Yes / The need to achieve high data rates in modern telecommunication systems, such as 5G standard, motivates the study and development of large antenna and multiple-input multiple-output (MIMO) systems. This study introduces a large antenna-order design of MIMO quasi-orthogonal space-time block code (QO-STBC) system that achieves better signal-to-noise ratio (SNR) and bit-error ratio (BER) performances than the conventional QO-STBCs with the potential for massive MIMO (mMIMO) configurations. Although some earlier MIMO standards were built on orthogonal space-time block codes (O-STBCs), which are limited to two transmit antennas and data rates, the need for higher data rates motivates the exploration of higher antenna configurations using different QO-STBC schemes. The standard QO-STBC offers a higher number of antennas than the O-STBC with the full spatial rate. Unfortunately, also, the standard QO-STBCs are not able to achieve full diversity due to self-interference within their detection matrices; this diminishes the BER performance of the QO-STBC scheme. The detection also involves nonlinear processing, which further complicates the system. To solve these problems, we propose a linear processing design technique (which eliminates the system complexity) for constructing interference-free QO-STBCs and that also achieves full diversity using Hadamard modal matrices with the potential for mMIMO design. Since the modal matrices that orthogonalize QO-STBC are not sparse, our proposal also supports O-STBCs with a well-behaved peak-to-average power ratio (PAPR) and better BER. The results of the proposed QO-STBC outperform other full diversity techniques including Givens-rotation and the eigenvalue decomposition (EVD) techniques by 15 dB for both MIMO and multiple-input single-output (MISO) antenna configurations at 10−3 BER. The proposed interference-free QO-STBC is also implemented for 16×NR and 32×NR MIMO systems, where NR≤2. We demonstrate 8 x 16 and 32 transmit antenna-enabled MIMO systems with the potential for mMIMO design applications with attractive BER and PAPR performance characteristics.

Yes / High Peak-to-Average-Power Ratio (PAPR) of transmitted signals is a common problem in broadband telecommunication systems using an orthogonal frequency division multiplexing (OFDM) modulation scheme, as it increases transmitter power consumption. In consumer applications where it impacts mobile terminal battery life and infrastructure running costs, this is a major factor in customer satisfaction. Companding techniques have been recently used to alleviate this high PAPR. In this paper, a companding scheme with an offset, amidst two nonlinear companding levels, is proposed to achieve better PAPR reduction while maintaining an acceptable bit error rate (BER) level, resulting in electronic products of higher power efficiency. Study cases have included the effect of companding on the OFDM signal with and without an offset. A novel closed-form approximation for the BER of the proposed companding scheme is also presented, and its accuracy is compared against simulation results. A method for choosing best companding parameters is presented based on contour plots. Practical emulation of a real time OFDM-based system has been implemented and evaluated using a Field Programmable Gate Array (FPGA).

