Filtros volterra adaptativos: estruturas interpoladas e modelos estocásticos

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2009.Este trabalho de pesquisa visa o estudo de filtros Volterra adaptativos objetivando desenvolver novas estruturas que apresentem um bom compromisso entre desempenho e complexidade computacional. Nesse contexto, abordagens interpoladas são consideradas em filtros Volterra adaptativos. Tais abordagens utilizam um filtro esparso (visando reduzir a complexidade) combinado com um interpolador para recriar os coeficientes zerados do filtro esparso. Dessa forma, diversas estruturas para a implementação eficiente de filtros Volterra adaptativos são obtidas. Algumas características importantes das estruturas interpoladas, como, por exemplo, a existência de um efeito de borda indesejável, são evidenciadas e estudas. Com vistas ao efeito de borda, um procedimento para a sua remoção é apresentado, melhorando consideravelmente o desempenho de filtros interpolados adaptativos tanto nos casos lineares quanto nos Volterra. Adicionalmente, são estudas estruturas interpoladas inteiramente adaptativas considerando filtros lineares como também filtros Volterra. Análises estatísticas de algumas estruturas Volterra adaptativas são também apresentadas com o objetivo de obter modelos estocásticos de primeira e segunda ordens para predizer o comportamento de tais estruturas. Exemplos de aplicações são considerados visando avaliar tanto os novos algoritmos desenvolvidos quanto seus modelos estatísticos

Anisotropic Diffusion Filter with Memory based on Speckle Statistics for Ultrasound Images

Ultrasound imaging exhibits considerable difficulties for medical visual inspection and for the development of automatic analysis methods due to speckle, which negatively affects the perception of tissue boundaries and the performance of automatic segmentation methods. With the aim of alleviating the effect of speckle, many filtering techniques are usually considered as a preprocessing step prior to automatic analysis methods or visual inspection. Most of the state-of-the-art filters try to reduce the speckle effect without considering its relevance for the characterization of tissue nature. However, the speckle phenomenon is the inherent response of echo signals in tissues and can provide important features for clinical purposes. This loss of information is even magnified due to the iterative process of some speckle filters, e.g., diffusion filters, which tend to produce over-filtering because of the progressive loss of relevant information for diagnostic purposes during the diffusion process. In this work, we propose an anisotropic diffusion filter with a probabilistic-driven memory mechanism to overcome the over-filtering problem by following a tissue selective philosophy. Specifically, we formulate the memory mechanism as a delay differential equation for the diffusion tensor whose behavior depends on the statistics of the tissues, by accelerating the diffusion process in meaningless regions and including the memory effect in regions where relevant details should be preserved. Results both in synthetic and real US images support the inclusion of the probabilistic memory mechanism for maintaining clinical relevant structures, which are removed by the state-of-the-art filters

Impact of Analog and Digital Pre-emphasis on the Signal-to-Noise Ratio of Bandwidth-limited Optical Transceivers

The ever-growing machine-to-machine traffic in data centers has stimulated the increase of transceiver data rate from 25Gb/s/λ to 100Gb/s/λ and beyond. It is believed that advanced modulation formats and digital-to-analog converters (DACs) will be employed in next generation short-reach transceivers. Digital pre-emphasis techniques are widely employed in DAC-based transceivers to compensate for the high frequency roll-off due to the RF and optoelectronics components in optical transceivers. However, digital pre-emphasis essentially reduces the magnitude of the signal low frequency components for a flat frequency response, which unavoidably increases quantization error, reducing the overall signal-to-noise ratio. This trade-off between SNR and bandwidth conflicts with the high SNR requirement of advanced modulation formats such as the Nyquist-shaped pulse amplitude modulation (PAM). To mitigate the quantization error induced SNR degradation, we show that analog pre-emphasis filters can be used in conjunction with digital pre-emphasis for improved system performance. To understand the impact of the analog pre-emphasis filter on system performance, we analyze the relationship between the flatness of the system frequency response and the SNR degradation due to digital pre-emphasis, and demonstrate 1.1-dB increase of receiver sensitivities, for both 64-Gb/s and 128-Gb/s intensity-modulation direct detection (IM-DD) 20 PAM4 signals, respectively employing a directly modulated laser (DML) and an electroabsorption modulator (EAM)

