In modern wireless communication systems, advanced modulation techniques are used to support more users by handling high data rates and to increase the utilization efficiency of the limited RF spectrum. These techniques are sensitive to the nonlinear distortions due to their high peak to average power ratios. Main source of nonlinear distortion in transmitter topologies are power amplifiers that determine the overall efficiency and linearity of the transmitter. To increase linearity without sacrificing efficiency, power amplifier linearization techniques may be a choice. Baseband predistortion technique is known to be one of the optimum methods due to its relatively low complexity and its convenience for adaptation. In this thesis, different memoryless baseband signal predistortion methods are investigated and analyzed by simulations. Look-Up Table(LUT) and Polynomial approaches are compared and LUT approach is found to be better in performance. Parameters, like indexing, training sequences and training duration are evaluated. An open loop testbench is built with a real amplifier and a different LUT predistortion method that is based on amplifier modeling is offered. It is evaluated by using two tone test and adjacent channel power suppression with 8PSK data. Also, some Look-Up Table parameters are re-investigated with the proposed method. The performances of the proposed method in dierent amplifier classes are observed. Along with these studies, a list of prerequisites for design of a predistortion system is determined.

Ce travail concerne la linéarisation des amplificateurs de haute puissance en utilisant la pré-distorsion numérique. L’amplificateur de haute puissance est un composant non-linéaire. La pré-distorsion numérique adaptative en bande de base est un technique efficace pour linéariser ses non-linéarités et ses effets de mémoire. Les modèles de la pré-distorsion numérique de basse complexité sont étudiés dans cette thèse. Un algorithme est proposé pour déterminer une structure optimale de modèle uni-étage ou multi-étage en prenant compte du compromis entre la précision de modélisation et la complexité. La structure cascadée, qui est avantageuse en complexité comparé avec celle d'uni-étage, est étudiée avec des méthodes d'identifications différentes. En termes d'implémentations expérimentales, l'étude d'impact des choix de gain différents est approfondie dans cette thèse. Toutes les études ont été évaluées par un amplificateur de puissance Doherty / This dissertation contributes to the linearization techniques of high power amplifier using digital predistortion method. High power amplifier is one of the most nonlinear components in radio transmitters. Unfortunately, for most current types of power amplifiers, a good efficiency is obtained at the price of a poor linearity especially with modern communication waveforms. Baseband adaptive digital predistortion is a powerful technique to linearize the power amplifiers and allows to push the power amplifier operation point towards its high efficiency region. Linearization of power amplifiers using digital predistortion with low complexities is the focus of this dissertation. An algorithm is proposed to determine an optimal model structure of single-stage or multi-stage predistorter according to a trade-off between modeling accuracy and model complexity. Multi-stage cascaded digital predistortions are studied with different identification methods, which have advantages on complexity of model identification compared with single-stage structure. The linearization performances are validated by experimental implementations on test bench. In terms of experimental implementations, this dissertation studies the impact of different gain choices on linearized power amplifier. All studies are evaluated with a Doherty power amplifier

In satellite communications, non-linear interference is created by the non-linear power amplifier aboard the satellite. Even in the case of a memoryless power amplifier, the channel is a non-linear system with memory due to the presence of linear filters on ground and aboard the satellite. The non-linear interference degrades the system performance, especially when considering high-order modulations or in case of several signals being amplified by the same power amplifier. In this thesis, we have proposed algorithms at the transmitter and at the receiver to digitally compensate this interference. In particular, a new predistortion algorithm has been proposed, which significantly improves state-of-the-art algorithms. Since the complexity of this algorithm is an issue, low-complexity algorithms have also been proposed and achieve almost the same performance as the initial algorithm. We have also proposed joint predistortion and turbo-equalization algorithms to further