Engineering Commons^™

Byu Micro-Sar: A Very Small, Low-Power Lfm-Cw Synthetic Aperture Radar, Michael Israel Duersch

Theses and Dissertations

Brigham Young University has developed a low-cost, light-weight, and low power consumption SAR for flight on a small unmanned aerial vehicle (UAV) at low altitudes. This micro-SAR, or uSAR, consumes only 18 watts of power, ideal for application on a small UAV. To meet these constraints, a linear frequency modulation-continuous wave (LFM-CW) transmit signal is utilized. Use of an LFM-CW signal introduces some differences from the typical strip map SAR processing model that must be addressed in signal processing algorithms. This thesis presents a derivation of the LFM-CW signal model and the associated image processing algorithms used for the uSAR …

Understanding And Improving Moment Method Scattering Solutions, Clayton Paul Davis

Theses and Dissertations

The accuracy of moment method solutions to electromagnetic scattering problems has been studied by many researchers. Error bounds for the moment method have been obtained in terms of Sobolev norms of the current solution. Motivated by the historical origins of Sobolev spaces as energy spaces, it is shown that the Sobolev norm used in these bounds is equivalent to the forward scattering amplitude, for the case of 2D scattering from a PEC circular cylinder. A slightly weaker relationship is obtained for 3D scattering from a PEC sphere. These results provide a physical meaning for abstract solution error bounds in terms …

Design Of Cmos Four-Quadrant Gilbert Cell Multiplier Circuits In Weak And Moderate Inversion, Craig Timothy Remund

Theses and Dissertations

This thesis presents four-quadrant CMOS current-mode multiplier architectures based on the bipolar Gilbert cell multiplier architecture. Multipliers are designed using the CMOS subthreshold region to take advantage of the subthreshold exponential I-V relationship that closely matches bipolar modeling. It is discovered that biasing to remove drift current components and to address higher order effects such as ideality factor mismatch, threshold mismatch, body effect, and short channel effects, is important to provide a linear multiplier. It is also shown that distortion caused by device size mismatch and offset input currents can be used to cancel the distortion introduced by drift currents …

Polarimetric Temperature Sensor Using Core-Replaced Fiber, Benjamin L. Ipson

Theses and Dissertations

Optical fibers are increasingly being used to create sensing devices. The D-fiber has an elliptical core and exhibits birefringence. This birefringence can be used to create a polarimetric sensor. The elliptical core supports two orthogonal modes that have separate effective indices of refraction. The indices of refraction change with a change in temperature. Since the effective indices of refraction change differently for the two modes, the birefringence also changes. This change in birefringence can be seen as a change in detected power through the fiber through the use of polarizers. The fiber then becomes a temperature sensor. The sensitivity of …

Frequency Estimation Of Linear Fm Scatterometer Pulses Received By The Seawinds Calibration Ground Station, Spencer S. Haycock

Theses and Dissertations

The SeaWinds Calibration Ground Station (CGS) is a passive ground station used to receive and sample transmissions from the SeaWinds scatterometer. During post processing, the received transmissions are characterized in order to verify proper instrument operation and to eliminate error in satellite telemetry and in data products generated from processing SeaWinds data. Sources of instrument error include uncertainties in transmitted power, pulse timing, and carrier frequency drift. Identifying these errors prevents their propagation to data products. A key aspect of this analysis involves accurately estimating the parameters of the SeaWinds transmissions. As better parameter estimates are researched and developed, the …

An Examination Into The Statistics Of The Singular Vectors For The Multi-User Mimo Wireless Channel, Scott Nathan Gunyan

Theses and Dissertations

Many capacity and near-capacity achieving methods in multiple-input-multipleoutput (MIMO) wireless channels make use of the singular value decomposition (SVD) of the channel matrix. For the multi-user case, the SVD of the channel matrix for each user may result in right and left singular vectors that are similar between users. This proposes another descriptive characterization of the multi-user MIMO channel. Closely aligned singular vectors between any two users could reduce the achievable signaling rates of signal processing communication methods as one user would be more difficult to resolve in space-time from another. An examination into how this alignment can be described …

