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Electrical and Computer Engineering

Brigham Young University

Series

2005

Articles 1 - 30 of 31

Full-Text Articles in Engineering

Performance Analysis Of Common Detectors For Shaped Offset Qpsk And Feher's Qpsk, Tom Nelson, Michael D. Rice, Erik Perrins Dec 2005

Performance Analysis Of Common Detectors For Shaped Offset Qpsk And Feher's Qpsk, Tom Nelson, Michael D. Rice, Erik Perrins

Faculty Publications

Sponsorship: US Air Force Grant FA9302-05-C-0001. A detector architecture capable of detecting both shaped offset quadrature phase shift keying (SOQPSK-TG) and Feher's quadrature phase shift keying (FQPSK-JR) is developed and analyzed. Both modulations are embodied as fully interoperable modulations in the Interrange Instrumentation Group (IRIG) standard IRIG-106. It is shown that the common detector achieves near optimal bit error rate performance without knowledge of which modulation is used by the transmitter. The detection techniques are based on a common trellis-coded modulation representation and a common continuous phase modulation (CPM) representation for these two modulations. In addition the common pulse amplitude …

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An Analysis Of Seawinds-Based Rain Retrieval In Severe Weather Events, David G. Long, Jeffrey R. Allen Dec 2005

An Analysis Of Seawinds-Based Rain Retrieval In Severe Weather Events, David G. Long, Jeffrey R. Allen

Faculty Publications

The Ku-band SeaWinds scatterometer estimates near-surface ocean wind vectors by relating measured backscatter to a geophysical model function for the near-surface vector wind. The conventional wind retrieval algorithm does not explicitly account for SeaWinds' sensitivity to rain, resulting in rain-caused wind retrieval error. A new retrieval method, termed "simultaneous wind/rain retrieval," that estimates both wind and rain from rain-contaminated measurements has been previously proposed and validated with Tropical Rain Measuring Mission data. Here, the accuracy of rains retrieved by the new method is validated through comparison with the Next Generation Weather Radar (NEXRAD) in coastal storm events. The rains detected …

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Modeling Microwave Emissions Of Erg Surfaces In The Sahara Desert, David G. Long, Haroon Stephen Dec 2005

Modeling Microwave Emissions Of Erg Surfaces In The Sahara Desert, David G. Long, Haroon Stephen

Faculty Publications

Sand seas (ergs) of the Sahara are the most dynamic parts of the desert. Aeolian erosion, transportation, and deposition continue to reshape the surface of the ergs. The large-scale features (dunes) of these bedforms reflect the characteristics of the sand and the long-term wind. Radiometric emissions from the ergs have strong dependence on the surface geometry. We model the erg surface as composed of tilted rough facets. Each facet is characterized by a tilt distribution dependent upon the surface roughness of the facet. The radiometric temperature (Tb) of ergs is then the weighted sum of the Tb from all the …

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Highly Efficient Fluorescence Detection In Picoliter Volume Liquid-Core Waveguides, Aaron R. Hawkins, John P. Barber, Dongliang Yin Nov 2005

Highly Efficient Fluorescence Detection In Picoliter Volume Liquid-Core Waveguides, Aaron R. Hawkins, John P. Barber, Dongliang Yin

Faculty Publications

We report loss improvement and fluorescence detection in integrated antiresonant reflecting optical waveguides with liquid cores. The minimum waveguide loss is reduced to 0.33/cm by compensating for thickness variations in the fabrication process. We demonstrate fluorescence detection from as few as 490 molecules in a 57 pl core using these optimized waveguides. We measure angular fluorescence collection factors as high as 15% per facet in good agreement with theory. This demonstrates the potential of integrated hollow-core waveguides as optical sensors for single-molecule spectroscopy.