improve the system performance. / En communications par satellite, de l’interférence non-linéaire est créée par l’amplificateur de puissance non-linéaire à bord du satellite. Même si l’amplificateur peut être considéré comme sans mémoire, le canal est malgré tout un système non-linéaire avec mémoire de par la présence de filtres linéaires au sol ou à bord du satellite. L'interférence non-linéaire dégrade les performances du système, en particulier lorsqu’on considère des modulations d’ordre élevé ou plusieurs signaux amplifiés par le même amplificateur de puissance. Dans cette thèse, nous avons proposé des algorithmes à l’émetteur et au récepteur pour compenser numériquement cette interférence. En particulier, nous avons proposé un nouvel algorithme de prédistorsion qui améliore de façon significative les algorithmes de l’état-de-l’art. La complexité de l’algorithme étant très élevée, nous avons proposé des algorithmes de plus faible complexité atteignant pratiquement les mêmes performances par rapport à l’algorithme initial. Nous avons aussi proposé des algorithmes de prédistorsion et d’égalisation conjointes, permettant d'atteindre des performances plus élevées qu'avec la prédistorsion seule. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The large unlicensed 3 GHz overlapping bandwidth that is available worldwide at 60 GHz has resulted in renewed interest in 60 GHz technology. This frequency band has made it attractive for short-range gigabit wireless communication. The power amplifier (PA) directly influences the performance and quality of this entire communication chain, as it is one of the final subsystems in the transmitter. Spectral efficient modulation schemes used at 60 GHz pose challenging requirements for the linearity of the PA. To improve the linearity, several external linearisation techniques currently exist, such as feedback, feedforward, envelope elimination and restoration, linear amplification with non-linear components and predistortion. This thesis is aimed at investigating and characterising the distortion components found in PAs at mm-wave frequencies and evaluating whether an adaptive predistortion (APD) linearisation technique is suitable to reduce these distortion components. After a thorough literature study and mathematical analysis, it was found that the third-order intermodulation distortion (IMD3) components were the most severe distortion components. Predistortion was identified as the most effective linearisation technique in terms of minimising these IMD3 components and was therefore proposed in this research. It does not introduce additional complexity and can easily be integrated with the PA. Furthermore, the approach is stable and has lower power consumption when compared to the aforementioned linearisation techniques. The proposed predistortion technique was developed compositely through this research by making it a function of the PA’s output power that was measured using a power detector. A comparator was used with the detected output power and the reference voltages to control the dynamic bias circuit of the variable gain amplifier. This provided control and flexibility on when to apply the predistortion to the PA and therefore allowing the linearity of the PA to be optimised. Three-stage non-linear and linear PAs were also designed at 60 GHz and implemented to compare the performance of the APD technique and form part of the hypothesis verification process. The 130 nm silicon-germanium (SiGe) bipolar and complementary metal oxide semiconductor (BiCMOS) technology from IBM was used for the simulation of the entire APD and PA design and for the fabrication of the prototype integrated circuits (ICs). This technology has the advantage of integrating the high performance, low power intensive SiGe heterojunction bipolar transistors (HBTs) with the CMOS technology. The SiGe HBTs have a high cut-off frequency ( > 200 GHz), which is ideal for mm-wave PA applications and the CMOS components were integrated in the control logic of the digital circuitry. The simulations and IC layout were accomplished with Cadence Virtuoso. The implemented IC occupies an area of 1.8 mm by 2.0 mm. The non-linear PA achieves a of 11.97 dBm and an of -10 dBm. With the APD technique applied, the linearity of the PA is significantly improved with an of -6 dBm and an optimum IMD3 reduction of 10 dB. Based on the findings and results of the applied APD technique, APD reduced intermodulation distortion (especially the IMD3) and is thus suitable to improve the linearity of PAs at mm-wave frequencies. To the knowledge of this author, no APD technique has been applied for PAs at 60 GHz, therefore the contribution of this research will assist future PA designers to characterise and optimise the reduction of the IMD3 components. This will