Ce travail de thèse s'intéresse à l'optimisation des performances de transmissions multimédias par une approche originale combinant des circuits radiofréquences, tel que l'am-plificateur de puissance et les distorsions du canal de transmission. Les signaux OFDM sont très sensibles aux non-linéarités de l'amplificateur à cause des fortes fluctuations du niveau du signal, caractérisées par le PAPR. Afin de réduire le PAPR, on propose tout d'abord d'améliorer la méthode TR en termes de rapidité de convergence et de réduction du PAPR, en comparant plusieurs algorithmes d'optimisation. On montre que l'algorithme du gradient con-jugué offre les meilleures performances tout en respectant les spécifications fréquentielles du standard IEEE 802.11a. Par la suite, la méthode TR est évaluée expérimentalement en pré-sence d'un amplificateur de puissance (SZP-2026Z) en utilisant un banc de mesures. On montre ainsi que la méthode TR permet une amélioration de la qualité de transmission. Cette amélioration peut être utilisée pour modifier le point de fonctionnement de l'amplificateur et per-mettre ainsi une réduction de 18 % de la puissance consommée. Les résultats expérimentaux ont conduit au choix d'un modèle réaliste d'amplificateur en considérant les effets mémoires. Ce dernier a été intégré dans une chaîne de simulation SISO comprenant également un modèle réaliste de canal de transmission. La chaîne décrite a permis d'évaluer les performances de la méthode TR dans des conditions de transmission réalistes. Enfin, on propose d'appliquer la méthode TR dans une chaîne MIMO-OFDM en boucle fermée dédiée à la transmission de contenus multimédias scalables dans un environnement réaliste, en utilisant le standard IEEE 802.11n. Cette étude présente une évaluation originale de l'impact de la méthode TR sur la qualité visuelle des images transmises, en prenant en compte le contenu multimédia, la non-linéarité de l'amplificateur et les distorsions apportées par le canal. / In this thesis, we are interested on the performances optimization of multimedia transmissions systems with an original contribution combining RF circuits' imperfections presented by the power amplifier (PA) nonlinearities and the transmission channel distortions. The studied system uses the OFDM technique which is the most widespread multicarrier modulation in recent radio communications systems. However, its major drawback is the high PAPR value, which degrades the transmission quality due to the PA nonlinearities. To reduce the PAPR, we first propose to improve the TR method in terms of convergence speed and PAPR reduction, by studying several optimization algorithms. We show that the conjugate gradient algorithm provides the best performance while respecting the frequency specifica-tions of the IEEE 802.11a standard. Thereafter, TR method has been evaluated experimentally in the presence of a commercial PA (SZP-2026Z) and using a measurement bench. It is shown that the TR method improves the quality of service (QoS), with 18% reduction in PA power consumption. The experimental study has resulted to choosing a realistic PA model consider-ing memory effects. This PA model has been integrated into a SISO simulation chain includ-ing also a realistic channel model. This chain is used to evaluate the TR method performances under realistic transmission conditions. Finally, we propose to apply the TR method in a closed-loop MIMO-OFDM chain dedicated to the transmission of scalable multimedia con-tent in a realistic context with the IEEE 802.1n standard. This study presents a new contribu-tion of the TR method evaluation to improve the visual quality of the JPWL transmitted imag-es, considering in the same time the multimedia content, the PA nonlinearity and the channel transmission distortions.

Cette thèse porte sur l'optimisation des performances des systèmes de transmission multimédias MIMO-OFDM prenant conjointement en compte les imperfections de l'amplificateur de puissance et les distorsions du canal. Les fluctuations d'amplitude des signaux OFDM, caractérisées par un PAPR élevé, rendent la transmission vulnérable à la non-linéarité de l'amplificateur de puissance. On propose dans un premier temps une méthode permettant d'améliorer les performances de la méthode Tone Reservation en termes de gain de réduction du PAPR et de rapidité de convergence, en associant les échantillons de l'Intervalle de Garde aux Sous-Porteuses Nulles. Les simulations en présence d'un amplificateur de puissance à effets mémoire et d'un canal radio basé sur un modèle de propagation réaliste montrent que la méthode proposée offre de bonnes performances tout en respectant les spécifications fréquentielles, dans le cadre du standard IEEE 802.11a. Dans un second temps, on propose d'étudier l'impact de la non-linéarité dans un système MIMO-OFDM précodé dédié à la transmission d'images JPWL, respectant la norme IEEE 802.11n. On montre que la non-linéarité affecte la robustesse de transmission contre les erreurs de transmission et dégrade considérablement la qualité visuelle des images reçues. Enfin, on propose une stratégie de précodage originale prenant conjointement en compte l'amplificateur de puissance, le canal de transmission et le contenu de l'image à transmettre. Cette stratégie alloue successivement la puissance sur les sous-canaux SISO issus de la décomposition du canal MIMO afin de maximiser la qualité visuelle des images reçues tout en réduisant la puissance totale d'émission. Les résultats de simulation montrent que cette nouvelle stratégie qui considère un amplificateur et un canal réalistes, permet de garantir la robustesse de transmission et d'améliorer la qualité visuelle des images reçues. / This thesis focuses on the optimization of multimedia transmissions in MIMO-OFDM systems by jointly taking into account the power amplifier non-linearity and the wireless channel distortions. The OFDM modulation generates a high peak fluctuation, measured by the PAPR, which is affected by the RF non-linearity such as the power amplifier, reducing the transmission quality. We first propose a new method to improve the Tone Reservation method performances in terms of PAPR reduction gain and convergence speed, by including the samples of the Guard Interval Signal in the optimization algorithm. Simulations results using a power amplifier model with memory effects and a radio channel based on a realistic propagation model show that the new method offers the better performances, while respecting the IEEE 802.11a spectrum mask. Secondly, we propose to study the impact of power amplifier nonlinearity on the transmission of scalable image contents over a precoded Closed-Loop MIMO-OFDM system. The simulations in a realistic context, under the standard IEEE 802.11n standard show that the RF non-linearity affects the robustness against transmission errors and highly degrades the visual quality of the received JPWL images. Finally, we propose a new precoding strategy which jointly takes into account the power amplifier, the radio channel and the image content to be transmitted. This strategy successively allocates power between the SISO sub-channels obtained from the MIMO channel decomposition in order to maximize the visual quality of the received images, while reducing the total output power. Simulations with a realistic power amplifier model, associated with a realistic channel model show that this new strategy ensures a robust transmission and improves the visual quality of the received images.

