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Mobile-to-Mobile (M2M) communication is a challenge, but fast growing since it has the potential to enhance the quality of data service with low energy consumption. This dual mobility generates non-stationarity properties of the propagation channel, which requires precise modeling, for simulation network and system design. This thesis aims for characterization and modeling of M2M channels based on stochastic approaches. Some common M2M aspects like the non-stationarity, Doppler and correlation properties were also analyzed. Stochastic channel models were proposed for Body to Body (B2B) and Vehicle to Pedestrian (V2P) channels based on measurements. The non-stationary fading behavior were observed as a function of mutual body orientation and the relative Tx-Rx distance. A general model for the auto-correlation function of the fading channel was derived assuming a typical M2M scenario in the presence of moving scatterers; and a simplify Doppler spectrum model was also developed for indoor M2M scenarios. Both models allow to reproduce with good accuracy the correlation and Doppler properties of different M2M scenarios including line-of-sight (LoS) and non-line of sight (NLoS) environments. Finally, implementation techniques able to reproduce the fading characteristics of M2M channels including the Doppler and correlation characteristics were proposed and successfully compared to the measurements. (FSA - Sciences de l'ingénieur) -- UCL, 2018

The objective of this master thesis is to develop an innovative framework enabling to model wireless networks and to assess their performance. This framework includes on the one hand Monte Carlo simulations and on the other hand analytical expressions derived thanks to the stochastic geometry theory. The result of this work aims at providing an optimization tool applicable to modern and future networks (e.g. relying on the 5G technology). We hence focus on three aspects that are considered to be crucial for such networks : the modeling of the propagation environment, the beamforming and the transmit power monitoring. Each of these topics is analyzed in order to gain insight into their impact on the global performance. Then, a heterogeneous network encompassing these three aspects is proposed. Master [120] : ingénieur civil électricien, Université catholique de Louvain, 2017

Single- and multi-antenna indoor systems have been designed and used for various applications for some years now, but still there is a room for improvements. Channel modeling is one of the aspects where researchers and engineers face many challenges. Since indoor environments consist of many scatterers, mobility of the nodes introduces non-stationarity in the propagation channel. To enable successful design of communication systems, such an important issue must be taken into account. With that perspective, dedicated measurement campaigns and realistic radio propagation channel models are required in order to exploit fully the improvement potential. The main contributions and findings of this thesis can be summarized as follows: - Three measurement campaigns of indoor-to-indoor radio propagation channels were conducted at 3.8 GHz. - The stationarity period duration varies between 0.8-1.5 s for different investigated cases depending on the environment. - It turns out that small-scale fading within one stationarity period follows a weighted combination of different known distributions. This mixed type of fading can be described by a Second Order Scattering Fading (SOSF) distribution which reflects any combination of Rician, Rayleigh, and double-Rayleigh fading. - New double-ring geometry-based reference and simulation models for narrowband single- and multi-antenna SOSF channels are proposed. Next, second order-statistics of these channels are derived and analyzed. - New model for temporal evolution of angular statistics is proposed. - It is shown that a Hidden Markov Model based approach can be used to reproduce time-variant statistics of small-scale fading. It can be parameterized from measurements: empirical estimation and transition matrices were extracted for the three investigated environments. We observed that predominant fading mechanism can be described by a mixture of Rayleigh and Double Rayleigh distributions. - A methodology of time-variant power delay profiles has been designed in the room-to-room dynamic scenario. - Normal distribution with zero-mean and the variance extracted from measurements can be used for mean large-scale fading modeling and dynamic large-scale fading follows a t-location scale distribution. (FSA - Sciences de l'ingénieur) -- UCL, 2017

Future vehicles will be equipped with increasing computational capabilities and various vehicular sensors, enabling intelligent vehicles to perceive their surroundings in a better way. Vehicle-to-vehicle (V2V) communication is envisioned as a complementary sensor with remarkable potential for safety-related applications. The reliability of the wireless communication link is crucial and directly related to the radio channel. Hence, a detailed understanding of the dynamic V2V propagation process is fundamental for the development of a suitable communication system. This thesis introduces insights related to the V2V radio channel and the communication performance in different vehicular scenarios. The work is based on an extensive set of wideband (1 GHz) channel sounding measurement data at 5.7 GHz and corresponding parameter estimation methods. The estimation results reveal statistical distributions for relevant wideband multipath parameters of the dynamic V2V propagation process in eight communication scenario. The intersection scenario is of particular interest for safety-related applications and the propagation therefore examined in detail. A categorization of urban intersections and three corresponding communication models are provided. In addition, a measurement-based ray tracing method is developed and applied, in order to estimate and model the locations of the scattering objects at intersections. The derived results are beneficial to realistic channel modeling approaches, in particular geometry-based stochastic channel modeling, and enhance developments towards highly reliable V2V communication systems., Zukünftig werden intelligente Fahrzeuge durch umfangreiche Sensorik und entsprechender Computerkapazität in der Lage sein ihre Umgebung umfassend wahrzunehmen. Die Fahrzeug-zu-Fahrzeug-Kommunikation erweitert maßgeblich diese Wahrnehmung und birgt für sicherheitsrelevante Anwendungen enorme Potenziale. Die hohe Zuverlässigkeit der drahtlosen Kommunikation ist dafür kritisch und hängt unmittelbar mit den Eigenschaften des Funkkanals zusammen. Eine sorgfältige Auseinandersetzung mit der dynamischen Funkausbreitung ist daher fundamental wichtig für die Entwicklung geeigneter Kommunikationssysteme. Diese Dissertation stellt Erkenntnisse zum Funkkanals und zu Leistungspotentialen der Fahrzeug-zu-Fahrzeug-Kommunikation in relevanten Verkehrssituationen vor. Die Ergebnisse der Arbeit basieren auf breitbandigen (1 GHz) Funkkanalmessdaten bei einer Trägerfrequenz von 5,7 GHz und geeigneten Parameterschätzverfahren. Die extrahierten Ergebnisse beschreiben statistisch den breitbandigen und dynamischen Mehrwegeausbreitungsprozesses in acht Kommunikationsszenarien. Das Kreuzungsszenario ist für sicherheitsrelevante Anwendungen von besonderer Bedeutung. Daher wird die entsprechende Mehrwegeausbreitung eingehend beleuchtet und drei Kreuzungskategorien mit entsprechenden Kommunikationsmodellen vorgestellt. Schließlich wird durch Anwendung eines auf Messdaten basierenden Raytracing-Verfahrens die Position der Streuer an Kreuzungen identifiziert und modelliert. Diese Ergebnisse dienen der Parametrisierung geometriebasierter, stochastischer Funkkanalmodelle und unterstützen damit die Entwicklung hochzuverlässiger Fahrzeug-zu-Fahrzeug-Kommunikationssysteme.

