Spelling suggestions: "subject:"distortion""
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Dynamic nonlinear pre-distortion of signal generators for improved dynamic rangeJawdat, Suzan January 2009 (has links)
<p>In this thesis, a parsimoniously parameterized digital predistorter is derived for linearization of the IQ modulation mismatch and the amplifier imperfection in the signal generator [1]. It is shown that the resulting predistorter is linear in its parameters, and thus they may be estimated by the method of least-squares. Spectrally pure signals are an indispensable requirement when the signal generator is to be used as part of a test bed. Due to the non-linear characteristic of the IQ modulator and power amplifier, distortion will be present at the output of the signal generator. The device under test was the IQ modulation mismatch and power amplifier deficiencies in the signal generator.</p><p>In [2], the dynamic range of low-cost signal generators are improved by employing model based digital pre-distortion and the designed predistorter seems to give some improvement of the dynamic range of the signal generator.</p><p>The goal of this project is to implement and verify the theory parts [1] using data program (Matlab) to improve the dynamic range of the signal generator. The design digital pre-distortion that is implemented in software so that the dynamic range of the signal generator output after predistortion is superior to that of the output prior to it. In this project, we have observed numerical<strong> </strong>problems in the proposed theory and we have found other methods to solve the problem.</p><p>The polynomial model is commonly used in power amplifier modeling and predistorter design. However, the conventional polynomial model exhibits numerical instabilities when higher order terms are included, we have used the conventional and orthogonal polynomial models. The result shows that the orthogonal polynomial model generally yield better power amplifier modeling accuracy as well as predistortion linearization performance then the conventional polynomial model.</p>
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Dynamic nonlinear pre-distortion of signal generators for improved dynamic rangeJawdat, Suzan January 2009 (has links)
In this thesis, a parsimoniously parameterized digital predistorter is derived for linearization of the IQ modulation mismatch and the amplifier imperfection in the signal generator [1]. It is shown that the resulting predistorter is linear in its parameters, and thus they may be estimated by the method of least-squares. Spectrally pure signals are an indispensable requirement when the signal generator is to be used as part of a test bed. Due to the non-linear characteristic of the IQ modulator and power amplifier, distortion will be present at the output of the signal generator. The device under test was the IQ modulation mismatch and power amplifier deficiencies in the signal generator. In [2], the dynamic range of low-cost signal generators are improved by employing model based digital pre-distortion and the designed predistorter seems to give some improvement of the dynamic range of the signal generator. The goal of this project is to implement and verify the theory parts [1] using data program (Matlab) to improve the dynamic range of the signal generator. The design digital pre-distortion that is implemented in software so that the dynamic range of the signal generator output after predistortion is superior to that of the output prior to it. In this project, we have observed numerical problems in the proposed theory and we have found other methods to solve the problem. The polynomial model is commonly used in power amplifier modeling and predistorter design. However, the conventional polynomial model exhibits numerical instabilities when higher order terms are included, we have used the conventional and orthogonal polynomial models. The result shows that the orthogonal polynomial model generally yield better power amplifier modeling accuracy as well as predistortion linearization performance then the conventional polynomial model.
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Optimisation conjointe de méthodes de linéarisation de l'émetteur pour des modulations multi-porteuses / Joint optimization of transmitter linearization methods in multi-carrier modulations contextBrandon, Mathilde 08 November 2012 (has links)
Les modulations multiporteuses apparaissent aujourd'hui comme une technologie éprouvée pour la transmission de données à haut-débits sur des canaux pouvant être très perturbés. L'OFDM (Orthogonal Frequency Division Multiplexing) a d'ailleurs été choisie dans plusieurs normes de télécommunications (ADSL, Wi-Max, IEEE 802.11a/g/n, LTE, DVB,...). Cependant un des inconvénients de ce type de modulation est la forte variation de la puissance instantanée à transmettre. Cette propriété rend ces modulations très sensibles aux non-linéarités des composants analogiques, en particulier celles de l'amplificateur de puissance à l'émission. Or l'amplificateur de puissance est un élément déterminant dans une chaîne de communication dans la mesure où il a une influence prépondérante sur le bilan global de la transmission en termes de puissance, de rendement et de distorsion. Plus l'on souhaite que l'impact de ses non linéarités soit faible et plus son rendement est faible, et inversement. Il est donc nécessaire d'effectuer un compromis linéarité/rendement.L'objectif de la thèse est d'éviter cette détérioration du rendement tout en conservant de bonnes performances de linéarité, de surcroit pour des signaux OFDM. Pour ce faire nous proposons d'utiliser conjointement des méthodes de linéarisation (prédistorsion numérique en bande de base) et d'amélioration du rendement (envelope tracking) de l'amplificateur de puissance ainsi qu'une méthode de réduction de la dynamique du signal (active constellation extension). La prédistorsion