Abstract This thesis focuses on THz band channel modeling and characterization. This vast frequency band spans from 100 GHz to 10 THz. The approximately 10,000 GHz bandwidth together with advances in THz capable electronics have made this band highly potential for many future applications, e.g., imaging and nanodevice-to-nanodevice communications. The latter is the reference application of this thesis and it focuses on the communication among very small and simple devices. The main focus of the thesis is on the THz channel characterization. Therefore, the channel models presented herein are also suitable for communications at macroscopic scale. The THz band offers opportunities, but has many problems as well. One of these is molecular absorption, which causes frequency selective fading to signals. The fading is caused by the signals’ energy absorption in the resonance frequencies of the molecules in the communication medium. Based on the conservation of energy, the absorption is understood to cause a new type of noise in the THz links: transmission induced noise. This noise component is analyzed from multiple physical viewpoints. The THz signals have short enough wavelengths to theoretically allow scattering on aerosols in the atmosphere. Scattering causes frequency dependent loss of the signals, but also a signal spread in time over multiple scattering events. It is shown here that in some specific atmospheric conditions the scattering causes signal loss and time spread. In addition to the theoretical channel models, measurements on a variety of propagation phenomena are con- ducted and analyzed. These include penetration losses, rough surface reflections and scattering, and diffraction. Through the measurements, it can be shown that the THz band communications is feasible in non-line-of-sight (NLOS) conditions in spite of the above phenomena. In the last part of this thesis, stochastic geometry is applied to the THz band in order to estimate the mean interference power and outage probabilities in dense networks formed from nanodevices. Because of the large losses in the channel, large interference levels require large numbers of devices. Stochastic geometry offers perfect tools to estimate the mean interference, and also in the case of directional antennas, which are most likely implemented in all the THz band devices due to large power losses in the channel. / Tiivistelmä Tämä väitöskirja paneutuu THz-taajuisien kanavien mallintamiseen. Tämä valtavan laaja kaista ulottuu sadasta gigahertsistä aina kymmeneen terahertsiin asti. Noin 10000 GHz:n kaistanleveys, yhdistettynä THz-taajuudet mahdollistavien elektroniikan komponenttien kehitykseen, tekee tästä kaistasta erittäin houkuttelevan vaihtoehdon moniin tulevaisuuden sovelluksiin. Näitä ovat mm. kuvantaminen ja nanolaitteiden välinen tietoliikenne. Viimeisin on tämän väitöskirjan viitekehys ja keskittyy hyvin pienien ja yksinkertaisien laitteiden väliseen viestintään. Työn keskittyy pääosin THz-kanavamallinnukseen, joten esitettyjä tuloksia voidaan hyödyntää myös nanoskaalaa suuremmissa verkoissa. THz-taajuudet avaavat mahdollisuuksia, mutta tuovat myös ongelmia. Yksi näistä on molekulaariabsorptio, joka aiheuttaa taajuusselektiivistä häipymää signaaleihin. Tämä ilmiö johtuu sähkömagneetisen energian absorbotumisesta ilman molekyylien resonanssitaajuuksilla. Sen on myös arveltu johtavan uudenlaisen kohinan syntyyn, lähetysten indusoimaan kohinaan, perustuen energian säilymislakiin. Lähetysten indusoimaa kohinaa tutkitaan tässä työssä erilaisista fysikaalisista näkökulmista. THz-taajuisen säteilyn aallonpituus on riittävän lyhyt mahdollistamaan sironta ilmassa olevista aerosoleista. Sironta aerosoleista johtaa taajusriippuvaan signaalitehon häviöön, mutta myös signaalitehon leviämiseen ajassa monisironnan kautta. Työssä todennetaan, että sopivissa olosuhteissa sironta lisää häviöitä ja viivehajetta kanavassa. Teoreettisten kanavamallien lisäksi analysoidaan mittauksin alemmilta taajuusalueilta tuttuja etenemisilmiöitä, kuten signaalin läpäisyä, heijastuksia ja sirontaa pinnoilta, sekä diffraktioita. Mittausten kautta voidaan näyttää, että THz-taajuinen tiedonsiirtolinkki voidaan luoda myös ilman näköyhteyttä yllä mainittujen ilmiöiden kautta. Työn viimeisessä osassa sovelletaan stokastista geometriaa THz-taajuuksille keskimääräisen häiriötehon ja toimintakyvyttömyystodennäköisyyden selvittämiseksi tiheissä nanolaitteiden muodostamissa verkoissa. Isojen kanavahäviöiden takia suuri häiriötaso vaatii suuren määrän laitteita. Stokastinen geometria antaa täydelliset työkalut häiriötason estimointiin. Tätä voidaan myös hyödyntää suuntaavien antennien tapauksessa, joita tullaan suurella todennäköisyydellä käyttämään kaikissa THz-laitteissa johtuen suurista signaalihäviöistä kanavassa.