Post Conversion Correction of Non-Linear Mismatches for Time Interleaved Analog-to-Digital Converters

Time Interleaved Analog-to-Digital Converters (TI-ADCs) utilize an architecture which enables conversion rates well beyond the capabilities of a single converter while preserving most or all of the other performance characteristics of the converters on which said architecture is based. Most of the approaches discussed here are independent of architecture; some solutions take advantage of specific architectures. Chapter 1 provides the problem formulation and reviews the errors found in ADCs as well as a brief literature review of available TI-ADC error correction solutions. Chapter 2 presents the methods and materials used in implementation as well as extend the state of the art for post conversion correction. Chapter 3 presents the simulation results of this work and Chapter 4 concludes the work. The contribution of this research is three fold: A new behavioral model was developed in SimulinkTM and MATLABTM to model and test linear and nonlinear mismatch errors emulating the performance data of actual converters. The details of this model are presented as well as the results of cumulant statistical calculations of the mismatch errors which is followed by the detailed explanation and performance evaluation of the extension developed in this research effort. Leading post conversion correction methods are presented and an extension with derivations is presented. It is shown that the data converter subsystem architecture developed is capable of realizing better performance of those currently reported in the literature while having a more efficient implementation

Epälineaarinen vääristymä laajakaistaisissa analogia-digitaalimuuntimissa

This thesis discusses nonlinearities of analog-to-digital converters (ADCs) and their mitigation using digital signal processing (DSP). Particularly wideband radio receivers are considered here including, e.g., the emerging cognitive radio applications. In this kind of receivers, a single ADC converts a mixture of signals at different frequency bands to digital domain simultaneously. Different signals may have considerably different power levels and hence the overall dynamic range can be very large (even 50–60 dB). Therefore, even the smallest ADC nonlinearities can produce considerable amount of nonlinear distortion, which may cause a strong signal to block significantly weaker signal bands. One concrete source of nonlinear distortion is waveform clipping due to improper signal conditioning in the input of an ADC. In the thesis, a mathematical model for this phenomenon is derived through Fourier analysis and is then used as a basis for an adaptive interference cancellation (AIC) method. This is a general method for reducing nonlinear distortion and besides clipping it can be used, e.g., to compensate integral nonlinearity (INL) originating from unintentional deviations of the quantization levels. Additionally, an interpolation method is proposed in this thesis to restore clipped waveforms and hence reduce nonlinear distortion. Through several computer simulations and corresponding laboratory radio signal measurements, the performance of the proposed post-processing methods is illustrated. It can be seen from the results that the methods are able to reduce nonlinear distortion from a weak signal band in a considerable manner when there are strong blocking signals in the neighboring channels. According to the results, the AIC method would be a highly recommendable post-processing technique for modern radio receivers due to its general ability to reduce nonlinear distortion regardless of its source. /Kir10Tässä työssä käsitellään analogia-digitaalimuuntimien (AD-muuntimien) epälineaarisuuksia ja niiden lieventämistä digitaalisen signaalinkäsittelyn (DSP) avulla. Tätä on tarkasteltu erityisesti laajakaistaisten radiovastaanottimien näkökulmasta, joka käsittää mm. tulevat kognitiiviseen radioon liittyvät sovellukset. Tällaisissa vastaanottimissa yksittäinen AD-muunnin muuntaa samanaikaisesti useita eri taajuuskaistoilla olevia signaaleita digitaaliseen muotoon, jolloin yhteenlaskettu dynaaminen alue voi olla hyvin suuri (jopa 50–60 dB). Tämän takia AD-muuntimen pienimmätkin epälineaarisuudet voivat aiheuttaa huomattavasti epälineaarista vääristymää, minkä vuoksi voimakas signaali saattaa häiriöllään peittää muilla taajuuskaistoilla olevia selkeästi heikompia signaaleja. Eräs konkreettinen epälineaarisen vääristymän aiheuttaja on aaltomuodon leikkaantuminen AD-muuntimen sisäänmenossa jännitealueen ylittymisen vuoksi. Tässä työssä johdetaan matemaattinen malli kyseiselle ilmiölle Fourier-analyysin avulla ja käytetään sitä lähtökohtana adaptiiviselle häiriönpoistomenetelmälle (AIC-menetelmä). Se on yleisluonteinen menetelmä epälineaarisen vääristymän vähentämiseksi, ja leikkaantumisen lisäksi sitä voidaan käyttää esimerkiksi kompensoimaan integraalista epälineaarisuutta (INL), joka on peräisin kvantisointitasojen tahattomista poikkeamista. Lisäksi tässä työssä esitellään interpolointimenetelmä leikkaantuneen aaltomuodon ehostamiseen siten, että epälineaarinen häiriö vähenee. Esiteltyjen jälkikäsittelymenetelmien suorituskykyä analysoidaan ja havainnollistetaan useilla tietokonesimulaatiolla sekä niitä vastaavilla radiosignaalien laboratoriomittauksilla. Tuloksista voidaan nähdä, että nämä menetelmät kykenevät poistamaan huomattavasti epälineaarista vääristymää heikolta signaalikaistalta silloin, kun naapurikaistoilla on voimakkaita häiriösignaaleja. Tulosten perusteella AIC-menetelmä olisi erittäin suositeltava jälkikäsittelytekniikka moderneihin radiovastaanottimiin, koska se pystyy yleisesti vähentämään epälineaarista vääristymää riippumatta häiriön alkuperästä

