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Articles 331 - 360 of 413
Full-Text Articles in Computer Engineering
Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas
Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas
Theses and Dissertations
With the rise of mobile computing and an increasing need for ubiquitous high speed data connections, Internet-in-the-sky solutions are becoming increasingly viable. To reduce the network overhead of one-to-many transmissions, the multicast protocol has been devised. The implementation of multicast in these Low Earth Orbit (LEO) constellations is a critical component to achieving an omnipresent network environment. This research examines the system performance associated with two terrestrial-based multicast mobility solutions, Distance Vector Multicast Routing Protocol (DVMRP) with mobile IP and On Demand Multicast Routing Protocol (ODMRP). These protocols are implemented and simulated in a six plane, 66 satellite LEO constellation. …
Turbo Codes For Wireless Mobile Communication Systems Applications, Moataz M. Salah
Turbo Codes For Wireless Mobile Communication Systems Applications, Moataz M. Salah
Theses and Dissertations
Research in coding theory has seen many proposals aimed at the construction of powerful codes using block and convolutional codes. Recently, a new forward error control code, known as turbo code, was introduced. This new code yields very good performance (near the Shannon limit) with relatively simple component codes and large interleavers in combination with an iterative decoding process. Among the most important applications of turbo codes are wireless mobile communication systems. A significant performance metric for this application is the minimization of end-to-end delay. In this dissertation, different ways to enhance the performance of turbo codes with short frames …
Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer
Mission Route Planning With Multiple Aircraft & Targets Using Parallel A* Algorithm, Ergin Sezer
Theses and Dissertations
The general Mission Route Planning (MRP) Problem is the process of selecting an aircraft flight path in order to fly from a starting point through defended terrain to target(s), and return to a safe destination. MRP is a three-dimensional, multi-criteria path search. Planning of aircraft routes involves an elaborate search through numerous possibilities, which can severely task the resources of the system being used to compute the routes. Operational systems can take up to a day to arrive at a solution due to the combinatorial nature of the problem, which is not acceptable, because time is critical in aviation. Also, …
A Performance Analysis Of A Joint Lmds/ Satellite Communication Network, Ronald J. Zwickel
A Performance Analysis Of A Joint Lmds/ Satellite Communication Network, Ronald J. Zwickel
Theses and Dissertations
The goal of this research is to provide a performance analysis of a joint terrestrial/ satellite communication network. The systems of interest are the Local Multipoint Distribution Service (LMDS) terrestrial system and the proposed Teledesic satellite network. This analysis is performed using the OPNET network simulation tool. Simulations are run for twelve separate scenarios involving three factors which include: number of users, modulation type, and Quality of Service (QoS). The key metrics for characterizing simulation scenarios are the end-to-end delay, bit error rate, and average system throughput. The results obtained display the benefit of improved throughput, approximately 20 Mbps for …
A Distributed Agent Architecture For A Computer Virus Immune System, Paul K. Harmer
A Distributed Agent Architecture For A Computer Virus Immune System, Paul K. Harmer
Theses and Dissertations
Information superiority is identified as an Air Force core competency and is recognized as a key enabler for the success of future missions. Information protection and information assurance are vital components required for achieving superiority in the Infosphere, but these goals are threatened by the exponential birth rate of new computer viruses. The increased global interconnectivity that is empowering advanced information systems is also increasing the spread of malicious code and current anti-virus solutions are quickly becoming overwhelmed by the burden of capturing and classifying new viral stains. To overcome this problem, a distributed computer virus immune system (CVIS) based …
A Methodology For Integrating Tools In A Web-Based Environment, Musa Serdar Arslan
A Methodology For Integrating Tools In A Web-Based Environment, Musa Serdar Arslan
Theses and Dissertations
Web-based technologies are evolving very rapidly. New technologies are introduced very frequently in the realm of the Web and Internet. This evolution also affects database management systems (DBMSs). Almost all DBMS vendors are making their systems "Web-enabled." The Internet and the World Wide Web are getting more important and bigger than ever. Because of the increase in the importance of the Internet and the Web, migrating old applications and tools to a web-based environment is becoming more important. When migrating old applications or tools to the web-based environment, integration of tools becomes an important issue. In this research, a step-by-step …
Modeling And Simulation Of Communication Systems In Opnet, David M. Banker
Modeling And Simulation Of Communication Systems In Opnet, David M. Banker
Theses and Dissertations
This research aims to present accurate computer models of a communication link and a Super High Frequency (SHF) radio communication system. Network Warfare Simulation (NETWARS) is a J-6 initiative aimed at modeling all communication traffic in the Department of Defense (DoD) for testing and analysis of specific real world scenarios. The AN/TSC-94 is a SHF radio system with satellite communication capabilities. The AN/TSC-94 incorporates a Direct Sequence Spread Spectrum (DSSS) radio link for certain Anti-Jam (AJ) features. A DSSS spreads' signal power over a large bandwidth, reducing power previously concentrated within the original system bandwidth. The simulations were performed using …
Network Security Versus Network Connectivity: A Framework For Addressing The Issues Facing The Air Force Medical Community, Franklin E. Cunningham Jr.
