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In this article, we propose a CMOS active balun targeting high linearity up to high voltage swing and over wide bandwidth for direct RF sampling applications. All the blocks of this active balun are derived using a common highly linear building block (HLBB). The HLBB is designed using an inverter with strong source degeneration. To increase the linearity of this HLBB further, its nonlinearity mechanisms are analyzed in detail. A bootstrapping technique is included in the HLBB to reduce the dominant nonlinearity. Furthermore, a pre-distortion technique cancels most of the non-linearity of the output driving stages. All the linearization techniques proposed are robust to process, voltage, and temperature (PVT) changes. The measured results of the active balun realized on-chip in a 22-nm FDSOI CMOS shows < - 44-dBc third harmonic distortion (HD3) up to 1.5- V p-p output swing over 0.01-5.4 GHz. The measured gain and phase errors of the balun action are less than 0.5 dB and ± 5, respectively. The chip is powered from a 5-V supply and dissipates 925 mW.

The satellite navigation system can provide high-precision navigation, positioning and timing services for all kinds of users around the world. Navigation signal quality is an important factor affecting system service performance. The transmission channel of navigation load has non-ideal characteristics, which will cause the change of navigation signal amplitude frequency characteristic and phase frequency characteristic. Therefore, the channel characteristics need to be compensated by means of pre-distortion. BDS-3 satellite is equipped with a pre-distortion filter in the digital segment. However, due to the limited resources on-board and the low accuracy of broadband pre-distortion algorithm. It is difficult for the navigation signal quality to converge to the index range in the process of pre-distortion adjustment. A piecewise high-precision predistortion method based on spaceborne digital filter is designed. Based on the existing parameters of the wideband filter, the pred-istortion compensation is carried out dynamically and elaborately according to the weights and adjustment requirements, which makes the key indexes of attention converge with higher precision. This method has been verified by 20 satellites in orbit and is an important technical means for in-orbit navigation signal quality optimization.

Mutual interference is a crucial issue for the visible light communication (VLC) systems to be addressed, including both co-channel interference (CCI) and inter-carrier interference (ICI). In this paper, to solve the CCI problem, a novel optical attocell network is introduced, which can be regarded as a hybrid network based on both single frequency network and multi-frequency network. Meanwhile, to eliminate the ICI, a pre-distorted enhanced asymmetrically clipped DC biased optical orthogonal frequency division multiplexing (PEADO-OFDM) approach is designed. In addition, the corresponding properties of PEADO-OFDM are analyzed, and different modulation schemes are employed for downlink and uplink in the same ADO-OFDM modulation framework to reduce the complexity of user processing. Simulation results indicate that the proposed PEADO-OFDM scheme outperforms the conventional ADO-OFDM approach in terms of bit error rate, while the processing latency and computational complexity are greatly reduced at the receiver.

The slides review applications of machine learning to the nonlinearity mitigation in the physical layer of optical telecommunications. The applications are grouped around the three use cases: equalization, pre-distortion, and end-to-end learning. Particular attention is brought to multi-stage neural-network-based nonlinearity equalizers and end-to-end learning of the long-haul high-baudrate fiber-optic communication links., This presentation was given as part of the ECOC'21 workshop "How machine learning can revolutionize optical fiber communications?" (https://www.ecoc2021.org/programme/programme-monday#mo1b-ws)