Metodologia Per la Caratterizzazione di amplificatori a basso rumore per UMTS

In questo lavoro si presenta una metodologia di progettazione elettronica a livello di sistema, affrontando il problema della caratterizzazione dello spazio di progetto dell' amplificatore a basso rumore costituente il primo stadio di un front end a conversione diretta per UMTS realizzato in tecnologia CMOS con lunghezza di canale .18u. La metodologia è sviluppata al fine di valutare in modo quantititativo le specifiche ottime di sistema per il front-end stesso e si basa sul concetto di Piattaforma Analogica, che prevede la costruzione di un modello di prestazioni per il blocco analogico basato su campionamento statistico di indici di prestazioni del blocco stesso, misurati tramite simulazione di dimensionamenti dei componenti attivi e passivi soddisfacenti un set di equazioni specifico della topologia circuitale. Gli indici di prestazioni vengono successivamente ulizzati per parametrizzare modelli comportamentali utilizzati nelle fasi di ottimizzazione a livello di sistema. Modelli comportamentali atti a rappresentare i sistemi RF sono stati pertanto studiati per ottimizzare la scelta delle metriche di prestazioni. L'ottimizzazione dei set di equazioni atti a selezionare le configurazione di interesse per il campionamento ha al tempo stesso richiesto l'approfondimento dei modelli di dispositivi attivi validi in tutte le regioni di funzionamento, e lo studio dettagliato della progettazione degli amplificatori a basso rumore basati su degenerazione induttiva. Inoltre, il problema della modellizzazione a livello di sistema degli effetti della comunicazione tra LNA e Mixer è stato affrontato proponendo e analizzando diverse soluzioni. Il lavoro ha permesso di condurre un'ottimizzazione del front-end UMTS, giungendo a specifiche ottime a livello di sistema per l'amplificatore stesso

