Digital Commons Network^™

Video Coding For Bit Rates 64kbps And Below, Geoffrey N. Alagoda

Theses : Honours

With digital motion video for either transmission or storage, there always exists a trade-off between the data transmission rate and the picture quality. The lower the transmission bit-rate is made, the more the quality of the image tends to degrade. With usual transform coding schemes the degradation usually occurs when low bit-rates, that is less than about 64Kbps, are used. The resultant image tends to suffer visually from a ''blocking" effect. This thesis therefore, is based on the development of a different implementation scheme, for motion video compression or encoding, so as to support both low bit-rates, around 64Kbps or …

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 …

Travelling Wave Electrode Optimization For High Speed Electro-Optic Modulators Using The Fourier Series Method, W. Boyu, X. Guangjun, Xiaomin Jin

Electrical Engineering

The performance of Z-cut Mach-Zehnder high speed LiNbO₃ amplitude modulators with a CPW traveling wave electrode, has been analyzed and optimally designed in detail by the Fourier series method. The effect of electrode and buffer layer thickness on the electric field distribution in the substract, effective micro- wave refractive index and characteristic impedance of CPW electrode, are discussed. Calculation shows that increasing the thickness of the electrode and SiO₂ buffer layer can improve the phase velocity mismatch between electric and optical waves, and the drive power required by the modulator with thin buffer layer and thick electrode is …

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 …

Multiclassifier Fusion Of An Ultrasonic Lip Reader In Automatic Speech Recognition, David L. Jennnings

Theses and Dissertations

This thesis investigates the use of two active ultrasonic devices in collecting lip information for performing and enhancing automatic speech recognition. The two devices explored are called the 'Ultrasonic Mike' and the 'Lip Lock Loop.' The devices are tested in a speaker dependent isolated word recognition task with a vocabulary consisting of the spoken digits from zero to nine. Two automatic lip readers are designed and tested based on the output of the ultrasonic devices. The automatic lip readers use template matching and dynamic time warping to determine the best candidate for a given test utterance. The automatic lip readers …

Instability In Self-Pulsation In Laser Diodes And Its Effect On All-Optical Synchonization, Jonathan Hyland, Gerald Farrell

Articles

The effect of short- and long-term frequency instability in self pulsation on all-optical synchronization using a twin-section laser diode is experimentally investigated. Short-term frequency instability broadens the unlocked full width at half maximum (FWHM) of the fundamental of the rf spectrum of the self-pulsating laser diode. We show experimentally that the value of the unlocked FWHM, and thus the level of short-term instability, has a direct effect on the optical power required to maintain synchronization. A novel means of reducing the FWHM is presented based on a reflective transmission line stub connected to the absorber of the twin-section self-pulsating laser …

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 …

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 …

Accelerating Conservative Parallel Simulation Of Vhdl Circuits, Joel F. Hurford

Theses and Dissertations

This research effort considers heuristic and cost model based techniques for the optimal partitioning of VHDL circuits for parallel simulation. Correlation statistics are gathered on a wide variety of graph-based a priori parameters. Linear regression is used to identify significant parameters for inclusion in a representative cost model. Driving a greedy search, this cost model is used to improve upon initial heuristic partitions. The influence of feedback dominated previous research so a no-feedback algorithm is used to create the initial partition The circuits studied range from 1,050 to 4,243 gates.

Analysis And Simulation Of Narrowband Gps Jamming Using Digital Excision Temporal Filtering, Gerald L. Falen

Theses and Dissertations

The purpose of this thesis is to investigate the performance of the Digital Excision Temporal Filter (DETF) to reject narrowband jammers used against the Global Positioning System (GPS). The DETF takes the Fast Fourier Transform (FFT) of the GPS signal and excises any FFT bins that are above a preselected threshold level. Then the excised signal is Inverse Fourier Transformed and fed to the GPS receiver. Several jammer types are simulated including Continuous Wave (CW), Pulse CW, Swept CW, Narrowband Spot Noise, and Wideband Barrage Noise jammers. Cases are also simulated using all but the Wideband Barrage Noise jammer at …

Distributed Interactive Simulation Virtual Cassette Recorder (Dis Vcr): A Datalogger With Variable Speed Replay, Jonathan L. Fortner

