Engineering Commons^™

On Modeling Of A Mobile Multipath Fading Channel, Heng Xiao

Dissertations and Theses

Multipath fading is one of the major practical concerns in wireless communications. A multipath transmission takes place when a transmitted signal arrives at a receiver by two or more paths of different delay. Such multiple paths may be due to atmospheric reflection or refraction, or reflections from buildings or other objects. A multipath fading channel is usually modeled as a time-variant tapped delay system. RAKE receiver can be used to detect the signal from the multipath fading channel. However, the number of delay taps, the time delay of each path, and the tap weight for each delay path need to …

Methodology For Accurate Speedup Prediction, Aruna Chittor

Dissertations and Theses

The effective use of computational resources requires a good understanding of parallel architectures and algorithms. The effect of the parallel architecture and also the parallel application on the performance of the parallel systems becomes more complex with increasing numbers of processors. We will address this issue in this thesis, and develop a methodology to predict the overall execution time of a parallel application as a function of the system and problem size by combining simple analysis with a few experimental results. We show that runtimes and speedup can be predicted more accurately by analyzing the functional forms of the sequential …

An Evolutionary Approach To Allocating Tasks In Hard Real-Time Distributed Systems, Christian Lang

Masters Theses

In real-time systems, correctness not only depends on the result of the computation but also on the time at which this result is available. The violation of timing constraints in hard real-time systems can be critical to human life or environment. Therefore, the scheduling algorithm for distributed systems has to allocate tasks to processing nodes so that no timing constraints can be violated. In addition to timing constraints, tasks have precedence and fault-tolerance constraints.

Static scheduling allocates tasks to processing nodes before the tasks are executed. Static scheduling problems are known to be NP-hard [4]. Therefore, heuristic techniques are necessary …

Applications Of ℓ1 And Mixed H2/ℓ1 Optimization, Mark S. Spillman

Theses and Dissertations

This thesis explores the use of ℓ₁ and mixed H2/ℓ1 optimization methods to design flight control systems. ℓ₁ optimization is used to handle tracking issues in the design of digital compensators. Control deflection and rate limitations, overshoot and undershoot limitations and steady-state error requirements are discussed. Model-matching techniques which produce acceptable tracking results with lower order controllers are also examined. New numerical methods for continuous H2/L1 and discrete H2/ℓ1 optimization are presented. These methods are used to design an aircraft controller in continuous and discrete time and the results are compared.

Next Generation Real-Time Systems: Investigating The Potential Of Partial-Solution Tasks, Robert E. J. Caley

Theses and Dissertations

While the cyclic executive and fixed-priority scheduling strategies have been sufficient to handle traditional real- time requirements. they are insufficient for dealing with the complexities of next-generation real-time systems. New methods of intelligent control must be developed for guaranteeing on-time task completion for real-time systems that are faced with unpredictable and dynamically changing requirements. Implementing real-time processes as partial-solution tasks is one technique that may be beneficial. This type of task. when combined with intelligent control, has the potential for increasing pre-runtime schedulability, system maintainability. and runtime robustness. This research investigates the benefits of partial-solution tasks by experimentally measuring the …

Adaptive Beamforming In Frequency-Dispersive Multipath Environments, David A. Murray

Theses and Dissertations

It is well known that an antenna array with N degrees of freedom (DOF) can cancel N - 1 interferers if they approach the array from directions other than that of the desired signal. It has been shown that there are cases in which it is possible for an array with N DOF to effectively cancel more than N - 1 interferers. Specifically, we show how this can be done when there is incident upon an N-element array not only the desired signal and a jammer signal, but more than N - 1 Doppler-shifted multipath copies of the jammer signal …

Electro-Hydrostatic Actuator Controller Design Using Quantitative Feedback Theory, Ki Ho Kang