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Social Utility Functions-Part I: Theory, Wynn C. Stirling Nov 2005

Social Utility Functions-Part I: Theory, Wynn C. Stirling

Faculty Publications

The dominant approaches to utility-based multiagent decision theory rely on the premise of individual rationality-the doctrine that each individual is committed to achieving the best outcome for itself, regardless of the effect doing so has on others. This fundamentally asocial concept is the basis of conventional von Neumann-Morgenstern (vN-M) utilities but is inadequate to characterize truly cooperative artificial systems. Social utility functions differ from conventional vN-M utilities in that they are functions of multiple decision-maker preferences, rather than actions, and thus permit individuals to expand their spheres of interest beyond the self. A logical basis for coherent reasoning in multiagent …

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Social Utility Functions-Part Ii: Applications, Wynn C. Stirling, Richard L. Frost Nov 2005

Social Utility Functions-Part Ii: Applications, Wynn C. Stirling, Richard L. Frost

Faculty Publications

Social utilities account for agent preferences and, thus, can characterize complex interrelationships, such as cooperation, compromise, negotiation, and altruism, that can exist between agents. Satisficing game theory, which is based on social utilities, offers a framework within which to design sophisticated multiagent systems. Key features of this approach are: a) an N-agent system may be represented by a 2N-dimensional Bayesian network, called a praxeic network; b) the theory accommodates a notion of situational altruism (a willingness to defer to others in a controlled way if so doing would actually benefit others under the condition that others wish to take advantage …

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Static And Dynamic Obstacle Avoidance For Miniature Air Vehicles, Jeffery Brian Saunders, Brandon Call, Andrew Curtis, Randal W. Beard, Timothy W. Mclain Sep 2005

Static And Dynamic Obstacle Avoidance For Miniature Air Vehicles, Jeffery Brian Saunders, Brandon Call, Andrew Curtis, Randal W. Beard, Timothy W. Mclain

Faculty Publications

Small unmanned air vehicles are limited in sensor weight and power such that detection and avoidance of unknown obstacles during flight is difficult. This paper presents a low power low weight method of detection using a laser range finder. In addition, a rapidly-exploring random tree algorithm to generate waypoint paths around obstacles known a priori is presented, and a dynamic geometric algorithm to generate paths around detected obstacles is derived. The algorithms are demonstrated in simulation and in flight tests on a fixed-wing miniature air vehicle (MAV).

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Impact Of Receive Amplifier Signal Coupling On Mimo System Performance, Michael A. Jensen, Matthew L. Morris Sep 2005

Impact Of Receive Amplifier Signal Coupling On Mimo System Performance, Michael A. Jensen, Matthew L. Morris

Faculty Publications

This paper uses a detailed model of multiple input multiple output (MIMO) systems to explore the impact of signal coupling in the receiver front end on communication capacity. The model is applied to assess the performance of a MIMO system with two transmit and receive antennas in a simulated multipath environment for different amplifier coupling levels. The results show that in practical scenarios where simple impedance matching techniques are used, the circuit coupling can reduce the signal-to-noise ratio at the receiver and therefore degrade the achievable MIMO capacity.

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Superdirectivity In Mimo Systems, Michael A. Jensen, Matthew L. Morris, Jon W. Wallace Sep 2005

Superdirectivity In Mimo Systems, Michael A. Jensen, Matthew L. Morris, Jon W. Wallace

Faculty Publications

Multiantenna systems such as devices for multiple-input-multiple-output (MIMO) communication can theoretically use array superdirectivity to optimally exploit the propagation channel. In traditional analyses of MIMO systems, such superdirectivity is not observed due to the commonly applied constraint that limits the excitation current magnitudes. However, when an electromagnetically appropriate constraint on the power radiated by the array is applied, the computed capacity can include effects of transmit superdirectivity. A similar result occurs at the receiver for spatially colored noise. This paper formulates the MIMO system capacity under these circumstances and provides a framework for computing this capacity when the level of …

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Embedded Slanted Grating Coupler For Vertical Coupling Between Fibers And Silicon-On-Insulator Planar Waveguides, Gregory P. Nordin, J. Jiang, B. Wang Sep 2005

Embedded Slanted Grating Coupler For Vertical Coupling Between Fibers And Silicon-On-Insulator Planar Waveguides, Gregory P. Nordin, J. Jiang, B. Wang

Faculty Publications

We propose a compact and efficient grating coupler for vertical coupling between optical fibers and planar waveguides. A grating with a parallelogram shape is designed to be etched through the entire high-index waveguide core. The coupler is optimized using a microgenetic algorithm coupled with a two-dimensional finite-difference time-domain method. Simulations show that up to 75.8% coupling efficiency can be obtained between a single-mode fiber and a 240-nm-thick silicon-on-insulator planar waveguide.