In this paper, an adaptive modulation scheme for visible light communication (VLC) system based on partially pre-distorted layered asymmetrically clipped optical orthogonal frequency division multiplexing (LACO-OFDM) is proposed. The clipping noise that falls on the higher layers in the conventional LACO-OFDM results in inter layer interference, which can be eliminated by the operation of pre-distortion at the expense of extra power consumption. The proposed partially pre-distorted scheme makes a tradeoff between error propagation and power cost to suit different transmission environments. The probability distribution functions of the conventional and pre-distorted LACO-OFDM schemes are analyzed and compared and the layers that should be pre-distorted in the proposed scheme is decided adaptively by maximizing the achievable rate. The computational complexity of the proposed scheme is also investigated, which is acceptable compared with the previous schemes. Simulation results show that the proposed scheme has a superior bit error rate performance compared with the conventional and pre-distorted LACO-OFDM schemes.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the key modulations for current and novel broadband communications standards. For example, Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) is an excellent choice for the ECMA-368 Ultra Wide-band (UWB) wireless communication standard. Nevertheless, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals reduces the power efficiency of the key element in mobile devices, the High Power Amplifier (HPA), due to non-linear distortion, known as the non-linear saturation of the HPA. In order to deal with this limiting problem, a new and efficient pre-distorter scheme using a Neural Networks (NN) is proposed and also implemented on Field Programmable Gate Array (FPGA). This solution based on the pre-distortion concept of HPA non-linearities offers a good trade-off between complexity and performance. Some tests and validation have been conducted on the two types of HPA: Travelling Wave Tube Amplifiers (TWTA) and Solid State Power Amplifiers (SSPA). The results show that the proposed pre-distorter design presents low complexity and low error rate. Indeed, the implemented architecture uses 10% of DSP (Digital Signal Processing) blocks and 1% of LUTs (Look up Table) in case of SSPA, whereas it only uses 1% of LUTs in case of TWTA. In addition, it allows us to conclude that advanced machine learning techniques can be efficiently implemented in hardware with the adequate design. This work was partly funded by projects TERESA-ADA (TEC2017-90093-C3-2-R) (MINECO/ AEI/FEDER, UE) and MFOC (Madrid Flight on Chip—Innovation Cooperative Projects Comunidad of Madrid—HUBS 2018/MadridFlightOnChip).

Organic photo-detector (OPD) is lightweight and physically flexible. It can transform plastic or glass into smart surfaces. Visible light communication (VLC) is considered as one of the promising technologies for the future wireless communications. VLC combines the advantages of lighting and communication simultaneously. Besides, it can be deployed using existing lighting infrastructure; hence little extra cost is needed to provide this wireless communication. As the OPD has a large optical detection area, it would be interesting to employ the OPD as VLC receiver (Rx). If the OPD can be used in the VLC systems, it can benefit the Internet-of-Thing (IoT) networks by providing efficient human-to-machine and machine-to-machine communications. However, implementing VLC using OPD Rx is challenging. Due to the slow charging and discharging processes of the OPD, the optical-to-electrical response speed is limited. Besides, the OPD requires external bias to be operated. Here, we propose and demonstrate using pre-distortion scheme for pulse-amplitude-modulation (PAM) signal to a self-powered PCBM:P3HT OPD to enhance the VLC transmission performance. The operation of the self-powered PCBM:P3HT OPD is discussed. Both experiments using PAM-2 and PAM-4 (with and without pre-distortion) are evaluated. The performance, requirement and capability limitations of the pre-distortion schemes are also analyzed and discussed by using numerical simulations.

In this paper, a low-complexity symbol-based equalizer that performs non-linear distortion cancellation is proposed for application at the user terminal in the DVB-S2X satellite forward link. The channel is comprehensively modeled, including the non-linear travelling wave tube amplifier characteristics, the input-multiplexing and output-multiplexing filter responses at the satellite transponder, and the phase noise at the user terminal, according to the very-small aperture terminal reference scenario. Two detectors in the cancellation loop are considered, comparing the packet-error rate (PER) performance of simple maximum likelihood demodulation with hard decision to soft information exchange with low-density parity-check decoder, and showing only marginal improvement with the latter solution. The PER performance is compared against a number of pre-distortion techniques at the transmitter, such as dynamic data pre-distortion, successive data pre-distortion, and static data pre-distortion. The novel receiver demonstrates superior performance even with one iteration of distortion cancellation, while the joint application of successive data pre-distortion and iterative symbol-based equalization shows up to 4.95-dB energy efficiency gain for 32-level amplitude and phase-shift keying (32-APSK). The computational complexity is also evaluated. The improved receiver is particularly suitable for application with higher order modulation, a wide-band carrier, and low roll-off factors.

In this paper, we propose and experimentally demonstrate an optical self-interference cancellation (OSIC) system with baseband predistortion for wideband over-the-air in-band full-duplex (IBFD) communication. The key factors of OSIC bandwidth limitation are analyzed, and the solution toward it is proposed for the first time. Experimental results show that, by traditional OSIC under over-the-air condition, only narrow even zero band is with enough cancellation depth to satisfy IBFD. But with our proposed baseband predistortion scheme, deep OSIC depth is achieved over the whole 1 GHz/5 GHz baseband within the total 7–25 GHz available band of horn antennas. The employment of baseband predistortion obviously broadens the cancellation bandwidth of an EML-based OSIC system. The largest OSIC bandwidth for over-the-air IBFD communication is demonstrated so far.

