MIMO designs for filter bank multicarrier and multiantenna systems based on OQAM

From the perspective of increasingly data rate requirements in mobile communications, it is deemed necessary to do further research so that the future goals can be reached. To that end, the radio-based communications are resorting to multicarrier modulations and spatial diversity. Until today, the orthogonal frequency division multiplexing (OFDM) modulation is regarded as the dominant technology. On one hand, the OFDM modulation is able to accommodate multiantenna configurations in a very straightforward manner. On the other hand, the poor stopband attenuation exhibited by the OFDM modulation, highlights that a definitely tight synchronization is required. In addition, the cyclic prefix (CP) has to be sufficiently long to avoid inter-block interference, which may substantially reduce the spectral efficiency. In order to overcome the OFDM drawbacks, the filter bank multicarrier modulation based on OQAM (FBMC/OQAM) is introduced. This modulation does not need any CP and benefits from pulse shaping techniques. This aspect becomes crucial in cognitive radio networks and communication systems where nodes are unlikely to be synchronized. In principle, the poor frequency confinement exhibited by OFDM should tip the balance towards FBMC/OQAM. However, the perfect reconstruction property of FBMC/OQAM systems does not hold in presence of multipath fading. This means that the FBMC/OQAM modulation is affected by inter-symbol and inter-carrier interference, unless the channel is equalized to some extent. This observation highlights that the FBMC/OQAM extension to MIMO architectures becomes a big challenge due to the need to cope with both modulation- and multiantenna-induced interference. The goal of this thesis is to study how the FBMC/OQAM modulation scheme can benefit from the degrees of freedom provided by the spatial dimension. In this regard, the first attempt to put the research on track is based on designing signal processing techniques at reception. In this case the emphasis is on single-input-multiple-output (SIMO) architectures. Next, the possibility of pre-equalizing the channel at transmission is investigated. It is considered that multiple antennas are placed at the transmit side giving rise to a multiple-input-single-output (MISO) configuration. In this scenario, the research is not only focused on counteracting the channel but also on distributing the power among subcarriers. Finally, the joint transmitter and receiver design in multiple-input-multiple-output (MIMO) communication systems is covered. From the theory developed in this thesis, it is possible to conclude that the techniques originally devised in the OFDM context can be easily adapted to FBMC/OQAM systems if the channel frequency response is flat within the subchannels. However, metrics such as the peak to average power ratio or the sensitivity to the carrier frequency offset constraint the number of subcarriers, so that the frequency selectivity may be appreciable at the subcarrier level. Then, the flat fading assumption is not satisfied and the specificities of FBMC/OQAM systems have to be considered. In this situation, the proposed techniques allow FBMC/OQAM to remain competitive with OFDM. In addition, for some multiantenna configurations and propagation conditions FBMC/OQAM turns out to be the best choice. The simulation-based results together with the theoretical analysis conducted in this thesis contribute to make progress towards the application of FBMC/OQAM to MIMO channels. The signal processing techniques that are described in this dissertation allow designers to exploit the potentials of FBMC/OQAM and MIMO to improve the link reliability as well as the spectral efficiency

Characterization of the effects of multi-tap filtering on FBMC/OQAM systems

The filter bank multicarrier modulation based on offset quadrature amplitude modulation (FBMC/OQAM) is being considered as an eligible technology for future wireless communications. However, the orthogonality may be destroyed in the presence of multipath fading, and thus, the demodulated data may be affected by inter-symbol and inter-carrier interference. To restore the orthogonality, it is deemed necessary to either precode the symbols to be transmitted or equalize the demodulated data. Under severe propagation conditions, both the precoders and equalizers should perform multi-tap filtering. In this paper, we try to determine whether it is the best choice to combat the channel at the transmit, or at the receive side. The answer to this question is not trivial, since with data precoding, the transmit power may increase, while equalization at the receive side may enhance the noise power. To cast light on this issue, this paper characterizes the average transmit and noise power to determine the influence of multi-tap filtering on the transmit signal power and on the noise variance. The analysis conducted in this paper reveals that if multi-tap precoding yields a power increase, then the noise variance would increase with the same magnitude if the same linear filter was moved from the transmit to the receive side. Therefore, if symbols are properly scaled when the transmit power increases, there is no degradation due to placing the complexity burden at the reception rather than at the transmission. To scale the symbols, it is mandatory to know the additional transmit power. In this sense, a low-complexity method to estimate the power increase is proposed. Simulation-based results confirm that the estimation is reasonably accurate.Peer ReviewedPostprint (published version