Theses and Dissertations

The overall objective of the Distributed Interactive Simulation Virtual Cassette Recorder (DIS VCR) is to add a flexible replay capability to any DIS environment and specifically to the Remote Debriefing Tool (RDT). The DIS VCR's abilities include selective filtering of incoming DIS Protocol Data Units (PDUs), variable-speed replays, ability to pause, fast-forward, rewind, efficient data storage and retrieval, and an interface that simplifies the execution of those functions. The thesis includes a DIS VCR-compatible design for concurrent replay of audio extracted from signal PDUs and an extension to the replay design that supports unmodifiable rendering or receiving applications. For variable-speed …

Head Related Transfer Function Approximation Using Neural Networks, John K. Millhouse

Theses and Dissertations

This thesis determines whether an artificial neural network (ANN) can approximate the Armstrong Aerospace Medical Research Laboratories (AAMRL) head related transfer functions (HRTF) data obtained from research at AAMRL during the fall of 1988. The first test determines whether HRTF lends any support in sound localization when compared to no HRTF (Interaural Time Delay only). There is a statistically significant interaction between the location of the sound and whether the HRTF or no HRTF is used. When this interaction is removed using the alternate F.Value, the statistics give the result of equal means for the filters and azimuth. This means …

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 …

Improving The Performance Of Spiral Antennas By Using Passive Scatterers, Joseph S. Zaren

Theses and Dissertations

The purpose of this study was to explore the viability of improving the performance of cavity-backed antennas. Traditionally antenna cavities are filled with electromagnetic absorber to mitigate interference effects that would otherwise cause the antenna radiation pattern to vary widely at different frequencies. The approach used in this research was to replace the absorber with dielectric slabs, some of which contained arrays of dipoles. These dipole arrays were modeled as frequency selective surfaces using two periodic moment method based - computer programs and one transmission line program. A systematic study was performed that identified the effect of changing the dipole …

Design, Fabrication, Modeling, And Optical Characterization Of Organic Polymer Nonlinear Directional Couplers, John N. Berry

Theses and Dissertations

This research was an investigation into the suitability of a recently developed polymer, polyphenylene, as a material for integrated optical circuits (IOCs). Polymers show great promise in the area of IOCs because of material processing advantages, compatibility with most existing integrated circuit technology, and relatively strong nonlinear optical characteristics. This thesis contains an overview of: dielectric waveguides, linear and nonlinear directional coupler theory; various models useful in the design and analysis of optical waveguides; the fabrication of three different waveguide designs; the experimental apparatus and procedure used to optically characterize the waveguides; and the experimental results of the characterization. Waveguiding …

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.

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, …

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 …

An Overview Of Flexible Ac Transmission Systems, P. Asare, T. Diez, A. Galli, E. O'Neill-Carillo, J. Robertson, R. Zhao

Department of Electrical and Computer Engineering Technical Reports

FACTS or "flexible AC transmission systems" is a term that has been suggested for the use of solid state devices to control bulk power flow in transmission systems. The Electric Power Research Institute supported this idea, and many researchers have invested efforts on the value and potential of FACTS. At this time, it appears that the main value of FACTS lies in improving transmission capability; increasing the flexibility of power flow control (e.g., for wheeling or for economic dispatch); for controlling voltage (and var flow); and possibly additional advantages in lower voltage systems (e.g., distribution systems). This report is an …

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 …

The Fat-Pyramid And Universal Parallel Computation Independent Of Wire Delay, Ronald I. Greenberg

Computer Science: Faculty Publications and Other Works

This paper shows that a fat-pyramid of area Θ(A) requires only O(log A) slowdown to simulate any competing network of area A under very general conditions. The result holds regardless of the processor size (amount of attached memory) and number of processors in the competing networks as long as the limitation on total area is met. Furthermore, the result is valid regardless of the relationship between wire length and wire delay. We especially focus on elimination of the common simplifying assumption that unit time suffices to traverse a wire regardless of its length, since the assumption becomes more and more …

Beam Propagation In Parabolically Tapered Graded-Index Waveguides, Anthony A. Tovar, Lee W. Casperson

Electrical and Computer Engineering Faculty Publications and Presentations

To a good approximation, the electromagnetic-propagation characteristics of graded-index waveguides can be written in terms of polynomial-Gaussian modes. For uniform quadratic-index waveguides the behavior of these modes is well known. However, there are sometimes practical reasons for using tapered waveguides, but detailed propagation solutions are known for only a few specific taper functions. The parabolic taper is perhaps the most important special case, and the solution-generating techniques that we generalize are used to obtain analytic solutions for this case.