Aujourd’hui, les systèmes MSPSR (Multi-Static Primary Surveillance Radar) passifs se sont installés de manière durable dans le paysage de la surveillance aérienne [1]. L’intérêt que suscitent ces nouveaux systèmes provient du fait qu’en comparaison aux radars mono-statiques utilisés actuellement, les systèmes MSPSR reposent sur une distribution spatiale d’émetteurs et de récepteurs offrant des avantages en termes de fiabilité (redondance), de coûts (absence de joints tournants et émetteurs moins puissants) et de performances (diversité spatiale). Toutefois, le défaut majeur du MSPSR passif réside en l’absence de formes d’ondes dédiées due à l’exploitation d’émetteurs d’opportunités tels que les émetteurs de radio FM (Frequency Modulation) et/ou de DVB-T (Digital Video Broadcasting-Terrestrial) [2]. Afin de pallier à ce défaut, il est envisagé d’utiliser des émetteurs dédiés permettant l’emploi de formes d’ondes optimisées pour une application radar, on parle alors de MSPSR actif. Cette thèse se place dans ce cadre et a pour objectif d’étudier et de définir la ou les formes d’ondes ainsi que les traitements associés permettant d’atteindre de meilleurs performances : une meilleure flexibilité sur la disposition du système (positionnement des émetteurs libres), une continuité de service (non dépendance d’un système tiers) et de meilleurs performances radars (e.g. en terme de précision des mesures, détections, …). Dans ce but, cette thèse étudie : - Les critères de sélection des codes : comportement des fonctions d’ambiguïtés, PAPR (Peak to Average Power Ratio), efficacité spectrale, etc... ; - Les formes d’ondes utilisées en télécommunication (scrambling code, OFDM) afin d’identifier leur possible réemploi pour une application radar ; - L’utilisation d’algorithmes cycliques pour générer des familles de séquences adaptées à notre problème ; - Une approche basée sur une descente de gradient afin de générer des familles de codes de manière plus efficiente ; - Et l’évaluation des performances de ces différents algorithmes à travers l’établissement d’une borne supérieure sur le niveau maximum des lobes secondaires et à travers le dépouillement des données enregistrées suite à des campagnes d’essais / Nowadays, MSPSR (Multi-Static Primary Surveillance Radar) systems are sustainably settled in air surveillance program [1]. Compared to mono-static radar currently in use, an MSPSR system is based on a sparse network of transmitters (Tx) and receivers (Rx) interconnected to a Central Unit and offers advantages in terms of reliability, cost and performance.Two kinds of MSPSR systems exist: the Passive form and the Active one. While the Passive MSPSR uses transmitters of opportunity such as radio Frequency Modulation (FM) transmitters and/or Digital Video Broadcasting-Terrestrial (DVB-T) transmitters [2], the Active MSPSR uses dedicated transmitters, which emit a waveform that is controlled and designed for a radar application. Each receiver processes the signal coming from all transmitters and reflected on the targets; and the Central Unit restores the target location by intersecting “ellipsoids” from all (transmitter, receiver) pairs. Compared to passive MSPSR, the main advantages of the active MSPSR are the use of dedicated waveforms that allow reaching better performances (like a better association of the transmitters’ contributions at the receiver level); more flexibility in the deployment of transmitters and receivers station (in order to meet the requirements in localisation accuracy and in horizontal and altitude coverages); and the guarantee of having a service continuity. On this purpose, this thesis analyses the differents codes criteria such as the ambiguity function behaviour, the PAPR (Peak to Average Power Ratio), the spectrum efficiency, etc... . Then, in order to find dedicated waveforms for MSPSR systems, one solution is to find easily-constructed families of sequences. Thus building on the works carried out by the Telecommunication field for solving multi-user issues, this document investigates the application of spreading codes and OFDM signals in MSPSR concept. Besides, another solution is to directly generate a set of sequences. Based on cyclic algorithms in [3] we derive a new algorithm that allows to optimize sets of sequences. Similarly, using a gradient descent approach, we develop a more efficient algorithm than the cyclic one. Finally, in order to evaluate the performances of the different algorithms, this thesis generalizes the Levenshtein Bound, establishes new lower bounds on the PSLR (Peak Sidelobe Level Ratio) in mismatched filter case, and studies real data recorded during some trials