Advanced Geoscience Remote Sensing

Nowadays, advanced remote sensing technology plays tremendous roles to build a quantitative and comprehensive understanding of how the Earth system operates. The advanced remote sensing technology is also used widely to monitor and survey the natural disasters and man-made pollution. Besides, telecommunication is considered as precise advanced remote sensing technology tool. Indeed precise usages of remote sensing and telecommunication without a comprehensive understanding of mathematics and physics. This book has three parts (i) microwave remote sensing applications, (ii) nuclear, geophysics and telecommunication; and (iii) environment remote sensing investigations

Higher order sinusoidal input describing functions : extending linear techniques towards non-linear systems analysis

In modern positioning systems, accuracy and speed requirements have increased significantly. These accuracies can only be realized if account is given to nonlinear system behavior in both the mechanical and the control design. This requires additional tools for frequency based identification of nonlinear system behavior since existing tools either are either too limited to successfully describe nonlinear behavior or the results are very difficult to interpret and as such do not relate to the background of the intended user. In this thesis an alternative concept for frequency based nonlinear system analysis is presented, the required measurement techniques are described and some application examples are shown. The method is applicable for the class of causal, stable, time-invariant non-linear systems which have a harmonic response to a sinusoidal excitation. This new concept is the generalization of the Sinusoidal Input Describing Function to Higher Order Sinusoidal Input Describing Functions (HOSIDF) as it yields the magnitude and phase relations between the individual higher harmonics in the response signal and the sinusoidal excitation signal, both as function of magnitude and frequency of the excitation signal. An essential element in the HOSIDF theory is the concept of the Virtual Harmonics Expander (VHE). This nonlinear function describes the transformation of a single sinusoid into an infinite amount of harmonics, each with equal amplitude as the input signal and with a phase equal to the phase of the input signal times the harmonic number. Nonlinear systems belonging to the class can be modeled as a parallel connection of an (infinite) amount of HOSIDF describing quasi-linear subsystems in series with the VHE. Two measurement methods for nonparametric identification of HOSIDF are presented. The Fast Fourier Transform based method on fast fourier transforms shows ideal characteristics due to its perfect selectivity. The IQ (In phase-Quadrature phase) demodulation method has limited performance due to non perfect selectivity. The bias in the HOSIDF estimates caused by harmonic components in the input signal is analyzed and a compensation algorithm is presented to reduce this bias. Accept- ing harmonic distortion in the excitation signal allows the application of non-constant amplitude-time profiles for testing. It is demonstrated that a ramped amplitude-time signal reduces the required settling time of the digital filters used in the IQ methode. The capabilities of the HOSIDF technique are demonstrated in a real measurement in which the stick to gross sliding transition of a mechanical system with dry friction is captured as function of frequency. The odd HOSIDF clearly reveal this transition which is not possible with the Frequency Response Function technique. From the HOSIDF the pre-sliding displacement and the friction-induced stiffness are determined and the friction force which must be present in the stick-phase is calculated. Validation with force measurements shows excellent agreement. Special attention is paid to the determination of the HOSIDF of a nonlinear plant operating in feedback. In a controlled systemthe harmonics generated by the non-linear system will be fed back to the input, changing the sinusoidal excitation into an harmonic excitation. Two different solutions are presented to deal with this problem. The first method applies a numerical compensatie techniques to compensate the bias caused by the harmonic components in the excitation signal. The secondmethod uses amodified repetitive control scheme to suppress the harmonic components in the excitation signal. The effectiveness of both methods is tested in simulation experiments of a mass operating in