Correlative Tracking Of Pseudo-Noise Codes Using A Phase Shifted Reference, Kurt Louis Kosbar, Hettiachchi Upul Gunawardana

Electrical and Computer Engineering Faculty Research & Creative Works

This work investigates a first-order correlation loop for tracking pseudo-noise (PN) codes. The local reference is produced by a PN sequence generator in series with a Hilbert transform filter. The tracking performance of this non-linear loop is compared with conventional early-late delay-lock loops (ELDLL). Using a conservative definition of bandwidth, the new loop was found to be superior at moderate to low signal-to-noise ratios (SNR). Another advantage of the new structure is that it has a very large (arguably infinite) lock range.

Performance Of Bandlimited Gaussian Noise As A Spreading Code In Awgn And Single Tone Interference Channels, Tze-Yu Chu, Kurt Louis Kosbar

Electrical and Computer Engineering Faculty Research & Creative Works

This paper examines the bit error rate (BER) of a direct sequence spread spectrum (SS) system that uses bandlimited white Gaussian noise (BLWGN) as a spreading code. The performance of this "bandlimited-SS" system is examined in both additive white Gaussian noise (AWGN) and single tone jamming environments. The BLWGN spreading code is inferior to conventional codes in AWGN channels, but is more robust when a narrow band interference signal is present.

Algorithms In Fault-Tolerant Clos Networks, Hyunyeop Lee

Dissertations

No abstract provided.

Cebus Demonstration System, Liang-Chuang Chen

Theses

A CEBus demonstration system is constructed and applied to aspects of home automation security. Two M68HC16Z1 evaluation boards are used as CEBus nodes. Two CEBus spread spectrum power line modems (SSC PLCEMS) interconnect the nodes. An SSC PLCEMS handles all spread spectrum signal generation and reception.

The application programs in the two boards are written in assembly language based upon CAL (Common Application Language), a CEBus standard.

The standard CEBus frame format and FCS (Frame Check Sequence) are implemented by software in the Data Link Layer. Encoding and decoding binary information into UST format are implemented in the Physical Layer. …

A Distributed Network Architecture For Video-On-Demand, Ge Dai

Theses

The objective of this thesis is to design a distributed network architecture that provides video - on - demand services to public subscribers. This architecture is proposed as an alternative to a centralized video service system. The latter system is currently being developed by Oracle Corporation and NCube Corporation.

A simulator is developed to compare the performance of both the distributed and centralized video server architectures. Moreover, an estimate of the cost of both systems is derived using current price data.

It is shown that the distributed video server architecture offers a better cost / performance trade-off than the centralized …

An Adaptive Correlator Receiver For Combined Suppression Of Co-Channel Interference And Narrow-Band Jammers In A Slowly Fading Channel, Raymond Carbone

Theses

This work deals with the adaptive correlation of a direct sequence spread spectrum signal in the presence of narrow-band, multipath and multiple user interference. The Least Mean Square and Recursive Least Square algorithms are employed for the adaptive convergence of the correlator receiver to minimize the mean squared error.

The performance of the adaptive correlator is compared with the matched filter correlator receiver and the conventional prediction filter for the suppression of narrow-band interference by calculating the bit error probability rate. The adaptive correlator is also compared with the RAKE receiver for multipath suppression and compared to the decorelating detector …

Data Broadcasting And Reduction, Prefix Computation, And Sorting On Reduced Hypercube (Rh) Parallel Computers, Arup Mukherjee

Theses

The binary hypercube parallel computer has been very popular due to its rich interconnection structure and small average internode distance which allow the efficient embedding of frequently used topologies. Communication patterns of many parallel algorithms also match the hypercube topology. The hypercube has high VLSI complexity. however. due to the logarithmic increase in the number of connections to each node with the increase in the number of dimensions of the hypercube. The reduced hypercube (RH) interconnection network. which is obtained by a uniform reduction in the number of links for each hypercube node. yields lower-complexity interconnection networks when compared to …