<p>Space-time block codes are a recently discovered, attractive modulation scheme for multiple antenna wireless channels. They are capable of providing full diversity over fading channels, at the same time requiring only low computational costs. Over the last few years, several distinct approaches to designing space-time codes have been proposed in the literature, including the layeredarchitecture, trellis codes, turbo codes and the orthogonal designs. Most work on space-time coding has focused on the problem of designing codes to perform well under quasi-static fading conditions. In practice, it is not unusual for a cellular handset to experience conditions which range from fast fading to nearly static within seconds (e.g., a vehicle suddenly braking). It is therefore of interest to design codes that are robust in the sense, that they perform well under a wide variety of channel fading conditions. A robust coding architecture called Bit-Interleaved Space-Time Coded Modulation is proposed for channels with multiple transmit and receive antennas. It is designed to perform well under a wide variety of channel fading conditions and which (when differentially encoded) does not require accurate channel estimates at the receiver. The architecture combines serial concatenation of short, full-diversity space-time block codes (inner code) with bit-interleaved coded modulation.This thesis examines the capacity aspects of this architecture namely, the ergodic capacity, the outage capacity and the ergodic and outage cut-off rates in Rayleigh flat-fading channels. It is shown that, if the inner block codes are chosen properly, not only is the capacity close to the information-theoretic limits, but also a better tradeoff between performance and coding complexity can be obtained.<P>

<p>The great challenge in signal processing is to devise computationally efficient and statistically optimal algorithms for estimating signals from noisy background and understanding their contents. This thesis treats the problem of multiscale signal processing and shape analysis for an Inverse Synthetic Aperture Radar (ISAR) imaging system. To address some of the limitations of conventional techniques in radar image processing, an information theoretic approach for target motion estimation is first proposed. A wavelet based multiscale method for shape enhancement is subsequently derived and followed by a regression technique for shape recognition.Building on entropy-based divergence measures which have shown promising results in many areas of engineering and image processing, we introduce in this thesis a new generalized divergence measure, namely the Jensen-Rényi divergence. Upon establishing its properties such as convexity and its upper bound etc., we apply it to image registration for ISAR focusing as well as related problems in data fusion. Attempting to extend current approaches to signal estimation in a wavelet framework, which have generally relied on the assumption of normally distributed perturbations, we propose a novel non-linear filtering technique, as a pre-processing step for the shapes obtained from an ISAR imaging system. The key idea is to project a noisy shape onto a wavelet domain and to suppress wavelet coefficients by a mask derived from curvature extrema in its scale space representation. For a piecewise smooth signal, it can be shown that filtering by this curvature mask is equivalent to preserving the signal pointwise Hölder exponents at the singular points, and to lifting its smoothness at all the remaining points. To identify a shape independently of its registration information, we propose matching two configurations by regression, using notations of general shape spaces and procrustean distances. In particular, we study the generalized matching by estimating mean shapes in two dimensions. Simulation results show that matching by way of a mean shape is more robust than matching target shapes directly.<P>

<p>The goal of this research was to determine the effects thatthe actual physical structure of an overlapped metal-oxide-semiconducter (MOS) capacitor and an etch bias have on the extraction of the gate-oxide thickness. Included in these concerns were the overlap of the field oxide by the gate electrode, the angle of the active-area sidewall, and the increase in size of the active area due to an etch bias. In addition, the growth of a contaminant layer, or ad-layer,on oxides that do not have a permanent gate-electrode was addressed. This ad-layer forms immediately after a wafer is exposed to the lab ambient and causes a significant increase (i.e., ~ 10%) in the apparent thickness of the oxide.The refinement of the total capacitance to the active-area capacitance uses measured data from Hg-gated capacitors on p-type Si wafers and Al / Poly-Si gated capacitors on both p- and n-type Si wafers. The effects of a non-vertical sidewall and an etch bias are addressed theoretically through the use of the classic treatment of capacitance. The capacitance-voltage characteristics from the MOS capacitors were used to extract the oxide thickness (tox).The extracted thickness was determined from a model-based methodology (i.e., the slope method) and a model-based analysis (i.e., NCSU's CVC model). It is shown that the effect of a non-vertical sidewall and an etch bias are negligible. The effect of the gate electrode overlap, while small, should be removed. It is also shown that a model-based analysis of the active-area capacitance characteristics results in a consistent oxide thickness over the range of capacitor areas that were available.The removal and re-growth of the ad-layer were investigated using current-voltage and capacitance-voltage characteristics from blanket oxides on both p- and n-type silicon wafers. The changes in these characteristics were quantified as the ad-layer grows over time. The C-V characteristics were analyzed using NCSU's CVC program in order to extract values for oxide thickness, flatband voltage, and interface trap densities. The ad-layer causes considerable inaccuracies in the model extraction of oxide thickness as well as the flatband voltage and interface trap density. Electrical and optical results on the p-type wafer both show that the ad-layer increases the apparent oxide thickness by ~ 0.25 nm and the electrical results show that the ad-layer shifts the flatband voltage by as much as 100 mV.<P>