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Navigation And Control Technologies For Autonomous Micro Vehicles, Randal Beard, Timothy W. Mclain Aug 2005

Navigation And Control Technologies For Autonomous Micro Vehicles, Randal Beard, Timothy W. Mclain

Faculty Publications

Sponsorship: Air Force Research Laboratory / Munitions Directorate. During this project we focused on four primary objectives which are listed below. 1. Magnetometer Integration. Integrate and flight test magnetometers with the current version of the autopilot (Spiral 1). 2. Height-Above-Ground Sensor Integration. Integrate and flight test height-above-ground sensors with the current version of the autopilot (Spiral 1). 3. Automatic Gain Adjustment. Develop and flight test automatic gain adjustment algorithms that automatically tune the servo loops of the autopilot. 4. Automatic Trim Seeking. Develop and flight test automatic trim seeking algorithms to recursively estimate the trim values of the UAV.

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Solid-State Current Amplifier Based On Impact Ionization, Aaron R. Hawkins, Hong-Wei Lee Aug 2005

Solid-State Current Amplifier Based On Impact Ionization, Aaron R. Hawkins, Hong-Wei Lee

Faculty Publications

The operation principle, fabrication, and measurement results for a stand-alone amplifier based on impact ionization are reported. The device was built in silicon using standard microelectronic processes. Testing was performed by connecting the device to both silicon and indium-gallium-arsenide photodiodes to demonstrate its compatibility with arbitrary current sources. Preamplified leakage currents of less than 1 nA were measured along with current gains greater than 100.

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Effects Of Mutual Coupling On Interference Mitigation With A Focal Plane Array, Michael A. Jensen, Karl F. Warnick Aug 2005

Effects Of Mutual Coupling On Interference Mitigation With A Focal Plane Array, Michael A. Jensen, Karl F. Warnick

Faculty Publications

A focal plane array feed of electrically small elements has been proposed as a means for achieving high sensitivity for radio astronomy applications in the presence of radio frequency interference (RFI). For a broadband system, mutual coupling effects become significant as the array element spacing becomes small relative to the electromagnetic wavelength. We present a theoretical framework for modeling the effects of mutual coupling and for determining the optimal multiport matching network between array elements and front-end transistor low-noise amplifiers for maximum signal-to-noise ratio (SNR). Numerical results are given for a model scenario including spillover and amplifier thermal noise and …

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Improved Network Analysis Of Coupled Antenna Diversity Performance, Michael A. Jensen, Matthew L. Morris Jul 2005

Improved Network Analysis Of Coupled Antenna Diversity Performance, Michael A. Jensen, Matthew L. Morris

Faculty Publications

This paper presents a new framework for the analysis of mutually coupled diversity antennas based on network theory. The network model incorporates the matching network between the antennas and front-end amplifiers and uses a realistic model for the amplifier noise. The resulting analysis includes the impact of the coupled-antenna radiation patterns and impedance characteristics in determining the branch signal-to-noise ratios (SNRs). Application of the formulation to coupled dipole antennas characterized using full-wave electromagnetic analysis illustrates that a matching network providing a minimum amplifier noise figure achieves significantly better diversity performance than one providing maximum power transfer.

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Correlation Of Fault-Injection To Proton Accelerator Persistent Cross Section Measurements, Keith S. Morgan, Michael J. Wirthlin Jun 2005

Correlation Of Fault-Injection To Proton Accelerator Persistent Cross Section Measurements, Keith S. Morgan, Michael J. Wirthlin

Faculty Publications

Sponsorship: Los Alamos National Laboratory. Field Programmable Gate Arrays (FPGAs) are an attractive solution for space system electronics. Unfortunately, FPGAs are susceptible to radiation-induced single-event upsets (SEU). As such, the FPGA Reliability Studies research group (http://reliability.ee.byu.edu) at Brigham Young University has studied ways to effectively measure the static, dynamic and persistent cross sections of an FPGA desgin; each of which are characterized in some way by how the part reacts to an SEU. One such method is to actually radiate an FPGA and monitor how it reacts to SEUs. A cheaper, more efficient solution is to use fault-injection to emulate …