numérique classique échouant aux fortes puissances, nous proposons une méthode d'amélioration de cette technique à ces puissances. Nos résultats sont validés par des mesures sur un amplificateur de puissance 50W. Nous proposons également une association des méthodes permettant d'améliorer simultanément les performances en terme de linéarité hors bande et de rendement en minimisant les dégradations des performances de taux d'erreur binaire. / Multi-carrier modulations appear as a well-tried technology for high-speed data transmission on potentially disrupted channels. OFDM (Orthogonal Frequency Division Multiplexing) has been chosen for that matter in several telecommunication standards (ADSL, Wi-Max, IEEE 802.11a/g/n, LTE, DVB,...). However one of the drawbacks of this modulation type is its high variation of the instantaneous power to transmit. This property makes these modulations very sensitive to the non-linearities of analog components, especially those related to power amplifiers. Yet the power amplifiers are critical elements in the communication chain as they have a major influence on the global assessment in terms of power, efficiency and distortion. More we want its non linearity impact is weak, more its efficiency is weak too. It is therefore necessary to make a trade-off between linearity and efficiency.The purpose of the thesis is to avoid this efficiency damage keeping at the same time the good linearity performance, moreover for OFDM signals. In this way we propose to jointly use a linearization technique (the base band digital predistortion) and a technique of efficiency improvement (the envelope tracking) for the power amplifier, together with a technique of signal dynamic reduction (the active constellation extension). The classic predistortion failing for high powers, we propose an improvement of this technique for these powers. Our results are validated by measurements on a 50W power amplifier. We also propose an association of the techniques allowing an improvement of the performance in terms of out-of-band linearity and efficiency, with smallbit error rate damages.
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Digital predistortion of semi-linear power amplifier / Digital predistorsion av semilineär effektförstärkareKarlsson, Robert January 2004 (has links)
<p>In this thesis, a new way of using predisortion for linearization of power amplifiers is evaluated. In order to achieve an adequate power level for the jamming signal, power amplifiers are used in military jamming systems. Due to the nonlinear characteristic of the power amplifier, distortion will be present at the output. As a consequence, unwanted frequencies are subject to jamming. To decrease the distortion, linearization of the power amplifier is necessary. </p><p>In the system of interest, a portion of the distorted power amplifier output signal is fed back. Using this measurement, a predistortion signal is synthesized to allow suppression of the unwanted frequency components. The predistortion signal is updated a number of times in order to achieve a good outcome. Simulations are carried out in Matlab for testing of the algorithm. </p><p>The evaluation of the new linearization technique shows promising results and that good suppression of distortion components is achieved. Furthermore, new predistortion features are possible to implement, such as predistorsion in selected frequency bands. However, real hardware testing needs to be carried out to confirm the results.</p>
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Complexity Reduced Behavioral Models for Radio Frequency Power Amplifiers’ Modeling and LinearizationFares, Marie-Claude January 2009 (has links)
Radio frequency (RF) communications are limited to a number of frequency bands scattered over the radio spectrum. Applications over such bands increasingly require more versatile, data extensive wireless communications that leads to the necessity of high bandwidth efficient interfaces, operating over wideband frequency ranges. Whether for a base station or mobile device, the regulations and adequate transmission of such schemes place stringent requirements on the design of transmitter front-ends. Increasingly strenuous and challenging hardware design criteria are to be met, especially so in the design of power amplifiers (PA), the bottle neck of the transmitter’s design tradeoff between linearity and power efficiency. The power amplifier exhibits a nonideal behavior, characterized by both nonlinearity and memory effects, heavily affecting that tradeoff, and therefore requiring an effective linearization technique, namely Digital Predistortion (DPD). The effectiveness of the DPD is highly dependent on the modeling scheme used to compensate for the PA’s nonideal behavior. In fact, its viability is determined by the scheme’s accuracy and implementation complexity. Generic behavioral models for nonlinear systems with memory have been used, considering the PA as a black box, and requiring RF designers to perform extensive testing to determine the minimal complexity structure that achieves satisfactory results. This thesis first proposes a direct systematic approach based on the parallel Hammerstein structure to determine the exact number of coefficients needed in a DPD. Then a physical explanation of memory effects is detailed, which leads to a close-form expression for the characteristic behavior of the PA entirely based on circuit properties. The physical expression is implemented and tested as a modeling scheme. Moreover, a link between this formulation and the proven behavioral models is explored, namely the Volterra series and Memory Polynomial. The formulation shows the correlation between parameters of generic behavioral modeling schemes when applied to RF PAs and demonstrates redundancy based on the physical existence or absence of modeling terms, detailed for the proven Memory polynomial modeling and linearization scheme.