The smart environments and the connected human seems to be the future of wireless communications. The development of new frequency bands in the millimeter range will allow us to create high data rate communications which will led to the Wireless Body Environment Networks. In this kind of scenarios, it is expected that the user and the environment will interact. In order to develop such new applications, it is necessary to first study the propagation mechanisms and then, the communication channel underlying body centric environments. This thesis treats of channel models for 60 GHz Body Area Networks and more particularly of three kinds of scenarios: (i) the communication between an external base station and a worn node (off-body); (ii) the communication between two worn nodes (on-body); the communication between an external base station and a hand-held device (near-body). An indoor off-body channel model is numerically proposed and implemented. The model is based on the IEEE 802.11ad indoor standard channel at 60 GHz and a fast computation solution of the scattering of a plane wave by a circular cylinder. The model is developed for two orthogonal polarizations and the communications performances are studied. The on-body propagation is studied for two different configurations: line-of-sight and non-line-of-sight communications on the body. These scenarios led to different solutions for the channel knowing as, respectively, Norton’s equations and creeping formulations. These solutions are obtained using simplified geometries which has been experimentally validated. Further, in order to improve the propagation on the human body, a technique using metallic plates has been proposed. This technique has been theoretically studied using Milligton’s equations and experimentally assessed on a flat phantom with the properties of the human skin. The proposed method allows to save up to 20 dB. Finally, the near-body communication scenario has been introduced and studied. The near-body region is extended from 5 to 30 cm away of the user body which corresponds to the arm’s reach and models a handheld device. A numerical algorithm has been proposed to model indoor near-body environments. Also, a special has been given to statistical body shadowing. It has been shown that the fading follows a Two-Wave Diffuse Power distribution., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