Imaging Techniques And Hardware For Inhomogeneous Mri, David A. Thayer

Theses and Dissertations

Magnetic Resonance Imaging (MRI) has become one of the most important medical imaging modalities over the past few decades because of its flexibility and low risk, along with other useful attributes. For traditional MRI, the static magnetic field, B_0, must be highly homogeneous. Obtaining this homogeneity can be difficult. Traditional MRI also requires linear gradient fields that are directed along the static field direction. Under these conditions a Fourier transform relationship exists between sampled data and the image to be reconstructed. In the case of an inhomogeneous static field, gradient fields that are not linear, or gradients that are not …

Microwave Remote Sensing Of The Greenland Ice Sheet: Models And Applications, Ivan S. Ashcraft

Theses and Dissertations

Spaceborne microwave sensors are powerful tools for monitoring the impacts of global climate change on the Greenland ice sheet. This dissertation focuses on refining methods for applying microwave data in Greenland studies by using new simple theoretical and empirical models to investigate (1) azimuth anisotropies in the data, (2) the microwave signature of the snow surface, (3) detection of snow melt, and (4) classification of snow melt. The results are applicable for identifying geophysical properties of the snow surface and monitoring changes on the ice sheet in relation to melt duration/extent, accumulation, and wind patterns. Azimuth dependence of the normalized …

A New Method For Melt Detection On Antarctic Ice-Shelves And Scatterometer Calibration Verification, Lukas Brad Kunz

Theses and Dissertations

Ku-band dual-polarization radar backscatter measurements from the SeaWinds on QuikScat scatterometer and microwave radiometer measurements from the Special Sensor Microwave/Imager (SSM/I) are used to determine periods of surface melt and freeze in the Antarctic ice-shelves. The normalized radar backscatter (sigma-0) and backscatter polarization ratio (PR) are used in the maximum likelihood estimation of the ice-state. This method is used to infer the daily ice-surface conditions for 25 selected study points located on the Ronne, Ross, Larsen, Fimbul, Amery, and Shackleton Ice-shelves. The temporal and spatial variations of the radar response are also observed for various neighborhood sizes surrounding each given …

Improving Electromagnetic Bias Estimates, Floyd W. Millet

Theses and Dissertations

The electromagnetic (EM) bias is the largest source of error in the TOPEX/Poseidon and Jason-1 satellite sea surface height (SSH) estimates. Due to incomplete understanding of the physical processes which cause the bias, current operational models are based on empirical relationships between the bias wind speed and significant wave height. These models reduce RMS estimation errors of the EM bias to approximately 4 cm.

To improve EM bias estimation the correlation between the bias and RMS long wave slope is studies using data from tower-based experiments in the Gulf of Mexico and Bass Straight, Australia. Models based on significant wave …

Unitary Space-Time Transmit Diversity For Multiple Antenna Self-Interference Suppression, Adam Lane Anderson

Theses and Dissertations

A common practice for government defense agencies and commercial aeronautical companies is to use dual antennas on test flight air vehicles in order to overcome occlusion issues during high-speed telemetric maneuvers. The dual antennas, though never being masked at the same time, unfortunately lead to a drastic increase in nulls in the signal pattern. The result of this interference pattern can be compared to the effect of fading in a multiple-input multiple-output (MIMO) multi-path scattering environment. Confidence in this comparison leads to the use of unitary space-time MIMO codes to overcome the signal self-interference. The possibility and performance of several …

A Ray-Based Investigation Of The Statistical Characteristics And Efficient Representation Of Multi-Antenna Communication Channels, Gus Ryan German