<p>Small planar antennas are becoming increasingly popular in personal wireless communication systems since these antennas offer advantages such as small size,light weight, robust construction, ease of integration into mobile handsets, reasonable radiation efficiency and gain. A new small microstrip antenna operating at 880MHz is designed using the Finite difference time domain technique incorporating the perfectly matched-layer formulation. Shorting pins are used to achieve the reduction in size.The size of this patch antenna is approximately four times less than that of the regular half wavelength patch antenna. An antenna array made of the new patch antennas is used ina multiple antenna system to reliably separate different users on the same channel using linearbeam steering techniques with the ultimate goal of increasing the channel capacity.Prototypes of the proposed dual shorted-pin-patch antenna are fabricated and measurements of their return loss compare well with the computational results.<P>

<p>The development of a distribution system simulator that can model new power electronic devices as well as new novel distribution schemes, such as DC distribution has been donehere. The simulator adopts the Electro-Magnetic Transient Programs (EMTP) platform to facilitate the simulation. Basic power electronic building blocks have been developed to extend the capabilities of the EMTP. These blocks include a rectifier module, a DC buck converter module, a 3-phase inverter module and a single-phase inverter module. The paper shows simulation of a new distribution scheme for naval ships to illustrate that such a simulator facilitates the study of new distribution system designs, especially theprotection and control issues associated with new designs.<P>

<p>Distributed object computing refers to allowing objects to be distributed across a network. These objects may be distributed across a number of different computers and across networks.This thesis presents a popular distributed object architecture, Remote Method Invocation (RMI). As RMI works on a Java framework, it provides the same features Java provides. Its portability, ability to transport objects as a whole, and power to connect to existing as well as legacy systems makes a strong choice amongst other competing technologies. Needless to say, the transport of objects across systems brings along with it the necessity for a strong security framework.The Secure Sockets Layer (SSL) is a widely popular protocol that currently provides the secure framework RMI needs. Most e-commerce applications these days run over SSL. However, SSL may not the right choice for every application requiring a security backbone. The motivation behind this thesis lies in this thought. The Secure Remote Password Protocol (SRP) provides a secure, simple and fast approach for providing client authentication. An attempt has been made to build a new infrastructure using SRP. The infrastructure that has been developed can provide authentication and privacy, as well as maintain message integrity. One such application domain is mobile computing. In this era where data is required to be accessible from anywhere and everywhere, mobile computing is a growing area. Again, due to the use of mobile agents in this area, security plays an important role. The security mechanism provided needs to be fast and simple and at the same time provide strong security. The new security overlay developed has been proposed as a possible solution.<P>

<p>Spatial power combining is a method of coherently combining the power of manyamplifying devices using free space as the power dividing/combining medium in contrastto traditional circuit based combiners. The spatial combiner is formed from anarray of amplifying unit cells, with each cell receiving a signal, amplifying it, and thenradiating it into free space. Two methods of spatial powercombining, tile and tray, are investigated in this thesis.The tile-based spatial combiner consists of a thick groundplane with receiving microstrip patch antennason one side and transmitting microstrip patch antennas on the other. In addition, amplifiers are placedon both sides of the thick groundplane, which provides efficient heat removal.This research is focused on the optimal array spacing, biasing,and feeding of tile-based arrays to achieve high output power levels atKa-band (Lockheed Martin was specifically interested in achieving greater than 25 Watts ofradiated power under a DARPA MAFET-3 program). Several arrays were developed, consisting of13, 45, and 98 elements. Noteworthy results were obtained from theexperiments with this design approach. A tray-based approach is also investigated in this thesis. This approach differsfrom the tile-based approach by having multiple groundplanes (trays) containingamplifiers stacked to form an array of amplifying unit cells. In addition,microstrip patch antennas are placed at the ends of the trays and radiate in an end-fire pattern with respectto the tray containing the amplifiers. For this purpose, an approach has been developedfor the feeding of the microstrip patch antennas. This feeding mechanismallows the amplifiers and radiating elements to be isolated. Thus moreroom is allowed for the amplifiers, while minimizing coupling that may causespurious oscillations. An X-band and Ka-band array have been developed,consisting of 25 and 49 elements, respectively. Both arrays provide efficientheat sinking through thick metal groundplanes. In addition, an experimentalanalysis on the array tolerance to device failure has been performed on both tray-basedarrays. This study examines the effect of device failure on the gain, power output, and radiationpattern.<P>