Theses and Dissertations

The Electro-Hydrostatic Actuator (EllA) technology offers a higher degree of combat survivability and easier maintainability of the aircraft flight control system, because all the components necessary to operate the actuator are collocated with the actuator. Quantitative Feedback Theory (QFT) is used to design a control system for the EHA. The impact of parameter variations, sensor noise, and flight conditions are explicitly considered in the design process. The solution utilizes a two loop QFT feedback structure. The inner loop structure stabilizes the motor's angular velocity and decreases the outer loop's uncertainty. The outer loop structure controls the RAM piston's position to …

An Integrated Gps-Ins-Baro And Radar Altimeter System For Aircraft Precision Approach Landings, Robert A. Gray

Theses and Dissertations

Currently, the Department of Defense (DoD) and the commercial airline industry are utilizing the Instrument Landing System (ILS) during aircraft landings for precision approaches. The replacement system for the aging ILS was thought to he the Microwave Landing System (MLS). Instead, use of the Global Positioning System (GPS) is now thought to be a viable replacement for ILS precision approaches. The majority of current precision landing research has exploited 'stand-alone' GPS receiver techniques. This thesis instead explores the possibilities of using an extended Kalman filter (EKF) that integrates an Inertial Navigation System (INS), GPS, Barometric Altimeter, Pseudolite and Radar Altimeter …

Silicon Based Microactuators For Telerobotic Tactile Stimulation, Britton C. Read Iii

Theses and Dissertations

Silicon based microelectromechanical (MEM) devices using both surface and bulk micromachining have been realized to provide tactile stimulation. The bulk MEM devices utilize the bimorph principle and are fabricated in a complementary metal oxide semiconductor (CMOS) process through MOS implementation system (MOSIS). The surface MEM devices utilize the electrostatic principle and are fabricated in a complementary metal oxide semiconductor (CMOS) process through MOS implementation system (MOSIS). The surface MEM devices utilize the electrostatic principle and are fabricated in the multi-user MEM process (MUMPS) through MCNC. Eleven major designs are presented and tested to determine if they are suitable to provide …

A Quantitative Feedback Theory Fcs Design For The Subsonic Envelope Of The Vista F-16 Including Configuration Variation, Scott N. Phillips

Theses and Dissertations

An aircraft's response to control inputs varies widely throughout its flight envelope. The aircraft configuration also impacts control response through variations in center of gravity and moments of inertia. Designing a flight control system (FCS) to accommodate the full flight envelope and configuration set of an aircraft is clearly a complex undertaking. Quantitative feedback theory (QFT) is a design tool which enables the engineer to attack this task in an efficient way. Although QFT is a robust control design technique, it is an interactive algorithm allowing the engineer full control over compensator order and gain. In this research effort, a …

Flow Visualization Of A Turbulent Shear Flow Using An Optical Wavefront Sensor, Daniel W. Jewell

Theses and Dissertations

The research reported here investigated the use of a shearing interferometer (SI) wavefront sensor to determine the effects of shear-layer turbulence on an optical wavefront. A collimated helium-neon laser beam was propagated through a plane shear-layer produced by mixing helium and nitrogen at different velocities. Since the gases have different indices of refraction, the optical wavefront was distorted by different amounts by each gas. The SI measured the wavefront slope across the sampled area of the wavefront. The shear-layer was viewed from two orthogonal directions. This document contains shadow graphs, interference patterns imaged by each of the SI's six cameras, …

Polarization Sensitivity Of Monopulse Radar Boresight Error Induced By Large, Ogive Radomes, Kelce S. Wilson

Theses and Dissertations

The dependence of Boresight Error (BSE) on incident Electric Field (E-Field) polarization tilt angle is investigated. BSE, defined as the angular difference between a target's actual and radar-indicated position, is influenced by the radome used to protect the antenna. A - reliable computer model for predicting the BSE of electrically large radar-radome systems has been demonstrated and used to investigate the dependence of radome-induced BSE for various combinations of scan angle, element polarization, and incident E-Field polarization. The analysis includes a development of a transmission-depolarization model to justify the results of the computer model. Results compare very well with empirical, …