Network Security Versus Network Connectivity: A Framework For Addressing The Issues Facing The Air Force Medical Community, Franklin E. Cunningham Jr.
Theses and Dissertations
The Air Force has instituted Barrier Reef to protect its networks. The Air Force medical community operates network connections that are incompatible with Barrier Reef. To overcome this problem, OASD(HA) directed the Tri-Service Management Program Office (TIMPO) to develop an architecture that protects all military health systems and allows them to link with all three services and outside partners. This research studied the underlying networking issues and formed a framework based on data from network experts from the Air Force's medical centers and their base network organizations. The findings were compared TIMPO and a composite framework was developed that more …
Timed Safety Automata And Logic Conformance, Frank C. D. Young
Timed Safety Automata And Logic Conformance, Frank C. D. Young
Theses and Dissertations
Timed Logic Conformance (TLC) is used to verify the behavioral and timing properties of detailed digital circuits against abstract circuit specifications when both are modeled as Timed Safety Automata (TSA) with real-valued clocks. TLC is a bisimulation-style partial order relationship defined over TSA state space. In contrast to timed simulation, Calculus of Timed Refinement, and time-abstracted bisimulation, TLC defines when one system is an acceptable implementation of another by asymmetric action-matching requirements for specification inputs and implementation outputs. TLC intuitively and pragmatically supports writing abstract specifications and verifying them against implementations. TLC scales up by substituting verified specifications for implementations …
Asymmetric Load Balancing On A Heterogeneous Cluster Of Pcs, Christopher A. Bohn
Asymmetric Load Balancing On A Heterogeneous Cluster Of Pcs, Christopher A. Bohn
Theses and Dissertations
In recent years, high performance computing with commodity clusters of personal computers has become an active area of research. Many organizations build them because they need the computational speedup provided by parallel processing but cannot afford to purchase a supercomputer. With commercial supercomputers and homogenous clusters of PCs, applications that can be statically load balanced are done so by assigning equal tasks to each processor. With heterogeneous clusters, the system designers have the option of quickly adding newer hardware that is more powerful than the existing hardware. When this is done, the assignment of equal tasks to each processor results …
Performance Analysis Of Tcp Enhancements In Satellite Data Networks, Ren H. Broyles
Performance Analysis Of Tcp Enhancements In Satellite Data Networks, Ren H. Broyles
Theses and Dissertations
This research examines two proposed enhancements to the well-known Transport Control Protocol (TCP) in the presence of noisy communication links. The Multiple Pipes protocol is an application-level adaptation of the standard TCP protocol, where several TCP links cooperate to transfer data. The Space Communication Protocol Standard - Transport Protocol (SCPS-TP) modifies TCP to optimize performance in a satellite environment. While SCPS-TP has inherent advantages that allow it to deliver data more rapidly than Multiple Pipes, the protocol, when optimized for operation in a high-error environment, is not compatible with legacy TCP systems, and requires changes to the TCP specification. This …
An Improved Asynchronous Implementation Of A Fast Fourier Transform Architecture For Space Applications, David J. Barnhart
An Improved Asynchronous Implementation Of A Fast Fourier Transform Architecture For Space Applications, David J. Barnhart
Theses and Dissertations
A second-generation fully asynchronous Fast Fourier Transform (FFT) processor for space applications is developed in this thesis. A high-performance patented FFT architecture invented by Suter and Stevens was used as the basis for a 16-point FFT (FFT-16) processor design. A brief derivation of the architecture, the asynchronous design methodologies used and space-based integrated circuit issues are presented. The Synopsys VLSI CAD system and a radiation tolerant design library developed by the Air Force Research Laboratory were used to implement the design. A critical building block of the FFT-16, the FFT-4, was fabricated as a cost-effective method to validate the cell …
Te Scattering From Bubbles In Ram, John G. Cochran
Te Scattering From Bubbles In Ram, John G. Cochran
Theses and Dissertations