feedback subjected to Coulomb friction, Stribeck-effect and hysteresis in the pre-sliding regime. The friction forces are modeled with the modified Leuven friction model. The results are compared with the HOSIDF measured under open loop condition and both methods yield correct results. It is shown that by rearranging the repetitive control loop, the output signal of a class of stable, time-invariant nonlinear systems becomes sinusoidal as response to an harmonic excitation. For this class of signals Higher Order Sinusoidal Output Describing Functions (HOSODF) can be defined as the dual of the HOSIDF. The HOSODF describe magnitude and phase relations between the individual higher harmonics in the input signal and the sinusoidal output signal, both as function of magnitude and frequency of the output signal. The required dual of the Virtual Harmonics Expander is defined as the Virtual Harmonics Compressor. This nonlinear function describes the transformation of an infinite amount of harmonics into a single sinusoid. Finally, an application example shows the extreme sensitivity of the HOSIDF technique for changes in friction characteristics, indicating interesting opportunities for application in the field of machine condition monitoring. De eisen die gesteld worden aan de snelheid en positioneringsnauwkeurigheid van moderne positioneringssystemen zijn significant toegenomen. Deze nauwkeurigheden kunnen alleen maar gerealiseerd worden als met niet-lineair systeemgedrag rekening wordt gehouden in zowel het mechanische als het regeltechnische ontwerp. In tegenstelling tot de tijddomein gebaseerde systeemidentificatie is de moderne regeltechniek op frequentiedomein technieken gebaseerd. Maar de transformatie van niet-lineaire tijddomeinmodellen naar het frequentiedomein is nietmogelijkmet alleen lineaire technieken. Dit vereist extra gereedschappen ten behoeve van de frequentiedomein gebaseerde identificatie van niet-linear systeemgedrag omdat de bestaande gereedschappen ofwel te beperkt zijn om met succes niet-linear gedrag te beschrijven ofwel resultaten leveren in een formaat dat moeilijk te interpreteren is en niet aansluit bij de achtergrond van de gebruiker. In dit proefschrift wordt een alternatief concept gepresenteerd voor een op frequentiedomeintechnieken gebaseerde niet-lineaire systeemanalyse. Eveneens worden de vereiste meetmethodes beschreven en enkele toepassingsvoorbeelden getoond. De methode is van toepassing op de klasse I gedefinieerd als de klasse van causale, stabiele, tijdsinvariante, niet-lineaire systemen welke een harmonische responsie hebben ten gevolge van een sinusvormige excitatie. Dit nieuwe concept is de generalisatie van de Sinusoidal Input Describing Function tot de Higher Order Sinusoidal Input Describing Functions (HOSIDF). De HOSIDF beschrijven de magnitude- en faserelaties die bestaan tussen de afzonderlijke hogere harmonische componenten in het responsiesignaal en de sinusvormige excitatie, allen als functie van amplitude en frequentie van dat excitatiesignaal. In de HOSIDF theorie wordt een essentiële plaats ingenomen door het begrip Virtual Harmonics Expander (VHE). Deze niet-lineaire functie beschrijft de transformatie van een zuiver sinusvormig signaal in een oneindige reeks harmonischen, elk met identieke amplitude gelijk aan de amplitude van het ingangssignaal en een fase gelijk aan de fase van het ingangssignaal maal het rangnummer van de harmonische component. Systemen die behoren tot de klasse I kunnen gemodelleerd worden als een parallel schakeling van een (oneindig) aantal HOSIDF in serie met de VHE. Twee meetmethodes voor de niet-parametrische identificatie van HOSIDF worden gepresenteerd. De op Fast Fourie

Real-time Digital Simulation of Guitar Amplifiers as Audio Effects

Práce se zabývá číslicovou simulací kytarových zesilovačů, jakož to nelineárních analogových hudebních efektů, v reálném čase. Hlavním cílem práce je návrh algoritmů, které by umožnily simulaci složitých systémů v reálném čase. Tyto algoritmy jsou prevážně založeny na automatizované DK-metodě a aproximaci nelineárních funkcí. Kvalita navržených algoritmů je stanovana pomocí poslechových testů.The work deals with the real-time digital simulation of guitar amplifiers considered as nonlinear analog audio effects. The main aim is to design algorithms which are able to simulate complex systems in real-time. These algorithms are mainly based on the automated DK-method and the approximation of nonlinear functions. Quality of the designed algorithms is evaluated using listening tests.