Reduction Of Off-Boresight Fields For A Tem Horn Antenna, Dennis J. Wolstenholme

Theses and Dissertations

This research involves the design, modeling, and testing of both tapered periodic surfaces (TPS) and transverse electromagnetic (TEM) horns. The goal is to reduce the off-boresight fields for a TEM horn and increase the peak-to-peak field levels on boresight. This is accomplished by applying a TPS to the free space end. Two tapers are designed - one that approximates an exponential impedance function and one that approximates a triangular impedance function. Both reduce the off-boresight fields of the TEM horn. In most cases the exponential taper reduces the field levels further than the triangular taper. This research shows that a …

Design And Characterization Of Resonant Cavity Light-Emitting Diodes, Thomas M. Fitzgerald

Theses and Dissertations

This thesis describes an investigation into the emission properties of Resonant Cavity Light Emitting Diodes (RCLED). RCLEDs are a new photonic device that promise laser-like properties of narrow output frequency spread and high output power, without the usual laser disadvantages of shorter lifetime and increased maintenance and lifetime costs. Specifically, this thesis examines the functional dependence between emitted wavelength and the RCLED microcavity, and attempts to correlate theory with experimental data. This thesis introduces a classical wave interference model that calculates the Spontaneous Emission Enhancement Factor (Z-) with angular dependence.

Voice Analysis Using The Bispectrum, Deborah A. Douglass

Theses and Dissertations

The theory of the bispectrum has been studied, though very few practical applications have yet been considered in any depth. One application mentioned in the literature is the use of the bispectrum for voice signal processing. The aim of this thesis was to research the bispectrum towards the particular application of speech enhancement. The technique is based on the fact that the bispectrum is zero for a Gaussian white noise signal, arid the bispectrum of two signals added together is the sum of the two signal bispectra. Theoretically, processing signals in the bispectra domain should increase the signal-to-noise ratio of …

Flight Control Design Using Mixed H2/Μ Optimization, Douglas D. Decker

Theses and Dissertations

This thesis examines the use of the mixed H2-Microns optimal control synthesis method in the design of a flight control system for the lateral-directional axes of the F-16 Variable Stability In-Flight Simulator Test Aircraft (VISTA). The method is designed to minimize the H2 norm (two-norm) for a given value of microns. This should provide adequate noise and disturbance rejection while maintaining robustness against several types of uncertainties in the system. This thesis finds that, for this problem, the two-norm is not an accurate representation of the outputs of interest. When the two-norm is broken up into its constituent parts an …

A Comparison Of The Neal-Smith And ΩSpΤΘ2, ΣSp, ΤΘ Flying Qualities Criteria, Brian A. Kish

Theses and Dissertations

Aircraft pitch response is a vital element of piloted vehicle flying qualities. There has been controversy over both the form and the substance of the requirements for short-term pitch response. Currently, MIL-STD- 1797A offers six different methods for evaluating short-term pitch response. These six methods often give conflicting results. Two methods are analyzed in this thesis - the Neal-Smith criteria and the ω_spΤ_θ2, ς_sp, τ_θ criteria. Domains from both criteria are mapped into each other identifying regions of conflict and regions of agreement. Parametric studies are performed and evaluated for trends. Further, a …

A Gain Scheduling Optimization Method Using Genetic Algorithms, Robert C. Martin Iv

Theses and Dissertations

Gain scheduling. the traditional method of providing adaptive control to a nonlinear system, has long been an ad hoc design process. Until recently; little theoretical guidance directed this practitioners' art. For this reason a systematic study of this design process and its potential for optimization has never been accomplished. Additionally, the nonlinearities and the large search space involved in gain scheduling also precluded such an optimization study. Traditionally, the gain scheduling process has been some variation of a linear interpolation between discrete design points. By using powerful non-traditional optimization tools such as genetic algorithms there are ways of improving this …

Improved Numerical Solution Of Mixed H2/H∞ Optimization With Applications, Linda D. Smith