This paper describes a 15.6-18.2GHz fractional-N bang-bang digital PLL fabricated in 28nm CMOS. To compensate for the nonlinearity of the digital-to-time converter and reduce the level of fractional spurs, two alternative predistortion techniques are introduced. The adoption of those algorithms operating continuously in background is demonstrated to reduce the level of the in-band fractional spur at 300kHz from −20dBc to −57dBc and −63dBc, respectively. The fabricated PLL achieves FoM of −237.2dB.

Esta dissertação descreve, inicialmente, um sistema implementado em FPGA para a geração de modulações digitais. Posteriormente, descreve uma plataforma capaz de realizar a estimação de modelos com coeficientes lineares e demonstra aplicações de pré-distorção. O trabalho começa com uma breve visão sobre os conceitos básicos envolvidos na dissertação. É descrito como se comportam os sinais e os sistemas no domínio discreto, é feito um resumo sobre o que é um FPGA e, após isso, são analisadas figuras de mérito, ferramentas matemáticas utilizadas para medir a qualidade dos modelos. No capítulo 3, é apresentada uma ferramenta em FPGA capaz de gerar sinais com diversas modulações digitais que serão utilizadas na identificação e pré-distorção. No capítulo 4 é abordado a construção e validação de um algoritmo de estimação eficiente utilizando o método de Mínimos Quadrados. A identificação de um filtro, utilizando um sinal de trem de impulsos, é mostrado na seção 4.2. A resposta do filtro no domínio da frequência é comparada com a resposta medida por um equipamento comercial, onde os resultados mostram que o modelo obtido representa bem um filtro real. A criação de um modelo de pré-distorção é mostrado no capítulo 5. A qualidade do modelo é avaliada por quatro Figuras de Mérito diferentes. As conclusões sobre o trabalho e as pesquisas futuras são apresentadas no último capítulo. This work describes initially a system implemented in FPGA for the generation of a digital modulations. After, it describes a platform capable of performing the estimation of a device under test. Finally, it shows applications of this platform for pre-distortion purposes. A brief overview of the basic concepts involved in the dissertation are presented, as signals and systems in the discrete domain, FPGA, and Figures of Merit, tools used to measure the quality of the models. In chapter 3, a FPGA tool capable of generating signals with various digital modulations is presented. This platform will lately be used for identification and pre-distortion purposes. Chapter 4 shows the construction of efficient estimation algorithm using the Least Squares method. The identification of a filter using a pulse wave signal is shown in the section 4.2, and the resulting frequency domain curve is compared to that generated by a commercial equipment, where results show that the estimated model represents well a real filter. A pre-distortion model of a filter is shown in the chapter 5. The quality of the model is evaluated by four different Figures of Merit. Conclusions about the work and future research are drawn in the last chapter.