Disertační práce se zabývá optickým digitálně-analogovým převodníkem, jako alternativou optické části koncové vysílací jednotky (optický front-end) určené pro VLC (visible light communication) aplikace. Stěžejní část práce, která se věnuje numerickému modelování optického kanálu, prezentuje vliv bitové hloubky, topologie koncové části optického vysílače a geometrického uspořádání na přenášený signál. Součástí práce je návrh, realizace a ověření parametrů optického digitálně-analogového převodníku vycházející z předcházejících simulací. V poslední řadě práce obsahuje demonstraci vysokorychlostní optické komunikace s využitím navrženého VLC optického vysílače.

No description available.

This dissertation presents research performed in the areas of radio wave propagation measurement and modeling, smart antenna arrays, and software-defined radio development. A four-channel, wideband, software-defined receiver was developed to serve as a test bed for wideband measurements and antenna array experiments. This receiver was used to perform vector channel measurements in terrestrial and air-to-ground environments using an antenna array. ent results served as input to radio channel simulations based on three geometric channel models. The simulation results were compared to measurement results to evaluate the performance of the radio channel models under test. Criteria for evaluation include RMS delay spread, excess delay spread, signal envelope fading, antenna diversity gain, and gain achieved through the use of a two-dimensional rake receiver. This research makes contributions to the wireless communications field through analysis, development, measurement, and simulation that builds upon past theoretical and experimental results. Contributions include a software-defined radio architecture, based on object oriented techniques, that has been developed and successfully demonstrated using the wideband receiver. This research has produced new wideband vector channel measurements to provide extensive characterization results facilitating simulation of emerging wireless technology for commercial and military communications systems. Original ways of interpreting multipath component strength and correlation for antenna arrays have been developed and investigated. A novel geometric air-to-ground ellipsoidal channel model has been developed, simulated, and evaluated. Other contributions include an evaluation of two popular radio channel models, a geometric channel simulator for producing channel impulse responses, and analytical derivation results related to channel modeling geometries and multipath channel measurement processing. In addition to new results, existing theory and earlier research results are discussed. Fundamental theory for antenna arrays, vector channels, multipath characterization, and channel modeling is presented. Contemporary issues in software radio and object orientation are described, and measurement results from other propagation research are summarized. / Ph. D.

Approved for public release, distribution is unlimited / Direct-Sequence Spread Spectrum (DSSS) modulation is being advanced as the physical-layer basis for Seaweb undersea acoustic networking. DSSS meets the need for channel tolerance, transmission security, and multi-user access. This thesis investigates the performance of subspace-decomposition blind-equalization algorithms as alternatives to RAKE processing of DSSS signals. This approach is tailored for superior performance in time-dispersive and frequency-dispersive channels characteristic of ocean acoustic propagation. Transmitter and receiver structures are implemented in Matlab and evaluated with a statistics-based model of a doubly spread channel with additive noise. Receiver performance is examined using Monte Carlo simulation. Biterror rates versus signal-to-noise ratio are presented for various multipath assumptions, noise assumptions, and receiver synchronization assumptions. / Lieutenant, Hellenic Navy

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.<p><p>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. <p><p>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. <p><p>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. <p><p>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. <p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