Theses and Dissertations

This study improved the numerical optimization technique used to compute mixed H₂/H_∞ controllers. The run time to generate the full curve of an H₂/H_∞ design was reduced by a factor of almost 200 for a specific example. This was accomplished by improving gradient calculations, upgrading the H_∞ norm calculation to capture multiple peaks in the singular value plot and using routines that minimized processing time. The optimization routine used was the MATLAB CONSTR' Sequential Quadratic Programming (SQP) routine. This SQP routine was compared to a FORTRAN SQP numerical optimizer, IMSL-DNCONG. The method was …

Total Ionizing Dose Effects In Mosfet Devices At 77 K, Kevin J. Daul

Theses and Dissertations

Total ionizing dose effects on thermal oxide and reoxidized nitrided oxide (RNO) MOSFET devices at 77 K were studied. The MOSFETs were immersed in liquid nitrogen and irradiated, using a ⁶⁰Co source, up to 1 Mrad(Si) at a dose rate of 107 rads(Si)-sec. Drain current-gate voltage characteristics were obtained and used to determine threshold voltage and transconductance. At 77 K the subthreshold slopes indicated no observed buildup of interface states in any of the transistors. Furthermore, all transistors experienced very little change in the transconductance. Typical negative shifts in threshold voltage as dose increased were observed in all of …

Photoluminescence Spectroscopy Of 4h- And 6h-Sic, William A. Davis

Theses and Dissertations

Typical undoped bulk grown SiC shows n- or p-type conductivity due to residual impurities such as nitrogen, boron, or aluminum. In order to produce high resistivity material, vanadium can be used as a compensating dopant. Since vanadium is an amphoteric dopant in SiC, it produces either a donor state, V_Si⁴⁺(3d¹) → V_Si⁵⁺(3d⁰), or an acceptor state, V_Si⁴⁺(3d¹) → V_Si³⁺(3d²). Thus, vanadium doping can compensate both n- and p-type conductivity. In this work, vanadium doped and undoped 4H- and 6H-SiC grown …

Model Of A Single Impurity In A Wide Bandgap Semiconductor Describing Electric Field Screening, Anthony N. Dills

Theses and Dissertations

A mathematical model of the influence on electric field screening arising from a single impurity in a wide bandgap semiconductor has been numerically investigated and compared with analytically derived solutions. The parameter set chosen to perform the comparison of analytical solution and numerical solution is based upon a bismuth silicate crystal. Both the analytical calculations and the numerical calculations are an attempt to mathematically model the internal electric field within a semiconductor. Two types of impurities were looked at: a single donor level and a single trap impurity level. In general, after an abrupt application of a voltage across the …

Multipoint Multirate Signal Processing, Roger L. Claypoole Jr.

Theses and Dissertations

This thesis provides a fundamentally new, systematic study of multipoint multirate signal processing systems. The multipoint multirate operators are analyzed via equivalent circuits comprised entirely of conventional multirate operators. Interconnections of the operators are demonstrated, and the multipoint noble identities are derived. The multipoint polyphase representation is presented, and the M channel multipoint multirate system with vector length N is presented as an MN channel multipoint polyphase system. The conditions sufficient for perfect reconstruction in the multipoint multirate system are derived. These conditions constrain the multipoint filter banks to be composed of comb filters generated from paraunitary sets of conventional …

The Enhanced Performance Of An Integrated Navigation System In A Highly Dynamic Environment, Brian J. Bohenek

Theses and Dissertations

For the U.S. Air Force to maintain an accurate and reliable Navigation Reference System (NRS) with Carrier-Phase Global Positioning System (CPGPS) measurements, it must develop an accurate and robust NRS in the face of cycle slips caused by highly dynamic maneuvers. This research investigates the implementation of a double differencing between receivers-satellites scheme to improve the accuracy of current NRS models. The removal of the 'perfect Doppler velocity aiding measurements' (a very poor assumption of past research) was completed with stable and accurate results. The double differencing implemented showed improvement in the accuracy of the NRS. An investigation of two …

Characterization And Redesign Of The Afit Multielectrode Array, Richard G. Darenberg Jr.