result in improved linear output power from the PA and the use of complex modulation schemes at 60 GHz. ## Die groot ongelisensieerde oorvleuelde bandwydte van 3 GHz wat wêreldwyd by 60 GHz beskikbaar is, het hernude belangstelling in 60 GHz-tegnologie tot gevolg gehad. Hierdie frekwensieband het dit aantreklik gemaak vir kortafstand-gigabis draadlose kommunikasie. Aangesien die drywingsversterker een van die finale subsisteme in die seintoestel is, het dit ’n direkte invloed op die werkverrigting en kwaliteit van die hele kommunikasieketting. Spektraaldoeltreffende modulasieskemas wat by 60 GHz gebruik word, stel uitdagende vereistes vir die lineariteit van die drywingsversterker. Om die lineariteit te verbeter, is daar tans verskeie eksterne linearisasietegnieke beskikbaar, soos terugvoer, vooruitvoer, omhullende eliminasie en -restorasie, lineêre versterking met nie-lineêre komponente en predistorsie. Hierdie tesis het ten doel om die distorsiekomponente wat by millimetergolffrekwensies in drywingsversterkers gevind word, te ondersoek en te karakteriseer en om te bepaal of ’n aanpassende predistorsielinearisasietegniek geskik is om hierdie distorsiekomponente te verminder. Na ’n deeglike literatuurstudie en wiskundige analise is gevind dat die derde-orde-intermodulasiedistorsiekomponente (IMD3) die ergste distorsiekomponente was. Predistorsie is geïdentifiseer as die mees effektiewe linearisasietegniek om hierdie IMD3-komponente te minimeer en die gebruik daarvan is gevolglik in hierdie navorsing voorgestel. Dit bring nie addisionele kompleksiteit mee nie en kan maklik met die drywingsversterker geïntegreer word. Daarbenewens is die benadering stabiel, met laer kragverbruik in vergelyking met die linearisasietegnieke wat voorheen genoem is. Die voorgestelde predistorsietegniek is in hierdie navorsing ontwikkel deur dit ’n funksie van die drywingsversterker se uitsetkrag te maak, wat gemeet is deur ’n kragdetektor te gebruik. ’n Vergelyker is saam met die gemete uitsetkrag en die verwysingspannings gebruik om die dinamiese voorspanningsbaan van die veranderlike winsversterker te beheer. Dit het toegelaat vir beheer en buigsaamheid in die aanwending van die predistorsie op die drywingsversterker en gevolglik vir die optimering van die lineêriteit van die drywingsversterker. Driefase- nie-lineêre en lineêre drywingsversterkers is ook by 60 GHz ontwerp en geïmplementeer om die werkverrigting van die aanpassende predistorsietegniek te vergelyk en dit vorm deel van die verifikasieproses van die hipotese. Die 130 nm-silikon-germanium (SiGe) bipolêre en metaaloksiedhalfgeleier- (BiCMOS) tegnologie van IBM is gebruik vir die simulasie van die hele aanpassende predistorsietegniek- en drywingsversterkerontwerp en vir die vervaardiging van die prototipe- geïntegreerde stroombane. Hierdie tegnologie het die voordeel dat dit die hoë werkverrigting en lae krag-intensiewe SiGe-heterovoegvlak-bipolêre transistors (HBTs) met die CMOS-tegnologie integreer. Die SiGe-HBTs het ’n hoë afsnyfrekwensie ( > 200 GHz), wat ideaal is vir mm-golfdrywingsversterkeraanwendings en die CMOS-komponente is in die beheer-logika van die digitale stroombaan geïntegreer. Die geïntegreerde stroombaan beslaan ’n area van 1.8 mm by 2.0 mm. Die nie-lineêre drywingsversterker behaal ’n van 11.97 dBm en ’n van -10 dBm. As die APD-tegniek toegepas word, word die lineariteit van die drywingsversterker beduidend verbeter tot ’n van -6 dBm en ’n optimum-IMD3-vermindering van 10 dB. Volgens die bevindings en resultate van die APD-tegniek wat toegepas is, verminder APD intermodulasiedistorsie (veral die IMD3) en is gevolglik geskik om die lineariteit van drywingsversterkers by mm-golffrekwensies te verbeter. Na die wete van hierdie skrywer is daar nie voorheen enige APD tegniek toegepas vir drywingsversterkers by 60 GHz nie, gevolglik sal die bydrae van hierdie navorsing toekomstige drywingsversterkerontwerpers help om die vermindering van die IMD3-komponente te karakteriseer en optimeer. Dit sal verbeterde lineêre uitsetkrag van die drywingsversterker tot gevolg hê, asook meer komplekse modulasieskemas by 60 GHz toelaat. / Thesis (PhD)--University of Pretoria, 2014. / lk2014 / Electrical, Electronic and Computer Engineering / PhD / unrestricted