Theses and Dissertations

Multi-antenna communication systems are attracting research interest as a means to increase the information capacity, reliability, and spectral efficiency of wireless information transfer. Ray-tracing methods predict the behavior of wireless channels using a model of the propagation environment and are a low-cost alternative to direct measurements. We use ray tracing simulations to validate the statistical time and angle of arrival characteristics of an indoor multipath channel and compare model parameter estimates with estimates derived from channel sounding measurements. Ray tracing predicts the time and angle clustering of multipaths observed in the measurements and provides model parameter estimates which are closely …

Architectures For Symbol Timing Synchronization In Mimo Communications, Kejing Liu

Theses and Dissertations

Maximum likelihood symbol timing estimation for communication over a frequency non-selective MIMO fading channel is developed. The cases of known data (data-aided estimation) and unknown data (non-data-aided estimation) together with known channel and unknown channel are considered. The analysis shows that the log-likelihood functions and their approximations can be interpreted as SISO log-likelihood functions operating on each of the receive antennas. Previously published symbol timing estimators are shown to be special cases of the more general framework presented. Architectures based on both block processing and sequential processing using a discrete-time phase-locked loop are summarized. Performance examples over a MIMO channel …

Consensus Seeking, Formation Keeping, And Trajectory Tracking In Multiple Vehicle Cooperative Control, Wei Ren

Theses and Dissertations

Cooperative control problems for multiple vehicle systems can be categorized as either formation control problems with applications to mobile robots, unmanned air vehicles, autonomous underwater vehicles, satellites, aircraft, spacecraft, and automated highway systems, or non-formation control problems such as task assignment, cooperative transport, cooperative role assignment, air traffic control, cooperative timing, and cooperative search. The cooperative control of multiple vehicle systems poses significant theoretical and practical challenges. For cooperative control strategies to be successful, numerous issues must be addressed. We consider three important and correlated issues: consensus seeking, formation keeping, and trajectory tracking. For consensus seeking, we investigate algorithms and …

Wideband Channel Characterization For Mimo Scenario, Justin T. Holzer

Theses and Dissertations

Because broadband wireless systems benefit from accurate channel characterization, there is growing interest in broadband wireless multiple-input multiple-output (MIMO) channel models. This thesis verifies the suitability of the Saleh Valenzuela with Angle (SVA) model for wideband MIMO communication models. While recent wideband MIMO measurements have been obtained by switching a single transmit/receive pair over all possible antenna pair combinations, a simultaneous probing system is superior because of the time required for the antenna-switching channel measurements. This work provides two different wideband channel estimation algorithms based on simultaneous transmission from and reception on all antennas. Simulated data from an electromagnetic ray …

Motion Compensation Of Interferometric Synthetic Aperture Radar, David P. Duncan

Theses and Dissertations

Deviations from a nominal, straight-line flight path of a synthetic aperture radar (SAR) lead to inaccurate and defocused radar images. This thesis is an investigation into the improvement of the motion compensation algorithm created for the BYU inteferometric synthetic aperture radar, YINSAR. The existing BYU SAR processing algorithm produces improved radar imagery but does not fully account for variations in attitude (roll, pitch, yaw) and does not function well with large position deviations. Results in this thesis demonstrate that a higher order motion compensation algorithm is not as effective as using a segmented reference track, coupled with the current lower-order …

Time Blanking For Gbt Data With Radar Rfi, Weizhen Dong

Theses and Dissertations

The 1215 MHz to 1400 MHz band is important for radio astronomers to observe redshifted extragalactic hydrogen ionic (HI). Observations at these frequencies are complicated by radio frequency interference (RFI) from strong man-made transmissions such as the ARSR-3 Air Surveillance Radar. In this thesis, we characterize some data files recorded at the National Radio Astronomy Observatory (NRAO) at Green Bank, West Virginia, USA, where this RADAR system causes significant data corruption. Using this data, we present a blanking technique to separate RFI from cosmic signal. There are generally two blanking approaches, time window blanking and detected pulse blanking. Compared with …

Dynamic Element Matching Techniques For Delta-Sigma Adcs With Large Internal Quantizers, Brent C. Nordick

