7 research outputs found

    Advanced multi-dimensional signal processing for wireless systems

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    Die florierende Entwicklung der drahtlosen Kommunikation erfordert innovative und fortschrittliche Signalverarbeitungsalgorithmen, die auf eine verbesserte Performance hinsichtlich der ZuverlĂ€ssigkeit, des Durchsatzes, der Effizienz und weiterer Faktoren abzielen. Die vorliegende Arbeit befasst sich mit der Lösung dieser Herausforderungen und prĂ€sentiert neue und faszinierende Fortschritte, um diesen Herausforderungen zu erfĂŒllen. HauptsĂ€chlich konzentrieren wir uns auf zwei innovative Aspekte der mehrdimensionalen Signalverarbeitung fĂŒr drahtlose Systeme, denen in den letzten Jahren große Aufmerksamkeit in der Forschung geschenkt wurde. Das sind MehrtrĂ€gerverfahren fĂŒr Multiple-Input Multiple-Output (MIMO) Systeme und die mehrdimensionale harmonische SchĂ€tzung (Harmonic Retrieval). Da es sich bei MIMO-Systemen und MehrtrĂ€gerverfahren um SchlĂŒsseltechnologien der drahtlosen Kommunikation handelt, sind ihre zahlreichen Vorteile seit langem bekannt und haben ein großes Forschungsinteresse geweckt. Zu diesen Vorteilen zĂ€hlen zum Beispiel die Steigerung der Datenrate und die Verbesserung der VerbindungszuverlĂ€ssigkeit. Insbesondere OFDM-basierte MIMO Downlink Systeme fĂŒr mehrere Teilnehmer (Multi-User MIMO Downlink Systems), die durch SDMA (Space-Division Multiple Access) getrennt werden, kombinieren die Vorteile von MIMO-Systemen mit denen von MehrtrĂ€ger-Modulationsverfahren. Sie sind wesentliche Elemente des IEEE 802.11ac Standards und werden ebenfalls fĂŒr 5G (die fĂŒnfte Mobilfunkgeneration) ausschlaggebend sein. Obwohl die bisherigen Arbeiten ĂŒber das Precoding (Vorcodierung) fĂŒr solche Multi-User MIMO Downlink Systeme schon fruchtbare Ergebnisse zeigten, werden neue Fortschritte benötigt, die den MehrtrĂ€ger-Charakter des Systems in einer effizienteren Weise ausnutzen oder auf eine höhere spektrale Effizienz des Gesamtsystems abzielen. Andererseits gilt die Filterbank-basierte MehrtrĂ€ger Modulation (Filter Bank-based Multi-Carrier modulation, FBMC) mit einem gut konzentrierten Spektrum und einer somit niedrigen Out-of-band Leackage als eine vielversprechende Alternative zu OFDM. FBMC ermöglicht eine effiziente Nutzung von Fragmenten im Frequenzspektrums, z. B. in 5G oder Breitband Professional Mobile Radio (PMR) Netzwerken. Jedoch leiden die vorhandenen Verfahren zur Sende- und-Empfangs-Verarbeitung fĂŒr FBMC-basierte MIMO Systeme unter EinschrĂ€nkungen in Bezug auf mehrere Aspekte, wie z. B. der erlaubten DimensionalitĂ€t des Systems und der zulĂ€ssigen FrequenzselektivitĂ€t des Kanals. Die Formen der MIMO Einstellungen, die in der Literatur untersucht wurden, sind noch begrenzt auf MIMO-Systeme fĂŒr einzelne Teilnehmer und vereinfachte Multi-User MIMO Systeme. Fortschrittlichere Techniken sind daher erforderlich, die diese EinschrĂ€nkungen der existierenden Verfahren aufheben. MIMO-Szenarien, die weniger EinschrĂ€nkungen unterliegen, mĂŒssen außerdem untersucht werden, um die Vorteile von FBMC zu weiter herauszuarbeiten. Im Rahmen der mehrdimensionalen harmonischen SchĂ€tzung (Harmonic Retrieval) hat sich gezeigt, dass eine höhere Genauigkeit bei der SchĂ€tzung durch Tensoren erreicht werden kann. Das liegt daran, dass die Darstellung mehrdimensionaler Signale mit Tensoren eine natĂŒrlichere Beschreibung und eine gute Ausnutzung ihrer mehrdimensionalen Struktur erlaubt, z. B. fĂŒr die ModellordnungsschĂ€tzung und die UnterraumschĂ€tzung. Wichtige offene Themen umfassen die statistische Robustheit und wie man die SchĂ€tzung in zeitlich variierenden Szenarien adaptiv gestalten kann. In Teil I dieser Arbeit prĂ€sentieren wir zunĂ€chst eine effiziente und flexible Übertragungsstrategie fĂŒr OFDM-basierten Multi-User MIMO Downlink Systeme. Sie besteht aus einer rĂ€umlichen Scheduling-Methode, der effizienten MehrtrĂ€ger ProSched (Efficient Multi-Carrier ProSched, EMC-ProSched) Erweiterung mit einer effektiven Scheduling-Metrik, die auf MehrtrĂ€ger-Systeme zugeschnitten wird. Weiterhin werden zwei neuartige Precoding Algorithmen vorgestellt, die lineare Precoding-basierte geometrische Mittelwert-Zerlegung (Linear Precoding-based Geometric Mean Decomposition, LP-GMD) und ein Coordinated Beamforming Algorithmus geringer KomplexitĂ€t (Low Complexity Coordinated Beamforming, LoCCoBF). Diese beiden neuen Precoding-Verfahren