The large unlicensed 3 GHz overlapping bandwidth that is available worldwide at 60 GHz has resulted in renewed interest in 60 GHz technology. This frequency band has made it attractive for short-range gigabit wireless communication. The power amplifier (PA) directly influences the performance and quality of this entire communication chain, as it is one of the final subsystems in the transmitter. Spectral efficient modulation schemes used at 60 GHz pose challenging requirements for the linearity of the PA. To improve the linearity, several external linearisation techniques currently exist, such as feedback, feedforward, envelope elimination and restoration, linear amplification with non-linear components and predistortion. This thesis is aimed at investigating and characterising the distortion components found in PAs at mm-wave frequencies and evaluating whether an adaptive predistortion (APD) linearisation technique is suitable to reduce these distortion components. After a thorough literature study and mathematical analysis, it was found that the third-order intermodulation distortion (IMD3) components were the most severe distortion components. Predistortion was identified as the most effective linearisation technique in terms of minimising these IMD3 components and was therefore proposed in this research. It does not introduce additional complexity and can easily be integrated with the PA. Furthermore, the approach is stable and has lower power consumption when compared to the aforementioned linearisation techniques. The proposed predistortion technique was developed compositely through this research by making it a function of the PA’s output power that was measured using a power detector. A comparator was used with the detected output power and the reference voltages to control the dynamic bias circuit of the variable gain amplifier. This provided control and flexibility on when to apply the predistortion to the PA and therefore allowing the linearity of the PA to be optimised. Three-stage non-linear and linear PAs were also designed at 60 GHz and implemented to compare the performance of the APD technique and form part of the hypothesis verification process. The 130 nm silicon-germanium (SiGe) bipolar and complementary metal oxide semiconductor (BiCMOS) technology from IBM was used for the simulation of the entire APD and PA design and for the fabrication of the prototype integrated circuits (ICs). This technology has the advantage of integrating the high performance, low power intensive SiGe heterojunction bipolar transistors (HBTs) with the CMOS technology. The SiGe HBTs have a high cut-off frequency (fT > 200 GHz), which is ideal for mm-wave PA applications and the CMOS components were integrated in the control logic of the digital circuitry. The simulations and IC layout were accomplished with Cadence Virtuoso. The implemented IC occupies an area of 1.8 mm by 2.0 mm. The non-linear PA achieves a Psat of 11.97 dBm and an IP1dB of -10 dBm. With the APD technique applied, the linearity of the PA is significantly improved with an IP1dB of -6 dBm and an optimum IMD3 reduction of 10 dB. Based on the findings and results of the applied APD technique, APD reduced intermodulation distortion (especially the IMD3) and is thus suitable to improve the linearity of PAs at mm-wave frequencies. To the knowledge of this author, no APD technique has been applied for PAs at 60 GHz, therefore the contribution of this research will assist future PA designers to characterise and optimise the reduction of the IMD3 components. This will result in improved linear output power from the PA and the use of complex modulation schemes at 60 GHz. / Thesis (PhD)--University of Pretoria, 2014. / Electrical, Electronic and Computer Engineering / PhD

The current consumption of the IQ modulator is a significant part of the totalcurrent consumption of a mobile transmitter platform and reducing it is of greatinterest. Also, as the WCDMA/LTE standards specifies full duplex transmissionsand Tx and Rx are most often using the same antenna, it is crucial to have asolution with low noise generation. Two new proposals have been studied with theaim to reduce the current consumption and noise contribution of the IQ modulator. A current mode envelope tracking IQM is the first of the studied designs. Thisimplementation lowers the bias currents in the circuit in relation to the amplitudeof the baseband input signals, meaning that a low input amplitude results in alowering of the current consumption. It proves to be very efficient for basebandsignals with a high peak-to-average ratio. Simulations and calculations have shownthat an average current reduction of 56 % can be achieved for an arbitrary LTEbaseband signal. The second is an entirely new passive mixer design where the baseband voltagesare sequentially copied to the RF node, removing the need for V-to-I conversion inthe mixer which reduces current consumption and noise. Results from simulationshas proven that this design is fully capable of improving both current consumptionas well as the noise levels. With an output power of 4.0 dBm, the power consumptionwas 43.3 mW, including clock generating circuits. This, combined with thefact that the design is small and simple, means that there is definitely a possibilityto replace the present IQM design with a passive mixer.

