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Full-Text Articles in Engineering
Applying Frequency-Domain Equalization To Code-Division Multiple Access And Transform-Domain Communications Systems, Alfred A. Tamayo Iii
Applying Frequency-Domain Equalization To Code-Division Multiple Access And Transform-Domain Communications Systems, Alfred A. Tamayo Iii
Theses and Dissertations
This research examined the theory and application of using orthogonal frequency division multiplexing (OFDM), or discrete multi-tone (DMT), frequency domain equalization (FEQ) with two communications systems that inherently possess unused carrier frequencies, or null-tones, in their respective transmission frequencies. The fundamental DMT-FEQ property relies on null-tones to equalize a non-ideal channel and mitigate the effects of interchannel interference (ICI), intersymbol interference (ISI), and noise. The two communications systems investigated were a Hadamard encoded code division multiple access (CDMA) communications system with up to 32 synchronous users and a transform domain communications system (TDCS) with only one user. Both communications systems …
Increasing Combat Aircraft Survivability Through Coherent Self-Protection Jammers, Soner Ozer
Increasing Combat Aircraft Survivability Through Coherent Self-Protection Jammers, Soner Ozer
Theses and Dissertations
When the battlefields were within the visual range, the objective of deception tactics in warfare was to deceive the human senses. In the battlefield of electromagnetic spectrum, the objective of deception is to deceive the sensors of the enemy weapon systems. The survivability of the aircraft operating in hostile environment is of prime importance to the mission planner. If the aircraft can deny its location information to the tracking radar of the radar guided threat missile system, this, in return, may increase its survivability. The deception, a tactic which stems from the wisdom of ancient battles, incarnated in the form …
Navigation Using Orthogonal Frequency Division Multiplexed Signals Of Opportunity, Jamie S. Velotta
Navigation Using Orthogonal Frequency Division Multiplexed Signals Of Opportunity, Jamie S. Velotta
Theses and Dissertations
The global positioning system (GPS) provides high-accuracy position measurements anywhere in the world. However, a limitation of this system is that a line of sight to multiple satellites is required; therefore, it is unsuitable to use indoors or in urban canyons. Also, in the presence of radio-frequency interference or jamming, GPS may be unavailable. Alternative methods of navigation and positioning are need to either compliment GPS as a backup or for use in areas unreachable by satellites. This research analyzes a feature-based correlation approach for determining reception differences between two Orthogonal Frequency Division receivers for the purpose of TDOA calculations. …
Device Discovery In Frequency Hopping Wireless Ad Hoc Networks, Brian S. Peterson
Device Discovery In Frequency Hopping Wireless Ad Hoc Networks, Brian S. Peterson
Theses and Dissertations
This research develops a method for efficient discovery of wireless devices for a frequency hopping spread spectrum, synchronous, ad hoc network comprised of clustered sub-networks. The Bluetooth wireless protocol serves as the reference protocol. The development of a discovery, or outreach, method for scatternets requires the characterization of performance metrics of Bluetooth piconets, many of which are unavailable in literature. Precise analytical models characterizing the interference caused to Bluetooth network traffic by inquiring devices, the probability mass function of packet error rates between arbitrary pairs of Bluetooth networks, and Bluetooth discovery time distribution are developed. Based on the characterized performance …
Multiple Access Interference Characterization For Direct-Sequence Spread-Spectrum Communications Using Chip Waveform Shaping, Matthew G. Glen
Multiple Access Interference Characterization For Direct-Sequence Spread-Spectrum Communications Using Chip Waveform Shaping, Matthew G. Glen
Theses and Dissertations
This research characterizes MAI effects on DS/SSMA system performance through simulation in Matlab , and explores the impact of multiple access code selection, chip waveform shaping, and multiple access code length on BER for both synchronous and asynchronous multiple access networks. In addition, the simulated DS/SSMA model permits rapid research into the effects of additional factors on BER. Prior to experimental testing, model validation is conducted through single user trials and by comparison with existing research for similar system designs. For synchronous and asynchronous networks, Gold coding improves BER by 7.5 and 4.0 dB, respectively, relative to aperiodic random spreading …
Interference Suppression In Multiple Access Communications Using M-Ary Phase Shift Keying Generated Via Spectral Encoding, Abel S. Nunez
Interference Suppression In Multiple Access Communications Using M-Ary Phase Shift Keying Generated Via Spectral Encoding, Abel S. Nunez
Theses and Dissertations
A conceptual transform domain communication system (TDCS) is shown capable of operating successfully using M-Ary phase shift keying (MPSK) data modulation in a multiple access environment. Using spectral encoding, the conceptual TDCS provides an effective means for mitigating interference affects while achieving multiple access communications. The use of transform domain processing with MPSK data modulation (TD-MPSK) provides higher spectral efficiency relative to other modulation techniques (antipodal signaling and cyclic shift keying) considered previously for TDCS applications. The proposed TD-MPSK technique uses spectral encoding for both data and multiple access phase modulations. Demodulation of the spectrally encoded TD-MPSK communication symbols is …
A Direct Sequence Code-Division Multiple-Access Local Area Network Model, James R. Rapallo Jr.
A Direct Sequence Code-Division Multiple-Access Local Area Network Model, James R. Rapallo Jr.