können flexibel entsprechend den Abmessungen des Systems gewĂ€hlt werden. Wir entwickeln auch einen System Level-Simulator, in dem die Parameter fĂŒr das Link-to-System Level Interface kalibriert werden können. Diese Kalibrierung ist Standard-spezifisch, z. B. kann der Standard IEEE 802.11ac gewĂ€hlt werden. Numerische Ergebnisse zeigen, dass diese Übertragungsstrategie Scheduling Fairness garantiert, einen weitaus höheren Durchsatz als die existierenden Verfahren erzielt, eine geringere KomplexitĂ€t besitzt und nur einen geringen Signalisierungsoverhead erfordert. Der Schwerpunkt des Rests von Teil I bilden MIMO Systeme basierend auf Filter Bank-basierten MehrtrĂ€ger-Verfahren mit Offset Quadrature Amplitude Modulation (FBMC/OQAM). Es wird ein umfassender Überblick ĂŒber FBMC gegeben. Nachfolgend werden fĂŒr verschiedene FBMC/OQAM-basierte MIMO Varianten neue Verfahren zur Sende- und Empfangs-Verarbeitung entwickelt, die unterschiedliche Grade von Frequenz-SelektivitĂ€t des Kanals voraussetzen. ZunĂ€chst wird die Verwendung von weitgehend linearer Verarbeitung (widely linear processing) untersucht. Ein Zwei-Schritt-EmpfĂ€nger wird fĂŒr FBMC/OQAM-basierte MIMO Systeme mit einzelnen Teilnehmern entwickelt. Hierbei ist die Frequenz-SelektivitĂ€t des Kanals niedrig. Verglichen mit linearen MMSE-EmpfĂ€nger ist die Leistung des Zwei-Schritt-EmpfĂ€ngers viel besser. Das Grundprinzip dieser Zwei-Schritt-EmpfĂ€nger ist zuerst die Verringerung der intrinsischen Interferenz, um die Ausnutzung von nicht-zirkulĂ€ren Signalen zu ermöglichen. Es motiviert weitere Studien ĂŒber weitgehend lineare Verfahren fĂŒr FBMC/OQAM-basierte Systeme. DarĂŒber hinaus werden zwei Coordinated Beamforming-Algorithmen fĂŒr FBMC/OQAM-basierte MIMO Systeme mit einzelnen Teilnehmern entwickelt. Sie verzichten auf die EinschrĂ€nkung der DimensionalitĂ€t der bestehenden Methode, bei der die Anzahl der Sendeantennen grĂ¶ĂŸer als die Anzahl der Empfangsantennen sein muss. Der Kanal auf jedem TrĂ€ger wird als flacher Schwund (Flat Fading) modelliert, was einer Klassifizierung als „intermediate frequency selective channel“ entspricht. Unter der Kenntnis der Kanalzustandsinformation am Sender (Channel-State-Information at the Transmitter, CSIT) basiert die Vorcodierung entweder auf einem Zero Forcing (ZF) Kriterium oder auf der Maximierung der Signal-to-Leackage-plus-Noise-Ratio (SLNR). Die Vorcodierungsvektoren und die Empfangsvektoren werden gemeinsam und iterativ berechnet. Daher fĂŒhren die zwei Coordinated Beamforming-Algorithmen zu einer wirksamen Verringerung der intrinsischen Interferenz in FBMC/OQAM-basierten Systemen. Die Vorteile der Coordinated Beamforming-Konzepte werden in FBMC/OQAM-basierten Multi-User MIMO Downlink Systeme und koordinierte Mehrpunktverbindung (Coordinated Multi-Point, CoMP-Konzepte) eingebracht. DafĂŒr werden drei intrinsische Interferenz mildernde koordinierte Beamforming-Verfahren (Intrinsic Interference Mitigating Coordinated Beamforming, IIM-CBF) vorgeschlagen. Die ersten beiden IIM-CBF Algorithmen werden fĂŒr die FBMC/OQAM-basierten Multi-User MIMO Downlink Varianten mit unterschiedlichen Dimensionen entwickelt. Es wird gezeigt, dass diese Verfahren zu einer AbschwĂ€chung der Multi-User-Interferenz (MUI) sowie einer Verringerung der intrinsischen Interferenz fĂŒhren. Bei der dritten IIM-CBF Methode wird ein neuartiges FBMC/OQAM-basiertes-CoMP Konzept vorgestellt. Dieses wird durch die gemeinsame Übertragung von benachbarten Zellen zu Teilnehmern, die sich am Zellenrand befinden, ermöglicht, um den Daten-Durchsatz am Zellenrand zu erhöhen. Die LeistungsfĂ€higkeit der vorgeschlagenen Algorithmen wird durch umfangreiche numerische Simulationen evaluiert. Das Konvergenzverhalten wird untersucht sowie das Thema der KomplexitĂ€t angesprochen. Außerdem wird die geringere AnfĂ€lligkeit von FBMC verglichen mit OFDM gegenĂŒber Frequenzsynchronisationsfehlern demonstriert. DarĂŒber hinaus wird auf die FBMC/OQAM-basierten Multi-User MIMO Downlink Systeme mit stark frequenzselektiven KanĂ€len eingegangen. DafĂŒr werden Lösungen erarbeitet, die fĂŒr die UnterdrĂŒckung der MUI, der Inter-Symbol Interferenz (ISI) sowie der Inter-Carrier Interferenz (ICI) anwendbar ist. Mehrere Kriterien der multi-tap Vorcodierung werden entwickelt, beispielsweise die Mean Squared Error (MSE) Minimierung sowie die Signal-to-Leakage-Ratio (SLR) und die SLNR Maximierung. An EndgerĂ€ten, die eine schwĂ€chere Rechenleistung besitzen