This research looks at various bubble sizes in one particular magnetic RAM (MAURAM) type, from grazing incidence (00) to 450 and at a frequency range from 2-18 GHz, TE polarization. The results from the absolute RCS measurement of the various sized RAM bubbles are discussed in terms of a frequency dependent increase in RCS. In the frequency band of interest, 2-18GHz, a RAM bubble increases the RCS at all angles, from grazing incidence (00) to 450. From 10-18GHz the RAM bubble does not cause an increase in RCS. In general the highest RCS is at 2GHz and tapers down as …
A Comparative Analysis Of Networks Of Workstations And Massively Parallel Processors For Signal Processing, David C. Gindhart
A Comparative Analysis Of Networks Of Workstations And Massively Parallel Processors For Signal Processing, David C. Gindhart
Theses and Dissertations
The traditional approach to parallel processing has been to use Massively Parallel Processors (MPPs). An alternative design is commercial-off-the-shelf (COTS) workstations connected to high-speed networks. These networks of workstations (NOWs) typically have faster processors, heterogeneous environments, and most importantly, offer a lower per node cost. This thesis compares the performance of MPPs and NOWs for the two-dimensional fast Fourier transform (2-D FFT). Three original, high-performance, portable 2-D FFTs have been implemented: the vector-radix, row-column and pipeline. The performance of these algorithms was measured on the Intel Paragon, IBM SP2 and the AFIT NOW, which consists of 6 Sun Ultra workstations …
A Modeling And Simulation Approach To Characterize Network Layer Internet Survivability, Leif S. King
A Modeling And Simulation Approach To Characterize Network Layer Internet Survivability, Leif S. King
Theses and Dissertations
The Air Force Core Competency of Information Superiority will be achieved in an age of decreasing AF manpower and corporate expertise. Increased AF reliance on COTS solutions, coupled with nearly ubiquitous points of entry to communication networks, create unique challenges in maintaining the Information Superiority edge. The protection of the internet is part of this equation. The internet supports the daily business traffic of the Air Force. Personnel, finance, and supply data flow through its routers. Controlling an adversary's access to our information systems, either the data, or the hardware and software that control the data and transform it into …
A Mammographic Registration Method Based On Optical Flow And Multiresolution Computing, Kevin A. Lee
A Mammographic Registration Method Based On Optical Flow And Multiresolution Computing, Kevin A. Lee
Theses and Dissertations
Mammography is a potent weapon in the fight against Breast Cancer, due in large part to its widespread availability and low cost. Despite the fact that mammography can detect small lesions as early as two years before they become palpable on physical exam, between 10 and 30 percent of cancerous lesions go undetected during evaluation by the radiologist. One approach to improving detection rates involves comparing mammograms of the same breast from successive years. Since most forms of breast cancer develop slowly, multiple view techniques might be able to detect subtle changes indicative of cancerous growth. This thesis proposes a …
A Performance Analysis Of The Faugeras Color Space As A Component Of Color Histogram-Based Image Retrieval, Chad A. Vander Meer
A Performance Analysis Of The Faugeras Color Space As A Component Of Color Histogram-Based Image Retrieval, Chad A. Vander Meer
Theses and Dissertations
The use of color histograms for image retrieval from databases has been implemented in many variations. Selecting the appropriate color space for similarity comparisons is an important part of a color histogram technique. This paper serves to introduce and evaluate the performance of a color space through the use of color histograms. Performance is evaluated by correlating the similarity results obtained from various color feature vector techniques (including color histgramming) to those gathered through a human perceptual test. The perceptual test required 36 human subjects to evaluate the similarity of 10 military aircraft images. The same 10 images were also …
Modeling And Simulation Support For Parallel Algorithms In A High-Speed Network, Dustin E. Yates
Modeling And Simulation Support For Parallel Algorithms In A High-Speed Network, Dustin E. Yates
Theses and Dissertations
This thesis investigates the ability of a simulation model to compare and contrast parallel processing algorithms in a high-speed network. The model extends existing modeling, analysis, and comparison of parallel algorithms by providing graphics based components that facilitate the measurement of system resources. Simulation components are based on the Myrinet local area network standard. The models provide seven different topologies to contrast the performance of five variations of Fast Fourier Transform (FFT) algorithms. Furthermore, the models were implemented using a commercially developed product that facilitates the testing of additional topologies and the investigation of hardware variations. Accurate comparisons are statistically …
