Дисертації з теми "Ionospheric techniques"
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Brosie, Kayla Nicole. "Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78710.
Повний текст джерелаMaster of Science
Locubiche-Serra, Sergi. "Robust Carrier Tracking Techniques for GNSS Receivers affected by Ionospheric Scintillation." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/668304.
Повний текст джерелаGlobal Navigation Satellite Systems (GNSS) have become an indispensable tool in different areas in our modern society for positioning purposes using radio-frequency ranging signals. Some application examples are the positioning and navigation in ground, maritime and aviation environments, as well as their use in agriculture, surveying and precise timing and synchronization in communication systems and finances. The tracking stage is one of the core tasks within a GNSS receiver to keep aligned with the satellites and, to date, most receivers equip conventional tracking techniques with ease of implementation that suffice to operate in environments with favorable working conditions. However, in the recent years, the success of GNSS in open-sky environments has led to the emergence of applications that expand toward scenarios with harsher conditions, such as urban canyons and soft-indoor environments. The trend is to provide user mobile terminals such as smartphones with positioning capabilities in scenarios where receivers face new technological challenges owing to the abounding propagation impairments. In this sense, the so-called ionospheric scintillation is one of the issues degrading the performance of GNSS receivers, particularly in equatorial regions and at high latitudes. It introduces rapid carrier phase and signal power variations, and has a detrimental effect particularly onto the tracking stage. The objective of this thesis is to design and develop new techniques for the robust tracking of GNSS signals affected by ionospheric scintillation disturbances. The presented approach is based on the use of Kalman filtering techniques, and the main contributions of the thesis are three. First, the analysis of ionospheric scintillation and the tracking of carrier dynamics despite the presence of the former. We design a Kalman filter with a hybrid formulation that allows the robust monitoring of both contributions separately. This arises from carrying out a detailed analysis of ionospheric scintillation which concludes that scintillation phase variations can be characterized through autoregressive processes, and thus be dealt with within the Kalman filter in a natural manner. Second, the design of adaptive Kalman filter-based techniques that allow self-adjusting their loop bandwidth to the actual scintillation conditions, which are rather time-varying in practice. This part includes a scintillation detector, a real-time estimator of the autoregressive model parameters, and an implementation to address the problem of non-linear signal amplitude attenuation introduced by scintillation itself. The goodness of the proposed techniques is later validated by carrying out an extensive simulation campaign using both synthetic data and real scintillation time series, and the outperformance region with respect to conventional tracking techniques is quantified. Third, a novel method for the derivation of expressions for the termed Bayesian Cramér-Rao bound (BCRB), which allow characterizing the behavior of Kalman filters in a closed-form manner, thus becoming a contribution to the literature of practical usefulness to design Kalman filters for any kind of application.
ROMERO, GAVIRIA RODRIGO MANUEL. "Estimation Techniques and Mitigation Tools for Ionospheric effects on GNSS Receivers." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2616928.
Повний текст джерелаBergadà, Caramés Pau. "Oblique Sounding and HF Communication Techniques for Very Long Haul Ionospheric Links." Doctoral thesis, Universitat Ramon Llull, 2015. http://hdl.handle.net/10803/285837.
Повний текст джерелаLos sistemas de radio de alta frecuencia (HF, en inglés) son usados por agencias gubernamentales y no gubernamentales en todo el mundo siempre que se necesite una alternativa a las comunicaciones por satélite: barcos en alta mar, aviones fuera del rango de cobertura de las redes radio de visión directa, operaciones militares, zonas donde la infraestructura ha sido destruida por algún desastre. Ésta ofrece una alternativa, o representa un sistema de backup, a las comunicaciones vía satélite, evitando los costes, la vulnerabilidad y los problemas de soberanía de las comunicaciones por satélite. En esta tesis se ha estudiado el enlace HF entre la base antártica española Juan Carlos I en la isla Livingston, en las Shetland del sur y España. El objetivo de este trabajo es el estudio de las limitaciones de la propagación ionosférica (como la relación señal a ruido e interferencia, la dispersión multicamino y la dispersión por efecto Doppler) y el diseño de la capa física de un enlace HF de baja velocidad, baja potencia y largo alcance. Se han estudiado un par de propuestas para este enlace, como son el espectro ensanchado por secuencia directa (DSSS, en inglés) y la multiplexación por división en frecuencia ortogonal (OFDM, en inglés). El reto ha sido definir las características que mejor se adecuan a este enlace para poder aprovechar la diversidad temporal y frecuencial que ofrece el canal HF. Desde el año 2003 diversas campañas de sondeo han permitido estudiar el canal HF pero no es hasta la campaña 2009/2010 que se consigue una fotografía de la actividad ionosférica tanto nocturna como diurna. En los artículos que se presentan en esta tesis hemos extendido los estudios previos a todo el rango de frecuencias HF y hemos mostrado las diferencias entre el día y la noche. Hemos usado estos resultados de caracterización del canal para diseñar y comparar símbolos DSSS y símbolos OFDM. Ambas posibilidades han resultado ser posibles candidatas para implementar un enlace HF de baja velocidad entre la Antártida y España. Sin embargo ambas técnicas representan dos aproximaciones distintas a la implementación del módem. Mientras que DSSS consigue un buen funcionamiento a baja velocidad en escenarios con baja relación señal a ruido, OFDM consigue tasas de transmisión más altas en escenarios más benignos.
