450 research outputs found

    Adaptive Interference Mitigation in GPS Receivers

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    Satellite navigation systems (GNSS) are among the most complex radio-navigation systems, providing positioning, navigation, and timing (PNT) information. A growing number of public sector and commercial applications rely on the GNSS PNT service to support business growth, technical development, and the day-to-day operation of technology and socioeconomic systems. As GNSS signals have inherent limitations, they are highly vulnerable to intentional and unintentional interference. GNSS signals have spectral power densities far below ambient thermal noise. Consequently, GNSS receivers must meet high standards of reliability and integrity to be used within a broad spectrum of applications. GNSS receivers must employ effective interference mitigation techniques to ensure robust, accurate, and reliable PNT service. This research aims to evaluate the effectiveness of the Adaptive Notch Filter (ANF), a precorrelation mitigation technique that can be used to excise Continuous Wave Interference (CWI), hop-frequency and chirp-type interferences from GPS L1 signals. To mitigate unwanted interference, state-of-the-art ANFs typically adjust a single parameter, the notch centre frequency, and zeros are constrained extremely close to unity. Because of this, the notch centre frequency converges slowly to the target frequency. During this slow converge period, interference leaks into the acquisition block, thus sabotaging the operation of the acquisition block. Furthermore, if the CWI continuously hops within the GPS L1 in-band region, the subsequent interference frequency is locked onto after a delay, which means constant interference occurs in the receiver throughout the delay period. This research contributes to the field of interference mitigation at GNSS's receiver end using adaptive signal processing, predominately for GPS. This research can be divided into three stages. I first designed, modelled and developed a Simulink-based GPS L1 signal simulator, providing a homogenous test signal for existing and proposed interference mitigation algorithms. Simulink-based GPS L1 signal simulator provided great flexibility to change various parameters to generate GPS L1 signal under different conditions, e.g. Doppler Shift, code phase delay and amount of propagation degradation. Furthermore, I modelled three acquisition schemes for GPS signals and tested GPS L1 signals acquisition via coherent and non-coherent integration methods. As a next step, I modelled different types of interference signals precisely and implemented and evaluated existing adaptive notch filters in MATLAB in terms of Carrier to Noise Density (\u1d436/\u1d4410), Signal to Noise Ratio (SNR), Peak Degradation Metric, and Mean Square Error (MSE) at the output of the acquisition module in order to create benchmarks. Finally, I designed, developed and implemented a novel algorithm that simultaneously adapts both coefficients in lattice-based ANF. Mathematically, I derived the full-gradient term for the notch's bandwidth parameter adaptation and developed a framework for simultaneously adapting both coefficients of a lattice-based adaptive notch filter. I evaluated the performance of existing and proposed interference mitigation techniques under different types of interference signals. Moreover, I critically analysed different internal signals within the ANF structure in order to develop a new threshold parameter that resets the notch bandwidth at the start of each subsequent interference frequency. As a result, I further reduce the complexity of the structural implementation of lattice-based ANF, allowing for efficient hardware realisation and lower computational costs. It is concluded from extensive simulation results that the proposed fully adaptive lattice-based provides better interference mitigation performance and superior convergence properties to target frequency compared to traditional ANF algorithms. It is demonstrated that by employing the proposed algorithm, a receiver is able to operate with a higher dynamic range of JNR than is possible with existing methods. This research also presents the design and MATLAB implementation of a parameterisable Complex Adaptive Notch Filer (CANF). Present analysis on higher order CANF for detecting and mitigating various types of interference for complex baseband GPS L1 signals. In the end, further research was conducted to suppress interference in the GPS L1 signal by exploiting autocorrelation properties and discarding some portion of the main lobe of the GPS L1 signal. It is shown that by removing 30% spectrum of the main lobe, either from left, right, or centre, the GPS L1 signal is still acquirable

