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Articles 1 - 11 of 11
Full-Text Articles in Signal Processing
Wideband Satcom Model: Evaluation Of Numerical Accuracy And Efficiency, Andrew J. Knisely, Andrew Terzuoli
Wideband Satcom Model: Evaluation Of Numerical Accuracy And Efficiency, Andrew J. Knisely, Andrew Terzuoli
Faculty Publications
The spectral method is typically applied as a simple and efficient method to solve the parabolic wave equation in phase screen scintillation models. The critical factors that can greatly affect the spectral method accuracy is the uniformity and smoothness of the input function. This paper observes these effects on the accuracy of the finite difference and the spectral methods applied to a wideband SATCOM signal propagation model simulated in the ultra-high frequency (UHF) band. The finite difference method uses local pointwise approximations to calculate a derivative. The spectral method uses global trigonometric interpolants that achieve remarkable accuracy for continuously differentiable …
Orthogonal Frequency Division Multiplexed Waveform Effects On Passive Bistatic Radar, Forrest D. Taylor
Orthogonal Frequency Division Multiplexed Waveform Effects On Passive Bistatic Radar, Forrest D. Taylor
Theses and Dissertations
Communication waveforms act as signals of opportunity for passive radars. However, these signals of opportunity suffer from range-Doppler processing losses due to their high range sidelobes and pulse-diverse waveform aspects. Signals such as the long term evolution (LTE) encode information within the phase and amplitude of the waveform. This research explores aspects of the LTE, such as the encoding scheme and bandwidth modes on passive bistatic Doppler radar. Signal space-time adaptive processing (STAP) performance is evaluated and parameters are compared with the signal to interference-plus-noise ratio (SINR) metric.
Sound Based Positioning, David L. Weathers
Sound Based Positioning, David L. Weathers
Theses and Dissertations
With a growing interest in non-GPS positioning, navigation, and timing (PNT), sound based positioning provides a precise way to locate both sound sources and microphones through audible signals of opportunity (SoOPs). Exploiting SoOPs allows for passive location estimation. But, attributing each signal to a specific source location when signals are simultaneously emitting proves problematic. Using an array of microphones, unique SoOPs are identified and located through steered response beamforming. Sound source signals are then isolated through time-frequency masking to provide clear reference stations by which to estimate the location of a separate microphone through time difference of arrival measurements. Results …
Satellite Communications In The V And W Band: Natural And Artificial Scintillation Effects, David A. Smith
Satellite Communications In The V And W Band: Natural And Artificial Scintillation Effects, David A. Smith
Theses and Dissertations
In a natural atmospheric environment the troposphere will be the primary source of loss with the ionosphere loss being negligible. If the ionosphere was disturbed from a high altitude nuclear explosion (HANE) more than three times the amount of electrons would be present in the ionosphere and could represent a source of significant loss. In order to determine the amount of electrons distributed from a HANE, GSCENARIO, developed by Defense Threat Reduction Agency was used. The two sources of loss that were examined was signal absorption and amplitude scintillation. Signal loss was determined using GSCENARIO and amplitude scintillation loss was …
Metrics For Emitter Selection For Multistatic Synthetic Aperture Radar, Sean R. Stevens
Metrics For Emitter Selection For Multistatic Synthetic Aperture Radar, Sean R. Stevens
Theses and Dissertations
A bistatic implementation of synthetic aperture radar (SAR) to form images of the ground from an aircraft makes use of separate emitters and receivers. When not using cooperative emitters, ground based communications systems can provide illumination. One way to improve performance of these waveforms, which are not designed for SAR, is a multistatic implementation, formed from multiple bistatic systems. This leads to the problem of selecting a subset from a potentially large set of emitters to use for image formation. A framework for this selection between sets of emitters is proposed using multiple objective optimization. This approach requires use of …
Automatic Modulation Classification Of Common Communication And Pulse Compression Radar Waveforms Using Cyclic Features, John A . Hadjis