In satellite broadcasting and broadband communications, two orthogonal polarizations can be employed for signalling. Typically, two independent carrier signals are transmitted on the horizontal and vertical linear polarizations. In this way the available frequency spectrum is used twice. Contrary to this independent use, the present work investigates the combined use of both polarizations for signalling and the possibly associated benefits. Two different modulation techniques are investigated. The first, polarization shift keying, modulates the state of polarization of the electromagnetic wave to convey information. It is based on the phase and amplitude relationship between both carriers and is advantageous for channels strongly impaired by phase noise. The second technique defines a four-dimensional signal space for the combined modulation of amplitude and phase on both carriers. It was initially introduced as 4-quadrature signalling and permits transmission with improved power efficiency. Both techniques come from optical fibre communications, where similar propagation conditions exist. The conducted investigation is based on an analysis, simulations and the experimental verification using a specially developed demonstration transmitter and receiver. The simulations compare the power efficiency of the proposed modulation techniques with that of alternatives currently in use and analyse their behaviour upon disturbance by phase noise or non-linear distortion. The demonstrator is used to validate the findings in experimental measurements and to confirm the feasibility of both proposed techniques through a live satellite transmission. En télédiffusion et dans les télécommunications à haut débit par satellite, deux polarisations orthogonales peuvent être employées pour la transmission. Habituellement, deux porteuses indépendantes sont transmises sur les polarisations linéaires horizontale et verticale. Cela rend possible une double exploitation des gammes de fréquences disponibles. Contrairement à une telle utilisation indépendante, le présent travail étudie l’utilisation combinée de ces deux polarisations pour les télécommunications ainsi que les éventuels avantages associés. Deux techniques de modulations sont soumises à l’examen : la première est la modulation de polarisation. Elle se sert de l’état de polarisation de l’onde électromagnétique pour transporter de l’information. Elle se base ainsi sur les relations de phase et d’amplitude entre les deux porteuses et se montre particulièrement avantageuse pour les canaux fortement dégradés par du bruit de phase. La seconde technique définit un espace quadridimensionnel dans lequel la modulation d’amplitude et de phase des deux porteuses est effectuée de façon conjointe. Nommée modulation 4-quadratures, elle permet une transmission avec une efficacité énergétique élevée. Ces deux techniques ont pour origine le domaine des télécommunications par fibre optique, pour lequel les conditions de propagation sont similaires. L’étude s’appuie sur une analyse préalable, des simulations et leur vérification expérimentale à l’aide de dispositifs de transmission et de réception développés spécialement à cet effet. Les simulations comparent l’efficacité énergétique des techniques proposées à celle d’alternatives utilisées actuellement et analysent leur comportement lors de perturbations par du bruit de phase et de la distorsion non-linéaire. Les résultats obtenus sont validés au moyen de mesures expérimentales avec les modèles d’exposition. Finalement, la faisabilité de ces deux techniques est démontrée lors d’une transmission en direct par satellite. Im Satellitenrundfunk und in der satellitengestützten Breitbandkommunikation können zwei orthogonal zueinanderstehende Polarisationen zur Übertragung genutzt werden. Im Allgemeinen werden dazu zwei unabhängige Trägersignale auf der linear waagerechten und senkrechten Polarisation gesendet. Die verfügbaren Frequenzbereiche werden somit doppelt genutzt. Im Gegensatz zu einer solchen unabhängigen Nutzung untersucht die vorliegende Arbeit die gemeinsame Nutzung beider Polarisationen zur Nachrichtenübertragung sowie der damit einhergehenden, möglichen Vorteile. Es werden zwei unterschiedliche Modulationsverfahren erforscht. Ersteres, die Polarisationsumtastung, verwendet den Polarisationszustand der elektromagnetischen Welle als eigentlichen Informationsträger. Sie beruht somit auf dem Phasen- und Amplitudenverhältnis beider Träger und ist besonders vorteilhaft in stark von Phasenrauschen gestörten Kanälen. Das zweite Verfahren definiert einen vierdimensionalen Signalraum in welchem die Phase und Amplitude beider Träger im Verbund moduliert werden. Die ursprünglich als 4-Quadratur Signalgebung eingeführte Technik erlaubt eine höhere Leistungseffizienz bei der Übertragung. Beide Verfahren kommen aus der optischen Übertragungstechnik, wo vergleichbare Ausbreitungsbedingungen vorherrschen. Die Untersuchung beruht auf einer vorhergehenden Analyse, Simulationen und der experimentellen Überprüfung mithilfe einer eigens zu diesem Zweck entwickelten Sende- und Empfangsvorrichtung. Die Simulationen vergleichen die Leistungseffizienz der vorgeschlagenen Verfahren mit der gegenwärtig genutzter Alternativen und analysieren das Verhalten im Fall von Beeinträchtigungen durch Phasenrauschen und nichtlineare Verzerrung. Die Simulationsresultate werden durch experimentelle Messungen am Vorführmodell bestätigt. Zusätzlich wird für beide Verfahren mittels einer Satelliten-Direktübertragung die Machbarkeit demonstriert. Для вещания и широкополосной передачи через спутники могут быть использованы две ортогональные поляризации. В общей практике передача двух независимых несущих сигналов осуществляется по горизонтальной и вертикальной линейным поляризациям. Таким образом, становится возможным двойное использование доступных диапазонов частот. В противоположность такому независимому применению, настоящее исследование посвящено изучению совместного применения обоих поляризаций в электросвязи, а так же его возможных преимуществ. Две техники модуляции вынесены на рассмотрение: первой является модуляция поляризации. В качестве носителя информации она использует состояние поляризации электромагнитной волны. Базируясь на отношении фаз и амплитуд двух несущих, она показывает себя особенно выгодной при наличии в канале фазового шума. Вторая техника определяет четырёхмерное пространство, в котором модуляция амплитуды и фазы двух несущих совершается комбинировано. Введённая под названием 4-квадратурной модуляции, она делает возможной передачу с повышенной энергетической эффективностью. Две описанные выше техники принадлежат области волоконно-оптической связи, условия распространения в которой являются сопоставимыми. Исследование основывается на предварительном анализе, симуляциях и их экспериментальной апробации при помощи специально разработанных приборов передачи и приёма. Симуляции служат для сравнения энергетической эффективности предложенных техник с используемыми в настоящее время альтернативами и анализируют их поведение во время нарушений фазовым шумом и нелинейным искажением. Результаты подтверждаются путём использования образцов в ходе экспериментальных измерений. Кроме этого, реализуемость двух предложенных техник продемонстрирована посредством прямой трансляции через спутник.