Ultra WideBand (UWB) over fiber is a promising technology for meeting the demands of future wireless local-area networks (WLANs) and wireless personal-area networks (WPANs). Thanks to the enormous bandwidth and fiber characteristics, a high communication quality may be established at long reach. UWB wireless propagation must be achieved with special power and spectral constraints fixed by the regulatory bodies (e.g. US Federal Communication Commission). The novelty of our work originates from exploiting the benefits of a Semiconductor Optical Amplifier (SOA) so as to get a reach extension at limited cost and complexity. However, the inherent nonlinear effects and Amplified Spontaneous Emission (ASE) noise associated to such device may affect the system performance.Overcoming these impairments has been of central importance in this study. SOA nonlinearities have been mitigated by applying analog pre-distortion in electrical domain. Phaser-based processing was also proposed to simultaneously reduce ASE influence and linearize SOA characteristics, thanks to up/down chirping performed on the transmitter/receiver sides. With Impulse Radio UWB transmission, due to the time properties of modulation patterns, discrete lines arise in the corresponding spectrum, which may violate FCC limit or reduce the power efficiency. A new shape randomization technique has been investigated, which proved to be effective in suppressing these spectral spikes. The three approaches have shown a great potential with On Off Keying and Pulse Position Modulation formats at long optical reach.The performance of Differential Chaos Shift Keying was finally examined in the over fiber system, a lower error probability was experimentally achieved in comparison with other non-coherent modulations.; La technologie Ultra WideBand (UWB) sur fibre est une solution prometteuse pour répondre aux enjeux des futurs réseaux de communication WLAN/WPAN. Les caractéristiques de la fibre, incluant son énorme bande passante, offrent la possibilité d'une bonne qualité de service à longue portée. La propagation sans-fil UWB doit être réalisée sous des contraintes de densité spectrale de puissance particulières, imposées par l'autorité de régulation (FCC pour les Etats-Unis). La nouveauté de notre travail provient de I' exploitation des avantages d'un amplificateur optique à semi-conducteurs (SOA) afin d'obtenir une extension de portée à un coût et une complexité limités. Cependant, les effets non linéaires et le bruit d'émission spontanée amplifiée (ASE), intrinsèques à ce type de composant, sont susceptibles de dégrader la performance du système. La réduction de ces effets indésirables a donc été d'une importance centrale dans cette étude. Les non-linéarités du SOA ont été compensées en appliquant une solution de pré-distorsion analogique des formes d'ondes électriques. Un traitement basé sur phaser a également été proposé pour réduire simultanément I' influence de I'ASE et linéariser les caractéristiques du SOA, grâce à des opérations de chirping réparties entre l'émetteur et le récepteur. Avec la transmission Impulse Radio, en raison des propriétés temporelles des formats de modulation, des raies spectrales apparaissent, ce qui peut violer la limite FCC ou réduire I' efficacité énergétique. Une nouvelle technique de randomisation de formes d'ondes a été étudiée, qui s'est révélée efficace pour supprimer ces pics spectraux. Les trois approches ont montré un grand potentiel avec les formats On Off Keying et Pulse Position Modulation, à longue portée optique. Les performances d'une modulation différentielle Chaos Shift Keying ont finalement été examinées; une probabilité d'erreur inférieure a été obtenue expérimentalement en comparaison avec d'autres modulations non cohérentes.

This paper describes a novel scheme for the fusion of spectrum sensing information in cooperative spectrum sensing for cognitive radio applications. The scheme combines a spectrum-efficient, pre-distortion-based fusion strategy with an energy-efficient censoring-based fusion strategy to achieve the combined effect of reduction in bandwidth and power consumption during the transmissions of the local decisions to the fusion center. Expressions for computing the key performance metrics of the spectrum sensing of the proposed scheme are derived and validated by means of computer simulations. An extensive analysis of the overall energy efficiency is made, along with comparisons with reference strategies proposed in the literature. It is demonstrated that the proposed fusion scheme can outperform the energy efficiency attained by these reference strategies. Moreover, it attains approximately the same global decision performance of the best among these strategies.

This work proposes a novel pre-distortion technique for the quantization noise cancellation of fractional-N frequency synthesizers. The proposed technique utilizes the coordinate rotation digital computer (CORDIC) algorithm to pre-distort the baseband signal of a wireless system with the quantization noise. The pre-distorted signal then modulates the noisy output signal of the fractional-N frequency synthesizer. The transmitter (Tx) modulation quality is thereby improved. In the receiver (Rx) mode, the phase noise of the Rx carrier signal can also be improved by modulation with a pre-distorted sinusoidal signal rather than a baseband signal. Experimental results demonstrate that the novel pre-distortion technique effectively improves the modulation quality of a Tx by an error vector magnitude (EVM) of about 10 % under a 13 Mbps QPSK modulation. The carrier in-band and out-band phase noise of the fractional-N frequency synthesizer is improved by approximately 6 dB and 10 dB, respectively.

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. Fourth-generation (4G) communication systems based on orthogonal frequency division multiplexing (OFDM) and the proposed backwards compatible fifth-generation (5G) variants, like filter-bank multicarrier (FBMC), are based on modulation techniques that allow significantly increased spectral efficiency and capacity in mobile radio access networks (RANs). However, the use of these modulation techniques impacts the requirements of the radio base stations, which have been traditionally the most energy-consuming element of mobile networks, accounting for up to 80% of the energy consumption of RANs [1]. Non-constant envelope-modulation techniques with high peak-to-average power ratios (PAPRs) require highly linear power amplifier (PA) amplitude and phase responses to fulfill stringent spectral mask and modulation accuracy requirements. This is often achieved with significant PA back-off, which considerably reduces PA efficiency because the PA's maximum efficiency is achieved near the saturation point.