Les travaux présentés dans ce mémoire de thèse portent sur la linéarisation large bande d'amplificateurs de puissance par prédistorsion analogique. Ce travail vise à réduire la pollution spectrale provoquée par leur comportement non-linéaire lors d'une transmission satellite. Ce travail de thèse débute par une présentation des amplificateurs de puissance utilisés dans les émetteurs, en exposant les conséquences de leur comportement non-linéaire sur la qualité du signal. Pour pallier à cela, les techniques de linéarisation couramment utilisées ont été recensées, en mettant l'accent sur leurs avantages et inconvénients. C'est sur la base de cet état de l'art qu'une structure de prédistorsion analogique a pu être identifiée. Il s'agit d'une structure en réflexion à base de diodes Schottky, dont une partie de ce mémoire est consacrée à l'analyse de leur comportement non-linéaire. Appuyée par des résultats de simulations et des mesures effectuées sur maquettes, cette analyse nous a conduit à la mise en œuvre de la structure en réflexion dans le cadre de la linéarisation d'un amplificateur à tube à onde progressive (ATOP) en bande Ku. Nos travaux se sont ensuite tournés vers une nouvelle structure plus innovante, basée sur la mise en cascade de deux circuits de prédistorsion. La structure proposée bénéficie d'une configuration plus flexible et plus précise que la précédente, ce qui nous a permis d'obtenir de meilleurs résultats en matière d'amélioration de la linéarité. La dernière partie de ce travail de thèse est dédiée à l'approche expérimentale de deux méthodes numériques de prédistorsion en bande de base. L'intérêt de cette approche repose sur l'évaluation expérimentale de l'amélioration possible de la linéarité de l'ATOP et la comparaison avec les résultats obtenus par prédistorsion analogique. / The research reported in this PhD Thesis is focused on power amplifier wideband linearization by analog predistortion. This work aims to reduce the spectral regrowth due to their nonlinear response over the satellite transmission. This dissertation starts with a presentation of power amplifiers used in transmitters. Through it, we expose their nonlinearity effects on the signal quality. To overcome those effects, the lattest linearization methods were reviewed, highlighting their strengths and weaknesses. Based on this state of art, an analog predistortion structure was identified. It relates to a reflective structure made up of Schottky diodes, of which a part of this thesis is devoted to the analysis of its nonlinear behavior. Drawn on simulations and measurements, this analysis led us to the implementation of the reflective structure for the purpose of a traveling wave tube amplifier linearization over the Ku band. Our work was then directed towards to a new more innovative structure built on two predistortion circuits wired in series. This new structure gets a more flexible and accurate configuration compared to the previous one and allowed us to obtain better results regarding linearity improvement. The last part of this thesis work is dedicated to an experimental approach of two base band digital predistortion methods. The aim of this approach rests on the achievable enhancement of TWTA linearity and the comparison between the results obtained with the analog predistortion.

Aquesta Tesi Doctoral se centra en el disseny d'un nou linealitzador de Predistorsió Digital (Digital Predistortion - DPD) capaç de compensar la dinàmica i els efectes no lineals introduïts pels Amplificadors de Potència (Power Amplifiers - PAs). Un dels trets més rellevants d'aquest nou predistorsionador digital i adaptatiu consisteix en ser deduïble a partir d'un model de PA anomenat Nonlinear Auto-Regressive Moving Average (NARMA). A més, la seva arquitectura multi-LUT (multi-Taula) permet la implementació en un dispositiu Field Programmable Gate Array (FPGA).La funció de predistorsió es realitza en banda base, per tant, és independent de la banda freqüencial on es durà a terme l'amplificació del senyal de RF, el que pot resultar útil si tenim en compte escenaris multibanda o reconfigurables. D'altra banda, el fet que aquest DPD tingui en compte els efectes de memòria introduïts pel PA, representa una clara millora de les prestacions aconseguides per un simple DPD sense memòria. En comparació amb d'altres DPDs basats en models més computacionalment complexos, com és el cas de les xarxes neuronals amb memòria (Time-Delayed Neural Networks - TDNN), la estructura recursiva del DPD proposat permet reduir el nombre de LUTs necessàries per compensar els efectes de memòria del PA. A més, la seva estructura multi-LUT permet l'escalabilitat, és a dir, activar or desactivar les LUTs que formen el DPD en funció de la dinàmica que presenti el PA.En una primera aproximació al disseny del DPD, és necessari identificar el model NARMA del PA. Un dels majors avantatges que presenta el model NARMA és la seva capacitat per trobar un compromís entre la fidelitat en l'estimació del PA i la complexitat computacional introduïda. Per reforçar aquest compromís, l' ús d'algoritmes heurístics de cerca, com són el Simulated Annealing o els Genetic Algorithms, s'utilitzen per trobar els retards que millor caracteritzen la memòria del PA i per tant, permeten la reducció del nombre de coeficients necessaris per caracteritzar-la. Tot i així, la naturalesa recursiva del model NARMA comporta que, de cara a garantir l'estabilitat final del DPD, cal dur a terme un