Beyond 4G wireless networks are envisioned to provide ubiquitous connectivity with ultra high capacity density in dense urban environments. For this purpose, an innovative architecture of the multi-beam Base Station (BS) providing high capacity backhaul links to distributed Relay Stations (RSs) which make access links to multiple users in a hierarchical wireless network is introduced recently. However, performance of any wireless network heavily depends on the underlying wireless propagation channel. This is even more important for the network which relies on aggressive frequency reuse (and thus heavy temporal and spectral interference), and unprecedented deployment scenarios (thus unseen spatial signal and interference propagation characteristics). With that perspective, three main components of such hierarchical wireless network are investigated in a top to bottom manner. Two modeling approaches, deterministic and empirical, are used in this thesis to characterize and model the underlying wireless propagation channels. An enhanced Ray-Tracing (RT) tool is used to characterize peculiarities of the multi-beam BS antenna and crucial parameters of relay designs, while two realistic measurement campaigns are conducted at 3.8 GHz in a typical urban microcellular environment to characterize various aspects of multi-user channels. Based on the novel BS architecture, a pathloss model is derived taking into account specicities of the narrow beamwidth antenna, and compared with existing channel models. Impact of the BS antenna on polarized Multiple-Input Multiple-Output (MIMO) aspects is investigated. Moreover, the potential of the array optimization technique in multi-beam antennas is explored to reduce the amount of Co-Channel Interference (CCI) due to excessive frequency reuse in narrow beams as well as Inter-Cell Interference (ICI) due to same frequency beams of the neighbouring cell. The system level simulations are included to show improvements in throughput densities and grade of service (delay and probability of retry). In order to ensure eciency of relay architecture designs in wireless networks, two critical parameters are investigated: (i) the orientation and (ii) the height of the RS. A signicant pathloss reduction of 10 to 15 dB is shown by orienting the relay antenna in the largest power ray direction through RT simulations. Further, the favourable RS height in terms of pathloss is investigated to provide high quality backhaul link. A trade-o between achievable pathloss and interference from the adjacent cell is suggested such that the RS is enabled with high Signalto- Interference Ratio (SINR). Multi-user MIMO (MU-MIMO) techniques consider multiple users in a single cell network to maximize the sum-throughput rather than the link throughput and to manage the resulting multi-user interference. However, the promised leverage of MU-MIMO largely depends upon the decorrelation (i.e. separation) between multi-user links. In this context, rst the validity of the Wide-Sense Stationarity (WSS) assumption is experimentally assessed for non-stationary (users) MIMO propagation channels through the Channel Matrix Collinearity (CMC) metric. Using an appropriate threshold value, typical averaged statioarity distances are found in a range of 5 to 23 m depending upon the scenario under investigation. It is followed with characterization of multi-user separation through three metrics, (i) the Shadow Fading Correlation (SFC), (ii) the CMC and (iii) the Wideband Spectral Divergence (WSD). The empirical evidence illustrates that multiple users can be considered separated in the sense of MU-MIMO when they are physically separated by a distance of 8 to 12 m or an angle of 2 to 6. Furthermore, multiuser separation results are shown roughly irrespective of the investigated metric (or, equivalently, the related signal processing aspect). For each evaluated metric, empirical multi-user separation models are also proposed. (FSA - Sciences de l) -- UCL, 2014

Historically, cryptography was created and used to deliver messages between people in such a way that only the intended receiver would be able to read them. The two persons communicating trusted each other, but not the rest of the world - for instance, not the message bearer. But what happens if we assume instead that even the receiver of a message may not be trusted by the sender, while both still have an interest in communicating? This problem is addressed by secure multi-party computation, that studies communication and shared computation between mutually distrusting parties. In a world where most of the communication happens over the Internet, and where an ever-increasing amount of computation is outsourced, for example to the cloud, multi-party computation is a subject of crucial importance. However, unconditionally secure multi-party protocols have never found practical application: the lack of realistic noisy channel models, that are required to achieve security against computationally unbounded adversaries, prevents implementation over real-world, standard communication protocols. In this thesis, we study the properties and characteristics of noisy channels, and we introduce new models based on real-world error sources that have never been studied in this context, such as delays. On the contrary, previous works mostly focused on theoretical noisy channels that have little in common with the reality of network communication. We show that the models we propose are suitable for multi-party computation by building on each of them a protocol for oblivious transfer, a fundamental cryptographic primitive that implies any secure computation. Thanks to the realism of our noisy channels, we are able to provide the first working implementation of unconditionally secure oblivious transfer over both wired and wireless networks and different Internet protocols, which we test thoroughly in an extensive set of experiments. Our constructions are not only more realistic, but also more flexible, as they allow larger ranges of error probabilities. This will eventually open the way for the widespread use of unconditionally secure multi-party computation. (FSA 3) -- UCL, 2013

In vehicular environments, the scattering environment can change very rapidly, owing to the mobility of the Tx and Rx vehicles, the relatively low height of the antennas and the potentially large number of scatterers in the surrounding environment. Vehicular radio propagation channels thus differ significantly from those of other wireless cellular networks, so that dedicated measurement campaigns and realistic radio propagation channel models are required to fully exploit their potentialities. The main contributions of this thesis are summarized as follows: - Two measurement campaigns of MIMO vehicular radio propagation channels were conducted at 5.3 GHz, - The validity of the WSS and US assumptions is assessed using the CMD, which characterizes the amount of change in the spatial structure of MIMO radio propagation channels. Stationarity distances and frequency bandwidth are 10 to 40 m long and 40 to 50 MHz wide, respectively, depending on the variability and richness of the scattering environment, - The non-stationary fading statistics are characterized stochastically, in terms of Ricean K-factor and RMS delay spread. Their time- and space-variations are strongly related to changes in the richness of the scattering environment and on the presence (or not) of a strong LoS component. They are modeled by multi-modal Gaussian distributions, - A vehicular GSCM is proposed, in which each scatterer is defined and characterized separately: the radio wave propagation with simplified ray-tracing tools and the scattering aspects with a classical fading model. The diffuse scattering is modeled in a purely stochastic manner. The GSCM is then completely parameterized and validated for SISO systems. (FSA - Sciences de l'ingénieur) -- UCL, 2013