Técnicas de igualização adaptativas com estimativas imperfeitas do canal para os futuros sistemas 5G

Wireless communication networks have been continuously experiencing an exponential growth since their inception. The overwhelming demand for high data rates, support of a large number of users while mitigating disruptive interference are the constant research focus and it has led to the creation of new technologies and efficient techniques. Orthogonal frequency division multiplexing (OFDM) is the most common example of a technology that has come to the fore in this past decade as it provided a simple and generally ideal platform for wireless data transmission. It’s drawback of a rather high peak-to-average power ratio (PAPR) and sensitivity to phase noise, which in turn led to the adoption of alternative techniques, such as the single carrier systems with frequency domain equalization (SC-FDE) or the multi carrier systems with code division multiple access (MC-CDMA), but the nonlinear Frequency Domain Equalizers (FDE) have been of special note due to their improved performance. From these, the Iterative Block Decision Feedback Equalizer (IB-DFE) has proven itself especially promising due to its compatibility with space diversity, MIMO systems and CDMA schemes. However, the IB-DFE requires the system to have constant knowledge of the communication channel properties, that is, to have constantly perfect Channel State Information (CSI), which is both unrealistic and impractical to implement. In this dissertation we shall design an altered IB-DFE receiver that is able to properly detect signals from SC-FDMA based transmitters, even with constantly erroneous channel states. The results shall demonstrate that the proposed equalization scheme is robust to imperfect CSI (I-CSI) situations, since its performance is constantly close to the perfect CSI case, within just a few iterations.Redes sem fios têm crescido de maneira contínua e exponencial desde a sua incepção. A tremenda exigência para altas taxas de dados e o suporte para um elevado número de utilizadores sem aumentar a interferência disruptiva originada por estes são alguns dos focos que levaram ao desenvolvimento de técnicas de compensação e novas tecnologias. “Orthogonal frequency division multiplexing” (OFDM) é um dos exemplos de tecnologias que se destacaram nesta última década, visto ter fornecido uma plataforma para transmissão de dados sem-fio eficaz e simples. O seu maior problema é a alta “peak-to-average power ratio” (PAPR) e a sua sensibilidade a ruído de fase que deram motivo à adoção de técnicas alternativas, tais como os sistemas “single carrier” com “frequency domain equalization” (SC-FDE) ou os sistemas “multi-carrier” com “code division multiple access” (MC-CDMA), mas equalizadores não lineares no domínio de frequência têm sido alvo de especial atenção devido ao seu melhor desempenho. Destes, o “iterative block decision feedback equalizer” (IB-DFE) tem-se provado especialmente promissor devido à sua compatibilidade com técnicas de diversidade no espaço, sistemas MIMO e esquemas CDMA. No entanto, IB-DFE requer que o sistema tenha constante conhecimento das propriedades dos canais usados, ou seja, necessita de ter perfeito “channel state information” (CSI) constantemente, o que é tanto irrealista como impossível de implementar. Nesta dissertação iremos projetar um recetor IB-DFE alterado de forma a conseguir detetar sinais dum transmissor baseado em tecnologia SC-FDMA, mesmo com a informação de estado de canal errada. Os resultados irão então demonstrar que o novo esquema de equalização proposto é robusto para situações de CSI imperfeito (I-CSI), visto que o seu desempenho se mantém próximo dos valores esperados para CSI perfeito, em apenas algumas iterações.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Advanced multi-dimensional signal processing for wireless systems