    Frequency domain FIR and IIR adaptive filters

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    A discussion of the LMS adaptive filter relating to its convergence characteristics and the problems associated with disparate eigenvalues is presented. This is used to introduce the concept of proportional convergence. An approach is used to analyze the convergence characteristics of block frequency-domain adaptive filters. This leads to a development showing how the frequency-domain FIR adaptive filter is easily modified to provide proportional convergence. These ideas are extended to a block frequency-domain IIR adaptive filter and the idea of proportional convergence is applied. Experimental results illustrating proportional convergence in both FIR and IIR frequency-domain block adaptive filters is presented

    Theory, design and application of gradient adaptive lattice filters

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    SIGLELD:D48933/84 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

    Split algorithms for LMS adaptive systems.

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    by Ho King Choi.Thesis (Ph.D.)--Chinese University of Hong Kong, 1991.Includes bibliographical references.Chapter 1. --- Introduction --- p.1Chapter 1.1 --- Adaptive Filter and Adaptive System --- p.1Chapter 1.2 --- Applications of Adaptive Filter --- p.4Chapter 1.2.1 --- System Identification --- p.4Chapter 1.2.2 --- Noise Cancellation --- p.6Chapter 1.2.3 --- Echo Cancellation --- p.8Chapter 1.2.4 --- Speech Processing --- p.10Chapter 1.3 --- Chapter Summary --- p.14References --- p.15Chapter 2. --- Adaptive Filter Structures and Algorithms --- p.17Chapter 2.1 --- Filter Structures for Adaptive Filtering --- p.17Chapter 2.2 --- Adaptation Algorithms --- p.22Chapter 2.2.1 --- The LMS Adaptation Algorithm --- p.24Chapter 2.2.1.1 --- Convergence Analysis --- p.28Chapter 2.2.1.2 --- Steady State Performance --- p.33Chapter 2.2.2 --- The RLS Adaptation Algorithm --- p.35Chapter 2.3 --- Chapter Summary --- p.39References --- p.41Chapter 3. --- Parallel Split Adaptive System --- p.45Chapter 3.1 --- Parallel Form Adaptive Filter --- p.45Chapter 3.2 --- Joint Process Estimation with a Split-Path Adaptive Filter --- p.49Chapter 3.2.1 --- The New Adaptive System Identification Configuration --- p.53Chapter 3.2.2 --- Analysis of the Split-Path System Modeling Structure --- p.57Chapter 3.2.3 --- Comparison with the Non-Split Configuration --- p.63Chapter 3.2.4 --- Some Notes on Even Filter Order Case --- p.67Chapter 3.2.5 --- Simulation Results --- p.70Chapter 3.3 --- Autoregressive Modeling with a Split-Path Adaptive Filter --- p.75Chapter 3.3.1 --- The Split-Path Adaptive Filter for AR Modeling --- p.79Chapter 3.3.2 --- Analysis of the Split-Path AR Modeling Structure --- p.84Chapter 3.3.3 --- Comparison with Traditional AR Modeling System --- p.89Chapter 3.3.4 --- Selection of Step Sizes --- p.90Chapter 3.3.5 --- Some Notes on Odd Filter Order Case --- p.94Chapter 3.3.6 --- Simulation Results --- p.94Chapter 3.3.7 --- Application to Noise Cancellation --- p.99Chapter 3.4 --- Chapter Summary --- p.107References --- p.109Chapter 4. --- Serial Split Adaptive System --- p.112Chapter 4.1 --- Serial Form Adaptive Filter --- p.112Chapter 4.2 --- Time Delay Estimation with a Serial Split Adaptive Filter --- p.125Chapter 4.2.1 --- Adaptive TDE --- p.125Chapter 4.2.2 --- Split Filter Approach to Adaptive TDE --- p.132Chapter 4.2.3 --- Analysis of the New TDE System --- p.136Chapter 4.2.3.1 --- Least-mean-square Solution --- p.138Chapter 4.2.3.2 --- Adaptation Algorithm and Performance Evaluation --- p.142Chapter 4.2.4 --- Comparison with Traditional Adaptive TDE Method --- p.147Chapter 4.2.5 --- System Implementation --- p.148Chapter 4.2.6 --- Simulation Results --- p.148Chapter 4.2.7 --- Constrained Adaptation for the New TDE System --- p.156Chapter 4.3 --- Chapter Summary --- p.163References --- p.165Chapter 5. --- Extension of the Split Adaptive Systems --- p.167Chapter 5.1 --- The Generalized Parallel Split System --- p.167Chapter 5.2 --- The Generalized Serial Split System --- p.170Chapter 5.3 --- Comparison between the Parallel and the Serial Split Adaptive System --- p.172Chapter 5.4 --- Integration of the Two Forms of Split Predictors --- p.177Chapter 5.5 --- Application of the Integrated Split Model to Speech Encoding --- p.179Chapter 5.6 --- Chapter Summary --- p.188References --- p.139Chapter 6. --- Conclusions --- p.191References --- p.19