宇宙応用シンポジウム(2012年6月28-29日, JAXA筑波宇宙センター), つくば市, 茨城県, Space applications symposium (June 28-29, 2012.Tsukuba Space Center, JAXA ),Tukuba,Ibaraki, Japan, 資料番号: ARDS12012000

This work proposes a novel pre-distortion technique for the quantization noise cancellation of fractional-N frequency synthesizers. The proposed technique utilizes the coordinate rotation digital computer (CORDIC) algorithm to pre-distort the baseband signal of a wireless system with the quantization noise. The pre-distorted signal then modulates the noisy output signal of the fractional-N frequency synthesizer. The transmitter (Tx) modulation quality is thereby improved. In the receiver (Rx) mode, the phase noise of the Rx carrier signal can also be improved by modulation with a pre-distorted sinusoidal signal rather than a baseband signal. Experimental results demonstrate that the novel pre-distortion technique effectively improves the modulation quality of a Tx by an error vector magnitude (EVM) of about 10 % under a 13 Mbps QPSK modulation. The carrier in-band and out-band phase noise of the fractional-N frequency synthesizer is improved by approximately 6 dB and 10 dB, respectively.

In order to achieve better performance of modern communication devices, that have to be operated on its physical limits, the nonlinear phenomena need to be taken into the account. This thesis brings insight into two different subjects related with nonlinear dynamical phenomena. The thesis itself is divided into two parts : the first part is focused on the domain of nonlinear power amplifiers from the system point of view. Several methods for modelization and linearization of power amplifiers have been designed and discussed. A test-bench has been assembled in order to evaluate the proposed methods on real power amplifiers. Then the robustness to time misalignment in the system and the ability to deal with spectral artifacts in the system of presented methods have been evaluated. Also a theoretical study has been conducted on the existence and management of multiple solutions in the frame of adaptive indirect learning approach. The second part deals with nonlinear dynamical systems that are exhibiting chaotic solutions. Such systems are well known, but techniques for identifying reliable such solutions are either missing or are computational intense. In this thesis several methods using also parallel computing are presented. Systems with fractional differential order are briefly discussed. It is as well shown, that there exists systems related with quantified nonlinear transfer functions for which the standard analyzing methods fails, L'augmentation des performances des futurs systèmes dynamiques nécessite la prise en compte des phénomènes physiques non linéaires. Cette thèse apporte un éclairage et des contributions sur deux sujets complémentaires liés aux phénomènes dynamiques non linéaires. Le mémoire de thèse est divisé en deux parties.La première partie porte sur les non-linéarités des amplificateurs de puissance dans le cadre d'applications destinées aux télécommunications ou à la diffusion audio-visuelle. Plusieurs méthodes de modélisation et de linéarisation des amplificateurs de puissance ont été conçues et discutées. Un banc de test a été développé afin d'évaluer les méthodes sur des amplificateurs réels. La robustesse de ces techniques à un mauvais alignement temporel des signaux ainsi que leur capacité à faire face à des artefacts spectraux ont été évaluées. Par ailleurs, nous avons effectué une étude théorique sur l'existence et la prise en compte de solutions multiples dans l'approche adaptative par apprentissage indirect. La deuxième partie traite des systèmes dynamiques non linéaires qui présentent des solutions chaotiques. Ces systèmes sont bien connus, mais les techniques d'identification de ces solutions manquent de fiabilité ou nécessitent une puissance de calcul importante. Dans cette thèse, plusieurs méthodes utilisant également le calcul parallèle sont présentées. Les systèmes à commande différentielle fractionnaire sont brièvement discutés. Il est aussi montré, qu'il existe des systèmes liés à des fonctions de transfert non linéaires avec quantification pour lesquels les méthodes d'analyse classiques échouent

In this paper the innovative time-domain pre-distortion method is proposed. This method (PWM-RC) uses raised-cosine (RC) pulse shaping and pulse-width modulation (PWM) scheme to achieve better output channel data response. The conventional pre-distortion methods based on finite impulse response (FIR) filtering are not compatible with modern low-power CMOS design. Existing perspective time-domain pre-distortion methods show many high frequency harmonic components in the pre-emphasized signal. It can cause more system crosstalk susceptibility, where the additional pre-emphasis boosted the undesirable high frequency components. The proposed method reduces the content of higher harmonic components at the pre-emphasized output signal and ISI (inter-symbol interference) effects. Advantageous properties of the PWM scheme such as high channel loss compensation are preserved. Finally, the simulation results realized in MathCAD and ADS Agilent Development Studio are introduced.