<p>DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. </p><p>The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. </p><p>This thesis talks about the improvement of the PAPR problem using the soft compression method. </p><p>The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.</p>

DVB (Digital Video Broadcasting) is the television digital system. It's however much more than a simple replacement for existing analogue television transmission, this system has many advantages such as picture quality and allows you a range of new features and services including subtitling, multiple audio tracks, interactive content, multimedia content. The system is based in the OFDM technology, which allows DVB system to exploit the spectrum frequencies in a better way, saving spectrum, but OFDM has an important drawback that is the peak to average power ratio problem. OFDM is based on the FFT algorithms generating orthogonal subcarriers. This thesis talks about the improvement of the PAPR problem using the soft compression method. The simulation has been developed in Simulink® and Matlab®. With all the information presented in this thesis, any user can simulate the system. Thus, this thesis can be improved using other techniques to solve the PAPR problem.

In order to improve the drawback of the high peak-to-average power ratio (PAPR) on the multi-carrier systems, in this paper we derive a statistical characterization approach of the time domain signal power variance metric by means of every user¡¦s spreading code combination and subcarrier scrambling. We obviously reduce the PAPR on the multi-carrier code division multiple access (MC-CDMA) systems by resorting the combination of spreading codes and scrambling the polarities of subcarriers. Due to the large calculative number of exhaustive search, we use a low complexity Replacement Search Method (RSM) to reduce the calculation times of searching, and obtain a good result. Moreover, we can get a better PAPR reduction performance by increasing the number of iteration.

Avec le besoin croissant en bande-passante, les technologies dites de radio-cognitive sont de plus en plus étudiées par la communauté scientifique. L'enjeu est d'utiliser au mieux le spectre disponible. L'une de ces technologies, Transform Domain Communication System (TDCS), dont les performances en termes d'efficacité énergétique et spectrale étaient jusqu'à présent méconnues, constitue le sujet d'étude de cette thèse. Après une présentation du contexte scientifique et industriel de la thèse, le système TDCS est introduit, ainsi que ses similarités et différences avec OFDM et MC-CDMA. Le système est ensuite décrit sous le formalisme algébrique des modulations linaires. Cela a permis d'établir une expression de l'efficacité spectrale du système. Plusieurs techniques sont alors proposées pour améliorer celle-ci tout en améliorant, dans certains cas, le taux d'erreur binaire. Étant composé d'un de plusieurs composantes sinusoïdales, le signal TDCS souffre d'un fort Peak-to-Average Power Ratio (PAPR). La théorie ensembliste est alors présentée puis mise à profit en troisième partie de cette thèse pour proposer les algorithmes Douglas- Rachford et ROCS de réduction du PAPR des signaux TDCS. Ces algorithmes convergent plus rapidement et vers des valeurs plus basses que l'algorithme POCS précédemment utilisé dans la littérature.

This thesis has sought to provide another look at RF interference at the fundamental level. While previous interference control and regulation methods have existed in the literature, they were more focused on preventing the interference from happening. On the contrary, we have taken a different approach of correcting the interference once it has happened. This allows the transmitters to be more nonlinear, passive filter design to be eased, and receivers to be aware of interference problems. Under this unifying theme of building intelligent radios where receivers are more cognizant of the transmission environment, we have presented a number of architectures.