    Dirty RF Signal Processing for Mitigation of Receiver Front-end Non-linearity

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    ï»żModerne drahtlose Kommunikationssysteme stellen hohe und teilweise gegensĂ€tzliche Anforderungen an die Hardware der Funkmodule, wie z.B. niedriger Energieverbrauch, große Bandbreite und hohe LinearitĂ€t. Die GewĂ€hrleistung einer ausreichenden LinearitĂ€t ist, neben anderen analogen Parametern, eine Herausforderung im praktischen Design der Funkmodule. Der Fokus der Dissertation liegt auf breitbandigen HF-Frontends fĂŒr Software-konfigurierbare Funkmodule, die seit einigen Jahren kommerziell verfĂŒgbar sind. Die praktischen Herausforderungen und Grenzen solcher flexiblen Funkmodule offenbaren sich vor allem im realen Experiment. Eines der Hauptprobleme ist die Sicherstellung einer ausreichenden analogen Performanz ĂŒber einen weiten Frequenzbereich. Aus einer Vielzahl an analogen Störeffekten behandelt die Arbeit die Analyse und Minderung von NichtlinearitĂ€ten in EmpfĂ€ngern mit direkt-umsetzender Architektur. Im Vordergrund stehen dabei Signalverarbeitungsstrategien zur Minderung nichtlinear verursachter Interferenz - ein Algorithmus, der besser unter "Dirty RF"-Techniken bekannt ist. Ein digitales Verfahren nach der VorwĂ€rtskopplung wird durch intensive Simulationen, Messungen und Implementierung in realer Hardware verifiziert. Um die LĂŒcken zwischen Theorie und praktischer Anwendbarkeit zu schließen und das Verfahren in reale Funkmodule zu integrieren, werden verschiedene Untersuchungen durchgefĂŒhrt. Hierzu wird ein erweitertes Verhaltensmodell entwickelt, das die Struktur direkt-umsetzender EmpfĂ€nger am besten nachbildet und damit alle Verzerrungen im HF- und Basisband erfasst. DarĂŒber hinaus wird die LeistungsfĂ€higkeit des Algorithmus unter realen Funkkanal-Bedingungen untersucht. ZusĂ€tzlich folgt die Vorstellung einer ressourceneffizienten Echtzeit-Implementierung des Verfahrens auf einem FPGA. Abschließend diskutiert die Arbeit verschiedene Anwendungsfelder, darunter spektrales Sensing, robuster GSM-Empfang und GSM-basiertes Passivradar. Es wird gezeigt, dass nichtlineare Verzerrungen erfolgreich in der digitalen DomĂ€ne gemindert werden können, wodurch die Bitfehlerrate gestörter modulierter Signale sinkt und der Anteil nichtlinear verursachter Interferenz minimiert wird. Schließlich kann durch das Verfahren die effektive LinearitĂ€t des HF-Frontends stark erhöht werden. Damit wird der zuverlĂ€ssige Betrieb eines einfachen Funkmoduls unter dem Einfluss der EmpfĂ€ngernichtlinearitĂ€t möglich. Aufgrund des flexiblen Designs ist der Algorithmus fĂŒr breitbandige EmpfĂ€nger universal einsetzbar und ist nicht auf Software-konfigurierbare Funkmodule beschrĂ€nkt.Today's wireless communication systems place high requirements on the radio's hardware that are largely mutually exclusive, such as low power consumption, wide bandwidth, and high linearity. Achieving a sufficient linearity, among other analogue characteristics, is a challenging issue in practical transceiver design. The focus of this thesis is on wideband receiver RF front-ends for software defined radio technology, which became commercially available in the recent years. Practical challenges and limitations are being revealed in real-world experiments with these radios. One of the main problems is to ensure a sufficient RF performance of the front-end over a wide bandwidth. The thesis covers the analysis and mitigation of receiver non-linearity of typical direct-conversion receiver architectures, among other RF impairments. The main focus is on DSP-based algorithms for mitigating non-linearly induced interference, an approach also known as "Dirty RF" signal processing techniques. The conceived digital feedforward mitigation algorithm is verified through extensive simulations, RF measurements, and implementation in real hardware. Various studies are carried out that bridge the gap between theory and practical applicability of this approach, especially with the aim of integrating that technique into real devices. To this end, an advanced baseband behavioural model is developed that matches to direct-conversion receiver architectures as close as possible, and thus considers all generated distortions at RF and baseband. In addition, the algorithm's performance is verified under challenging fading conditions. Moreover, the thesis presents a resource-efficient real-time implementation of the proposed solution on an FPGA. Finally, different use cases are covered in the thesis that includes spectrum monitoring or sensing, GSM downlink reception, and GSM-based passive radar. It is shown that non-linear distortions can be successfully mitigated at system level in the digital domain, thereby decreasing the bit error rate of distorted modulated signals and reducing the amount of non-linearly induced interference. Finally, the effective linearity of the front-end is increased substantially. Thus, the proper operation of a low-cost radio under presence of receiver non-linearity is possible. Due to the flexible design, the algorithm is generally applicable for wideband receivers and is not restricted to software defined radios