This work presents the synthesis, design and testing of a fourth-order Chebyshev predistorted filter centred at 20 GHz and with 300 MHz bandwidth, implemented in substrate integrated waveguide (SIW) technology. Although the dielectric material adopted in this work allows for obtaining SIW resonators with a quality factor Q = 500, the use of predistortion permits to realise a filter response with an in-band flatness equivalent to a filter with Q = 2000, not achievable otherwise with the adopted material in SIW technology. Additionally, this work presents the design and testing of a conventional SIW filter (without predistortion) implemented with the same dielectric material. Comparison of the measured filter responses demonstrates the benefits of using predistortion technique in SIW technology for achieving improved performance at high frequency.

A new and simple Power Amplifier (PA) linearization method is proposed and demonstrated using a very high efficiency yet inherently nonlinear inverse class-F PA. This was conducted in the presence of a generic variable envelope RF signal in order to extract its AM-AM and AM-PM characteristics. Deducing the polynomial pre-distortion parameters from the AM-AM and AM-PM characteristic has resulted in the successful linearization of the PA in the presence of 3GPP Long Term Evolution (LTE) signals. The results obtained for the PA - a 12W GaN HEMT inverse Class-F structure designed to operate at 900MHz - demonstrate the proof of concept and the efficiency of the proposed linearization technique with significant advantageous reduction in base-band resources for 3GPP LTE applications. A new and simple power amplifier (PA) linearization method is proposed and demonstrated using a very high efficiency yet inherently nonlinear inverse class-F PA. This was conducted in the presence of a generic variable envelope RF signal in order to extract its AM-AM and AM-PM characteristics. Deducing the polynomial pre-distortion parameters from the AM-AM and AM-PM characteristic has resulted in the successful linearization of the PA in the presence of 3GPP long term evolution (LTE) signals. The results obtained for the PA - a 12 W GaN HEMT inverse class-F structure designed to operate at 900 MHz - demonstrate the proof of concept and the efficiency of the proposed linearization technique with significant advantageous reduction in base-band resources for 3GPP LTE applications.