Message-Bundle Converting In Intenet Protocol Multicast-Based High Level Architecture Exercises, Tracy A. Bobo
Message-Bundle Converting In Intenet Protocol Multicast-Based High Level Architecture Exercises, Tracy A. Bobo
Theses and Dissertations
The Department of Defense is pushing for more wide-spread and realistic interactive training simulations which increases the demand on network capacity and resources. While network bandwidth is a measurable resource, packet bandwidth, or the number of packets-per-second (Pk/s) a host can handle, is a shifting commodity. This research analyzes host performance characteristics under varying data loads. The hosts include SGI single and multi-processor systems and Intel Pentium platforms using both Windows 95 and Linux Operating Systems. The networking media covers Ethernet, ATM and FDDI. For the ATM network, both AAL5 and IP over ATM were analyzed. With the data from …
Self-Assembly Of Microstructures, Paul E. Kladitis
Self-Assembly Of Microstructures, Paul E. Kladitis
Theses and Dissertations
Four areas are investigated in this research: erecting microstructures normal to the substrate plane without direct human intervention (self-assembled), providing low resistance electrical connections to the erected microstructure, realizing circular motion normal to the substrate plane, and implementing a micro-robot. The designs in this research concentrate on erecting and providing power to a leg designed for use with the micro-robot. The leg and the attached low resistance electrical connectors were not self-assembled because the accompanying actuators were not powerful enough. However, the novel connectors provide the most practical, versatile, and lowest possible resistance connections for the MUMPs fabrication process. The …
A Reconfigurable Superscalar Architecture, Christopher B. Mayer
A Reconfigurable Superscalar Architecture, Christopher B. Mayer
Theses and Dissertations
The invention of the Field Programmable Gate Array (FPGA) has led to a number of interesting developments. One is the idea of providing custom hardware support for applications running on a computer. These reconfigurable computers have been shown to decrease the execution time for some applications. Based on past results, attention has subsequently turned to using reconfigurable computing in general-purpose computers (e.g. desktop and workstation environments). This thesis develops a design for just such a computer. The design, FPGADLX, is based on a hypothetical superscalar computer running the DLX instruction set and is generic enough in principle to be adapted …
Fpga Processor Implementation For The Forward Kinematics Of The Umdh, Steven M. Parmley
Fpga Processor Implementation For The Forward Kinematics Of The Umdh, Steven M. Parmley
Theses and Dissertations
The focus of this research was on the implementation of a forward kinematic algorithm for the Utah MIT Dexterous Hand (UMDH). Specifically, the algorithm was synthesized from mathematical models onto a Field Programmable Gate Array (FPGA) processor. This approach is different from the classical, general purpose microprocessor design where all robotic controller functions including forward Kinematics are executed serially from a compiled programming language such as C. The compiled code and subsequent real time operating system must be stored on some form of nonvolatile memory, typically magnetic media such as a fixed or hard disk drive, along with other computer …
A Framework For An Automated Compilation System For Reconfigurable Architectures, George R. Roelke Iv
A Framework For An Automated Compilation System For Reconfigurable Architectures, George R. Roelke Iv
Theses and Dissertations
The advent of the Field Programmable Gate Array has allowed the implementation of runtime reconfigurable computer systems. These systems are capable of configuring their hardware to provide custom hardware support for software applications. Since these architectures can be reconfigured during operation, they are able to provide hardware support for a variety of applications, without removal from the system. The Air Force is currently investigating reconfigurable architectures for avionics and signal processing applications. This thesis investigates the problem of automating the application development process for reconfigurable architectures. The lack of automated development support is a major limiting factor in the use …
A Crosstalk Correcting Router That Uses Online Noise Simulation To Route High Speed Multichip Modules, Kenneth J. Mcclellan Jr.
A Crosstalk Correcting Router That Uses Online Noise Simulation To Route High Speed Multichip Modules, Kenneth J. Mcclellan Jr.