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Predicting On-Orbit Seu Rates, Keith S. Morgan, Michael J. Wirthlin Jun 2005

Predicting On-Orbit Seu Rates, Keith S. Morgan, Michael J. Wirthlin

Faculty Publications

As process geometry sizes continue to decrease, microelectronics are becoming more vulnerable to the effects of radiation. Of particular concern are the effects of Single-Event Upsets (SEU) in Field Programmable Gate Arrays (FPGA). An SEU causes a dynamic memory element, such as a flip-flop or latch, to unwantedly change state. Since FPGAs are becoming an increasingly attractive solution for space system electronics, it is desirable to predict static on-orbit SEU rates likely to be encountered by a particular device for any particular orbit. Mean Time Between Failure (MTBF) can directly be calculated from a static SEU rate, allowing a system …

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Differentiation Between Melt And Freeze Stages Of The Melt Cycle Using Ssm/I Channel Ratios, David G. Long, Ivan S. Ashcraft Jun 2005

Differentiation Between Melt And Freeze Stages Of The Melt Cycle Using Ssm/I Channel Ratios, David G. Long, Ivan S. Ashcraft

Faculty Publications

Microwave remote sensing detection of snow melt and ablation generally focuses on the detection of liquid moisture in the snow-pack. For ablation estimation, it is important to determine if wet snow is in the process of melting or freezing. The different stages of the melt cycle are observed in the diurnal variation of Tb measurements from the Special Sensor Microwave Imager (SSM/I) over Greenland. SSM/I channel ratios exhibit patterns indicating that they are sensitive to melt and freeze stages of the daily melt cycle. The horizontal to vertical polarization ratio is sensitive to surface wetness associated with melting. The 19-37-GHz …

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Stratified Waveguide Grating Coupler For Normal Fiber Incidence, Gregory P. Nordin, D. M. Chambers, J. Jiang, B. Wang Apr 2005

Stratified Waveguide Grating Coupler For Normal Fiber Incidence, Gregory P. Nordin, D. M. Chambers, J. Jiang, B. Wang

Faculty Publications

We propose a new stratified waveguide grating coupler (SWGC) to couple light from a fiber at normal incidence into a planar waveguide. SWGCs are designed to operate in the strong coupling regime without intermediate optics between the fiber and the waveguide. Two-dimensional finite-difference time-domain simulation in conjunction with microgenetic algorithm optimization shows that about 72% coupling efficiency is possible for fiber (core size of 8.3 μm and ∆=0.36%) to slab waveguide (1.2- μm core and ∆=3.1%) coupling. We show that the phase-matching and Bragg conditions are simultaneously satisfied through the fundamental leaky mode.

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Reducing Energy In Fpga Multipliers Through Glitch Reduction, Nathaniel Rollins, Michael J. Wirthlin Apr 2005

Reducing Energy In Fpga Multipliers Through Glitch Reduction, Nathaniel Rollins, Michael J. Wirthlin

Faculty Publications

Sponsorship: NASA Earth Science Technology Office (ESTO). While FPGAs provide exibility for performing high-performance DSP functions, they consume a significant amount of power. For arithmetic circuits, a large portion of the dynamic power is wasted on unproductive signal glitches. Pipelining can be used to significantly reduce the unproductive power wasted in signal glitches. This paper presents a methodology for estimating the amount of power consumed by glitches and applies this methodology to non-pipelined, pipelined, and digit-serial multipliers. This glitch estimation is used to evaluate these multipliers using four energy metrics: energy per operation, energy delay, energy throughput, and energy density. …

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Calibrating Seawinds And Quikscat Scatterometers Using Natural Land Targets, David G. Long, Lucas B. Kunz Apr 2005

Calibrating Seawinds And Quikscat Scatterometers Using Natural Land Targets, David G. Long, Lucas B. Kunz