The aim of the research accomplished in this thesis is to introduce linearization techniques applied to power amplifier for broadband radio- ommunications. In this context, we put forward base-band adaptive pre-distortion techniques using neural networks. After showing the non-linear behavior of power amplifier on both the spectrum and the transmitted signal quality, the classic techniques of linearity improvement are introduced. In the second section, neural networks are presented in particular the multilayer perceptrons as well as their learning techniques. Next, we defined the necessary steps for the establishment of a neural pre-distortion architecture able to offer very good performances within a reasonable complexity forthe non-linearity’s compensation of stationary and memoryless power amplifier, in the context of OFDM systems. The pre-distortion architecture chosen proved good performances in terms of the error rate reducing even with relatively low values of IBO. It equally proved a good correction of the transmitted signal quality in both inside and outside his band. The performance degradation correction following the non-stationary behavior ofpower amplifier has been stressed. Hence, a new architecture of adaptive predistortion has been proposed which allowed to obtain good performances using Levenberg-Marquard algorithm that proved to be the most efficient compared to several other algorithms, in terms of reducing time to adapt to power amplifier behavior changes while noting a reduced complexity. The obtained simulation results justify this hypothesis.Finally, a theoretical analysis allowed to highlight the dispersion origins in the power amplifier response and led to the emergence of new neural architecture of predistortion able to take into account memory effects. This survey concludes with some perspectives for research able to extend the work done during this thesis., Les travaux de recherche menés dans cette thèse de doctorat ont visé l’étude et la mise en œuvre des techniques de linéarisation d’amplificateurs de puissance destinés aux émetteurs radiofréquences à large bande. Dans ce cadre, nous avons proposé des techniques de pré-distorsion adaptative en bande de base en utilisant les réseaux de neurones. Après avoir montré les conséquences du comportement non linéaire de l’amplificateur sur le spectre et la qualité du signal transmis, les techniques classiques d’amélioration de la linéarité sont présentées. Dans une deuxième partie, les réseaux de neurones sont présentés et en particulier les perceptrons multicouches sans oublier également les techniques d’apprentissage de ces derniers. Ensuite, nous avons défini les étapes nécessaires pour l’établissement d’une architecture neuronale de pré- istorsion capable d’offrir de très bonnes performances avec une complexité raisonnable pour la compensation des non-linéarités d’un amplificateur considéré stationnaire et sans mémoire, dans le contexte des systèmes de communication OFDM. L’architecture de pré-distorsion choisie a montré de très bonnes performances en terme de réduction du taux d’erreur dans la transmission même avec des IBO assez faibles. Elle a montré également une bonne correction du signal à l’intérieur de sa bande utile et en dehors de celle-ci. La dégradation des performances de correction suite à la non-stationnarité de l’amplificateur de puissance a été soulignée. Ainsi, une nouvelle architecture de pré-distorsion adaptative a été proposée. Cette architecture a permis d’obtenir de bonnes performances en utilisant l’algorithme de Levenberg-Marquardt qui s’est avéré le plus efficace, par rapport à plusieurs autres algorithmes, en terme de réduction du temps d’adaptation aux changements du comportement de l’amplificateur tout en notant une complexité réduite. Les résultats de simulation obtenus justifient cette hypothèse. Finalement, une analyse théorique a permis de mettre en évidence les origines de dispersion dans la réponse de l’amplificateur de puissance et a conduit à proposer de nouvelles architectures neuronales de pré-distorsion capables de tenir compte des effets de mémoire. Ce mémoire se conclut par quelques perspectives de recherche pouvant prolonger les travaux accomplis durant cette thèse.

The antagonism between information capacity and energetic fficiency in the context of wireless communications, more precisely : the trade-off between transmitter linearity and its efficiency ; is the main driver of this thesis. A FPGA5-based architecture for digital predistortion (DPD) linearizers for RF power amplifiers is proposed in this thesis. By means of separating the adaptation process from the predistortion itself, a convenient, simple hardware building block for the DPD architecture inside the FPGA -the Basic Predistortion Cell (BPC)- has been identified. A BPC-based architecture provides independency from the particular DPD function derivation method, and it is easily scalable and reconfigurable, depending on the operation mode and degree of impairments introduced by the transmitter chain in each particular case. In order to support those claims and provide experimental evidence, two main different prototyping scenarios have been developed. In the first one, a DPD adaptive linearizer based on the passivity theory (hyperstable systems) has been designed and implemented on a low-cost mixed FPGA/DSP6 platform. Besides experimental results, complementary signal proces- sing techniques to DPD are also addressed, thus giving a wide insight on realistic scenarios of DPD systems. In the second scenario, an advanced, adaptive DPD system aimed at compensa- ting not only PA's nonlinear behavior, but also its memory effects, is presented. It is based on a Nonlinear Auto-Regressive Moving Average structure which is mapped into hardware using a BPC grid-structure. Besides the experimental results on PA efficiency and linearity, FPGA implementation issues -such as adaptation and power consumption- are also studied. The manipulation of the PA class of operation to improve its efficiency, provided that DPD may be unavoidable due to the impact of memory effects, is discussed as well. Finally, to further improve efficiency, a DPD linearizer with dynamic supply built-in cap abilities has been proposed and implemented as discussed in the last part of this thesis. There, an efficient, bandwidth limited, switched DC-DC converter is in charge of the PA supply modulation. The thorough design procedure targeting a FPGA implementation shows how the necessary functions for commanding the supply modulator can be seamlessly integrated within the DPD processor. The experimental results highlight how the proposed solution maintains linearity and enhances the PA efficiency when compared to a DPD-only method.; L'antagonisme entre la capacité d'émission d'informations haut débit (linéarité) et le rendement énergétique, dans le contexte des émetteurs radio, est l'axe des travaux de cette thèse. Nous proposons une architecture matérielle basé sur circuits FPGA1 pour l'implémentation de fonctionnalités de prédistorsion numérique (DPD) pour la linéarisation d'amplificateurs RF. Nous articulons nos approches à partir de la séparation entre les processus de prédistorsion et d'adaptation. Ainsi, nous pouvons proposer une structure matérielle -le BPC2 ou Cellule Basique de Predistorsion- bien adaptée pour l'implémentation du module de prédistorsion. Le module de prédistorsion basé sur BPC peut être reconfigurable au besoin, et, en plus, il reste indépendant de la méthodologie particulière de dérivation de la fonction de prédistorsion. Afin d'effectuer des validations, deux prototypes permettant de tester des stratégies de prédistorsion performantes et novatrices ont été mis en oeuvre. Dans un premier temps, nous avons implémenté un système DPD basé sur la théorie des systèmes hyperstables sur une plateforme mixte FPGA/DSP3. En complément des résultats expérimentaux, nous rentrons dans le détail des fonc- tions complémentaires à la prédistorsion et l'adaptation nécessaires pour produire la prédistorsion. Le deuxième prototype adresse la linéarisation et la compensation des e®ets mémoire de l'amplificateur RF. Nous présentons et validons expérimentalement une structure de prédistorsion du type NARMA4, implémentée au moyen d'un réseau de cellules BPC. Au passage, nous étudions la consommation de la prédistorsion et son impact sur le rendement. Si l'utilisation de la prédistorsion s'avére inévitable pour contrer les effets mémoire, nous proposons de dégrader la Classe de l'am- plificateur, dans le but d'obtenir un émetteur aussi linéaire mais plus performant énergétiquement. Finalement, au delà de la prédistorsion seule, nous proposons, analysons et va- lidons expérimentalement un sys tème de prédistorsion + commande dynamique de l'alimentation de l'amplificateur RF. La structure de traitement du signal numérique développée, permet de : 1/prédistordre le signal et 2/commander des modulateurs d'amplitude lents (par rapport à la largeur de bande de l'application cible, mais ayant de forts rendements de conversion). L'inclusion de capacités de pilotage de l'alimentation autour de la prédistorsion s'avère peu coûteuse et permet d'atteindre des rendements améliorés sans perte de linéarité.