Die florierende Entwicklung der drahtlosen Kommunikation erfordert innovative und fortschrittliche Signalverarbeitungsalgorithmen, die auf eine verbesserte Performance hinsichtlich der Zuverlässigkeit, des Durchsatzes, der Effizienz und weiterer Faktoren abzielen. Die vorliegende Arbeit befasst sich mit der Lösung dieser Herausforderungen und präsentiert neue und faszinierende Fortschritte, um diesen Herausforderungen zu erfüllen. Hauptsächlich konzentrieren wir uns auf zwei innovative Aspekte der mehrdimensionalen Signalverarbeitung für drahtlose Systeme, denen in den letzten Jahren große Aufmerksamkeit in der Forschung geschenkt wurde. Das sind Mehrträgerverfahren für Multiple-Input Multiple-Output (MIMO) Systeme und die mehrdimensionale harmonische Schätzung (Harmonic Retrieval). Da es sich bei MIMO-Systemen und Mehrträgerverfahren um Schlüsseltechnologien der drahtlosen Kommunikation handelt, sind ihre zahlreichen Vorteile seit langem bekannt und haben ein großes Forschungsinteresse geweckt. Zu diesen Vorteilen zählen zum Beispiel die Steigerung der Datenrate und die Verbesserung der Verbindungszuverlässigkeit. Insbesondere OFDM-basierte MIMO Downlink Systeme für 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 Mehrträger-Modulationsverfahren. Sie sind wesentliche Elemente des IEEE 802.11ac Standards und werden ebenfalls für 5G (die fünfte Mobilfunkgeneration) ausschlaggebend sein. Obwohl die bisherigen Arbeiten über das Precoding (Vorcodierung) für solche Multi-User MIMO Downlink Systeme schon fruchtbare Ergebnisse zeigten, werden neue Fortschritte benötigt, die den Mehrträger-Charakter des Systems in einer effizienteren Weise ausnutzen oder auf eine höhere spektrale Effizienz des Gesamtsystems abzielen. Andererseits gilt die Filterbank-basierte Mehrträger 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 für FBMC-basierte MIMO Systeme unter Einschränkungen in Bezug auf mehrere Aspekte, wie z. B. der erlaubten Dimensionalität des Systems und der zulässigen Frequenzselektivität des Kanals. Die Formen der MIMO Einstellungen, die in der Literatur untersucht wurden, sind noch begrenzt auf MIMO-Systeme für einzelne Teilnehmer und vereinfachte Multi-User MIMO Systeme. Fortschrittlichere Techniken sind daher erforderlich, die diese Einschränkungen der existierenden Verfahren aufheben. MIMO-Szenarien, die weniger Einschränkungen unterliegen, müssen außerdem untersucht werden, um die Vorteile von FBMC zu weiter herauszuarbeiten. Im Rahmen der mehrdimensionalen harmonischen Schätzung (Harmonic Retrieval) hat sich gezeigt, dass eine höhere Genauigkeit bei der Schätzung durch Tensoren erreicht werden kann. Das liegt daran, dass die Darstellung mehrdimensionaler Signale mit Tensoren eine natürlichere Beschreibung und eine gute Ausnutzung ihrer mehrdimensionalen Struktur erlaubt, z. B. für die Modellordnungsschätzung und die Unterraumschätzung. Wichtige offene Themen umfassen die statistische Robustheit und wie man die Schätzung in zeitlich variierenden Szenarien adaptiv gestalten kann. In Teil I dieser Arbeit präsentieren wir zunächst eine effiziente und flexible Übertragungsstrategie für OFDM-basierten Multi-User MIMO Downlink Systeme. Sie besteht aus einer räumlichen Scheduling-Methode, der effizienten Mehrträger ProSched (Efficient Multi-Carrier ProSched, EMC-ProSched) Erweiterung mit einer effektiven Scheduling-Metrik, die auf Mehrträger-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 Komplexität (Low Complexity Coordinated