als sie an der Basisstation vorhanden ist, wird dadurch nur ein single-tap Empfangsfilter benötigt. Teil II der Arbeit konzentriert sich auf die mehrdimensionale harmonische SchĂ€tzung (Harmonic Retrieval). Der Einbau von statistischer Robustheit in mehrdimensionale ModellordnungsschĂ€tzverfahren wird demonstriert.The thriving development of wireless communications calls for innovative and advanced signal processing techniques targeting at an enhanced performance in terms of reliability, throughput, robustness, efficiency, flexibility, etc.. This thesis addresses such a compelling demand and presents new and intriguing progress towards fulfilling it. We mainly concentrate on two advanced multi-dimensional signal processing challenges for wireless systems that have attracted tremendous research attention in recent years, multi-carrier Multiple-Input Multiple-Output (MIMO) systems and multi-dimensional harmonic retrieval. As the key technologies of wireless communications, the numerous benefits of MIMO and multi-carrier modulation, e.g., boosting the data rate and improving the link reliability, have long been identified and have ignited great research interest. In particular, the Orthogonal Frequency Division Multiplexing (OFDM)-based multi-user MIMO downlink with Space-Division Multiple Access (SDMA) combines the twofold advantages of MIMO and multi-carrier modulation. It is the essential element of IEEE 802.11ac and will also be crucial for the fifth generation of wireless communication systems (5G). Although past investigations on scheduling and precoding design for multi-user MIMO downlink systems have been fruitful, new advances are desired that exploit the multi-carrier nature of the system in a more efficient manner or aim at a higher spectral efficiency. On the other hand, a Filter Bank-based Multi-Carrier modulation (FBMC) featuring a well-concentrated spectrum and thus a low out-of-band radiation is regarded as a promising alternative multi-carrier scheme to OFDM for an effective utilization of spectrum fragments, e.g., in 5G or broadband Professional Mobile Radio (PMR) networks. Unfortunately, the existing transmit-receive processing schemes for FBMC-based MIMO systems suffer from limitations in several aspects, e.g., with respect to the number of supported receive antennas (dimensionality constraint) and channel frequency selectivity. The forms of MIMO settings that have been investigated are still limited to single-user MIMO and simplified multi-user MIMO systems. More advanced techniques are therefore demanded to alleviate the constraints imposed on the state-of-the-art. More sophisticated MIMO scenarios are yet to be explored to further corroborate the benefits of FBMC. In the context of multi-dimensional harmonic retrieval, it has been demonstrated that a higher estimation accuracy can be achieved by using tensors to preserve and exploit the multidimensional nature of the data, e.g., for model order estimation and subspace estimation. Crucial pending topics include how to further incorporate statistical robustness and how to handle time-varying scenarios in an adaptive manner. In Part I of this thesis, we first present an efficient and flexible transmission strategy for OFDM-based multi-user MIMO downlink systems. It consists of a spatial scheduling scheme, efficient multi-carrier ProSched (EMC-ProSched), with an effective scheduling metric tailored for multi-carrier systems and two new precoding algorithms, linear precoding-based geometric mean decomposition (LP-GMD) and low complexity coordinated beamforming (LoCCoBF). These two new precoding schemes can be flexibly chosen according to the dimensions of the system. We also develop a system-level simulator where the parameters for the link-to-system level interface can be calibrated according to a certain standardization framework, e.g., IEEE 802.11ac. Numerical results show that the proposed transmission strategy, apart from guaranteeing the scheduling fairness and a small signaling overhead, achieves a much higher throughput than the state-of-the-art and requires a lower complexity. The remainder of Part I is dedicated to Filter Bank-based Multi-Carrier with Offset Quadrature Amplitude Modulation (FBMC/OQAM)-based MIMO systems. We begin with a thorough overview of FBMC. Then we present new transmit-receive processing techniques for FBMC/OQAM-based MIMO settings ranging from the single-user MIMO case to the Coordinated