Theses and Dissertations

Since 1978, faculty and graduate students from the Air Force Institute of Technology (AFIT) have been working on an implantable circuit array that can record visual signals from the brain or stimulate the brain. In the current design the circuit is a 16 x 16 array of pads, each pad being 160 x 160 micrometers with 250 micrometers spacing with an 'L' shaped reference pad used as a ground reference. The array is multiplexed so that only one I-O line is required to access all 256 pads. This research was twofold: first to analyze the existing circuit and identify sources …

Survey And Implementation Of Commercial Manual Controllers For A Generic Telerobotics Architecture, Thomas E. Deeter

Theses and Dissertations

The purpose of this study is to determine an input device for the Air Force's generic telerobotics architecture for large aircraft maintenance and repair. One area of concern is the human to machine interface, more specifically, which manual controller should be used for the specified tasks in this architecture. We mailed a survey to 68 companies in order to compile a list of possible input devices that the telerobotics architecture could use. 32 companies responded which gave me enough data to generate a list that described the physical traits of the input devices. We then divided the required tasks into …

A 3-D Finite Difference Time Domain Investigation Of Microwave Propagation Through Inhomogeneous Biological Materials, David B. Dunn Jr.

Theses and Dissertations

This paper extends past analysis of an optimal source distribution around a homogeneous sphere of muscle tissue by using a 3-D finite difference time domain (FDTD) scenario in which an anatomically correct human head model is irradiated. It first duplicates the analytical solution within an FDTD space using an FDTD computer code developed at Penn State University. This duplication uses a 9.45 cm radius sphere represented in an FDTD space of 2.35 mm cubic cells. FDTD simulations are then performed on four, three, and two layer laminated spheres, designed to provide simple models of a head. Finally, four simulations were …

Implementation And Demonstration Of A Multiple Model Adaptive Estimation Failure Detection System For The F-16, Peter K. Eide

Theses and Dissertations

A Multiple Model Adaptive Estimation (MMAE) algorithm is implemented with the fully nonlinear six-degree-of-motion, Simulation Rapid-Prototyping Facility (SRF) VISTA F-16 software simulation tool. The algorithm is demonstrated to be capable of identifying flight critical aircraft actuator and sensor failures at a low dynamic pressure (20,000 ft, .4 Mach). Research included single and dual complete failures. Tuning methods for accommodating model mismatch, including addition of discrete dynamics pseudonoise and continuous measurement pseudonoise, are discussed and demonstrated. Scalar residuals within each filter are also examined and characterized for possible use as an additional failure declaration voter. Robustness to sensor failures provided by …

Classification Of Ultra High Range Resolution Radar Using Decision Boundary Analysis, Christopher L. Eisenbies

Theses and Dissertations

This thesis examines the discrimination of targets with Ultra High Range Resolution (UHRR) radar data. Using these measured signals from frontal aspect angles of four aircraft classes, the baseline performance of the Adaptive Gaussian Classifier (AGC) is tested with respect to aligning exemplars to templates. Alignment plays a crucial role in the AGC's classification performance which can degrade by 11% for a target class. The AGC is compared to non-parametric classifiers, but no statistically significant degradation of performance is found. Data separability is analyzed by hounding the Bayes error. The data is well separated in a statistical sense. A feature …

The Design And Analysis Of Integrated Navigation Systems Using Real Ins And Gps Data, Curtis D. Evans

Theses and Dissertations

An extended Kalman filter (EKF) is used to combine the information obtained from a Global Positioning System (GPS) receiver and an Inertial Navigation System (INS) to provide a navigation solution. This research compares the results of an actual tightly-coupled GPS-INS integrated system with those obtained in computer simulation. Differences between the simulation and actual hardware results, such as navigation solutions and tuning values, are shown in the research. An analysis of various GPS models was studied to determine the best representation for a system truth model. Measurement updates and their effects upon position accuracies was considered and preliminary research was …