Beamforming, LoCCoBF). Diese beiden neuen Precoding-Verfahren können flexibel entsprechend den Abmessungen des Systems gewählt werden. Wir entwickeln auch einen System Level-Simulator, in dem die Parameter für das Link-to-System Level Interface kalibriert werden können. Diese Kalibrierung ist Standard-spezifisch, z. B. kann der Standard IEEE 802.11ac gewählt werden. Numerische Ergebnisse zeigen, dass diese Übertragungsstrategie Scheduling Fairness garantiert, einen weitaus höheren Durchsatz als die existierenden Verfahren erzielt, eine geringere Komplexität besitzt und nur einen geringen Signalisierungsoverhead erfordert. Der Schwerpunkt des Rests von Teil I bilden MIMO Systeme basierend auf Filter Bank-basierten Mehrträger-Verfahren mit Offset Quadrature Amplitude Modulation (FBMC/OQAM). Es wird ein umfassender Überblick über FBMC gegeben. Nachfolgend werden für verschiedene FBMC/OQAM-basierte MIMO Varianten neue Verfahren zur Sende- und Empfangs-Verarbeitung entwickelt, die unterschiedliche Grade von Frequenz-Selektivität des Kanals voraussetzen. Zunächst wird die Verwendung von weitgehend linearer Verarbeitung (widely linear processing) untersucht. Ein Zwei-Schritt-Empfänger wird für FBMC/OQAM-basierte MIMO Systeme mit einzelnen Teilnehmern entwickelt. Hierbei ist die Frequenz-Selektivität des Kanals niedrig. Verglichen mit linearen MMSE-Empfänger ist die Leistung des Zwei-Schritt-Empfängers viel besser. Das Grundprinzip dieser Zwei-Schritt-Empfänger ist zuerst die Verringerung der intrinsischen Interferenz, um die Ausnutzung von nicht-zirkulären Signalen zu ermöglichen. Es motiviert weitere Studien über weitgehend lineare Verfahren für FBMC/OQAM-basierte Systeme. Darüber hinaus werden zwei Coordinated Beamforming-Algorithmen für FBMC/OQAM-basierte MIMO Systeme mit einzelnen Teilnehmern entwickelt. Sie verzichten auf die Einschränkung der Dimensionalität der bestehenden Methode, bei der die Anzahl der Sendeantennen größer als die Anzahl der Empfangsantennen sein muss. Der Kanal auf jedem Träger 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 führen 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. Dafür werden drei intrinsische Interferenz mildernde koordinierte Beamforming-Verfahren (Intrinsic Interference Mitigating Coordinated Beamforming, IIM-CBF) vorgeschlagen. Die ersten beiden IIM-CBF Algorithmen werden für die FBMC/OQAM-basierten Multi-User MIMO Downlink Varianten mit unterschiedlichen Dimensionen entwickelt. Es wird gezeigt, dass diese Verfahren zu einer Abschwächung der Multi-User-Interferenz (MUI) sowie einer Verringerung der intrinsischen Interferenz führen. 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 Leistungsfähigkeit der vorgeschlagenen Algorithmen wird durch umfangreiche numerische Simulationen evaluiert. Das Konvergenzverhalten wird untersucht sowie das Thema der Komplexität angesprochen. Außerdem wird die geringere Anfälligkeit von FBMC verglichen mit OFDM gegenüber Frequenzsynchronisationsfehlern demonstriert. Darüber hinaus wird auf die FBMC/OQAM-basierten Multi-User MIMO Downlink Systeme mit stark frequenzselektiven Kanälen eingegangen. Dafür werden Lösungen erarbeitet, die für die Unterdrückung 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 Endgeräten, die eine schwächere 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 Schätzung (Harmonic Retrieval). Der Einbau von statistischer Robustheit in mehrdimensionale Modellordnungsschätzverfahren 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