In this thesis the multi-polarized Cognitive Radios are studied. Cognitive Radios are proposed as an interesting way to more efficiently use the frequency resources. A Cognitive Radio secondary user finds the frequency bands which are not utilized by primary users and communicates on them without interfering with the primary users. In order to achieve this goal the secondary user must be able to detect reliably and quickly the presence of a primary user in a frequency band. In this thesis, the impact of polarization on the spectrum sensing performances of cognitive radio systems is studied.First the depolarization occurring in the wireless channel is studied for two cognitive radio scenarios. This is done through an extensive measurement campaign in two outdoor-to-indoor and indoor-to-indoor scenarios where the parameters characterizing the radiowaves polarization are characterized at three different spatial scales: small-scale variation, large-scale variation and distance variation. Second, a new approach is proposed in modeling of multi-polarized channels. The polarization of received fields is characterized from an electromagnetic point of view by modeling the polarization ellipse. Theoretical formulations are proposed in order to obtain the parameters characterizing the polarization ellipse based on the signals received on three cross-polarized antennas. A system-based statistical model of the time-dynamics of polarization is proposed based on an indoor-to-indoor measurement campaign. The analytical formulations needed in order to project the polarization ellipse onto a polarized multi-antenna system are given and it is shown how the model can be generated. Third, the impact of polarization on the spectrum sensing performances of energy detection method is presented and its importance is highlighted. The performance of spectrum sensing with multi-polarized antennas is compared with unipolar single and multi-antenna systems. This analysis is based on an analytical formulation applied to the results obtained from the multi-polarized measurement campaign. The detection probability as a function of distance between the primary transmitter and the secondary terminal and the inter-antenna correlation effect on the spectrum sensing performance are studied. An important limitation of energy detector is its dependence on the knowledge of the noise variance. An uncertainty on the estimation of the noise variance considerably affects the performance of energy detector. This limitation is resolved by proposing new multi-polarized spectrum sensing methods which do not require any knowledge neither on the primary signal nor on the noise variance. These methods, referred to as “Blind spectrum sensing methods”, are based on the use of three cross-polarized antennas at the secondary terminal. Based on an analytical formulation and the results obtained from the measurement campaign, the performances of the proposed methods are compared with each-other and with the energy detection method. The effect of antenna orientation on the spectrum sensing performance of the proposed methods and the energy detection method is studied using the proposed elliptical polarization model., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Cooperative wireless communication is an attractive technique to explore the spatial channel resources by coordination across multiple links, which can greatly improve the communication performance over single links. In this dissertation, we study the cooperative multi-link channel properties by geometric approaches in body area networks (BANs) and cellular networks respectively.In the part of BANs, the dynamic narrowband on-body channels under body motions are modeled statistically on their temporal and spatial fading based on anechoic and indoor measurements. Common body scattering is observed to form inter-link correlation between links closely distributed and between links having synchronized movements of communication nodes. An analytical model is developed to explain the physical mechanisms of the dynamic body scattering. The on-body channel impacts to simple cooperation protocols are evaluated based on realistic measurements. In the part of cellular networks, the cluster-level multi-link COST 2100 MIMO channel model is developed with concrete modeling concepts, complete parameterization and implementation methods, and a compatible structure for both single-link and multi-link scenarios. The cluster link-commonness is introduced to the model to describe the multi-link properties. The multi-link impacts by the model are also evaluated in a distributed MIMO system by comparing its sum-rate capacity at different ratios of cluster link-commonness., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Antenna array design has recently focused on non-periodic structures. The possibility of having arbitrary antenna positions provides additional degrees of freedom that allow one to achieve radiation characteristics that would not be possible with periodic arrays made of the same number of elements. The sparse nature of non-periodic arrays avoids the overlap of effective areas at lower frequencies (and, hence, coupling efficiency issues) and the non-periodicity discards the presence of eigenmodes. This type of array can be used for imaging, radioastronomy, telemetry and defense applications. This calls for the development of efficient numerical methods for the analysis of non-periodic antenna arrays. In this dissertation, an efficient Method of Moments solution of non-periodic arrays has been addressed using a class of non-iterative methods that reduce the effective number of unknowns. The reduction of unknowns is achieved assuming that the currents on one of the antennas in the array can be decomposed in terms of a limited number of current distributions or Macro Basis Functions (MBFs). Then, one may perform an LU decomposition of the reduced system of equations and solve for multiple right-hand sides. This is useful as it provides a complete description of the array, i.e., the array impedance matrix and all the embedded element patterns. For most practical cases, the reduction of the MoM system of equations using MBFs becomes the dominant contribution to computation time. Two novel methods have been developed to overcome this limitation. The first one exploits multipole expansions to compute the reaction integral between MBFs. The reaction integral between two MBFs is efficiently obtained integrating over the unit sphere the scalar product between the (pre-computed) far-field patterns of these MBFs multiplied by a translation operator. In the second method, the reaction integrals between MBFs are fitted, after three physically-based transformations, to a low-order harmonic-polynomial form, using a small number of sampling points. Then, while filling the reduced MoM impedance matrix, the computational complexity devoted to obtain the interaction between two MBFs is completely independent from the number of elementary basis functions per antenna. This process is independent of the array geometry, which enables the optimization of the antennas' positions at a very low computational cost, while taking into account mutual coupling. The aforementioned methods can also be applied to the case of antenna arrays in a planar layered medium. This is possible after expressing the spatial-domain Green's function in closed-form as a finite sum of cylindrical waves and one spherical wave. In the multipole-based method, the computation of the reaction integrals is dominated by the operations associated with the spherical wave term. Thus, the presence of a planar layered medium can be accounted for without significantly increasing the computational complexity one would have in the case of a homogeneous medium. Regarding the second method, the number of harmonic-polynomial expressions that need to be evaluated is higher than in the homogeneous medium case. However, this method remains competitive and is more efficient than the one based on multipole expansions, after the fitting process. Finally, the efficient calculation of the array factors and the radiation patterns of non-periodic antenna arrays has been also addressed. First, the Non-uniform Fast Fourier Transform (NFFT) is used to evaluate array factors. Second, it is shown how the NFFT can be combined with the Macro Basis Function method to express the embedded element patterns as a series of pattern multiplication problems, each term being related to a macro basis function. The proposed formulation leads to the efficient calculation of the array factors and the array patterns of non-periodic antenna arrays. (FSA 3) -- UCL, 2012

