703 research outputs found
Frequency estimation for single-carrier and OFDM signals in communication and radar systems
Eine der klassischen Problemstellungen in der Signalverarbeitung
ist die Schaetzung der Frequenz eines Signals, das von weissem
Rauschen additiv ueberlagert ist. Diese bedeutende Aufgabe
stellt sich in vielen verschiedenen Anwendungsbereichen wie der
Kommunikationstechnik, beim Doppler-Radar, beim Radar mit
synthetischer Apertur (SAR), beim Array Processing, bei
Radio-Frequency-IDentification (RFID), bei Resonanz-Sensoren usw.
Die Anforderungen bezueglich der Leistungsfaehigkeit des
Frequenzschaetzers haengen von der Anwendung ab. Die
Leistungsfaehigkeit ist dabei oft unter Beruecksichtigung
der folgenden 4 Punkte definiert: i) Genauigkeit,
Richtigkeit der Schaetzung, ii) Arbeitsbereich
(estimation range), iii) Grenzwerte der Schaetzung (im
Vergleich zu einer theoretisch moeglichen Schwelle) und
iv) Komplexitaet der Implementierung. Diese
Anforderungen koennen nicht unabhaengig voneinander
betrachtet werden und stehen sich teilweise gegenueber.
Beispielsweise erfordert die Erzielung von Ergebnissen nahe an der
theoretisch moeglichen Schwelle eine hohe Komplexitaet.
Ebenso kann ein Schaetz-ergebnis von hoher Genauigkeit oftmals
nur fuer einen stark eingeschraenkten Arbeitsbereich erzielt
werden. Die Frequenzschaetzung ist im Falle von durch Fading
hervorgerufenem multiplikativem Rauschen noch herausfordernder. Es
handelt sich dann um den allgemeinen Fall der
Frequenzschaetzung. Bisher hat man bereits viel Arbeit in die
Ableitung eines Schaetzers fĂĽr diesen allgemeinen Fall
investiert. Ein Schaetzer, der optimal bezueglich aller oben
genannten Kriterien ist, duerfte allerdings nur schwer zu
finden sein.
In dieser Dissertation wird mit Blick auf Kommunikationstechnik
und Radaranwendungen ein verallgemeinerter, in geschlossener Form
vorliegender, Frequenzschaetzer eingefuehrt, der alle
genannten Kriterien der Leistungs-faehigkeit
beruecksichtigt. Die Herleitung des Schaetzers beruht auf
dem Prinzip der kleinsten Fehlerquadrate fuer den nichtlinearen
Fall in Verbindung mit der Abelschen partiellen Summation. Zudem
werden verschiedene modifizierte Frequenzschaetzer vorgestellt,
die sich fuer Faelle in denen kein Fading oder nur sehr
geringes Fading auftritt, eignen.Estimating the frequency of a signal embedded in additive white
Gaussian noise is one of the classical problems in signal
processing. It is of fundamental importance in various
applications such as in communications, Doppler radar,
synthetic aperture radar (SAR), array processing, radio
frequency identification (RFID), resonance sensor, etc.
The requirement on the performance of the frequency estimator
varies with the application. The performance is often defined
using four indexes: i). estimation accuracy, ii).
estimation range, iii). estimation threshold, and
iv). implementation complexity. These indexes may be in
contrast with each other. For example, achieving a low threshold
usually implies a high complexity. Likewise, good estimation
accuracy is often obtained at the price of a narrow estimation
range. The estimation becomes even more difficult in the presence
of fading-induced multiplicative noise which is considered to be
the general case of the frequency estimation problem. There have
been a lot of efforts in deriving the estimator for the general
case, however, a generalized estimator that fulfills all indexes
can be hardly obtained.
Focusing on communications and radar applications, this thesis
proposes a new generalized closed-form frequency estimator that
compromises all performance indexes. The derivation of the
proposed estimator relies on the nonlinear least-squares principle
in conjunction with the well known summation-by-parts formula. In
addition to this, several modified frequency estimators suitable
for non-fading or very slow fading scenarios, are also introduced
in this thesis
Precise Point Positioning Inertial Navigation Integration for Kinematic Airborne Applications
UAVs have the potential for autonomous airborne remote sensing applications that require rapid response to natural hazards (e.g. volcano eruptions, earthquakes). As these applications require very accurate positioning, tightly coupled Global Positioning System (GPS) Precise Point Positioning (PPP) Inertial Navigation Systems (INS) are an attractive method to perform real-time aircraft positioning. In particular, PPP can achieve a level of positioning accuracy that is similar to Real-Time Kinematic (RTK) GPS, without the need of a relatively close GPS reference station. However, the PPP method is known to converge to accurate positioning estimate more slowly when compared to RTK, a drawback of PPP that is amplified whenever the receiver platform is faced with GPS challenged environments, such as poor satellite visibility and frequent phase breaks.;This thesis presents the use of a simulation environment that characterizes the position estimation performance sensitivity of PPP/INS through a Monte Carlo analysis that is considered under various conditions: such as, the intensity of multipath errors, the number of phase breaks, the satellite geometry, the atmospheric conditions, the noise characteristics of the inertial sensor, and the accuracy of GPS orbit products. After the PPP/INS formulation was verified in a simulation environment, the INS formulation was incorporated into NASA JPL\u27s Real-Time GIPSY-x. This software was then verified using eight recorded flight data sets provided by the National Geodetic Survey (NGS), National Oceanic and Atmospheric Administration (NOAA) program called Gravity for the Redefinition of the American Vertical Datum (GRAV-D)
Performance Analysis of Constrained Loosely Coupled GPS/INS Integration Solutions
The paper investigates approaches for loosely coupled GPS/INS integration. Error performance is calculated using a reference trajectory. A performance improvement can be obtained by exploiting additional map information (for example, a road boundary). A constrained solution has been developed and its performance compared with an unconstrained one. The case of GPS outages is also investigated showing how a Kalman filter that operates on the last received GPS position and velocity measurements provides a performance benefit. Results are obtained by means of simulation studies and real dat
Effects of Parent and Peer Behaviors on Adolescent Sexual Behavior: Are Positive and Negative Peer Behaviors Moderators?