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

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 Linearization of Energy Efficiency Power Amplifier in Nonlinear OFDM Transmitter for LTE-5G Applications. Simulation and measurements of energy efficiency power amplifier in the presence of nonlinear OFDM transmitter system and digital predistortion based on Hammerstein-Wiener method

This research work has made an effort to understand a novel line of radio frequency power amplifiers (RFPAs) that address initiatives for efficiency enhancement and linearity compensation to harmonize the fifth generation (5G) campaign. The objective is to enhance the performance of an orthogonal frequency division multiplexing-long term evolution (OFDM-LTE) transmitter by reducing the nonlinear distortion of the RFPA. The first part of this work explores the design and implementation of 15.5 W class AB RF power amplifier, adopting a balanced technique to stimulate efficiency enhancement and redeeming exhibition of excessive power in the transmitter. Consequently, this work goes beyond improving efficiency over a linear RF power amplifier design; in which a comprehensive investigation on the fundamental and harmonic components of class F RF power amplifier using a load-pull approach to realise an optimum load impedance and the matching network is presented. The frequency bandwidth for both amplifiers was allocated to operate in the 2.620-2.690 GHz of mobile LTE applications. The second part explores the development of the behavioural model for the class AB power amplifier. A particular novel, Hammerstein-Wiener based model is proposed to describe the dynamic nonlinear behaviour of the power amplifier. The RF power amplifier nonlinear distortion is approximated using a new linear parameter approximation approach. The first and second-order Hammerstein-Wiener using the Normalised Least Mean Square Error (NLMSE) algorithm is used with the aim of easing the complexity of filtering process during linear memory cancellation. Moreover, an enhanced adaptive Wiener model is proposed to explore the nonlinear memory effect in the system. The proposed approach is able to balance between convergence speed and high-level accuracy when compared with behavioural modelling algorithms that are more complex in computation. Finally, the adaptive predistorter technique is implemented and verified in the OFDM transceiver test-bed. The results were compared against the computed one from MATLAB simulation for OFDM and 5G modulation transmitters. The results have confirmed the reliability of the model and the effectiveness of the proposed predistorter.Fundacão para a Ciência e a Tecnologia, Portugal, under European Union’s Horizon 2020 research and innovation programme ... grant agreement H2020-MSCA-ITN- 2016 SECRET-722424 I also acknowledge the role of the National Space Research and Development Agency (NASRDA) Sokoto State Government Petroleum Technology Trust Fund (PTDF

Retournement temporel : application aux réseaux mobiles

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 thèse étudie la technique dite de ‘Retournement Temporel’ afin d’améliorer l’efficacité énergétique des futurs réseaux mobiles d’une part, et réduire le coût des futurs terminaux mobiles, d’autre part. Le retournement temporel consiste à utiliser l’inverse temporel de la réponse impulsionnelle du canal de propagation entre un émetteur et un récepteur pour préfiltrer l’émission d’un signal de données. Avantageusement, le signal ainsi préfiltré est reçu avec une puissance renforcée (c’est la focalisation spatiale) et un écho principal qui est renforcé par rapport aux échos secondaires (c’est la compression temporelle). Lors d’une étape préalable d’apprentissage, l’émetteur estime le canal en mesurant un signal pilote provenant du récepteur. 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 données : c’est la condition de ‘réciprocité du canal’. De nombreux travaux montrent que la focalisation spatiale permet de réduire la puissance émise nécessaire pour atteindre une puissance cible au récepteur d’une part, et que la compression temporelle permet de réduire la complexité du récepteur nécessaire pour gérer l’effet des échos multiples, d’autre part. Cependant, les études sur la réduction de la complexité du récepteur se limitent à l’ultra large bande. Des travaux de cette thèse (basés sur des simulations et des mesures expérimentales) montrent que pour des bandes de fréquences plus typiques des futurs réseaux mobiles (fréquence porteuse à 1GHz et spectre de 30 MHz à 100 MHz), grâce au retournement temporel, un récepteur simple et un signal monoporteuse suffisent pour atteindre de hauts débits. En outre, la condition de réciprocité du canal n’est pas vérifiée dans deux scénarios typiques des réseaux mobiles. Tout d’abord, dans la plupart des réseaux mobiles européens, le mode de duplex en fréquence est utilisé. Ce mode implique que l’émetteur et le récepteur communiquent l’un avec l’autre sur des fréquences porteuses distinctes, et donc à travers des canaux de propagations différents. De plus, lorsqu’on considère un récepteur sur un véhicule connecté en mouvement, l’émetteur et le récepteur communiquent l’un avec l’autre à des instants distincts, correspondants à des positions distinctes du véhicule, et donc à travers des canaux de propagations différents. Des travaux de cette thèse proposent des solutions pour obtenir la focalisation spatio-temporelle dans ces deux scenarios. Enfin, des travaux de la thèse explorent la combinaison du retournement temporel avec d’autres techniques de traitement de signal récentes (la modulation spatiale, d’une part, et une nouvelle forme d’onde multiporteuse, d’autre part), ou des scenarios de déploiement nouveaux (ondes millimétriques et très grands réseaux d’antennes pour inter-connecter les noeuds d’un réseau ultra dense) ou de nouvelles applications (guidage et navigation) envisageables pour les futurs réseaux mobiles