Theses and Dissertations
The United States Air Force relies heavily on computer networks for every-day operations. The medium access control (MAC) protocol currently used by most local area (LAN) permits a single station to access the network at a time (e.g. CSMA/CD or Ethernet). This limits network throughput to, at most, the maximum transmission rate of a single node with overhead neglected. Significant delays are observed when a LAN is overloaded by multiple users attempting to access the common medium. In CSMA/CD, collisions are detected and the data sent by the nodes involved are delayed and transmitted at a later time. The retransmission …
Wavelet Domain Communication System (Wdcs): Packet-Based Wavelet Spectral Estimation And M-Ary Signaling, Marion Jay F. Lee
Wavelet Domain Communication System (Wdcs): Packet-Based Wavelet Spectral Estimation And M-Ary Signaling, Marion Jay F. Lee
Theses and Dissertations
A recently proposed Wavelet Domain Communication System (WDCS) using transform domain processing demonstrated excellent interference avoidance capability under adverse environmental conditions. This work extends previous results by: 1) incorporating a wavelet packet decomposition technique, 2) demonstrating M-Ary signaling capability, and 3) providing increased adaptivity over a larger class of interference signals. The newly proposed packet-based WDCS is modeled and its performance characterized using MATLAB®. In addition, the WDCS response to two scenarios simulating Doppler effects and physical separation of transceivers are obtained. The fundamental metric for analysis and performance evaluation is bit error rate (Pb). Relative to …
Wavelet Domain Communication System (Wdcs): Design, Model, Simulation, And Analysis, Randall W. Klein
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 …
Using Direct-Sequenced Spread Spectrum In A Wired Local Area Network, Robert J. Bonner
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.
Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park
Interference Suppression For Spread Spectrum Signals Using Adaptive Beamforming And Adaptive Temporal Filter, Wonjin Park
Theses and Dissertations
Interference and jamming signals are a serious concern in an operational military communication environment. This thesis examines the utility and performance of combining adaptive temporal filtering with adaptive spatial filtering (i.e. adaptive beamforming) to improve the signal-to-jammer ratio (SJR) in the presence of narrowband and wideband interference. Adaptive temporal filters are used for narrowband interference suppression while adaptive beamforming is used to suppress wideband interference signals. A procedure is presented for the design and implementation of a linear constraints minimum variance generalized sidelobe canceler (LCMV-GSC) beamformer. The adaptive beamformer processes the desired signal with unity gain while simultaneously and adaptively …
Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo
Analysis Of Multimode Low-Probability-Of-Intercept (Lpi) Communications With Atmospheric Effects, Ala Ghordlo
Theses and Dissertations
This research expanded Low Probability of Intercept (LPI) communications analysis in two areas. First, multimode communication was included to account for ground to ground and air to ground links in addition to the standard air to air links traditionally used in LPI analysis. The propagation equations for the three modes of interest were derived and included in LPI analytic models in the form of a mode quality factor to account for multimode LPI scenarios. This new quality factor was used in studying several communication and interception link combinations. Variations due to differences between the communication and interception modes were presented …
Effects Of Jamming And Excision Filtering Upon Error Rates And Detectability Of A Spread Spectrum Communication System, Christopher B. Madden
Effects Of Jamming And Excision Filtering Upon Error Rates And Detectability Of A Spread Spectrum Communication System, Christopher B. Madden
Theses and Dissertations
This thesis examines the effects of a digital excision filter (DEF) upon the error rates and detectability of a Direct Sequence Binary Phase Shift Keyed communication signal in the presence of both continuous wave (CW) and pulsed jammers. Simulations were performed using the Comdisco Signal Processing Worksystem. Detector models used were the wideband radiometer and two forms of the chip-rate detector. Twelve jamming scenarios were used to test the performance of the DEF in the presence of the CW and pulsed jammers. In addition, the effects of the CW jammer frequency, the pulsed jammer duty cycle, and the pulsed jammer …
Narrowband Interference Suppression In Spread Spectrum Communication Systems, James A. Lascody
Narrowband Interference Suppression In Spread Spectrum Communication Systems, James A. Lascody
Theses and Dissertations
Of significant interest to the United States military is the ability of an enemy to deny or disrupt the operation of the Global Positioning System. To combat this threat the GPS JPO initiated the Tactical GPS AntiJam Technology project, which yielded a prototype Digital Excision Filter (DEF) to remove narrowband jammers. This research describes the work performed to get the DEF hardware operational and extends the previous research performed in this area. Comdisco's Signal Processing Worksystem was used to examine the effect of the DEF on the probability of bit error. This research uses peak to average correlation value, probability …
Analysis And Simulation Of A Gps Receiver Design Using Combined Delay-Lock And Modified Tanlock Loops, George D. Harris
Analysis And Simulation Of A Gps Receiver Design Using Combined Delay-Lock And Modified Tanlock Loops, George D. Harris
Theses and Dissertations
The purpose of this thesis was to investigate the performance of two types of tracking loops used in Global Positioning System (GPS) receivers. The first loop, the Delay-Lock Loop (DLL), is responsible for maintaining synchronization with the received PN sequence. The second loop, the Modified Tanlock Loop (MTLL), is responsible for maintaining synchronization with the carrier signal. The performance of the two loops is investigated first separately then their performance is evaluated when operated together. This thesis is an investigation on the ability of these two loops to overcome corruption of the input signal due to noise. Expanding the dynamic …