Automatic Modulation Classification Of Common Communication And Pulse Compression Radar Waveforms Using Cyclic Features, John A . Hadjis
Theses and Dissertations
This research develops a feature-based MAP classification system and applies it to classify several common pulse compression radar and communication modulations. All signal parameters are treated as unknown to the classifier system except SNR and the signal carrier frequency. The features are derived from estimated duty cycle, cyclic spectral correlation, and cyclic cumulants. The modulations considered in this research are BPSK, QPSK, 16-QAM, 64-QAM, 8-PSK, and 16-PSK communication modulations, as well as Barker coded, Barker coded, Barker coded, Frank coded, Px49 coded, and LFM pulse compression modulations. Simulations show that average correct signal modulation type classification %C 90% is achieved …
An Approach To Large Scale Radar-Based Modeling And Simulation, Lester C. Long Iv
An Approach To Large Scale Radar-Based Modeling And Simulation, Lester C. Long Iv
Theses and Dissertations
This research presents a method of aggregating, or reducing the resolution, of a commonly available Department of Defense (DoD) simulation. It addresses the differences between varying levels of resolution and scope used in the DoD’s hierarchy of models pyramid. A data representation that aggregates engagement-level simulation data to use at a lower resolution level, the mission-level, is presented and analyzed. Two formats of implementing this data representation are developed and compared: the rigid cylinder format and the expanding tables format. The rigid cylinder format provides an intuitive way to visualize the data and is used to develop the theory. The …
Development And Evaluation Of A Multistatic Ultrawideband Random Noise Radar, Matthew E. Nelms
Development And Evaluation Of A Multistatic Ultrawideband Random Noise Radar, Matthew E. Nelms
Theses and Dissertations
This research studies the AFIT noise network (NoNET) radar node design and the feasibility in processing the bistatic channel information of a cluster of widely distributed noise radar nodes. A system characterization is used to predict theoretical localization performance metrics. Design and integration of a distributed and central signal and data processing architecture enables the Matlab®-driven signal data acquisition, digital processing and multi-sensor image fusion. Experimental evaluation of the monostatic localization performance reveals its range measurement error standard deviation is 4.8 cm with a range resolution of 87.2(±5.9) cm. The 16-channel multistatic solution results in a 2-dimensional localization error of …
Integrated Approach To Airborne Laser Communication, James A. Louthain
Integrated Approach To Airborne Laser Communication, James A. Louthain
Theses and Dissertations
Lasers offer tremendous advantages over RF communication systems in bandwidth and security, due to their ultra-high frequency and narrow spatial beamwidth. Atmospheric turbulence causes severe received power variations and high bit error rates (BERs) in airborne laser communication. Airborne optical communication systems require special considerations in size, complexity, power, and weight. Conventional adaptive optics systems correct for the phase only and cannot correct for strong scintillation, but here the two transmission paths are separated sufficiently so that the strong scintillation is \averaged out" by incoherently summing up the two beams in the receiver. This requisite separation distance is derived for …
Length Selectable, Hardware Efficient Pseudorandom Code Generator, John F. Brendle Jr., James P. Stephens Sr., Michael A. Temple, Robert S. Parks
Length Selectable, Hardware Efficient Pseudorandom Code Generator, John F. Brendle Jr., James P. Stephens Sr., Michael A. Temple, Robert S. Parks
AFIT Patents
A method and device for generating a pseudorandom electrical signal for enabling spread spectrum communication scrambling by directing data entry into pseudorandom number generator integrated circuit chip controlling registers using a length selectable feedback logic data sequence and either computer programmable selector means or manual selector means to communicate the logic data sequence characters to buffers. The logic data sequence characters are clocked to a pseudorandom number generating register of an integrated circuit chip and the pseudorandom electrical signal is generated by selectively tapping a signal code therefrom. The method and device features a pseudorandom electrical signal length varying capability …
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 …