Multi-Point (CoMP) downlink considering various degrees of channel frequency selectivity. The use of widely linear processing is first investigated. A two-step receiver is designed for FBMC/OQAM-based point-to-point MIMO systems with low frequency selective channels. It exhibits a significant performance superiority over the linear MMSE receiver. The rationale in this two-step receiver is that the intrinsic interference is first mitigated to facilitate the exploitation of the non-circularity residing in the signals. It sheds light upon further studies on widely linear processing for FBMC/OQAM-based systems. Moreover, two coordinated beamforming algorithms are devised for FBMC/OQAM-based point-to-point MIMO systems to relieve the dimensionality constraint of existing schemes that the number of transmit antennas must be larger than the number of receive antennas. The channel on each subcarrier is assumed to be flat fading, which is categorized as the class of intermediate frequency selective channels. With the Channel State Information at the Transmitter (CSIT) known, the precoder designed based on a Zero Forcing (ZF) criterion or the maximization of the Signal-to-Leakage-plus-Noise-Ratio (SLNR) is jointly and iteratively computed with the receiver, leading to an effective mitigation of the intrinsic interference inherent in FBMC/OQAM-based systems. The benefits of the coordinated beamforming concept are successfully translated into the FBMC/OQAM-based multi-user MIMO downlink and the CoMP downlink. Three intrinsic interference mitigating coordinated beamforming (IIM-CBF) schemes are developed. The first two IIM-CBF schemes are proposed for FBMC/OQAM-based multi-user MIMO downlink settings with different dimensions and are able to effectively suppress the Multi-User Interference (MUI) as well as the intrinsic interference. A novel FBMC/OQAM-based CoMP concept is established via the third IIM-CBF scheme which enables the joint transmission of adjacent cells to the cell edge users to combat the strong interference as well as the heavy path loss and to boost the cell edge throughput. The performance of the proposed algorithms is evaluated via extensive numerical simulations. Their convergence behavior is studied, and the complexity issue is also addressed. In addition, the stronger resilience of FBMC over OFDM against frequency misalignments is demonstrated. Furthermore, we cover the case of highly frequency selective channels and provide solutions to the very challenging task of suppressing the MUI, the Inter-Symbol Interference (ISI), as well as the Inter-Carrier Interference (ICI) and supporting per-user multi-stream transmissions. Several design criteria of the multi-tap precoders are devised including the Mean Squared Error (MSE) minimization as well as the Signal-to-Leakage-Ratio (SLR) and SLNR maximization. By rendering a larger computational load at the base station, only single-tap spatial receive filters are required at the user terminals with a weaker computational capability, which enhances the applicability of the proposed schemes in real-world multi-user MIMO downlink systems. Part II focuses on the context of multi-dimensional harmonic retrieval. We demonstrate the incorporation of statistical robustness into multi-dimensional model order estimation schemes by substituting the sample covariance matrices of the unfoldings of the measurement tensor with robust covariance estimates. It is observed that in the presence of a very severe contamination of the measurements due to brief sensor failures, the robustified tensor-based model order estimation schemes lead to a satisfactory estimation accuracy. This philosophy of introducing statistical robustness also inspires robust versions of parameter estimation algorithms. Last but not the least, we present a generic framework for Tensor-based subspace tracking via Kronecker-structured projections (TeTraKron) for time-varying multi-dimensional harmonic retrieval problems. It allows to extend arbitrary matrix-based subspace tracking schemes to track the tensor-based subspace estimate in an elegant and efficient manner. By including forward-backward-averaging, we show that TeTraKron can also be employed to devise real-valued tensor-based subspace tracking algorithms. Taking a few matrix-based subspace tracking approaches as an example, a remarkable improvement of the tracking accuracy is observed in case of the TeTraKron-based tensor extensions. The performance of ESPRIT-type parameter estimation schemes is also assessed where the subspace estimates obtained by the proposed TeTraKron-based subspace tracking algorithms are used. We observe that Tensor-ESPRIT combined with a tensor-based subspace tracking scheme significantly outperforms the combination of standard ESPRIT and the corresponding matrix-based subspace tracking method. These results open the way for robust multi-dimensional big data signal processing applications in time-varying environments