Faculty Publications

The SeaWinds-on-QuikSCAT (QuikSCAT) and SeaWinds-on-ADEOS-2 (SeaWinds) scatterometers measure the normalized radar backscatter (O) of the earth's surface. These identical radar sensors are on different spaceborne platforms in similar orbits. QuikSCAT and SeaWinds data are used to infer near-surface wind vectors, polar sea-ice extent, polar-ice melt events, etc. In order to verify the relative calibration of these sensors, a simple cross calibration based on land backscatter measurements is performed. A first-order polynomial model is used to remove the incidence angle dependence of O for selected regions of the Amazon rainforest and the Sahara Desert. It is shown that the two sensors …

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Sea Ice Mapping Method For Seawinds, David G. Long, Hyrum S. Anderson Mar 2005

Sea Ice Mapping Method For Seawinds, David G. Long, Hyrum S. Anderson

Faculty Publications

A sea ice mapping algorithm for SeaWinds is developed that incorporates statistical and spatial a priori information in a modified maximum a posteriori (MAP) framework. Spatial a priori data are incorporated in the loss terms of a Bayes risk formulation. Conditional distributions and priors for sea ice and ocean statistics are represented as empirical histograms that are forced to conform to a set of expected histograms via principal component filtering. Tuning parameters for the algorithm allow adjustments in the algorithm's performance. Results of the algorithm exhibit high correlation with the Remund-Long sea ice mapping algorithm for SeaWinds and the Special …

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The Detection Efficiency Of Artm Cpm In Aeronautical Telemetry, Michael D. Rice, Erik Perrins Feb 2005

The Detection Efficiency Of Artm Cpm In Aeronautical Telemetry, Michael D. Rice, Erik Perrins

Faculty Publications

ARTM CPM is a partial response, two-index continuous-phase modulation that was adopted as a standard in IRIG 106-04 for aeronautical telemetry. This waveform was selected because it achieves approximately three times the spectral efficiency of PCM/FM. However, the optimum receiver requires 128 real-valued matched filters and keeps track of the waveform state with a trellis of 512 states and 2048 branches. Various complexity reducing techniques are applied and the resulting loss in detection efficiency is quantified. It is shown that the full 512-state trellis is not required to achieve the desired detection efficiency: two different 32-state configurations were found to …

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Pam Representation Of Ternary Continuous Phase Modulation, Michael D. Rice, Erik Perrins Feb 2005

Pam Representation Of Ternary Continuous Phase Modulation, Michael D. Rice, Erik Perrins

Faculty Publications

It is well-known that binary continuous phase modulation (CPM) waveforms can be exactly represented as a pulse amplitude modulation (PAM) waveforms. This has also been shown for nonbinary CPM waveforms with even-sized symbol alphabets. In this paper we show how this is also accomplished for ternary CPM waveforms. We focus the development on signals with shorter frequency pulses, since these cases have the most practical value in designing reduced-complexity detectors. However, we also show the pattern by which these results can be extended to arbitrary frequency pulse durations and also to arbitrary odd-sized symbol alphabets, although little practical value is …

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Microwave Backscatter Modeling Of Erg Surfaces In The Sahara Desert, David G. Long, Haroon Stephen Feb 2005

Microwave Backscatter Modeling Of Erg Surfaces In The Sahara Desert, David G. Long, Haroon Stephen

Faculty Publications

The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter (σ˚) modulation with azimuth angle (∅). We use σ˚ measurements observed at various incidence angles and ∅ from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission's Precipitation Radar to model the σ˚ response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes …

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Observation And Characterization Of Radar Backscatter Over Greenland, David G. Long, Ivan S. Ashcraft Feb 2005

Observation And Characterization Of Radar Backscatter Over Greenland, David G. Long, Ivan S. Ashcraft

Faculty Publications

Characterization of the microwave signature of the Greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change. A new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle, azimuth angle, spatial gradient, and temporal rate of change. The individual model parameters are discussed in depth with examples using data from the NASA Scatterometer (NSCAT) and from the C-band European Remote Sensing (ERS) satellite Advanced Microwave Instrument in scatterometer mode. The contribution …

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Electromagnetically Induced Transparency In Alkali Atoms Integrated On A Semiconductor Chip, Aaron R. Hawkins, Holger Schmidt Jan 2005

Electromagnetically Induced Transparency In Alkali Atoms Integrated On A Semiconductor Chip, Aaron R. Hawkins, Holger Schmidt

Faculty Publications

We analyze the integration of electromagnetically induced transparency in alkali atoms on a semiconductor chip. We propose the use of antiresonant reflecting optical waveguides with hollow cores to realize the necessary waveguiding capability and optical mode areas of a few square micrometers. We derive the scaling laws and limitations for the reduction in group velocity and single-photon phase shifts as a function of waveguide dimension. We show that miniaturization leads to a large enhancement of single-photon cross-phase modulation, despite the presence of additional limitations due to coherence dephasing and waveguide loss.