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Complexity Reduced Behavioral Models for Radio Frequency Power Amplifiers’ Modeling and LinearizationFares, Marie-Claude January 2009 (has links)
Radio frequency (RF) communications are limited to a number of frequency bands scattered over the radio spectrum. Applications over such bands increasingly require more versatile, data extensive wireless communications that leads to the necessity of high bandwidth efficient interfaces, operating over wideband frequency ranges. Whether for a base station or mobile device, the regulations and adequate transmission of such schemes place stringent requirements on the design of transmitter front-ends. Increasingly strenuous and challenging hardware design criteria are to be met, especially so in the design of power amplifiers (PA), the bottle neck of the transmitter’s design tradeoff between linearity and power efficiency. The power amplifier exhibits a nonideal behavior, characterized by both nonlinearity and memory effects, heavily affecting that tradeoff, and therefore requiring an effective linearization technique, namely Digital Predistortion (DPD). The effectiveness of the DPD is highly dependent on the modeling scheme used to compensate for the PA’s nonideal behavior. In fact, its viability is determined by the scheme’s accuracy and implementation complexity. Generic behavioral models for nonlinear systems with memory have been used, considering the PA as a black box, and requiring RF designers to perform extensive testing to determine the minimal complexity structure that achieves satisfactory results. This thesis first proposes a direct systematic approach based on the parallel Hammerstein structure to determine the exact number of coefficients needed in a DPD. Then a physical explanation of memory effects is detailed, which leads to a close-form expression for the characteristic behavior of the PA entirely based on circuit properties. The physical expression is implemented and tested as a modeling scheme. Moreover, a link between this formulation and the proven behavioral models is explored, namely the Volterra series and Memory Polynomial. The formulation shows the correlation between parameters of generic behavioral modeling schemes when applied to RF PAs and demonstrates redundancy based on the physical existence or absence of modeling terms, detailed for the proven Memory polynomial modeling and linearization scheme.
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Nonlinear System Identification and Analysis with Applications to Power Amplifier Modeling and Power Amplifier PredistortionRaich, Raviv 07 April 2004 (has links)
Power amplifiers (PAs) are important components of communication
systems and are inherently nonlinear. When a non-constant modulus
signal goes through a nonlinear PA, spectral regrowth (broadening)
appears in the PA output, which in turn causes adjacent channel
interference (ACI). Stringent limits on the ACI are imposed by
regulatory bodies, and thus the extent of the PA nonlinearity must
be controlled. PA linearization is often necessary to suppress
spectral regrowth, contain adjacent channel interference, and
reduce bit error rate (BER). This dissertation addresses the
following aspects of power amplifier research: modeling,
linearization, and spectral regrowth analysis.
We explore the passband and baseband PA input/output relationships
and show that they manifest differently when the PA exhibits
long-term, short-term, or no memory effects. The so-called
quasi-memoryless case is especially clarified. Four particular
nonlinear models with memory are further investigated. We provide
experimental results to support our analysis.
The benefits of using the orthogonal polynomials as opposed to the
conventional polynomials are explored, in the context of digital
baseband PA modeling and predistorter design. A closed-form
expression for the orthogonal polynomial basis is derived. We
demonstrate the improvement in numerical stability associated with
the use of orthogonal polynomials for predistortion.
Spectral analysis can help to evaluate the suitability of a given
PA for amplifying certain signals or to assist in predistortion
linearization algorithm design. With the orthogonal polynomials
that we derived, spectral analysis of the nonlinear PA becomes a
straightforward task. We carry out nonlinear spectral analysis
with digitally modulated signal as input. We demonstrate an
analytical approach for evaluating the power spectra of filtered
QPSK and OQPSK signals after nonlinear amplification.
Many communications devices are nonlinear and have a peak power or
peak amplitude constraint. In addition to possibly amplifying the
useful signal, the nonlinearity also generates distortions. We
focus on signal-to-noise-and-distortion ratio (SNDR) optimization
within the family of amplitude limited memoryless nonlinearities.
We obtain a link between the capacity of amplitude-limited
nonlinear channels with Gaussian noise to the SNDR.
