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Digital Communications and Networking Commons™

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Air Force Institute of Technology

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Articles 151 - 166 of 166

Full-Text Articles in Digital Communications and Networking

Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein Mar 2001

Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein

Theses and Dissertations

A proposed wavelet domain communication system (WDCS) using transform domain processing is demonstrated as having enhanced interference avoidance capability under adverse environmental conditions. The WDCS system samples the environment and uses the wavelet transform, to determine interference presence and time/scale location. A digital communication waveform (basis function) is subsequently designed in the wavelet domain to specifically avoid regions containing interference. The WDCS basis function is data modulated prior to transmission. Assuming perfect synchronization, the receiver replicates a locally generated basis function for correlating with the received signal and demodulating the data. The proposed system is modeled and simulation results are …

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Routing Of Time-Sensitive Data In Mobile Ad Hoc Networks, Necdet Kilic Mar 2001

Routing Of Time-Sensitive Data In Mobile Ad Hoc Networks, Necdet Kilic

Theses and Dissertations

This research focuses on routing of time-sensitive data in mobile ad hoc networks. Routing protocols that were developed for ad hoc networks have been reviewed. Ad Hoc On-demand Distance Vectoring (AODV) routing protocol, which is a prominent routing protocol among these protocols have been implemented in OPNET, a discrete-event simulation tool. Taking AODV as a point of departure, a routing protocol named Real Time Routing Protocol (RTRP) has been developed and also implemented in simulation environment. The performance of these routing protocols have been observed by simulating them in various experiments where the workload has been chosen to be time-sensitive …

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Multicast Algorithms For Mobile Satellite Communication Networks, Ryan W. Thomas Mar 2001

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. …

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Using Direct-Sequenced Spread Spectrum In A Wired Local Area Network, Robert J. Bonner Mar 2001

Using Direct-Sequenced Spread Spectrum In A Wired Local Area Network, Robert J. Bonner

Theses and Dissertations

Code division multiple access provides an ability to share channel bandwidth amongst users at the same time. Individual user performance is not degraded with the addition of more users, unlike traditional Ethernet. Using direct sequenced spread spectrum in a wired local area network, network performance is improved. For a network in overload conditions, individual station throughput is increased by nearly 212% while mean end-to-end delay was reduced by 800%. The vast improvement demonstrated by this research has the capability to extend legacy-cabling infrastructures for many years to come while easily accommodating new bandwidth intensive multimedia applications.

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Turbo Codes For Wireless Mobile Communication Systems Applications, Moataz M. Salah Jun 2000

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 …

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Modeling And Simulation Of Communication Systems In Opnet, David M. Banker Mar 2000

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 …

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A Performance Analysis Of A Joint Lmds/ Satellite Communication Network, Ronald J. Zwickel Mar 2000

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 …

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Network Security Versus Network Connectivity: A Framework For Addressing The Issues Facing The Air Force Medical Community, Franklin E. Cunningham Jr. Dec 1999

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 …

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Performance Analysis Of Tcp Enhancements In Satellite Data Networks, Ren H. Broyles Mar 1999

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 …

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A Modeling And Simulation Approach To Characterize Network Layer Internet Survivability, Leif S. King Dec 1997

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 …

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Modeling And Simulation Support For Parallel Algorithms In A High-Speed Network, Dustin E. Yates Dec 1997

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 …

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Performance Analysis Of Preemption Algorithms In An Idnx Circuit Switch Communications Network, Eric C. Gumbs Dec 1996

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 …

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Performance Analysis Of Dynamic Routing Protocols In A Low Earth Orbit Satellite Data Network, Richard F. Janoso Dec 1996

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. …

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Local Area Network Implementation At The 4950th Test Wing: A Study Of The Relationship Between Individual Factors And The Effectiveness Of A Local Area Network, Doyle F. Cone, David J. Donahoo Dec 1993

Local Area Network Implementation At The 4950th Test Wing: A Study Of The Relationship Between Individual Factors And The Effectiveness Of A Local Area Network, Doyle F. Cone, David J. Donahoo

Theses and Dissertations

This research investigated the individual factors which directly impacted the effectiveness of the 4950th Test Wing local area network (LAN). Areas of interest included the relationships between demographic and user attitude factors and LAN effectiveness. A literature review provided the basis for: 1) operationally defining effectiveness as a subjective measure of user satisfaction; 2) identifying specific factors which impact information system effectiveness; and 3) developing a research instrument to measure user attitudes and user satisfaction. A questionnaire was administered to 342 LAN users 173 were returned (a response rate of 51 percent). Sixteen factors (eight demographic factors and eight attitude …

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Satcom General Purpose Modem Dscs Iii Sct Beacon Telemetry Display, James D. Coppola Dec 1992

Satcom General Purpose Modem Dscs Iii Sct Beacon Telemetry Display, James D. Coppola

Theses and Dissertations

This thesis documents the design and implementation of a DSCS III single Channel Transponder (SCT) beacon telemetry display. The system is a personal computer based design which interfaces to three SCT beacon receiver/demodulators. The software was designed to decode and display both the DSCS III A and DSCS HI B satellite beacons. Recordings of the SCT beacon display can be made on paper and/or magnetic media when triggered by the user, a watchdog timer, or the SCT command accept telemetry bit. In addition, the system can be configured with an IRIG B Universal Time Coordinates (UTC) card which enables the …

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Computer Simulation Of A General Purpose Satellite Modem, William L. Montgomery Jr. Dec 1992

Computer Simulation Of A General Purpose Satellite Modem, William L. Montgomery Jr.

Theses and Dissertations

The purpose of this research was to model and simulate the performance of a digital phase shift keyed satellite modem. The probability of bit error (P sub b) at different levels of energy per bit to noise power ratio (E sub b/N sub o) was the performance measure. The channel was assumed to contribute only additive white Gaussian noise. A second order Costas loop performs demodulation in the modem and was the key part of the simulation. The Costas loop with second order Butterworth arm filters was tested by finding the response to a phase or frequency step. The Costas …

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