    Compensating Chromatic Dispersion and Phase Noise using Parallel AFB-MBPS For FBMC-OQAM Optical Communication System

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    Filter Bank Multi-Carrier Offset-QAM (FBMC-OQAM) is one of the hottest topics in research for 5G multi-carrier methods because of its high efficiency in the spectrum, minimal leakage in the side lobes, zero cyclic prefix (CP), and multiphase filter design. Large-scale subcarrier configurations in optical fiber networks need the use of FBMC-OQAM. Chromatic dispersion is critical in optical fiber transmission because it causes different spectral waves (color beams) to travel at different rates. Laser phase noise, which arises when the phase of the laser output drifts with time, is a major barrier that lowers throughput in fiber-optic communication systems. This deterioration may be closely related among channels that share lasers in multichannel fiber-optic systems using methods like wavelength-division multiplexing with frequency combs or space-division multiplexing. In this research, we use parallel Analysis Filter Bank (AFB) equalizers in the receiver part of the FBMC OQAM Optical Communication system to compensate for chromatic dispersion (CD) and phase noise (PN). Following the equalization of CD compensation, the phase of the carriers in the received signal is tracked and compensated using Modified Blind Phase Search (MBPS). The CD and PN compensation techniques are simulated and analyzed numerically and graphically to determine their efficacy. To evaluate the FBMC\u27s efficiency across various equalizers, 16-OQAM is taken into account. Bit Error Rate (BER), Optical Signal-to-Noise Ratio (OSNR), Q-Factor, and Mean Square Error (MSE) were the primary metrics we utilized to evaluate performance. Single-tap equalizer, multi-tap equalizer (N=3), ISDF equalizer with suggested Parallel Analysis Filter Banks (AFBs) (K=3), and MBPS were all set aside for comparison. When compared to other forms of Nonlinear compensation (NLC), the CD and PN tolerance attained by Parallel AFB equalization with MBPS is the greatest

    D13.1 Fundamental issues on energy- and bandwidth-efficient communications and networking

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    Deliverable D13.1 del projecte europeu NEWCOM#The report presents the current status in the research area of energy- and bandwidth-efficient communications and networking and highlights the fundamental issues still open for further investigation. Furthermore, the report presents the Joint Research Activities (JRAs) which will be performed within WP1.3. For each activity there is the description, the identification of the adherence with the identified fundamental open issues, a presentation of the initial results, and a roadmap for the planned joint research work in each topic.Preprin

    Design and Analysis of GFDM-Based Wireless Communication Systems

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    Le multiplexage gĂ©nĂ©ralisĂ© par rĂ©partition en frĂ©quence (GFDM), une mĂ©thode de traitement par blocs de modulation multiporteuses non orthogonales, est une candidate prometteuse pour les technologies de forme d'onde pour les systĂšmes sans fil au-delĂ  de la cinquiĂšme gĂ©nĂ©ration (5G). La capacitĂ© du GFDM Ă  ajuster de maniĂšre flexible la taille du bloc et le type de filtres de mise en forme des impulsions en fait une mĂ©thode appropriĂ©e pour rĂ©pondre Ă  plusieurs exigences importantes, comme une faible latence, un faible rayonnement hors bande (OOB) et des dĂ©bits de donnĂ©es Ă©levĂ©s. En appliquant aux systĂšmes GFDM la technique des systĂšmes Ă  entrĂ©es multiples et sorties multiples (MIMO), la technique de MIMO massif ou des codes de contrĂŽle de paritĂ© Ă  faible densitĂ© (LDPC), il est possible d'amĂ©liorer leurs performances. Par consĂ©quent, l'Ă©tude de ces systĂšmes combinĂ©s sont d'une grande importance thĂ©orique