Theses and Dissertations

This thesis presents two methods that enable high internal quantizer resolution in delta-sigma analog-to-digital converters. Increasing the quantizer resolution in a delta-sigma modulator can increase SNR, improve stability and reduce integrator power consumption. However, each added bit of quantizer resolution also causes an exponential increase in the power dissipation, required area and complexity of the dynamic element matching (DEM) circuit required to attenuate digital-to-analog converter (DAC) mismatch errors. One way to overcome these drawbacks is to segment the feedback signal, creating a "coarse" signal and a "fine" signal. This reduces the DEM circuit complexity, power dissipation, and size. However, it …

Design Of An Autopilot For Small Unmanned Aerial Vehicles, Reed Siefert Christiansen

Theses and Dissertations

This thesis presents the design of an autopilot capable of flying small unmanned aerial vehicles with wingspans less then 21 inches. The autopilot is extremely small and lightweight allowing it to fit in aircraft of this size. The autopilot features an advanced, highly autonomous flight control system with auto-launch and auto-landing algorithms. These features allow the autopilot to be operated by a wide spectrum of skilled and unskilled users. Innovative control techniques implemented in software, coupled with light weight, robust, and inexpensive hardware components were used in the design of the autopilot.

Design And Analysis Of Charge-Transfer Amplifiers For Low-Power Analog-To-Digital Converter Applications, William Joel Marble

Theses and Dissertations

The demand for low-power A/D conversion techniques has motivated the exploration of charge-transfer amplifiers (CTAs) to construct efficient, precise voltage comparators. Despite notable advantages over classical, continuous-time architectures, little is understood about the dynamic behavior of CTAs or their utility in precision A/D converters. Accordingly, this dissertation presents several advancements related to the design and analysis of charge-transfer amplifiers for low-power data conversion.

First, an analysis methodology is proposed which leads to a deterministic model of the voltage transfer function. The model is generalized to any timing scheme and can be extended to account for nonlinear threshold modulation. The model …

Hardware Synthesis Of Synchronous Data Flow Models, Matthew R. Koecher

Theses and Dissertations

Synchronous Dataflow (SDF) graphs are a convenient way to represent many signal processing and dataflow operations. Nodes within SDF graphs represent computation while arcs represent dependencies between nodes. Using a graph representation, SDF graphs formally specify a dataflow algorithm without any assumptions on the final implementation. This allows an SDF model to be synthesized into a variety of implementation techniques including both software and hardware.

This thesis presents a technique for generating an abstract hardware representation from SDF models. The techniques presented here operate on SDF models defined structurally within the Ptolemy modeling environment. The behavior of the nodes within …

Source Level Debugging Of Circuits Synthesized From High Level Language Descriptions, Karl S. Hemmert

Theses and Dissertations

The rapid increase in the density of modern FPGAs has allowed ever increasingly complex designs to be mapped to FPGAs. However, this increase in logic resources is accompanied by an increase in the complexity of describing and verifying the operation of an application. This has prompted the search for new approaches to the design, debug and verification of circuits. The desire to find more effecient approaches to designing these large FPGA circuits has led to the creation of synthesizing compilers that can create hardware from high-level descriptions based on general purpose programming languages. Being able to describe the application at …

Transmission Strategies For Wireless Multi-User, Multiple-Input, Multiple-Output Communication Channels, Quentin H. Spencer

Theses and Dissertations

Multiple-Input, Multiple-Output (MIMO) processing techniques for wireless communication are of interest for next-generation systems because of their potential to dramatically improve capacity in some propagation environments. When used in applications such as wireless LAN and cellular telephony, the MIMO processing methods must be adapted for the situation where a base station is communicating with many users simultaneously. This dissertation focuses on the downlink of such a channel, where the base station and all of the users have antenna arrays. If the transmitter has advance knowledge of the users' channel transfer functions, it can use that information to minimize the interuser …

Analysis And Design Of Low-Jitter Oscillators, Justin Jennings Fitzpatrick

Theses and Dissertations

This thesis presents an examination of the jitter performance of different oscillator types in the presence of flicker noise, white noise and power supply noise. Key results are achieved using time domain simulations to determine cycle jitter of several different oscillator architectures, semiconductor processes and component features. In the end, a design procedure is developed for creating a low-jitter oscillator in a TSMC .25mm CMOS semiconductor process.