High Frequency (HF) radio is used by governmental and non nongovernmental agencies worldwide whenever an alternative to satellites for sky wave communication is needed: ships at sea, aircraft out of range of line-of-sight radio networks, military operations, disaster areas with communication infrastructure destroyed or distant regions lacking other communications. It offers an alternative to satellites, or a backup, for long-haul communications, thus avoiding the costs, vulnerabilities and sovereignty concerns of satellite communications. In this thesis the HF link between the Antarctic Spanish Station Juan Carlos I in Livingston Island, South Shetlands and Spain is studied. The aim of this study is to address the impairments that affect HF propagation (i.e., signal-to-noise plus interference ratio, multipath and Doppler shift and spread) and to design the physical layer of a low rate, low power and long-haul HF link. Some proposals regarding this last issue are addressed, i.e., direct sequence spread spectrum (DSSS) and orthogonal frequency division multiplexing (OFDM). The challenge is to define the symbol characteristics that best fit the link to benefit from time and frequency diversity that offers the HF channel. Since 2003 several transmission campaigns have allowed to study the HF channel but it is not until the 2009/2010 campaign that we have achieved a whole picture of both diurnal and nocturnal ionospheric activity. In the papers presented in this thesis we have extended the previous research to the whole range of HF frequencies and we have shown the differences on performance between day and night. We have used the results from channel characterization to design and compare the performance of DSSS and OFDM symbols. Both techniques have turned out to be possible candidates to implement a low rate HF link between Antarctica and Spain. However, both techniques stand for different approaches of the modem: DSSS achieves good performance at low data rate in low SNR scenarios, whereas OFDM achieves higher data rate in benign channels
Elvidge, Sean. "On the use of multi-model ensemble techniques for ionospheric and thermospheric characterisation." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5526/.
Повний текст джерелаKindervatter, Tim. "Survey of Ionospheric Propagation Effects and Modeling Techniques for Mitigation of GPS Error." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515106508878179.
Повний текст джерелаMahmoudian, Alireza. "New-Measurement Techniques to Diagnose Charged Dust and Plasma Layers in the Near-Earth Space Environment Using Ground-Based Ionospheric Heating Facilities." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19239.
Повний текст джерелаsource region associated with mesospheric dusty space plasmas may be modulated by radio wave heating with ground-based ionospheric heating facilities. These experiments show great promise as a diagnostic for the associated dusty plasma in the Near-Earth Space Environment which is believed to have links to global change. This provides an alternative to more complicated and costly space-based observational approaches to investigating these layers. This dissertation seeks to develop new analytical and computational models to investigate fundamental physics of the associated dusty plasmas as well as utilize experimental observations during High Frequency HF ground-based heating experiments to develop practical techniques for diagnosing these dusty plasma layers.
The dependency of the backscattered signal strength (i.e. Polar Mesospheric Summer Echoes PMSEs) after the turn-on and turn-off of the radio wave heating on the radar frequency is an unique phenomenon that can shed light on the unresolved issues associated with the basic physics of the natural charged mesospheric dust layer. The physical process after turn-on and turn-off of radio wave heating is explained by competing ambipolar diffusion and dust charging processes. The threshold radar frequency and dust parameters for the enhancement or suppression of radar echoes after radio wave heating turn-on are investigated for measured mesospheric plasma parameters. The effect of parameters such as the electron temperature enhancement during radiowave heating, dust density, dust charge polarity, ion-neutral collision frequency, electron density and dust radius
on the temporal evolution of electron irregularities associated with PMSE is investigated.
The possibility of observing the turn-on overshoot (enhancement of radar echoes after the
radiowave turn-on) in the high frequency HF radar band is discussed based on typical mesospheric
parameters. It has been shown that predicted enhancement of electron irregularity
amplitude after heater turn-on at HF band is the direct manifestation of the dust charging
process in the space. Therefore further active experiments of PMSEs should be pursued
at HF band to illuminate the fundamental charging physics in the space environment to
provide more insight on this unique medium. Preliminary observation results of HF PMSE
heating experiment with the new 7.9 MHz radar at the European Incoherent Scatter EISCAT
facility appear promising for the existence of PMSE turn-on overshoot. Therefore, future
experimental campaigns are planned to validate these predictions.
Computational results are used to make predictions for PMSE active modification experiments at 7.9, 56, 139, 224 and 930MHz corresponding to existing ionospheric heating facilities. Data from a 2009 very high frequency VHF (224 MHz) experiment at EISCAT
is compared with the computational model to obtain dust parameters in the PMSE. The
estimated dust parameters as a result of these comparison show very reasonable agreement to dust radius and density at PMSE altitudes measured during a recent rocket experiment providing validation to the computational model.