<p>Differentiated Services (DiffServ) enable quality-of-service provisioning by coupling traffic aggregates with a specific forwarding path treatment. Per-Hop forwarding Behavior (or PHB) describes the forwarding path behavior required in network nodes, while the Per-Domain Behavior (or PDB) describes the behavior experienced by a particular set of packets as they cross a DiffServ domain. PHB and PDB implementations with traffic conditioners, provisioning strategies and billing models are building blocks used in Services Level Agreements (SLA).The goal of the project was to construct an SLA test-bed using soft DiffServ routing nodes. This test-bed, and the associated tools, is intended for in-depth studies of SLA translation and mapping algorithms. The specific objectives of the work reported in this thesis were to construct the test-bed, and then verify, validate and evaluate different elements of the SLA test-bed. Specifically, proof-of-concept experiments were conducted to show that one can implement a general Services Level Agreement (SLA) based on DiffServ, to show how to translate SLA requirements into real test-bed parameters, and then run experiments, collect data and make performance measurements.. The study is empirical and involves implementation of some of the quality of service (QoS) related IETF drafts and RFCs in a five-node soft DiffServ-based SLA testbed. This includes implementation and empirical evaluation of Expedite Forwarding (EF) PHB, Assured Forwarding (AF) PHB, Virtual Wire (VW) PDB, and of Assured Forwarding PDB.Virtual Wire PDB was implemented using both the Priority Scheduler and a Weighted Fair Queuing Scheduler. The effect of Best Effort packet size and rate on the protected EF traffic was investigated empirically. This provided proof of concept data on how successful can a VW implementation be in protecting Voice over IP (VoIP) streams. We used both emulated VoIP streams, and real VoIP phones in highly congested traffic environments.Assured Rate PDB was implemented using appropriate traffic conditioning, buffer management and scheduling techniques. The issue of what to do with non-conforming AF traffic was investigated empirically - whether to drop the non-conforming packets or to downgrade them to Best Effort. It was noticed that strict dropping of the non-conforming packets will sometimes underutilize the channel, while downgrading them to Best Effort will create a reordering problem.<P>

<p>Optical memory effects in III-V Nitrides have been investigated. In order to have further understanding of this effect, qualitative and then quantitative measurements were performed to investigate this memory effect. A microscopic model consistent with most of the experimental observations was developed. Finally, verification of the model was performed.Experimental observations indicate that optical memory effects are flux-dependent effects, which require no lower power limit of the excitation source in order to produce them. Photoluminescence and cathodoluminescence studies indicate the yellow patterns are the result of increased yellow luminescence intensity from the sample. Heating up the samples can erase this memory effect.Blue luminescence, with an energy about 2.8 eV, is important in the explanation of the memory effect since it appears in the photoluminescence spectra of all the samples that exhibit memory effects. This leads to a model with two different transitions, yellow and blue luminescence, competing with each other to explain the memory effects. The blue luminescence is caused by electron transitions from a localized oxygen level to the deep isolated and hydrogenated gallium vacancies. Transitions from shallow silicon donor levels to the gallium vacancies result in the yellow luminescence. Intense ultraviolet light will remove hydrogen from the hydrogenated gallium vacancies and these vacancies will form complexes with neighboring oxygen atoms. These complexes will result in more yellow luminescence. Less blue luminescence and more yellow luminescence result in the yellow memory patterns observed. This model is consistent with most of the observations and several experiments strongly support this model. Potential applications for memory effects include optical data storage and optical signal processing. Further understanding of this effect could lead to the realization of all optical memory cells and could also be used to improve the quality of III-nitrides materials.<P>

<p>CAVANAUGH, CURTIS C. An Adaptive Electronic Interface for Gas Sensors (Under the direction of H. Troy Nagle).This thesis focuses on the development of an adaptive electronic interface for gas sensors that are used in the NC State electronic nose. We present an adaptive electronic interface that allows for the accurate mapping of the sensor?s voltage output to sensor resistance profiles. The adaptive interface uses a linearized Wheatstone bridge in a constant current configuration. The balancing of the bridge and the adjustment of the subsequent gain stage is performed using programmable variable resistors. The programmable resistors are controlled by a LabVIEW® program. The same control program also determines and records all the resistor values in the interface circuit. The resistance of each sensor is accurately computed by LabVIEW® using the interface-circuit, resistor values, and the voltage output of the circuit. Compensating for sensor drift can be done in LabVIEW® by adjusting the programmable resistor values so that a zero-voltage output is produced during the reference cycle. By doing this zero adjustment between each ?sniff? of an odorant, the baseline drift can be minimized.A single channel of the adaptive electronic interface has been designed and tested. The interface can be calibrated so that it is 99% accurate when performing sensor resistance measurements.A new conducting polymer sensor chamber has also been designed and tested. The new radial flow sensor chamber was minimizes the dead volume in the chamber and also deliver the odorant to each sensor at the same time. Two operating modes were compared: continuous-flow and sniff-and-hold. Both modes gave good classification performance while testing four different coffee samples. Experimental testing indicates that sensor response is highly correlated with the sample flow rate. Future work to more fully characterize this correlation is recommended.<P>