Autonomous Landing Of A Rotary Unmanned Aerial Vehicle In A Non-Cooperative Environment Using Machine Vision, Joshua Martin Hintze

Theses and Dissertations

Landing an Unmanned Aerial Vehicle (UAV) is a non-trivial problem. Removing the ability to cooperate with the landing site further increases the complexity. This thesis develops a multi-stage process that allows a UAV to locate the safest landing site, and then land without a georeference. Machine vision is the vehicle sensor used to locate potential landing hazards and generate an estimated UAV position. A description of the algorithms, along with validation results, are presented. The thesis shows that software-simulated landing performs adequately, and that future hardware integration looks promising.

Design Of A High Speed Mixed Signal Cmos Mutliplying Circuit, David Ray Bartholomew

Theses and Dissertations

This thesis presents the design of a mixed-signal CMOS multiplier implemented with short-channel PMOS transistors. The multiplier presented here forms the product of a differential input voltage and a five-bit digital code. A TSMC 0.18 µm MOSFET model is used to simulate the circuit in Cadence Design Systems. The research presented in this thesis reveals a configuration that allows the multiplier to run at a speed of 8.2 GHz with end-point nonlinearity less than 5%. The high speed and low nonlinearity make this circuit ideal for applications such as filtering and digital to analog conversion.

Implementation Issues Of Real-Time Trajectory Generation On Small Uavs, Derek B. Kingston

Theses and Dissertations

The transition from a mathematical algorithm to a physical hardware implementation is non-trivial. This thesis discusses the issues involved in the transition from the theory of real-time trajectory generation all the way through a hardware experiment. Documentation of the validation process as well as modifications to the existing theory as a result of hardware testing are treated at length. The results of hardware experimentation show that trajectory generation can be done in real-time in a manner facilitating coordination of multiple small UAVs.

Beamforming Techniques And Interference Mitigation Using A Multiple Feed Array For Radio Astronomy, Chad K. Hansen

Theses and Dissertations

Radio frequency interference has become a large problem to radio astronomers. This thesis proposes the idea that radio frequency interference can be mitigated using a phased array feed in conjunction with a large reflector. A phased array feed would allow radio astronomers to observe fainter signals than is currently possible, while at the same time enabling rapid sky surveys. A phased array feed was designed and simulated, and sensitivity optimization was performed on the array feed. It was shown that higher sensitivity can be achieved using a 7-element phased array feed than with a conventional waveguide feed. Simulations were ran …

Integrated Microbattery Charger For Autonomous Systems, Brian W. Lefevre

Theses and Dissertations

This thesis presents a microbattery recharging circuit suitable for autonomous microsystems. The battery charger chosen for this design is a constant current battery charger. Two methods of regulating the constant-current are discussed. A published shunt regulator design is analyzed and is presented with enhancements to the design. A series regulator that controls the current to the battery with a switch is designed and fabricated in a 1.5µm CMOS process. The fabricated prototype occupies less than 2.20x2.20mm and is expected to dissipate less than 25µW of power. A discrete model of the integrated circuit is constructed and tested to demonstrate that …

Studies In Multiple-Antenna Wireless Communications, Christian Bruce Peel

Theses and Dissertations

Wireless communications systems are used today in a variety of milieux, with a recurring theme: users and applications regularly require higher throughput. Multiple antennas enable higher throughput and/or more robust performance than single-antenna communications, with no increase in power or frequency bandwidth. Systems are required which achieve the full potential of this "space-time" communication channel under the significant challenges of time-varying fading, multiple users, and the choice of appropriate coding schemes. This dissertation is focused on solutions to these problems. For the single-user case, there are many well-known coding techniques available; in the first part of this dissertation, the performance …