The first comprehensive analytical model for the temporal evolution of PMSE after heater
turn-on is developed and compared to a more accurate computational model as a reference.
It is shown that active PMSE heating experiments involving multiple observing frequencies
at 7.9 (HF), 56, and 224 MHz (VHF) may contribute further diagnostic capabilities since
the temporal evolution of radar echoes is substantially different for these frequency ranges.
It is shown that conducting PMSE active experiments at HF and VHF band simultaneously
may allow estimation of the dust density altitude profile, dust charge state variation during
the heating cycle, and ratio of electron temperature enhancement in the irregularity source
region. These theoretical and computational models are extended to study basic physics of the evolution of relevant dusty plasma instabilities thought to play an important role in irregularity production in mesospheric dust layers. A key focus is the boundary layer of these charged dust clouds. Several aspects of the cloud\'s structure (thickness of boundary layer, average particle size and density, collisional processes, and cloud expansion speed) and the ambient plasma are varied to determine the effect of these quantities on the resulting irregularities.
It was shown that for high collision frequencies, the waves may be very weakly excited (or
even quenched) and confined to the boundary layer. The excited dust acoustic waves inside
the dust cloud with frequency range of 7-15Hz and in the presence of electron bite-outs is
consistent with measured low frequency waves near 10 Hz by sounding rocket experiments
over the past decade. The observed radar echoes associated with the artificially created dust
clouds at higher altitudes in the ionosphere including space shuttle exhaust and upcoming
active space experiments in which localized dust layers will be created by sounding rockets
could be related to the excited acoustic waves predicted.
Finally, variation of spatial structures of plasma and dust (ice) irregularities in the PMSE
source region in the presence of positively charged dust particles is investigated. The correlation and anti-correlation of fluctuations in the electron and ion densities in the background plasma are studied considering the presence of positive dust particle formation. Recent rocket payloads have studied the properties of aerosol particles within the ambient plasma environment in the polar mesopause region and measured the signature of the positively charged particles with number densities of (2000 cm"3) for particles of 0.5-1 nm in radius.
The measurement of significant numbers of positively charged aerosol particles is unexpected from the standard theory of aerosol charging in plasma. Nucleation on the cluster ions is one of the most probable hypotheses for the positive charge on the smallest particles. The utility being that it may provide a test for determining the presence of positive dust particles.
The results of the model described show good agreement with observed rocket data. As an
application, the model is also applied to investigate the electron irregularity behavior during
radiowave heating assuming the presence of positive dust particles. It is shown that the
positive dust produces important changes in the behavior during Polar Mesospheric Summer Echo PMSE heating experiments that can be described by the fluctuation correlation and anti-correlation properties.
The second part of this dissertation is dedicated to Stimulated Electromagnetic Emissions SEEs produced by interaction of high power electromagnetic waves in the ionosphere. Nearearth ionospheric plasma presets a neutral laboratory for investigation of nonlinear wave phenomena in plasma which can not be studied in the laboratory environment due to the effect of physical boundary conditions. This process has been of great interest due to the
important diagnostic possibilities involving ability to determine mass of constitutive ions in
the interaction region through measurements of various gyro-frequencies. Objectives include
the consideration of the variation of the spectral behavior under pump power, proximity to
the gyro-harmonic frequency, and beam angle. Also, the relationship between such spectral
features and electron acceleration and creation of plasma irregularities was an important
focus.
Secondary electromagnetic waves excited by high power electromagnetic waves transmitted
into the ionosphere, commonly know as Stimulated Electromagnetic Emissions SEEs,
produced through Magnetized Stimulated Brillouin Scatter MSBS are investigated. Data
from two recent research campaigns at the High Frequency Active Auroral Research Program
facility HAARP is presented in this work. These experiments have provided additional
quantitative interpretation of the SEE spectrum produced by MSBS to yield diagnostic measurements of the electron temperature in the heated ionosphere. SEE spectral emission lines corresponding to ion acoustic IA and electrostatic ion cyclotron EIC modes were observed with a shift in frequency up to a few tens of Hz from radio waves transmitted near the third harmonic of the electron gyro-frequency 3fce. The threshold of each emission line has been measured by changing the pump wave amplitude. The experimental results aimed to show the threshold for transmitter power to excite IA waves propagating along the magnetic field lines as well as for EIC waves excited at oblique angles relative to the background magnetic field. A full wave solution has been used to estimate the amplitude of the electric field at the interaction altitude. The estimated growth rate using the theoretical model is compared with the threshold of MSBS lines in the experiment and possible diagnostic information for the background ionospheric plasmas is discussed. Simultaneous formation of artificial field aligned irregularities FAIs and suppression of the MSBS process is investigated. Recently, there has been significant interest in ion gyro-harmonic structuring the Stimulated Electromagnetic Emission SEE spectrum due to the potential for new diagnostic information available about the heated volume and ancillary processes such as creation of artificial ionization layers. These relatively recently discovered emission lines have almost exclusively been studied for second electron gyro-harmonic heating. The first extensive systematic investigations of the possibility of these spectral features for third electron gyro-harmonic heating are provided here. Discrete spectral features shifted from the transmit frequency ordered by harmonics of the ion gyro-frequency were observed for third electron gyro-harmonic heating for the first time at a recent campaign at a High Frequency Active Auroral Research Program Facility HAARP. These features were also closely correlated with a broader band feature at a larger frequency shift from the transmit frequency known as the Downshifted Peak DP. The power threshold of these spectral features was measured, as well as their behavior with heater
beam angle, and proximity of the transmit frequency to the third electron gyro-harmonic frequency. Comparisons were also made with similar spectral features observed during 2nd
electron gyro-harmonic heating during the same campaign. A theoretical model is provided
that interprets these spectral features as resulting from parametric decay instabilities in
which the pump field ultimately decays into high frequency upper hybrid/electron Bernstein
and low frequency neutralized ion Bernstein IB and/or obliquely propagating ion acoustic
waves at the upper hybrid interaction altitude. Coordinated optical and SEE observations
were carried out in order to provide a better understanding of electron acceleration and precipitation
processes. Optical emissions were observed associated with SEE gyro-harmonic
features for pump heating near the second electron gyro-harmonic during the campaign. The
observations affirm strong correlation between the gyro-structures and the airglow.