    Signal Processing and Restoration

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    Towards the Development of a Wearable Tremor Suppression Glove

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    Patients diagnosed with Parkinson’s disease (PD) often associate with tremor. Among other symptoms of PD, tremor is the most aggressive symptom and it is difficult to control with traditional treatments. This thesis presents the assessment of Parkinsonian hand tremor in both the time domain and the frequency domain, the performance of a tremor estimator using different tremor models, and the development of a novel mechatronic transmission system for a wearable tremor suppression device. This transmission system functions as a mechatronic splitter that allows a single power source to support multiple independent applications. Unique features of this transmission system include low power consumption and adjustability in size and weight. Tremor assessment results showed that the hand tremor signal often presents a multi-harmonics pattern. The use of a multi-harmonics tremor model produced a better estimation result than using a monoharmonic tremor model

    Adaptive filtering algorithms for quaternion-valued signals

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    Advances in sensor technology have made possible the recoding of three and four-dimensional signals which afford a better representation of our actual three-dimensional world than the ``flat view'' one and two-dimensional approaches. Although it is straightforward to model such signals as real-valued vectors, many applications require unambiguous modeling of orientation and rotation, where the division algebra of quaternions provides crucial advantages over real-valued vector approaches. The focus of this thesis is on the use of recent advances in quaternion-valued signal processing, such as the quaternion augmented statistics, widely-linear modeling, and the HR-calculus, in order to develop practical adaptive signal processing algorithms in the quaternion domain which deal with the notion of phase and frequency in a compact and physically meaningful way. To this end, first a real-time tracker of quaternion impropriety is developed, which allows for choosing between strictly linear and widely-linear quaternion-valued signal processing algorithms in real-time, in order to reduce computational complexity where appropriate. This is followed by the strictly linear and widely-linear quaternion least mean phase algorithms that are developed for phase-only estimation in the quaternion domain, which is accompanied by both quantitative performance assessment and physical interpretation of operations. Next, the practical application of state space modeling of three-phase power signals in smart grid management and control systems is considered, and a robust complex-valued state space model for frequency estimation in three-phase systems is presented. Its advantages over other available estimators are demonstrated both in an analytical sense and through simulations. The concept is then expanded to the quaternion setting in order to make possible the simultaneous estimation of the system frequency and its voltage phasors. Furthermore, a distributed quaternion Kalman filtering algorithm is developed for frequency estimation over power distribution networks and collaborative target tracking. Finally, statistics of stable quaternion-valued random variables, that include quaternion-valued Gaussian random variables as a special case, is investigated in order to develop a framework for the modeling and processing of heavy-tailed quaternion-valued signals.Open Acces