estudi previ sobre l'estabilitat del model.Una vegada s'ha obtingut el model NARMA del PA i s'ha verificat l'estabilitat d'aquest, es procedeix a l'obtenció de la funció de predistorsió a través del mètode d'identificació predictiu. Aquest mètode es basa en la continua identificació del model NARMA del PA i posteriorment, a partir del model obtingut, es força al PA perquè es comporti de manera lineal. Per poder implementar la funció de predistorsió en la FPGA, cal primer expressar-la en forma de combinacions en paral·lel i cascada de les anomenades Cel·les Bàsiques de Predistorsió (BPCs), que són les unitats fonamentals que composen el DPD. Una BPC està formada per un multiplicador complex, un port RAM dual que actua com a LUT (taula de registres) i un calculador d'adreces. Les LUTs s'omplen tenint en compte una distribució uniforme dels continguts i l'indexat d'aquestes es duu a terme mitjançant el mòdul de l'envoltant del senyal. Finalment, l'adaptació del DPD consisteix en monitoritzar els senyals d'entrada i sortida del PA i anar duent a terme actualitzacions periòdiques del contingut de les LUTs que formen les BPCs. El procés d'adaptació del contingut de les LUTs es pot dur a terme en la mateixa FPGA encarregada de fer la funció de predistorsió, o de manera alternativa, pot ser duta a terme per un dispositiu extern (com per exemple un DSP - Digital Signal Processor) en una escala de temps més relaxada. Per validar l'exposició teòrica i provar el bon funcionalment del DPD proposat en aquesta Tesi, es proporcionen resultats tant de simulació com experimentals que reflecteixen els objectius assolits en la linealització del PA. A més, certes qüestions derivades de la implementació pràctica, tals com el consum de potència o la eficiència del PA, són també tractades amb detall. / This Ph.D. thesis addresses the design of a new Digital Predistortion (DPD) linearizer capable to compensate the unwanted nonlinear and dynamic behavior of power amplifiers (PAs). The distinctive characteristic of this new adaptive DPD is its deduction from a Nonlinear Auto Regressive Moving Average (NARMA) PA behavioral model and its particular multi look-up table (LUT) architecture that allows its implementation in a Field Programmable Gate Array (FPGA) device.The DPD linearizer presented in this thesis operates at baseband, thus becoming independent on the final RF frequency band and making it suitable for multiband or reconfigurable scenarios. Moreover, the proposed DPD takes into account PA memory effects compensation which representsan step forward in overcoming classical limitations of memoryless predistorters. Compared to more computational complex DPDs with dynamic compensation, such Time-Delayed Neural Networks (TDNN), this new DPD takes advantage of the recursive nature of the NARMA structure to relax the number of LUTs required to compensate memory effects in PAs. Furthermore, its parallel multi-LUT architecture is scalable, that is, permits enabling or disabling the contribution of specific LUTs depending on the dynamics presented by a particular PA.In a first approach, it is necessary to identify a NARMA PA behavioral model. The extraction of PA behavioral models for DPD linearization purposes is carried out by means of input and output complex envelope signal observations. One of the major advantages of the NARMA structure regards its capacity to deal with the existing trade-off between computational complexity and accuracy in PA behavioral modeling. To reinforce this compromise, heuristic search algorithms such the Simulated Annealing or Genetic Algorithms are utilized to find the best sparse delays that permit accurately reproducing the PA nonlinear dynamic behavior. However, due to the recursive nature of the NARMA model, an stability test becomes a previous requisite before advancing towards DPD linearization.Once the PA model is identified and its stability verified, the DPD function is extracted applying a predictive predistortion method. This identification method relies just on the PA NARMA model and consists in adaptively forcing the PA to behave as a linear device. Focusing in the DPD implementation, it is possible to map the predistortion function in a FPGA, but to fulfill this objective it is first necessary to express the predistortion function as a combined set of LUTs.In order to store the DPD function into a FPGA, it has to be stated in terms of parallel and cascade Basic Predistortion Cells (BPCs), which are the fundamental building blocks of the NARMA based DPD. A BPC is formed by a complex multiplier, a dual port RAM memory block acting as LUT and an address calculator. The LUT contents are filled following an uniform spacing procedure and its indexing is performed with the amplitude (modulus) of the signal's envelope.Finally, the DPD adaptation consists in monitoring the input-output data and performing frequent updates of the LUT contents that conform the BPCs. This adaptation process can be carried out in the same FPGA in charge of performing the DPD function, or alternatively can be performed by an external device (i.e. a DSP device) in a different time-scale than real-time operation.To support all the theoretical design and to prove the linearization performance achieved by this new DPD, simulation and experimental results are provided. Moreover, some issues derived from practical experimentation, such as power consumption and efficiency, are also reported and discussed within this thesis.