Ph. D.
Oronsaye, Samuel Iyen Jeffrey. "Updating the ionospheric propagation factor, M(3000)F2, global model using the neural network technique and relevant geophysical input parameters." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001609.
Повний текст джерелаDamtie, B. (Baylie). "New incoherent scatter radar measurement techniques and data analysis methods." Doctoral thesis, Oulun yliopisto, 2004. http://urn.fi/urn:isbn:9514273125.
Повний текст джерелаOriginal papers The original papers are not included in the electronic version of the dissertation. Lehtinen, M., Markkanen, J., Väänänen, A., Huuskonen, A., Damtie, B., Nygrén, T., & Rahkola, J. (2002). A new incoherent scatter technique in the EISCAT Svalbard Radar. Radio Science, 37(4), 3-1-3–14. https://doi.org/10.1029/2001rs002518 Damtie, B., Nygrén, T., Lehtinen, M. S., & Huuskonen, A. (2002). High resolution observations of sporadic-E layers within the polar cap ionosphere using a new incoherent scatter radar experiment. Annales Geophysicae, 20(9), 1429–1438. https://doi.org/10.5194/angeo-20-1429-2002 Damtie, B., Lehtinen, M. S., & Nygrén, T. (2004). Decoding of Barker-coded incoherent scatter measurements by means of mathematical inversion. Annales Geophysicae, 22(1), 3–13. https://doi.org/10.5194/angeo-22-3-2004 Lehtinen, M. S., Damtie, B., & Nygrén, T. (2004). Optimal binary phase codes and sidelobe-free decoding filters with application to incoherent scatter radar. Annales Geophysicae, 22(5), 1623–1632. https://doi.org/10.5194/angeo-22-1623-2004
Cruz, Edith Liliana Macotela. "Contribuição ao estudo de distúrbios ionosféricos utilizando a técnica de VLF." Universidade Presbiteriana Mackenzie, 2015. http://tede.mackenzie.br/jspui/handle/tede/1301.
Повний текст джерелаConselho Nacional de Desenvolvimento Científico e Tecnológico
The Earth-Low ionosphere system behaves as a waveguide for the propagation of radio waves of very low frequency (VLF). If in this system the electrical conductivity of its boundaries is perturbed, the propagation of the VLF waves will also be perturbed. There is a diversity of transient physical phenomena that are able to alter significantly the electrical conductivity of the lower ionosphere. The disturbance in this region is able to produce phase and amplitude variations with respect to a quiescent level of these waves. The aim of the present work is to study the response of the lower ionosphere to phenomena originated in the Earth, our solar system or even much farther away. For this purpose, VLF data obtained by SAVNET (South American VLF Network) during the solar cycle 24 was used. It was found that the correction by both the length of the path illuminated by the flare and the reference height coefficient allows normalizing the effect of ionospheric disturbances observed in the VLF phase signals that propagated along trajectories with a north-south or west-east direction, separately. The lower limit of detection for disturbances caused by the X-ray radiation excess is 1.8×10−9 Jm-2 and 2.6×10−7 Jm-2 for the nighttime and daytime lower ionosphere, respectively. Changes in the periodicities of the VLF signal, in the infrasonic band, were observed between 6 and 14 days prior to the seismic events, of magnitude 7, occurred in Haiti in 2010 and in Peru in 2011. Increases in the periodicities of the order of few minutes were observed when the shadow of the total solar eclipse of 2010 was moving on the Earth. Due to the solar eclipse the ionospheric reference height increased in ~3 km and the electron density decreased in 60 % of its quiescent level. Finally, it was found that the effective recombination coefficient, for 80 km height, was 1.1×10−5 cm-3s-1 during the time of the eclipse, which is an intermediate value between the diurnal and nocturnal conditions.