With the rapid expansion of wireless technologies such as wireless on-body sensors, mobile devices, and wireless implants, there is a growing need to investigate the effect of human presence on the wireless communication channel. We use the electromagnetics fundamentals to model the interaction of antennas located very close to the human body, represented as a simplified cylindrical model. As a first step, the propagation trends due to an infinitesimal current source with arbitrary polarization are studied inside and outside the body. For sources with tangential-to-cylinder polarization, cylindrical wave decompositions provide the harmonics of incident fields. In case of normal-to-cylinder sources, the related boundary conditions cannot be satisfied and we derive the cylindrical wave decomposition of fields from a proposed modified addition theorem. In the second part, an in-house MoM (Method of Moment) code is developed to find the excited and coupled current distributions on two dipole antennas located very close to the cylinder. A very good agreement has been obtained between the dipole transmittances provided by the analytical/MoM model, CST Microwave Studio simulations, and experiments, including interference effects attributed to the body-attached radiating waves. Afterwards, a Parseval type transform is applied to cylindrical field harmonics to extract a compact and easy equation to find the power absorption, for normal, vertical, and horizontal polarizations of the source. Finally, a compact antenna is designed that can radiate a maximum of power along the body surface. It allows the excitation of surface waves that can carry energy along the surface of the body and maximize the coupling between antennas. (FSA 3) -- UCL, 2012

The characterization of the wireless propagation channel has always been an important issue in radio communications. However, in recent years, given the dramatic increase of demand in terms of capabilities of wireless systems, e.g. data rate, quality of service etc., the study of propagation has become of crucial importance. As measurements are generally costly and time consuming, channel models are widely used for this purpose. The modeling of propagation may rely on different types of models: empirical, statistical and deterministic. Typically, the latter, based on the electromagnetic properties of the propagating waves, relies on Ray-Tracing (RT), a geometrical optic technique used to evaluate the paths followed by rays as they interact with the environment. This technique has been widely used to predict the behavior of propagation both in outdoor and indoor scenarios. Classic RT tools take into account line of sight propagation, specular reflection and diffraction, with penetration included when indoor propagation is considered. With the advent of diversity techniques and MIMO systems, whose goal is to exploit the multi-dimensional properties of a channel, it is required that the prediction models are capable to analyze propagation in depth, i.e. including polarization, delay and angular behavior of a channel. A 3-D RT tool has the great advantage to be able to provide inherently that kind of information, but to achieve a sufficient accuracy, it is necessary to develop an advanced prediction tool. To this goal, a pre-existent RT tool has been improved by implementing in it propagation mechanisms as penetration, diffuse scattering and contributions by vegetation. (FSA 3) -- UCL, 2012