Theses and Dissertations
Existing MultiChip Module (MCM) auto-routers either ignore crosstalk or use over simplified crosstalk approximations. Of the routers that do consider crosstalk, very few have the capability to correct crosstalk problems after they occur. This dissertation describes a router that not only has an internal crosstalk model for high speed MCMs which is more accurate than that of other existing routers, but also has the capability to use an online simulator to more accurately determine noise levels. After crosstalk problems occur, the router has the ability to correct these problems. Through memory usage reductions and routing efficiency improvements, this maze router …
An Object-Oriented Discrete-Event Simulation System For Hierarchical Parallel Simulations, Kenneth W. Stauffer
An Object-Oriented Discrete-Event Simulation System For Hierarchical Parallel Simulations, Kenneth W. Stauffer
Theses and Dissertations
The purpose of this research is to design and implement an object-oriented discrete-event simulation system which supports hierarchically constructed players in a parallel or distributed environment. This system design considers modularity and portability so additional modules may be implemented to experiment with new algorithms for both partitioning and synchronization. A simulation system which meets these requirements was partially implemented on an eight-node Intel Hypercube in C. A desired goal was to maintain the functionality of the existing BattleSim application. Test cases used measure the performance and correct operation of the new simulation architecture using a BattleSim subclass. Test results prove …
Performance Analysis Of Preemption Algorithms In An Idnx Circuit Switch Communications Network, Eric C. Gumbs
Performance Analysis Of Preemption Algorithms In An Idnx Circuit Switch Communications Network, Eric C. Gumbs
Theses and Dissertations
Access to communication networks is increasing rapidly. The increase access to these networks results in delays and at times loss of data. At times of peak traffic or when trunks or nodes are down, very important customers' communications requirements are not met. One way to combat this problem is to prioritize the network and provide different levels of grade of service (GOS) for each priority. Call preemption provides an effective method of obtaining different levels of GOS. This research seeks to design the best circuit switch communications network preemption model for the DoD by analyzing previously developed preemption algorithms. Four …
Performance Analysis Of Dynamic Routing Protocols In A Low Earth Orbit Satellite Data Network, Richard F. Janoso
Performance Analysis Of Dynamic Routing Protocols In A Low Earth Orbit Satellite Data Network, Richard F. Janoso
Theses and Dissertations
Modern warfare is placing an increasing reliance on global communications. Currently under development are several Low Earth Orbit (LEO) satellite systems that propose to deliver voice and data traffic to subscribers anywhere on the globe. However, very little is known about the performance of conventional routing protocols under orbital conditions where the topology changes on a scale of minutes rather than days. This thesis compares two routing protocols in a LEO environment. One (Extended Bellman-Ford) is a conventional terrestrial routing protocol, while the other (Darting) is a new protocol which has been proposed as suitable for use in LEO networks. …
Data-Driven Process Discovery: A Discrete Time Algebra For Relational Signal Analysis, David M. Conrad
Data-Driven Process Discovery: A Discrete Time Algebra For Relational Signal Analysis, David M. Conrad
Theses and Dissertations
This research presents an autonomous and computationally tractable method for scientific process analysis, combining an iterative algorithmic search and a recognition technique to discover multivariate linear and non-linear relations within experimental data series. These resultant data-driven relations provide researchers with a potentially real-time insight into experimental process phenomena and behavior. This method enables the efficient search of a potentially infinite space of relations within large data series to identify relations that accurately represent process phenomena. Proposed is a time series transformation that encodes and compresses real-valued data into a well-defined, discrete-space of 13 primitive elements where comparative evaluation between variables …
The Automated Wingman: An Airborne Companion For Users Of Dis Compatible Flight Simulators, Mark M. Edwards
The Automated Wingman: An Airborne Companion For Users Of Dis Compatible Flight Simulators, Mark M. Edwards
Theses and Dissertations
A major problem encountered by users of distributed virtual environments is the lack of simulators available to populate these environments. This problem is usually remedied by using computer generated entities. Unfortunately, these entities often lack adequate human behavior and are readily identified as non-human. This violates the realism premise of distributed virtual reality and is a major problem, especially in training situations. This thesis addresses the problem by presenting a computer generated entity called the Automated Wingman. The Automated Wingman is a semi-automated computer generated aircraft simulator that operates under the control of a designated lead simulator and integrates distributed …
An Architecture For Dynamic Meta-Level Process Control For Model-Based Troubleshooting, John E. Friskie
An Architecture For Dynamic Meta-Level Process Control For Model-Based Troubleshooting, John E. Friskie
Theses and Dissertations
There are numerous methods used for troubleshooting devices. Each method has certain domains, knowledge requirements, and assumptions required for it to perform well. However, oftentimes no one method by itself is sufficient to completely solve a troubleshooting problem. Therefore, an architecture is required to control the combined use of many problem solving methods. The combination of multiple problem solving methods makes the troubleshooting process more robust in terms of device domains that can be dealt with and quality of diagnoses produced. Troubleshooting has two tasks: diagnosis and problem resolution. This research provides an architecture that allows dynamic method selection during …