This dissertation studies the design of an efficient adaptive digital baseband predistorter for modern cellular handsets that combines low power consumption, low implementation complexity, and high performance. The proposed enhancements are optimized for hardware implementation. We first present a thorough study of the optimal spacing of linearly-interpolated lookup table predistorters supported by theoretical calculations and extensive simulations. A constant-SNR compander that increases the predistorter's supported input dynamic range is derived. A corresponding low-complexity approximation that lends itself to efficient hardware design is also implemented in VHDL and synthesized with the Synopsys Design Compiler. This dissertation also proposes an LMS-based predistorter adaptation that is optimized for hardware implementation and compares the effectiveness of the direct and indirect learning architectures. A novel predistorter design with quadrature imbalance correction capability is developed and a corresponding adaptation scheme is proposed. This robust predistorter configuration is designed by combining linearization and I/Q imbalance correction into a single function with the same computational complexity as the widespread complex-gain predistorter.

L'amplificateur de puissance est le module le plus critique dans les équipements de communication radio. Il détermine la qualité de la liaison par sa linéarité et a une contribution conséquente dans la consommation de l'émetteur ; environ 60% de l'énergie consommée est consacré à l'amplification. Il est donc crucial de le faire fonctionner avec un rendement énergétique élevé. Cependant, ces deux spécifications principales de l'amplificateur que sont la linéarité et le rendement énergétique sont antagoniques. Par conséquent, la conception d'un module d'amplification de puissance suppose de trouver un compromis entre la linéarité et le rendement. L'optimisation de ce compromis est la raison d'être des techniques de linéarisation d'amplificateurs et d'amélioration du rendement, parmi lesquelles la prédistorsion numérique (DPD) et les techniques de réduction du PAPR du signal (CFR).Le cœur de cette thèse est la linéarisation d'amplificateurs RF haute-puissance et large-bande par prédistorsion numérique (DPD). Dans ces travaux, nous abordons trois problématiques liées à la prédistorsion et qui constituent des verrous technologiques importants. Le premier aspect concerne l'implémentation de la prédistorsion numérique dans un contexte multi-bande où le signal à linéariser comporte plusieurs formes d'ondes, situées à des fréquences différentes. La seconde problématique est l'utilisation conjointe de la prédistorsion avec une technique de CFR. Dans la majorité des applications haute-puissance, les techniques de DPD et de CFR sont présentes de manière complémentaire, cependant elles sont utilisées de façon autonome et disjointe. Celles-ci gagneraient en performances de linéarisation en étant implémentées de manière plus concertée. . Le dernier thème abordé par cette thèse est l'effet des désadaptations d'impédance de l'antenne sur le mode de fonctionnement de l'amplificateur. La variation de l'impédance d'antenne entraine des réflexions de signal vers l'amplificateur qui modifient ses spécifications de linéarité et de rendement. Nous améliorons la linéarité du système DPD + AP, lorsque l'amplificateur est soumis à des variations de l'impédance à sa charge, grâce à une correction adaptative de gain / Power amplifier is one of the most critical element within radiocommunications systems. The PA is their main source of nonlinearities and it has a great contribution on the emitter's power consumption. Running the PA with highest power efficiency is thus as crucial as having it linear for a good communication quality. However these two specifications of the PA are antagonistic and PA manifacturers need to find a compromise between linearity and power efficiency. Digital Predistortion (DPD) and Crest factor Reduction techniques are intended to improve power efficiency while preserving linearity or inversely. Linearization of wideband RF power amplifiers using Digital Predistortion is the focus of this thesis. Three DPD issues are investigated in these works. The first issue deals with multiband linearization where signals with various waveforms located at different frequency bands are amplified. The second objective of this thesis is to study a concurrent DPD/CFR systems based on an automatic estimation of the necessary CFR gain. The last part of this dissertation deals with PA linearization under antenna load variations. Indeed, the impedance of antenna may vary because of electromagnetic objects that are present in its vicinity. Those impedance variations may instigate signal reflections toward the PA, that modify some of its main specifications (linearity, delivered power and efficiency). Our goal in this field is to preserve DPD linearization performances under antenna load mismatch