Spectrally pure signals are an indispensable requirement when the Signal Generator (SG) is to be used as part of a test bed. However, even sophisticated equipment may not comply with the needs imposed by certain applications. This work approaches the problem by using Digital Pre-Distortion (DPD) based on a polynomial memory-less model obtained for the SG. Using the SG in arbitrary mode (ARB) an input signal is computer-generated and reproduced by the SG. Measurement accuracy is ensured using coherence sampling and grid matching to the Signal Analyzer (SA). Finally, careful time alignment is used to compare the transmitted and received three-tone signals to obtain the polynomials coefficients. Results show that the accuracy of the model and the effectiveness of pre-distortion may vary depending on the amplitude of the three-tone signal. However, using polynomials of 5th and 9th degrees up to 15dB reduction of the 3rd order Inter-Modulation products can be obtained, and spurious powers may be lowered down to 70dBc.

Gran parte de los nuevos estándares para sistemas de comunicación digital, concebidos para superar la creciente demanda por mayores velocidades de transmisión y niveles de eficiencia espectral, consideran el uso de modulaciones de amplitud no constante tales como M-QAM en formatos de OFDM. Una de las limitaciones más críticas para el funcionamiento de estos sistemas es la distorsión no lineal típicamente introducida por los amplificadores de alta potencia presentes en la cadena de transmisión. Este artículo resume la propuesta de un algoritmo de procesado de señal para la estimación adaptativa de la característica inversa de ganancia compleja de un amplificador no lineal en un esquema de pre/post-distorsión. Algunos resultados de simulaciones son presentados a fin de evaluar la efectividad del proceso de linealización propuesto y considerar posibles líneas futuras de investigación. Many of the new digital communication standards, conceived to overcome the ever greater demands on bit rate capacity and spectral efficiency, consider the use of non-constant amplitude modulations such as M-QAM in OFDM formats. One of the major limitations on the performance of such systems is the non linear distortion typically introduced by high power amplifiers (HPA) in the transmission chain. This paper summarizes the proposal of a new signal processing algorithm for the adaptive estimation of the complex gain characteristic of a nonlinear HPA, in a pre/post-distortion scheme. Some simulation results are presented in order to evaluate the effectiveness of this linearization procedure and future related research to consider.