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Efficient Capacity-Based Antenna Selection For Mimo Systems, Michael A. Jensen, Matthew L. Morris Jan 2005

Efficient Capacity-Based Antenna Selection For Mimo Systems, Michael A. Jensen, Matthew L. Morris

Faculty Publications

The achieved capacity of the multiple-input-multiple-output wireless channel is typically dependent on the array configurations at the transmitter and receiver. Maximizing system capacity or throughput therefore requires that the arrays adapt to changing channel conditions, which may be accomplished by selecting an appropriate subset of available antenna elements for connection to the electronic transmit and receive modules. This work presents algorithms, derived using relatively straightforward information theoretic considerations, for efficiently and effectively selecting the antenna elements. Computational examples using a realistic channel model for indoor environments illustrate the performance of the techniques.

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Network Model For Mimo Systems With Coupled Antennas And Noisy Amplifiers, Michael A. Jensen, Matthew L. Morris Jan 2005

Network Model For Mimo Systems With Coupled Antennas And Noisy Amplifiers, Michael A. Jensen, Matthew L. Morris

Faculty Publications

This work presents a framework for the analysis of mutually-coupled antennas in a multiple-input multiple-output system. The approach uses network theory to formulate the transfer matrix relating the signals input to the transmit antennas to the signals at the output of the receiver front end. This transfer function includes the coupled transmit and receive antennas, the multipath propagation channel, the receiver matching network, and a realistic noise model for the receive amplifiers. Application of the formulation to coupled dipole antennas characterized using full-wave electromagnetic analysis illustrates the performance gains possible from matching the coupled antenna/receive amplifier subsystem for minimum noise …

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Spatial Resolution And Processing Tradeoffs For Hydros: Application Of Reconstruction And Resolution Enhancement Techniques, David G. Long, Michael W. Spencer, Eni G. Njoku Jan 2005

Spatial Resolution And Processing Tradeoffs For Hydros: Application Of Reconstruction And Resolution Enhancement Techniques, David G. Long, Michael W. Spencer, Eni G. Njoku

Faculty Publications

Recent developments in reconstruction and resolution enhancement for microwave instruments suggest a possible tradeoff between computation, resolution, and downlink data rate based on postcollection reconstruction/resolution enhancement processing. The Hydrospheric State (HYDROS) mission is designed to measure global soil moisture and freeze/thaw state in support of weather and climate prediction, water, energy, and carbon cycle studies, and natural hazards monitoring. It will use an active and passive L-band microwave system that optimizes measurement accuracy, spatial resolution, and coverage. The active channels use synthetic aperture radar-type processing to achieve fine spatial resolution, requiring a relatively high downlink data rate and ground processor …

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Autonomous Vehicle Technologies For Small Fixed-Wing Uavs, Randal Beard, Derek Kingston, Morgan Quigley, Deryl Snyder, Reed Christiansen, Walt Johnson, Timothy Mclain, Michael A. Goodrich Jan 2005

Autonomous Vehicle Technologies For Small Fixed-Wing Uavs, Randal Beard, Derek Kingston, Morgan Quigley, Deryl Snyder, Reed Christiansen, Walt Johnson, Timothy Mclain, Michael A. Goodrich

Faculty Publications

The objective of this paper is to describe the design and implementation of a small semi-autonomous fixed-wing unmanned air vehicle. In particular we describe the hardware and software architectures used in the design. We also describe a low weight, low cost autopilot developed at Brigham Young University and the algorithms associated with the autopilot. Novel PDA and voice interfaces to the UAV are described. In addition, we overview our approach to real-time path planning, trajectory generation, and trajectory tracking. The paper is augmented with movie files that demonstrate the functionality of the UAV and its control software.

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