identifies the benefits of cooperation when some of the theoretical assumptions are relaxed or changed. Several techniques are introduced to reduce the complexity of the system with minimal performance loss. We set up a framework for system design and show adaptability of our techniques to different scenarios. Our main focus is on the decode-and-forward relaying strategy with low density parity check (LDPC) codes. The thesis contributions in the field of cooperative communications fall into two main categories: algorithms and architectures. First, we focus on the complexity reduction in the algorithms and propose 'distributed partial decoding'. We demonstrate the benefits of partially decoding the codeword at the relay and distributing the decoding load between the relay and the destination. This results in major savings in terms of processing power and time at the relay with a very small loss in system performance. The architectural complexity and overhead of this scheme is much smaller than the original decode and forward strategy. The second contribution of this thesis is the design and implementation of a flexible LDPC decoder architecture that supports a family of LDPC with a variety of code rates and block lengths. This architecture is very suitable for cooperative environments where the cooperating pair and channel conditions and hence the code parameters are not known in advance. The third contribution relates to leveraging puncturing in cooperation. This work is the first to analyze cooperative communication with punctured LDPC codes. We propose structured puncturing patterns for quasi-cyclic LDPC codes and analyze the tradeoffs in designing good puncturing patterns for cooperative environments.

Wireless communication is frequently employed for the bi-directional exchange of information between devices with disparate capabilities. Mobile devices such as cellular phones and laptops are subject to stringent size weight and power constraints relative to the base stations or access points they communicate with. Asymmetry of constraints results in asymmetry of the cost of computation. This disparity in cost motivates efforts to shift signal processing such as channel estimation and equalization from cost sensitive devices to those with more relaxed constraints. In this work we develop a two-way training channel estimation and precoding scheme that shifts all the computation involved in dealing with multiplicative channel gain as well as frequency selective channels to the base station. This work demonstrates the first tractable implementation of a precoding based transceiver scheme of this class on the Rice University Wireless Open Access Research Platform (WARP).

Carbon nanotubes and graphene provide high carrier mobility for ballistic transport, high carrier velocity for fast switching, and excellent mechanical and thermal conductivity. As a result, they are widely considered as next generation candidate materials for nanoelectronics. In this thesis, I first propose a physics-based semi-analytical model for Schottky-barrier (SB) carbon nanotube (CNT) and graphene nanoribbon (GNR) transistors. The model reduces the computational complexity in the two critical but time-consuming steps, namely the calculation of the tunneling probability and the self-consistent evaluation of the surface potential in the transistor channel. Since SB-type CNT and GNR transistors exhibit ambipolar conduction that is not preferable in digital applications, I further propose a semi-analytical model for the double-gate transistor structure that is able to control the ambipolar conduction in-field. Future directions, including the modeling of new CNT and GNR devices and novel circuits based on the in-field controllability of ambipolar conduction, will also be described.

There has been a recent paradigm shift within the wireless communications academic community towards implementation-based algorithm validation. In the past, this task was left to industrial affiliates but in order to close the theory to implementation loop faster research groups are actively developing proof-of-concept demonstrations of their theoretical protocols. In this work we present the Wireless Open-Access Research Platform for Networks (WARPnet) that provides all the computational power and data resources needed to prototype novel physical and MAC layers for emerging technologies. The platform is built to be deployed enabling large-scale network-wide experiments. Scheduling experiments and gathering data can be accomplished with a central server connected to the nodes. We characterize the dedicated control channel built for remote control and statistics aggregation, present frameworks for data transfer and implement example applications that show the methodology for benchmarking distributed wireless experiments.