Modelling, Dimensioning and Optimization of 5G Communication Networks, Resources and Services

This reprint aims to collect state-of-the-art research contributions that address challenges in the emerging 5G networks design, dimensioning and optimization. Designing, dimensioning and optimization of communication networks resources and services have been an inseparable part of telecom network development. The latter must convey a large volume of traffic, providing service to traffic streams with highly differentiated requirements in terms of bit-rate and service time, required quality of service and quality of experience parameters. Such a communication infrastructure presents many important challenges, such as the study of necessary multi-layer cooperation, new protocols, performance evaluation of different network parts, low layer network design, network management and security issues, and new technologies in general, which will be discussed in this book

Performance Analysis of Cognitive Radio Systems with Imperfect Channel Knowledge

An analytical framework is established to characterize the effects such as time allocation and variation, arising due to the incorporation of imperfect channel knowledge, that are detrimental to the performance of the cognitive radio systems. In order to facilitate hardware deployment of a cognitive radio system, received power-based estimation, a novel channel estimation technique is employed for the channels existing between the primary and the secondary systems, thus fulfilling low-complexity and versatility requirements

Cooperative Radio Communications for Green Smart Environments

The demand for mobile connectivity is continuously increasing, and by 2020 Mobile and Wireless Communications will serve not only very dense populations of mobile phones and nomadic computers, but also the expected multiplicity of devices and sensors located in machines, vehicles, health systems and city infrastructures. Future Mobile Networks are then faced with many new scenarios and use cases, which will load the networks with different data traffic patterns, in new or shared spectrum bands, creating new specific requirements. This book addresses both the techniques to model, analyse and optimise the radio links and transmission systems in such scenarios, together with the most advanced radio access, resource management and mobile networking technologies. This text summarises the work performed by more than 500 researchers from more than 120 institutions in Europe, America and Asia, from both academia and industries, within the framework of the COST IC1004 Action on "Cooperative Radio Communications for Green and Smart Environments". The book will have appeal to graduates and researchers in the Radio Communications area, and also to engineers working in the Wireless industry. Topics discussed in this book include: • Radio waves propagation phenomena in diverse urban, indoor, vehicular and body environments• Measurements, characterization, and modelling of radio channels beyond 4G networks• Key issues in Vehicle (V2X) communication• Wireless Body Area Networks, including specific Radio Channel Models for WBANs• Energy efficiency and resource management enhancements in Radio Access Networks• Definitions and models for the virtualised and cloud RAN architectures• Advances on feasible indoor localization and tracking techniques• Recent findings and innovations in antenna systems for communications• Physical Layer Network Coding for next generation wireless systems• Methods and techniques for MIMO Over the Air (OTA) testin