    Hybrid DDS-PLL based reconfigurable oscillators with high spectral purity for cognitive radio

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    Analytical, design and simulation studies on the performance optimization of reconfigurable architecture of a Hybrid DDS – PLL are presented in this thesis. The original contributions of this thesis are aimed towards the DDS, the dithering (spur suppression) scheme and the PLL. A new design of Taylor series-based DDS that reduces the dynamic power and number of multipliers is a significant contribution of this thesis. This thesis compares dynamic power and SFDR achieved in the design of varieties of DDS such as Quartic, Cubic, Linear and LHSC. This thesis proposes two novel schemes namely “Hartley Image Suppression” and “Adaptive Sinusoidal Interference Cancellation” overcoming the low noise floor of traditional dithering schemes. The simulation studies on a Taylor series-based DDS reveal an improvement in SFDR from 74 dB to 114 dB by using Least Mean Squares -Sinusoidal Interference Canceller (LM-SIC) with the noise floor maintained at -200 dB. Analytical formulations have been developed for a second order PLL to relate the phase noise to settling time and Phase Margin (PM) as well as to relate jitter variance and PM. New expressions relating phase noise to PM and lock time to PM are derived. This thesis derives the analytical relationship between the roots of the characteristic equation of a third order PLL and its performance metrics like PM, Gardner’s stability factor, jitter variance, spur gain and ratio of noise power to carrier power. This thesis presents an analysis to relate spur gain and capacitance ratio of a third order PLL. This thesis presents an analytical relationship between the lock time and the roots of its characteristic equation of a third order PLL. Through Vieta’s circle and Vieta’s angle, the performance metrics of a third order PLL are related to the real roots of its characteristic equation

    RF phase modulation of optical signals and optical/electrical signal processing

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    Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 125-127).Analog RF phase modulation of optical signals has been a topic of interest for many years, mainly focusing on Intensity Modulation Direct Detection (IMDD). The virtues of coherent detection combined with the advantages of Frequency Modulation, however, have not been explored thoroughly. By employing Frequency Modulation Coherent Detection (FMCD), the wide optical transmission bandwidth of optical fiber can be traded for higher signal-to-noise performance. In this thesis, we derive the FM gain over AM modulation -- the maximum achievable signal-to-noise ratio (by spreading the signal's spectrum) for specific carrier-to-noise ratio. We then employ FMCD for a scheme of remote antennas for which we use optical components and subsystem to perform signal processing such as nulling of interfering signals. The performance of optical processing on different modulation schemes are compared, and some important conclusions are reported relating to the use of conventional FMCD, FMCD with optical discriminator (FMCD O-D), and IMDD. Specifically, the superiority of conventional FMCD is shown; and, on the other hand, the inferiority of FMCD O-D is shown (same performance as IMDD) because of the use of an O-D. Finally, the remote antenna scheme is generalized for N antennas and N users.by Nikolas I. Andrikogiannopoulos.S.M
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