O sistema Terra-baixa ionosfera se comporta como um guia de onda para a propagação de ondas de rádio de frequências muito baixa (VLF). Se neste sistema a condutividade elétrica das fronteiras é perturbada, a propagação da onda é também perturbada. Existe uma variedade de fenômenos físicos transientes que alteram significativamente a condutividade elétrica da baixa ionosfera. Essas alterações são observadas como variações da fase e/ou amplitude com respeito ao nível quiescente. O presente trabalho tem como finalidade estudar a resposta da baixa ionosfera a fenômenos que produzidos na Terra, no sistema solar e até aqueles produzidos muito além do sistema solar. Com esse fim foram utilizados dados de VLF de fase e de amplitude fornecidos pela rede SAVNET (South America VLF NETwork) para o ciclo solar 24. Foi encontrado que a correção pelo fator de distância iluminada e o coeficiente de altura de referência permitem normalizar o efeito do distúrbio ionosférico a partir do sinal de VLF propagado em trajetos com direção de propagação norte-sul ou oeste-leste. O limiar de detecção das perturbações causadas pelo excesso na incidência dos raios-X é 1,8×10−9 Jm-2 para a ionosfera noturna e 2,6×10−7 Jm-2 para a ionosfera diurna. Perturbações ionosféricas observadas como alterações nos períodos do sinal de VLF, na faixa de infrassom, foram observadas entre 6 e 14 dias antes dos eventos sísmicos de magnitude 7 acontecidos no Haiti no ano 2010 e no Peru no ano 2011. Alterações nas periodicidades, da ordem de dezenas de minutos, foram observadas quando a sombra do eclipse solar total de 2010 se deslocava sobre a Terra. Devido ao eclipse, a altura de referência da ionosfera aumentou em ~3 km e a densidade eletrônica diminuiu em 60% com respeito do nível quiescente. Finalmente, foi encontrado que o coeficiente de recombinação efetiva, para o tempo do eclipse e para uma altura de 80 km, foi de 1,1×10−5 cm-3s-1, que é um valor intermediário entre as condições diurnas e noturnas.
wang, xiaoni. "A STUDY OF EQUATORIAL IONOPSHERIC VARIABILITY USING SIGNAL PROCESSING TECHNIQUES." Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2415.
Повний текст джерелаPh.D.
School of Electrical Engineering and Computer Science
Engineering and Computer Science
Electrical Engineering PhD
Qahwash, Murad M. "High frequency communication system modeling and performance enhancement, employing novel adaptive DSP techniques." Doctoral diss., University of Central Florida, 2002. http://digital.library.ucf.edu/cdm/ref/collection/RTD/id/1383.
Повний текст джерелаHigh Frequency (HF) communication has been shown to be a useful communication technique from the very beginning of World War I and it accelerated during World War 11. This is attributed to its simplicity, ability to provide near globe connectivity at low power without repeaters, moderate cost, and ease of proliferation [I]. In fact, the HF communication system utilizes the ionosphere [2][3][4] to refract the skywave signals to a distant receiver. This ionospheric channel has some disadvantages. First, it is a non-stationary channel as the HF frequency propagation is a function of the sun spot activities, solar winds, and diurnal variations of the ionization level [5]. Second, the channel produces distortion in both signal amplitude and phase. As the different ionospheric layers move up or down, independent Doppler shifts on each propagation mode are introduced. Multipath fading [6] caused by multiple refractions of the signal fiom the ionosphere with or without ground reflection causes performance degradation in the HF system. Some techniques have been developed to improve HF performance [I]. One example is Space-Diversity [7], which uses more than one antenna at distant spaces to combine the received signal. Angle-of-Arrival Diversity that takes advantage of the fact that different modes have different arrival angles at the receiver, and so, highly directional antenna for example, can be used to improve the system performance. Another method of improving HF performance is to use different frequencies to transmit and receive messages. This method is known as Frequency diversity. Using timediversity, one can add a degree of redundancy to the transmitted message through the use of different types of coding, interleaving, etc. In the military standard, MIL-STD- 1 88- 1 1 OA [8], a convolutional encoder [9][10] followed by interleaver [Ill-[14] was used to scramble and transmit the data in different bit rates. In the presence of multipath fading [ 1 51, a training sequence is transmitted in an interleaved fashion with the data symbols with a 50% duty cycle. This has the disadvantage of losing half the bandwidth. At present, the recent advances of the Digital Signal Processing (DSP) [16][17] make it possible to reduce the bit-error-rate BEY and increase the transmission bit rate [18] through the usage of adaptive equalization [ 191-[2 11 which will be the focus of this dissertation. Equalizers such as, Transversal Equalizer [ 1 61, Blind Equalizer [22], Training waveform Equalizer [23], and Minimum Mean Square Error (MMSE) [20] Adaptive Equalizer have been applied into various communication systems. This proposal work will be to initially apply some of the previous developed equalizer to the HF channel specifically. Thereafter, new adaptive channel equalization [24],[25] will be developed to compensate for transmission channel impairments due to bandwidth limitations, multipath propagation, and rayleigh fading [2 11 conditions in mobile environments. A new technique for frequency offset prediction has been developed and finally, a new approach for MIL-STD- 1 88- 1 1 0A high frequency single-tone modem employing orthogonal Walsh-PN codes has been implemented.