This thesis treats of channel models for polarized multi-antenna wireless systems. Polarized multi-antenna systems are systems that use perpendicularly polarized, co-located antennas at the base station and at the mobile terminal, in order to benefit from the so-called polarization diversity. Such systems benefit from the advantages of MIMO systems while still maintaining a compact equipment size. Two models will be presented in this thesis. The first one is the Polarized-Input Polarized-Output (PIPO) channel model, the second one is the Polarized-Diffuse-Directional channel model. The PIPO model is a statistical channel model for tri-polarized to tri-polarized communication systems. A tri-polarized antenna system is a tranceiver using three perpendicular antennas. The aim of the PIPO channel model is to have a model that has a simple mathematical structure, so it can be used for solving precoding equations or capacity calculations. Although the PIPO model has a very simple structure, it takes the following parameters into account: coherent channel component, cross-polar channel power imbalance, inter-channel correlation, short- and long-scale time variance. Experimental measurements are used to parameterize the model. It is shown how the model parameters are extracted from experimental measurements, and the results are analyzed to allow further simplification of the model. The PDD model, on the other hand, is a geometry-based stochastic channel model. It models the channel as a sum of clusters, where each cluster consists of groups of multipath components (MPCs). The PDD model includes two novelties that will be developed in detail in this thesis. - The model considers polarization on a per-cluster basis. This permits to have a more accurate description of the polar-angular spectrum. - The diffuse multipath component (DMC) is included by considering a diffuse component for each cluster. The diffuse cluster component is then modeled as the sum of a set of diffuse MPCs. The model is specified in detail, and it is shown how the model can be generated. Experimental measurements were carried out to parameterize the model. A new extraction technique for extracting the specular-diffuse clusters from the measurements is proposed. This technique is based on joint clustering of the specular MPCs and the bins of the diffuse component. The experimental results are analyzed, and superimposed with environment information to gain further insight into the physical aspects of clustered propagation. Finally, both models are validated. Several validation metrics are introduced, and their pertinence in the context of polarized MIMO systems is highlighted. Both models are successfully validated, and the advantages and limitations of each models are investigated. Cette thèse traite des modèles de canal pour systèmes sans-fils multi-antennes polarisés. Des systèmes multi-antennes polarisés sont des systèmes qui utilisent des antennes polarisées perpendiculairement co-localisées à la station de base et au terminal mobile, dans le but de bénéficier de la diversité de polarisation. De tels systèmes peuvent bénéficier des avantages des systèmes MIMO tout en diminuant l'encombrement des équipements. Deux modèles seront présentés dans cette thèse. Le premier est le modèle Polarized-Input Polarized-Output (PIPO), le second est le modèle Polarized-Diffuse-Directional (PDD). Le modèle PIPO est un modèle statistique pour des systèmes de communication tri-polaire à tri-polaire. Un système tri-polaire est un émetteur ou un récepteur qui utilise trois antennes perpendiculaires. Le but du modèle de canal PIPO est d'avoir un modèle qui a une structure mathématique simple, afin qu'il puisse être utilisé pour résoudre des équations de précodage ou des calculs de capacité. Malgré la structure simple du modèle PIPO, il tient compte des paramètres suivants: la composante cohérente du canal, les différences de puissance entre canaux cross-polaires, la corrélation entre canaux, les variations à courte et à longue échelle de temps. Des mesures expérimentales ont été réalisées afin de paramétriser le modèle. Les techniques pour extraire les paramètres du modèle des mesures expérimentales sont présentées, et les résultats sont analysés afin de permettre une simplification supplémentaire du modèle. Le modèle PDD, quant à lui, est un modèle de canal stochasique-géométrique. Il modélise le canal comme une somme de clusters, où chaque clusters est composé d'un groupe de chemins multi-trajets. Le modèle PDD inclut les deux nouveautés suivantes qui seront développées en détail dans cette thèse. - Le modèle considère une polarisation par cluster. Ceci permet d'avoir une description plus exacte du spectre angulaire-polaire. - La composante diffuse est prise en compte en incluant une composante diffuse pour chaque cluster. La composante diffuse d'un cluster est alors modelisée comme une somme de multi-trajets diffus. Le modèle est spécifié en détail, et il est présenté comment le modèle peut être généré. Des mesures expérimentales ont été faites afin de paramétriser le modèle. Une nouvelle technique d'extraction est proposée pour extraire les clusters spéculaires-diffus. Cette technique est basée sur le clustering conjoint des multi-trajets spéculaires et des "bins" de la composante diffuse. Les résultats expérimentaux sont analysés, et superposés avec l'information de l'environnement de mesure afin d'avoir une connaissance accrue des aspects physiques de la propagation par clusters. Finalement, les deux modèles sont validés. Plusieurs métriques de validations sont introduites, et leur pertinence dans le cadre des systèmes MIMO polarisés est mis en avant. Les deux modèles sont validés avec succès, et les avantages et limitations de chaque modèle sont investigués., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

This thesis treats of channel models for polarized multi-antenna wireless systems. Polarized multi-antenna systems are systems that use perpendicularly polarized, co-located antennas at the base station and at the mobile terminal, in order to benefit from the so-called polarization diversity. Such systems benefit from the advantages of MIMO systems while still maintaining a compact equipment size. Two models will be presented in this thesis. The first one is the Polarized-Input Polarized-Output (PIPO) channel model, the second one is the Polarized-Diffuse-Directional channel model. The PIPO model is a statistical channel model for tri-polarized to tri-polarized communication systems. A tri-polarized antenna system is a tranceiver using three perpendicular antennas. The aim of the PIPO channel model is to have a model that has a simple mathematical structure, so it can be used for solving precoding equations or capacity calculations. Although the PIPO model has a very simple structure, it takes the following parameters into account: coherent channel component, cross-polar channel power imbalance, inter-channel correlation, short- and long-scale time variance. Experimental measurements are used to parameterize the model. It is shown how the model parameters are extracted from experimental measurements, and the results are analyzed to allow further simplification of the model. The PDD model, on the other hand, is a geometry-based stochastic channel model. It models the channel as a sum of clusters, where each cluster consists of groups of multipath components (MPCs). The PDD model includes two novelties that will be developed in detail in this thesis. - The model considers polarization on a per-cluster basis. This permits to have a more accurate description of the polar-angular spectrum. - The diffuse multipath component (DMC) is included by considering a diffuse component for each cluster. The diffuse cluster component is then modeled as the sum of a set of diffuse MPCs. The model is specified in detail, and it is shown how the model can be generated. Experimental measurements were carried out to parameterize the model. A new extraction technique for extracting the specular-diffuse clusters from the measurements is proposed. This technique is based on joint clustering of the specular MPCs and the bins of the diffuse component. The experimental results are analyzed, and superimposed with environment information to gain further insight into the physical aspects of clustered propagation. Finally, both models are validated. Several validation metrics are introduced, and their pertinence in the context of polarized MIMO systems is highlighted. Both models are successfully validated, and the advantages and limitations of each models are investigated. Cette thèse traite des modèles de canal pour systèmes sans-fils multi-antennes polarisés. Des systèmes multi-antennes polarisés sont des systèmes qui utilisent des antennes polarisées perpendiculairement co-localisées à la station de base et au terminal mobile, dans le but de bénéficier de la diversité de polarisation. De tels systèmes peuvent bénéficier des avantages des systèmes MIMO tout en diminuant l'encombrement des équipements. Deux modèles seront présentés dans cette thèse. Le premier est le modèle Polarized-Input Polarized-Output (PIPO), le second est le modèle Polarized-Diffuse-Directional (PDD). Le modèle PIPO est un modèle statistique pour des systèmes de communication tri-polaire à tri-polaire. Un système tri-polaire est un émetteur ou un récepteur qui utilise trois antennes perpendiculaires. Le but du modèle de canal PIPO est d'avoir un modèle qui a une structure mathématique simple, afin qu'il puisse être utilisé pour résoudre des équations de précodage ou des calculs de capacité. Malgré la structure simple du modèle PIPO, il tient compte des paramètres suivants: la composante cohérente du canal, les différences de puissance entre canaux cross-polaires, la corrélation entre canaux, les variations à courte et à longue échelle de temps. Des mesures expérimentales ont été réalisées afin de paramétriser le modèle. Les techniques pour extraire les paramètres du modèle des mesures expérimentales sont présentées, et les résultats sont analysés afin de permettre une simplification supplémentaire du modèle. Le modèle PDD, quant à lui, est un modèle de canal stochasique-géométrique. Il modélise le canal comme une somme de clusters, où chaque clusters est composé d'un groupe de chemins multi-trajets. Le modèle PDD inclut les deux nouveautés suivantes qui seront développées en détail dans cette thèse. - Le modèle considère une polarisation par cluster. Ceci permet d'avoir une description plus exacte du spectre angulaire-polaire. - La composante diffuse est prise en compte en incluant une composante diffuse pour chaque cluster. La composante diffuse d'un cluster est alors modelisée comme une somme de multi-trajets diffus. Le modèle est spécifié en détail, et il est présenté comment le modèle peut être généré. Des mesures expérimentales ont été faites afin de paramétriser le modèle. Une nouvelle technique d'extraction est proposée pour extraire les clusters spéculaires-diffus. Cette technique est basée sur le clustering conjoint des multi-trajets spéculaires et des "bins" de la composante diffuse. Les résultats expérimentaux sont analysés, et superposés avec l'information de l'environnement de mesure afin d'avoir une connaissance accrue des aspects physiques de la propagation par clusters. Finalement, les deux modèles sont validés. Plusieurs métriques de validations sont introduites, et leur pertinence dans le cadre des systèmes MIMO polarisés est mis en avant. Les deux modèles sont validés avec succès, et les avantages et limitations de chaque modèle sont investigués., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/published