Adolescents and young adults account for a significantly high proportion of unintended pregnancy and sexually transmitted infection cases in the United States. According to Jessor\u27s Problem Behavior Theory, combined protective factors, such as exposure to positive parenting and peer behaviors, create an environment that is supportive of conventional behaviors and discouraging of problem behaviors. There is an extensive amount of literature on parent and peer influences on adolescent sexual behavior but few studies address the interactive influence of both parent and peer behaviors on adolescent sexual risk-taking. The purpose of this study was to examine the relationship between maternal supportiveness and strictness on adolescent sexual risk-taking, as well as the moderating influence of peer involvement in positive or negative activities. A sample of 14-16 year old adolescents was drawn from the National Longitudinal Survey of Youth-1997 (NLSY-97; N = 4,008, 50.5% male, 59.4% White, 26.5% Black, and 13.3% other). Higher levels of maternal supportiveness, maternal strictness, and positive peer behaviors were each associated with lower levels of sexual risk-taking two years later. High levels of negative peer behaviors were related to high sexual-risk taking two years later. No interaction terms were significant. Important implications for positive peer relationships were also found. Future research should focus on the comparison of parental warmth and control variables as moderators for the relationship between peer influence and adolescent sexual risk-taking
Interferometric synthetic aperture sonar system supported by satellite
Tese de doutoramento. Engenharia Electrotécnica e de Computadores. Faculdade de Engenharia. Universidade do Porto. 200
Validation of CReSIS Synthetic Aperture Radar Processor and Optimal Processing Parameters
Sounding the ice sheets of Greenland and Antarctica is a vital component in determining the effect of global warming on sea level rise. Of particular importance are measurements of the bedrock topography of the outlet glaciers that transport ice from the ice sheet's interior to the margin where it calves into icebergs, contributing to sea level rise. These outlet glaciers are difficult to sound due to crevassing caused by the relatively fast movement of the ice in the glacial channel and higher signal attenuation caused by warmer ice. The Center for Remote Sensing of Ice Sheets (CReSIS) uses multi-channel airborne radars which employ methods for achieving better resolution and signal-to-noise ratio (SNR) to better sound outlet glaciers. Synthetic aperture radar (SAR) techniques are used in the along-track dimension, pulse compression in the range dimension, and an antenna array in the cross-track dimension. CReSIS has developed the CReSIS SAR processor (CSARP) to effectively and efficiently process the data collected by these radars in each dimension. To validate the performance of this processor a SAR simulator was developed with the functionality to test the implementation of the processing algorithms in CSARP. In addition to the implementation of this simulator for validation of processing the data in the along-track, cross-track and range dimensions, there are a number of data-dependent processing steps that can affect the quality of the final data product. CSARP was tested with an ideal simulated point target in white Gaussian noise. The SNR change achieved by range compression, azimuth compression, array combination with and without matched filtering, and lever arm application were all within .2 dB of the theoretical expectation. Channel equalization, when paired with noise-based matched filtering, provided 1-2 dB of gain on average but significantly less than the expected gain. Extending the SAR aperture length to sound bedrock will improve the along-track resolution, but at the expense of SNR. Increasing the taper of a window in the fast-time and slow-time will slightly improve the SNR of the data. Changing the relative permittivity used to process the data improved the resulting SNR by no more than 0.025 dB for the test dataset
Motion Compensation for Near-Range Synthetic Aperture Radar Applications
The work focuses on the analysis of influences of motion errors on near-range SAR applications and design of specific motion measuring and compensation algorithms. First, a novel metric to determine the optimum antenna beamwidth is proposed. Then, a comprehensive investigation of influences of motion errors on the SAR image is provided. On this ground, new algorithms for motion measuring and compensation using low cost inertial measurement units (IMU) are developed and successfully demonstrated
Advanced Integration of GNSS and External Sensors for Autonomous Mobility Applications
L'abstract è presente nell'allegato / the abstract is in the attachmen
The 26th Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting
This document is a compilation of technical papers presented at the 26th Annual PTTI Applications and Planning Meeting. Papers are in the following categories: (1) Recent developments in rubidium, cesium, and hydrogen-based frequency standards, and in cryogenic and trapped-ion technology; (2) International and transnational applications of Precise Time and Time Interval technology with emphasis on satellite laser tracking, GLONASS timing, intercomparison of national time scales and international telecommunications; (3) Applications of Precise Time and Time Interval technology to the telecommunications, power distribution, platform positioning, and geophysical survey industries; (4) Applications of PTTI technology to evolving military communications and navigation systems; and (5) Dissemination of precise time and frequency by means of GPS, GLONASS, MILSTAR, LORAN, and synchronous communications satellites
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