Ph.D.
Doctorate;
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering and Computer Science
198 p.
xviii, 198 leaves, bound : ill., (some col.) ; 28 cm.
Jain, Ankit. "Detection on HF radio transmitters using passive geolocation techniques." Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2019. http://www.theses.fr/2019IMTA0128/document.
Повний текст джерелаLong-range radio transmission in the HF band can cover large geographical areas using light and mobile equipment. It is therefore well suited for communications during military operations orfor the rapid deployment of an agile communication network during humanitarian operations. In this context, it is important to determine the geographic location of the transmitters by analyzing the electromagnetic communication signals. The aim of the thesis is to develop an alternative, complementary geolocation technique, entitled Time Difference of Arrival (TDoA) that has rarely been studied in the case of ionospheric propagation. As a first step, HF geolocation algorithm based on TDoA is setup and analyzed by parametric software simulations. Simulation results demonstrate that increasing the number of receivers leads to a significant improvement in the geolocation accuracy. In order to study the feasibility of a practical HF geolocation system based on TDoA, multiple remotely controllable HF receivers are designed using software defined radio (SDR) modules and a country wide operational receiver network is deployed in France. A concept of cross-channel sounding along with its mathematical description is proposed to evaluate the propagation duration differences between the signals captured by two distinct receivers. Preliminary experimental results show that it is possible to locate the HF transmitters under favorable conditions with a relative geolocation error ranging from about 0.1 to 10% of the actual ground distance. Data captured during the large scale measurement campaign are analyzed statistically to evaluate the performance of the geolocation algorithm and define parameters that could be considered in an operational approach
Silva, Adriano Magno Rodrigues da. "Estudo dos efeitos de explosões solares na região D ionosférica por meio de ondas em VLF." Universidade Estadual da Paraíba, 2017. http://tede.bc.uepb.edu.br/jspui/handle/tede/2875.
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The D Region is the lowest portion of Ionosphere and its formation depends on the solar radiation, mainly of Lyman-α. Because of this, the D Region only exists during the day. A solar flare releases X-Rays, which are able to penetrate into the D Region and increase the ionization level, consequently inducing its lowering. Once the D Region act as a boundary of Earth-Ionosphere Waveguide, any modification produces important variations both in Very Low Frequency (VLF) radio signals amplitude and in phase. For this research was used X- Rays flow measurements obtained from the Geostationary Operational Environmental Satellite and VLF data during the period of March (2011) and July (2012), obtained by South America VLF Network. These chosen VLF signal paths correspond to the NAA Transmitter Station in Cutler, USA, and from two Receptor Stations in South America: ATI Station in Atibaia, Brazil, and the PLO Station at Punta Lobos, Peru. The VLF data allows through alterations, both in signal amplitude and in phase, alongside with X-Rays flows data to identify Ionospheric events caused by solar flares. The results of this study indicate alterations occurred in analyzed signals; this happened because of the D Region lowering caused by ionization, which came from X-Rays released through Solar Flares. One of these analyzed events started at 6:08 p.m. UTC on March 8th, 2011, and peak X-Ray release at 6:28 p.m. UTC. The signal’s amplitude increments on the pre-event state was until 11.43% to the route: NAA–ATI, and until 12.13% to the route: NAA–PLO during the mentioned Solar Flare.
A Região D é a porção mais baixa da Ionosfera e a sua formação depende da Radiação Solar, principalmente a Lyman-α. Por esse motivo, tal região existe apenas durante o dia. Sabe-se que uma explosão solar emite raios X, os quais são capazes de penetrar até a Região D e aumentar o nível de ionização, provocando o seu rebaixamento. Uma vez que a Região D comporta-se como fronteira do Guia de Onda Terra-Ionosfera, qualquer modificação nela produz variações importantes, tanto na amplitude como na fase de sinais de rádio em Very Low Frequency (VLF). Nesta Pesquisa, foram utilizadas medições dos fluxos de raios X, obtidos por meio do Satélite Geostationary Operational Environmental Satellite e dados de VLF correspondentes ao período do mês de março de 2011 e Julho de 2012, obtidos da rede South America VLF Network. Os trajetos dos sinais de VLF escolhidos correspondem à Estação Transmissora NAA em Cutler, nos Estados Unidos da América e duas Estações Receptoras na América do Sul: Estação ATI em Atibaia no Brasil e a Estação PLO em Punta Lobos, no Peru. Os dados de VLF permitem, por meio das alterações, tanto na amplitude como na fase dos sinais, juntamente com os dados de fluxo de raios X, identificar eventos ionosféricos promovidos pelas explosões solares. Os resultados deste estudo indicam que as alterações ocorridas nos sinais analisados aconteceram devido a um rebaixamento da Região D, ocasionado pela ionização advinda da emissão de raios X das Explosões Solares. Um dos eventos analisados ocorreu a partir das 18h08min UT do dia 08/03/2011 e houve por volta das 18h28min UT, o momento de maior emissão de raios X. Os incrementos nas amplitudes dos sinais, relativamente ao estado de pré-evento, foram de até 11,43% para o trajeto entre NAA– ATI e de até 12,13% para o trajeto NAA–PLO durante a Explosão Solar descrita.