et pratique. Dans cette thĂšse, nous Ă©tudions les systĂšmes de communication sans fil basĂ©s sur le GFDM en considĂ©rant trois aspects. Tout d'abord, nous dĂ©rivons une borne d'union sur le taux d'erreur sur les bits (BER) pour les systĂšmes MIMO-GFDM, technique qui est basĂ©e sur des probabilitĂ©s d'erreur par paires exactes (PEP). La PEP exacte est calculĂ©e en utilisant la fonction gĂ©nĂ©ratrice de moments(MGF) pour les dĂ©tecteurs Ă  maximum de vraisemblance (ML). La corrĂ©lation spatiale entre les antennes et les erreurs d'estimation de canal sont prises en compte dans l'environnement de canal Ă©tudiĂ©. DeuxiĂšmement, les estimateurs et les prĂ©codeurs de canal de faible complexitĂ© basĂ©s sur une expansion polynomiale sont proposĂ©s pour les systĂšmes MIMO-GFDM massifs. Des pilotes sans interfĂ©rence sont utilisĂ©s pour l'estimation du canal basĂ©e sur l'erreur quadratique moyenne minimale(MMSE) pour lutter contre l'influence de la non-orthogonalitĂ© entre les sous-porteuses dans le GFDM. La complexitĂ© de calcul cubique peut ĂȘtre rĂ©duite Ă  une complexitĂ© d'ordre au carrĂ© en utilisant la technique d'expansion polynomiale pour approximer les inverses de matrices dans l'estimation MMSE conventionnelle et le prĂ©codage. De plus, nous calculons les limites de performance en termes d'erreur quadratique moyenne (MSE) pour les estimateurs proposĂ©s, ce qui peut ĂȘtre un outil utile pour prĂ©dire la performance des estimateurs dans la rĂ©gion de Eₛ/N₀ Ă©levĂ©. Une borne infĂ©rieure de CramĂ©r-Rao(CRLB) est dĂ©rivĂ©e pour notre modĂšle de systĂšme et agit comme une rĂ©fĂ©rence pour les estimateurs. La complexitĂ© de calcul des estimateurs de canal proposĂ©s et des prĂ©codeurs et les impacts du degrĂ© du polynĂŽme sont Ă©galement Ă©tudiĂ©s. Enfin, nous analysons les performances de la probabilitĂ© d'erreur des systĂšmes GFDM combinĂ©s aux codes LDPC. Nous dĂ©rivons d'abord les expressions du ratio de vraisemblance logarithmique (LLR) initiale qui sont utilisĂ©es dans le dĂ©codeur de l'algorithme de somme de produits (SPA). Ensuite, basĂ© sur le seuil de dĂ©codage, nous estimons le taux d'erreur de trame (FER) dans la rĂ©gion de bas E[indice b]/N₀ en utilisant le BER observĂ© pour modĂ©liser les variations du canal. De plus, une borne infĂ©rieure du FER du systĂšme est Ă©galement proposĂ©e basĂ©e sur des ensembles absorbants. Cette borne infĂ©rieure peut agir comme une estimation du FER dans la rĂ©gion de E[indice b]/N₀ Ă©levĂ© si l'ensemble absorbant utilisĂ© est dominant et que sa multiplicitĂ© est connue. La quantification a Ă©galement un impact important sur les performances du FER et du BER. Des codes LDPC basĂ©s sur un tableau et construit alĂ©atoirement sont utilisĂ©s pour supporter les analyses de performances. Pour ces trois aspects, des simulations et des calculs informatiques sont effectuĂ©s pour obtenir des rĂ©sultats numĂ©riques connexes, qui vĂ©rifient les mĂ©thodes proposĂ©es.8 372162\u a Generalized frequency division multiplexing (GFDM) is a block-processing based non-orthogonal multi-carrier modulation scheme, which is a promising candidate waveform technology for beyond fifth-generation (5G) wireless systems. The ability of GFDM to flexibly adjust the block size and the type of pulse-shaping filters makes it a suitable scheme to meet several important requirements, such as low latency, low out-of-band (OOB) radiation and high data rates. Applying the multiple-input multiple-output (MIMO) technique, the massive MIMO technique, or low-density parity-check (LDPC) codes to GFDM systems can further improve the systems performance. Therefore, the investigation of such combined systems is of great theoretical and practical importance. This thesis investigates GFDM-based wireless communication systems from the following three aspects. First, we derive a union bound on the bit error rate (BER) for MIMO-GFDM systems, which is based on exact pairwise error probabilities (PEPs). The exact PEP is calculated using the moment-generating function (MGF) for maximum likelihood (ML) detectors. Both the spatial correlation between antennas and the channel estimation errors are considered in the investigated channel environment. Second, polynomial expansion-based low-complexity channel estimators and precoders are proposed for massive MIMO-GFDM systems. Interference-free pilots are used in the minimum mean square error (MMSE) channel estimation to combat the influence of non-orthogonality