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Hybrid Digital/RF Envelope Predistortion Linearization for High Power Amplifiers in Wireless Communication SystemsWoo, Wangmyong 27 April 2005 (has links)
Hybrid Digital/RF Envelope Predistortion Linearization for High Power Amplifiers in Wireless Communication Systems
Wangmyong Woo
151 Pages
Directed by Dr. J. Stevenson Kenney
The objective of this research is to implement a hybrid digital/RF envelope predistortion linearization system for high-power amplifiers used in wireless communication systems. It is well known that RF PAs have AM/AM (amplitude modulation) and AM/PM (phase modulation) nonlinear characteristics. Moreover, the distortion components generated by a PA are not constant, but vary as a function of many input conditions such as amplitude, signal bandwidth, self-heating, aging, etc. Memory effects in response to past inputs cause a hysteresis in the nonlinear transfer characteristics of a PA. This hysteresis, in turn, creates uncertainty in predictive linearization techniques. To cope with these nonlinear characteristics, distortion variability, and uncertainty in linearization, an adaptive digital predistortion technique, a hybrid digital/RF envelope predistortion technique, an analog-based RF envelope predistortion technique, and a combinational digital/analog predistortion technique have been developed.
A digital adaptation technique based on the error vector minimization of received PA output waveforms was developed. Also, an adaptive baseband-to-baseband test system for the characterization of RF PAs and for the validation of linearization algorithms was implemented in conjunction with the adaptation technique. To overcome disadvantages such as limited correction bandwidth and the need for a baseband input signal in digital predistortion, an adaptive, wideband RF envelope predistortion system was developed that incorporates a memoryless predistortion algorithm. This system is digitally controlled by a look-up table (LUT). Compared with conventional baseband digital approaches, this predistortion architecture has a correction bandwidth that is from 20 percent to 33 percent wider at the same clock speeds for third to fifth order IMDs and does not need a digital baseband input signal.
For more accurate predistortion linearization for PAs with memory effects, an RF envelope predistortion system has been developed that uses a combination of analog-based envelope predistortion (APD) working in conjunction with digital LUT-based adaptive envelope predistortion (DPD). The resulting combination considerably decreases the computational complexity of the digital system and significantly improves linearity and efficiency at high power levels.
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Adaptive Power Amplifier Linearization by Digital Pre-Distortion with Narrowband Feedback using Genetic AlgorithmsSperlich, Roland 19 July 2005 (has links)
This dissertation presents a study of linearization techniques that have been applied to power amplifiers in the cellular communication
industry. The objective of this work is to understand the limitations of power amplifiers, specifically the limitations introduced by the use of spectrally efficient modulation schemes.
The digitization of communication systems has favored the use of new techniques and technologies capable of increasing the efficiency of costly power amplifiers. The work explores traditional and digital linearization systems; an algorithm based on the principles of natural recombination is proposed to directly address the
limitations of previous embodiments. Previous techniques, although effective, have significant implementation costs that increase exponentially with the increasing signal bandwidths. The proposed software-hardware architecture significantly reduces implementation costs and the overall complexity of the design without sacrificing performance.
To fulfill the requirements of this study, multiple systems are implemented through simulation and closed-loop hardware. Both simulation and hardware embodiments meet the expected performance metrics, providing validation of the proposed algorithm. The application of the algorithm to memory power amplifier linearization is a new approach to adaptive digital pre-distortion using narrowband feedback. The work will show performance improvements on an amplifier with memory effects suggesting that this technique can be employed as a lower-cost solution to meet requirements when compared to typical system implementations.
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Linearization Of Rf Power Amplifiers By Using Memory Polynomial Digital Predistortion TechniqueErdogdu, Gozde 01 June 2012 (has links) (PDF)
In modern wireless communication systems, new modulation types are introduced in order to support more users by considering spectral efficiency. These new signals are ensitive to nonlinearity when they have high peak to average ratio. The main part in the system that causes nonlinearity is the power amplifier. For power amplifiers, between linearity and efficiency, there is a trade-off. However, by using predistortion techniques, both linearity and efficiency
can be obtained. In this thesis, various predistortion methods are explained and memory polynomial digital predistortion is studied because of its great advantages. The results are obtained by simulations through MATLAB and experiments. An open loop test bench is built up with real amplifier. During experimental procedure, as input two tone signal, 8psk modulated signal and pi/2 bpsk modulated signal are used. Predistortion with memory and memoryless predistortion performances are compared and superiority of the predistortion with memory is shown. Predistortion performance with respect to memory depth and polynomial order is also studied. Moreover, predistortion model range is investigated through evaluation of performance by applying predistorter function estimated at a specific bandwidth and power to
other signals having different bandwidth and power. Besides these works, the details of predistortion algorithm and the problems that can be countered in practice are explained.
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