Wadley, T. L. "Heterodyne techniques in specialised radio instrumentation." Thesis, 2015. http://hdl.handle.net/10539/18064.
Повний текст джерелаYeh, Wen-Hao, and 葉文豪. "Retrieval and Simulation Techniques for FORMOSAT-3/COSMIC Radio Occultation Data and Applications on Analysis of Ionospheric Sporadic-E Layer." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/90599882281469108832.
Повний текст джерела國立中央大學
電機工程學系
101
Radio occultation (RO) technique, which has been used in planetary science, is a method to obtain the parameter profiles of the atmosphere. With the advent of Global Positioning System (GPS), to observe the global atmosphere and ionosphere of the Earth becomes possible by using low Earth orbit (LEO) satellites to receive the signal of GPS. In 2006, Taiwan launched six LEO satellites as a RO constellation mission, known as Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC, or F-3) and the data of F-3 is used in this thesis. The motivation of this thesis is bring up the methods to understand the influence of atmospheric anomaly, which occurs on the signal trajectory, on the observational and retrieval results in order to increase the retrieval accuracy in the future. In order to reach the motivation, three steps are contained in this thesis: (1) A retrieval algorithm is developed to understand the process of the RO data retrieval; (2) A ray tracing model for GPS signal is proposed to understand the signal propagating process in the atmosphere; (3) The ionospheric sporadic-E (Es) layer is used to be an example of atmospheric anomaly to simulate its influence on the amplitude profile by using ray tracing model and compare with the observational data. In order to know the influence of atmospheric anomaly on the observational and retrieval results, a retrieval algorithm should be developed first. A retrieval algorithm, NCURO (National Central University Radio Occultation), is developed in this thesis to obtain the information of atmospheric parameter profiles. The focus of the algorithm development is on the correction of the excess phase of the signal received with open loop (OL) technique, and the criteria for assessment of the data quality. When the OL is activated, the excess phase of the GPS signal is modulated with navigation messages of satellites. In our algorithms, two methods are incorporated to recover the excess phase. Moreover, as the altitude of the received signal decreases, the quality of the GPS signal generally deteriorates, and eventually the signal is too noisy to be processed. In order to assess the quality of the signal, instead of the signal-to-noise ratio (SNR), the degree of unclearness is defined and used in the algorithm. In this thesis, the algorithm including the phase correction methods and the criteria for the quality assessment will be described. The data retrieval using the algorithm will be compared with those obtained from CDAAC at UCAR and Pingtung radiosonde measurement. Some intermediate results of the NCURO algorithm will also be demonstrated. Except considering the atmospheric anomaly influenced on the observational and retrieval results, the influence of atmospheric anomaly on the signal propagation should be known. A three-dimensional ray tracing model for GPS signal is proposed to make simulation conform to the realistic RO signal propagation. In the model, two aiming algorithms are developed to ensure the initial and end points of the ray trajectory located in the prescribed region. In past studies, the ray tracing algorithms are often used to support the retrieval algorithms and assess the impact of data assimilation. The ray tracing techniques applied to the RO signal simulation usually assumed a spherically symmetric atmosphere for simplicity. Also, the exact locations of of GPS and LEO satellites are not considered in the simulation. These two assumptions make the simulation unrealistic for the GPS signal propagation in RO technique. In the proposed model, the shape of the Earth is assumed as an ellipse. The information from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis is used to setup the atmosphere in the simulation. Two aiming algorithms are developed to determine the initial propagating direction of GPS signal. The aiming algorithms will also make the simulated signal start from the prescribed GPS satellite position and end in the close vicinity of the LEO satellite position. The proposed model is examined and demonstrated in the designed simulation using three atmospheric structures: the ideal structure of spherical symmetry, the ECMWF analysis with the consideration of the Earth’s flattening, and the artificial perturbation added in ECMWF analysis which allows consideration of gravity waves and the tropopause. For the ideal atmospheric structure, the fractional difference between real and simulated refractivity results is less than 0.6%. For the ECMWF analysis and the consideration of the Earth’s flattening, all the simulated end points are located in the prescribed region. And for the artificial perturbation added in ECMWF, the simulated results show the corresponding characteristics of the artificial perturbation. The signal propagating through the ionospheric Es layer, which is an example of atmospheric anomaly, is simulated by using the ray tracing model. The relation between the amplitude of RO signals and the electron density profiles of the ionosphere is simulated and compare with the observational data. Furthermore, the RO data recorded in the time period from mid-2008 to mid-2011 are used for the analysis. Based on the simulation results, the multiple-layer-type (MLT) and the single-layer-type (SLT) Es layers which are defined by the shape of SNR, are used to analyze the global distribution of Es layer. The seasonal MLT Es layer is compared with the seasonal wind shear, which is obtained from the Horizontal Wind Model (HWM07). Furthermore, the seasonal MLT Es layer is compared with the SLT Es layer, and the global altitude distributions of MLT and SLT Es layers are similar while the magnitude distributions are different. Unlike the MLT Es layer, the global distribution of the SLT Es layer is similar to the distribution of E region peak electron density (NmE), which is related to the solar zenith angle. In this thesis, the ionospheric Es layer is an example to show the influence of atmospheric anomaly on RO data by using ray tracing model. And the influence of the atmospheric anomaly on retrieval results also can be anticipated by using the retrieval algorithm. With the information of the influence caused by atmospheric anomaly, the retrieval algorithm can be corrected and developed to retrieve atmospheric parameter profiles with more accuracy in the future.