A Land Mobile Satellite System (LMSS) is a satellite-based communication system that provides voice and data communications services as Internet, telephone, radio, TV, etc., to terrestrial mobile users. In a LMSS, the signal information travels from the satellite to the final moving terminal at the Earth. Furthermore, before arriving at the terminal, the signal propagates across the ionosphere and the troposphere causing impairments to the wave. Terrain, trees and buildings will cause the main distortions in the signal. All the impairments and distortions need to be characterized in order to understand the propagation phenomena affecting the channel, and to develop propagation models obtaining rules to relate these phenomena to the frequency, speed between the satellite and the mobile terminal, elevation angle or type of antenna. During the different stages of developing new systems and terminals, the channel characteristics need to be known, as they affect in the design of the different components of the system as the modem, the codec, etc. A wide range of experimental measurements have been performed on satellite mobile communication systems to obtain essential channel characteristics and to modelize the LMS channel. In this thesis, the Versatile Two-State statistical Land Mobile Satellite (LMS) channel model was taken as starting point. The model has been analyzed and improved. An automatic algorithm has been developed to extract the model parameters from experimental measurements. Finally a time series synthesizer has been implemented to reproduce the time-varying nature of the channel in order to help the system designer. (FSA 3) -- UCL, 2011

Les avancées technologiques de ces dernières années, combinées au succès avéré et toujours croissant des communications sans fil, ont tout naturellement donné naissance à un nouveau type de réseaux sans fil, communément appelés Body Area networks. A terme, ces réseaux corporels sans fil doivent permettre à un ensemble de senseurs bio-médicaux répartis sur le corps humain de communiquer, soit pour échanger des informations en vue d'un traitement en temps réel du patient, soit pour enregistrer des données physiologiques en vue d'une analyse ultérieure.L’objectif de cette Thèse vise la réduction de la consommation énergétique au niveau des senseurs de sorte à leur garantir une autonomie de quelques mois, voire de quelques années. En réponse à cette contrainte énergétique, une association innovante de deux technologies émergentes est proposée, à savoir une combinaison des transmissions à ultra-large bande aux systèmes à multiples antennes. Une nouvelle architecture pour les réseaux corporels sans fil est donc envisagée pour laquelle les performances doivent être évaluées. Notre principale contribution à cet objectif consiste en la proposition d'une modélisation spatio-temporelle complète du canal de transmission dans le cadre de senseurs répartis autour du corps. Cette modélisation fait appel à la définition de nouveaux modèles, l'élaboration d'outils spécifiques d'extraction de paramètres et une compréhension fine des mécanismes de propagation liés à la proximité du corps humain. Ce manuscrit présente les résultats majeurs de nos recherches en cette matière., Doctorat en Sciences de l'ingénieur, info:eu-repo/semantics/nonPublished

Projecte final de carerra fet en col.laboració amb Université Catholique de Louvain This document has been divided in 5 chapters. The rst one has consisted on an introduction to better understand the aims of this project, a brief description of the state-of-the-art and how the project is structured. Chapter 2 explains in detail how measurements are set and all the instruments involved with them. In Chapter 3 the statistical analysis of the channels is developed from the VNA measurements results. Chapter 4 investigates the diversity bene ts in terms of both BER and variance. Finally, Chapter 5 contains the nal conclusions of the project and future work. Actually, there is also Chapter 6, which is composed of the Annexes, where there is the complete set of measurements results and all the gures that were not shown in the document because of spatial reasons.