between subcarriers in GFDM. The cubic computational complexity can be reduced to square order by using the polynomial expansion technique to approximate the matrix inverses in the conventional MMSE estimation and precoding. In addition, we derive performance limits in terms of the mean square error (MSE) for the proposed estimators, which can be a useful tool to predict estimators performance in the high Eₛ/N₀ region. A CramĂ©r-Rao lower bound (CRLB) is derived for our system model and acts as a benchmark for the estimators. The computational complexity of the proposed channel estimators and precoders, and the impacts of the polynomial degree are also investigated. Finally, we analyze the error probability performance of LDPC coded GFDM systems. We first derive the initial log-likelihood ratio (LLR) expressions that are used in the sum-product algorithm (SPA) decoder. Then, based on the decoding threshold, we estimate the frame error rate (FER) in the low E[subscript b]/N₀ region by using the observed BER to model the channel variations. In addition, a lower bound on the FER of the system is also proposed based on absorbing sets. This lower bound can act as an estimate of the FER in the high E[subscript b]/N₀ region if the absorbing set used is dominant and its multiplicity is known. The quantization scheme also has an important impact on the FER and BER performances. Randomly constructed and array-based LDPC codes are used to support the performance analyses. For all these three aspects, software-based simulations and calculations are carried out to obtain related numerical results, which verify our proposed methods

    Retournement temporel : application aux réseaux mobiles

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    This thesis studies the time reversal technique to improve the energy efficiency of future mobile networks and reduce the cost of future mobile devices. Time reversal technique consists in using the time inverse of the propagation channel impulse response (between a transceiver and a receiver) as a prefilter. Such pre-filtered signal is received with a stronger power (this is spatial focusing) and with a strong main echo, relatively to secondary echoes (this is time compression). During a previous learning phase, the transceiver estimates the channel by measuring the pilot signal emitted by the receiver. Space-time focusing is obtained only at the condition that the propagation remains identical between the learning phase and the data transmission phase: this is the ‘channel reciprocity’ condition. Numerous works show that spatial focusing allows for the reduction of the required transmit power for a given target received power, on the one hand, and that time compression allow for the reduction of the required complexity at the receiver side to handle multiple echoes, on the other hand. However, studies on complexity reduction are limited to ultra wideband. Some works of this thesis (based on simulations and experimental measurements) show that, for bands which are more typical for future networks (a carrier frequency of 1GHz and a spectrum of 30 MHz to 100 MHz), thanks to time reversal, a simple receiver and a mono-carrier signal are sufficient to reach high data rates. Moreover, the channel reciprocity condition is not verified in two scenarios which are typical from mobile networks. Firstly, in most European mobile networks, the frequency division duplex mode is used. This mode implies that the transceiver and the receiver communicate on distinct carriers, and therefore through different propagation channels. Secondly, when considering a receiver on a moving connected vehicle, the transceiver and the receiver communicate one with each other at distinct instants, corresponding to distinct positions of the vehicles, and therefore through different propagation channels. Some works of this thesis propose solutions to obtain space-time focusing for these two scenarios. Finally, some works of this thesis explore the combination of time reversal with other recent signal processing techniques (spatial modulation, on the one hand, a new multi-carrier waveform, on the other hand), or new deployment scenarios (millimeter waves and large antenna arrays to interconnect the nodes of an ultra dense network) or new applications (guidance and navigation) which can be envisaged for future mobile networks.Cette thĂšse Ă©tudie la technique dite de ‘Retournement Temporel’ afin d’amĂ©liorer l’efficacitĂ© Ă©nergĂ©tique des futurs rĂ©seaux mobiles d’une part, et rĂ©duire le coĂ»t des futurs terminaux mobiles, d’autre part. Le retournement temporel consiste Ă  utiliser l’inverse temporel de la rĂ©ponse impulsionnelle du canal de propagation entre un Ă©metteur et un rĂ©cepteur pour prĂ©filtrer l’émission d’un signal de donnĂ©es. Avantageusement, le signal ainsi prĂ©filtrĂ© est reçu avec une puissance renforcĂ©e (c’est la focalisation spatiale) et un Ă©cho principal qui est renforcĂ© par rapport aux Ă©chos secondaires (c’est la compression temporelle). Lors d’une Ă©tape prĂ©alable d’apprentissage, l’émetteur estime le canal en mesurant un signal pilote provenant du rĂ©cepteur. La focalisation spatiotemporelle n’est obtenue qu’à condition que la propagation demeure identique entre la phase d’apprentissage et la phase de transmission de donnĂ©es : c’est la condition de ‘rĂ©ciprocitĂ© du canal’. De nombreux travaux montrent que la focalisation spatiale permet de rĂ©duire la puissance Ă©mise nĂ©cessaire pour atteindre une puissance cible au rĂ©cepteur d’une part, et que la compression temporelle permet de rĂ©duire la complexitĂ© du rĂ©cepteur nĂ©cessaire pour gĂ©rer l’effet des Ă©chos multiples, d’autre part. Cependant, les Ă©tudes sur la rĂ©duction de la complexitĂ© du rĂ©cepteur se limitent Ă  l’ultra large bande. Des travaux de cette thĂšse (basĂ©s sur des simulations et des mesures expĂ©rimentales) montrent que pour des bandes de frĂ©quences plus typiques des futurs rĂ©seaux mobiles (frĂ©quence porteuse Ă  1GHz et spectre de 30 MHz Ă  100 MHz), grĂące au retournement temporel, un rĂ©cepteur simple et un signal monoporteuse suffisent pour atteindre de hauts dĂ©bits. En outre, la condition de rĂ©ciprocitĂ© du canal n’est pas vĂ©rifiĂ©e dans deux scĂ©narios typiques des rĂ©seaux mobiles. Tout d’abord, dans la plupart des rĂ©seaux mobiles europĂ©ens, le mode de duplex en frĂ©quence est utilisĂ©. Ce mode implique que l’émetteur et le rĂ©cepteur communiquent l’un avec l’autre sur des frĂ©quences porteuses distinctes, et donc Ă  travers des canaux de propagations diffĂ©rents. De plus, lorsqu’on considĂšre un rĂ©cepteur sur un vĂ©hicule connectĂ© en mouvement, l’émetteur et le rĂ©cepteur communiquent l’un avec l’autre Ă  des instants distincts, correspondants Ă  des positions distinctes du vĂ©hicule, et donc Ă  travers des canaux de propagations diffĂ©rents. Des travaux de cette thĂšse proposent des solutions pour obtenir la focalisation spatio-temporelle dans ces deux scenarios. Enfin, des travaux de la thĂšse explorent la combinaison du retournement temporel avec d’autres techniques de traitement de signal rĂ©centes (la modulation spatiale, d’une part, et une nouvelle forme d’onde multiporteuse, d’autre part), ou des scenarios de dĂ©ploiement nouveaux (ondes millimĂ©triques et trĂšs grands rĂ©seaux d’antennes pour inter-connecter les noeuds d’un rĂ©seau ultra dense) ou de nouvelles applications (guidage et navigation) envisageables pour les futurs rĂ©seaux mobiles

    Single-Tap Precoders and Decoders for Multi-User MIMO FBMC-OQAM under Strong Channel Frequency Selectivity

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    The design of linear precoders or decoders for multiuser multiple-input multiple-output filterbank multicarrier (FBMC) modulations in the case of a strong channel frequency selectivity is presented. The users and the base station (BS) communicate using space division multiple access. The low complexity proposed solution is based on a single tap per-subcarrier precoding/decoding matrix at the BS in the downlink/uplink. As opposed to classical approaches that assume flat channel frequency selectivity at the subcarrier level, the BS does not make this assumption and takes into account the distortion caused by channel frequency selectivity. The expression of the FBMC asymptotic mean squared error (MSE) in the case of strong channel selectivity derived in earlier works is developed and extended. The linear precoders and decoders are found by optimizing the MSE formula under two design criteria, namely zero forcing or minimum MSE. Finally, simulation results demonstrate the performance of the optimized design. As long as the number of BS antennas is larger than the number of users, it is shown that those extra degrees of freedom can be used to compensate for the channel frequency selectivity
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