Tsai, Hong Li, and 蔡宏利. "An Investigation of the Low Latitude Ionosphere Using the Tomographic Technique." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/13993941080271903829.
Повний текст джерелаHuang, Chi-Ruei, and 黃啟瑞. "Development abd Applications of Tomography technique to investigate the ionosphere in the Equatorial Aomaly Region." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/09802608293583889837.
Повний текст джерела國立中央大學
電機工程學系
85
Abstract The type of Computerized Ionospheric Tomography (CIT) studied in this thesis is suitable for investigating ionospheric structures of horizontal scales of several hundred kilometers or greater. One region where these large-scale ionospheric variations occur daily is the Equatorial Anomaly (EA) region. In this thesis this technique was used to study the ionospheric electrodynamics in the EA region. First, improvement for the differential Doppler measurement technique was implemented and the CIT technique was modified specially for the applications in the EA region. In addition, observational data deduced from "Low-latitude Ionospheric Tomography Network (LITN)" were used to investigate the day to day variations and the low latitude ionosphere. Finally, the response of the low latitude ionosphere during Solar Eclipse was studied using the modified CIT technique.A modified ionosonde-Doppler method was developed to deduce the initial Doppler phase. This technique combined ionosonde and Differential Doppler records to determine the "unknown constant." Currently, several CIT research groups combined Total Electron Content (TEC) data with differential Doppler phase records to develop the so called three dimensional (3D) CIT technique. We found that the TEC obtained from Global Positional Satellite (GPS) measurements were in general 2-3 times greater than the actual values between sunset and noontime of the next day. Consequently, it should be carefully checked when using TEC derived from GPS measurements. The geometry of CIT is a "limited angle tomography" problem. The best way to develop the CIT technique is to include "A priori information" in the image reconstruction procedure for compensating the "missing horizontal ray" problem in CIT. For this reason, the thesis proposed a combination method to make use the "a priori information" such as ionosonde records, ionosphere model, empirical F2 peak distribution and the vertical TEC derived from differential Doppler records. This method generated an image as the initial guess for iterative reconstruction algorithm. Model simulations and reconstructions for measured data proved that this method can be used for reconstructing the electron density distributions in the EA region. In addition, a method for verification of the reconstructed image with global ionosonde data was proposed and implemented in the thesis..Previous studies revealed that low-latitude ionosphere experiences day to day variations. Initial investigations utilizing multiple Differential Doppler records provided by the LITN facility revealed that the latitudinal distribution of vertical TEC depends on (1)the conversion height of ionosphere, (2)the location of receiver, (3)integration constant and (4)the number of receiver. In this thesis, the modified multi-station method and reconstruction algorithm were used to investigate the day to day variations of October, 1994 and October 1995. It revealed that the crest started to develop after sunrise and decay after the sunset during low solar activity epoch, but persisted late into the night during the solar maximum. It was characterized by a trough at the magnetic equator and one hump at about 10oN of magnetic equator around 14:00 Local Standard Time in this season. The advantages of Computerized Ionospheric Tomography technique were not only the capability to observe the large scale latitudinal TEC distributions but also the possibility to provide the electron density profiles for studying the ionospheric electrodynamics.The investigation during the Total solar eclipse of October 24, 1995 revealed that the low-latitude ionosphere was affected by the combination of electrodynamics and photochemical processes. Two-dimensional (2D) images of ionospheric electron density during the eclipse period were reconstructed. These images and the corresponding results from a nearby ionosonde were compared with those for a reference day. It was shown that during the eclipse day the ionosphere experienced several episodes of electron density enhancement and depression. However, due to large day to day variation, only two depressions were identified as caused by solar eclipse effects. (1) The largest electron density depression occurred roughly 2 hours after the maximum obscuration at approximately 12oN geomagnetic latitude and on both the bottom and topside ionosphere. (2) The second depression occurred about 4 hours after maximum obscuration at approximately 5.5oN and mainly on the topside ionosphere. The former might have been caused by complicated photochemical and ion transportation processes, and the latter could come from the transportation delay of ion from the conjugate point. These observations were interpreted within the framework of ionospheric dynamics in the equatorial anomaly region.(Keywords: Tomography, image reconstruction algorithm, Ionosphere, Equatorial Anomaly, Low-latitude Ionospheric Tomography Network, Differential Doppler, Total Electron Content, Solar Eclipse)