The band around 60 GHz is interesting for BAN applications mainly for lowerinterference than at microwave frequencies, wide available band adapted to On-Off Keying(OOK) modulation for low energy consumption and low data rate communication (under10 Mbps), antenna miniaturization. Nevertheless, due to high attenuation at this frequency,the design of a reliable and energy-effective communications for BANs requires a detailedanalysis of the body channel. A planar and compact SIW horn antenna was designed and usedfor body channel measurements at 60 GHz. The main contribution in the antenna design is thebandwidth enhancement covering the whole available band around 60 GHz compared to thesame antenna type available at this frequency. The on-body measurements with this antennashow that short-distance and LOS (Line Of Sight) links are possible at 60 GHz. The bodydynamic is taken into account by statistical off-body channel measurements. For the firsttime, measurements are done for the same scenarios at 60 GHz and another frequency in theUltra WideBand suitable with OOK impulse radio modulation. By taking into accounttransmission power standards and low power consumption receivers sensitivity in theliterature, the potentiality of 60 GHz for BAN is shown with an outage probability lower than8 % whereas this parameter is lower than 15 % at 4 GHz. When characterizing antenna onbody, difficulties arise for antenna de-embedding due to the antenna-body coupling. In fact,the antenna gain depends on transmitter-receiver distance on body. For the first time, aformulation of the vertical dipole gain on body is given. Also a new theoretical approachbased on the complex images method is proposed to compare two types of canonical antennaradiating on body. A vertical dipole and different rectangular apertures are normalizedthrough their input impedance with the same accepted power. The aperture input impedanceformulation has been developed during this study. The aperture efficiencies are 10% higherwhen antennas are at a height lower than 3 mm above the body phantom. The received powerincreases with the antenna size only for phantom direct touch, the difference among antennasis lower than 4 dB for the considered antennas limited with a monomode configuration. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Machine-to-machine (M2M) communication is becoming an important aspect of warehouse management, remote control, robotics, traffic control, supply chain management, fleet management and telemedicine. M2M is expected to become a significant portion of the Industrial Internet and, more broadly, the Internet of Things (IoT). The environments in which M2M systems are expected to operate may be challenging in terms of radio wave propagation due to their cluttered, multipath nature, which can cause deep signal fades and signal depolarization. Polarization diversity in two dimensions is a well-known technique to mitigate such fades. But in the presence of reflectors and retarders where multipath components arrive from any direction, we find the detrimental effects to be three-dimensional and thus consider herein mitigation approaches that are also 3D. The objectives of this dissertation are three. First, to provide a theoretical framework for depolarization in three dimensions. Second, to prepare a tripolar antenna design that meets cost, power consumption, and simplicity requirements of M2M applications and that can mitigate the expected channel effects. Finally, to develop new channel models in three dimensional space for wireless systems. Accordingly, this dissertation presents a complete description of 3D electromagnetic fields, in terms of their polarization characteristics and confirms the advantage of employing tripolar antennas in multipath conditions. Furthermore, the experimental results illustrate that highly variable depolarization occurs across all three spatial dimensions and is dependent on small changes in frequency and space. Motivated by these empirical results, we worked with a collaborating institution to develop a three-dimensional tripolar antenna that can be integrated with a commercially available wireless sensor. This dissertation presents the testing results that show that this design significantly improves channels over traditional 2D approaches. The implications of tripolar antenna integration on M2M systems include reduction in energy use, longer wireless communication link distances, and/or greater link reliability. Similar results are shown for a planar antenna design that enables four different polarization configurations. Finally, the work presents a novel three-dimensional geometry-based stochastic channel model that builds the channel as a sum of shell-like sub-regions, where each sub-region consists of groups of multipath components. The model is validated with empirical data to show the approach may be used for system analyses in indoor environments.

Au cours de ces dernières années, le réseau électrique est devenu un candidat incontournable pour la transmission de données à haut débit à l’intérieur des bâtiments. De nombreuses solutions sont actuellement à l’étude afin d’optimiser ces technologies connues sous le nom Courants Porteurs en Ligne (CPL) ou PLC (Power-Line Communications). La technique MIMO (Multiple-Input Multiple-Output) a été tout récemment transposée au réseau filaire électrique pour lequel différents modes d’alimentation peuvent être envisagés entre la phase, le neutre et la terre. Dans le cadre de cette thèse, nous proposons deux contributions originales à l’étude des communications numériques sur le réseau électrique à l’intérieur des bâtiments. La première contribution concerne la modélisation du canal MIMO-PLC. En repartant d’un modèle du canal paramétrique SISO (Single-Input Single-Output) connu dans la littérature, nous proposons un modèle du canal MIMO en considérant un nouveau paramètre caractérisant la corrélation spatiale. Le modèle proposé permet de représenter fidèlement la corrélation spatiale des mesures effectuées à l’échelle européenne. La deuxième contribution concerne le bruit impulsif présent sur le réseau électrique domestique qui constitue un problème majeur dans les systèmes de communications. Nous proposons une méthode basée sur la notion de capacité de coupure afin d’optimiser le débit moyen dans les systèmes OFDM (Orthogonal Frequency Division Multiplexing) soumis aux bruits impulsifs. D’abord, nous étudions la capacité du système en fonction d’une marge de bruit fournie aux symboles transmis. Ensuite, nous déterminons l’expression analytique de la probabilité de coupure (outage) d’un symbole OFDM en fonction de cette marge, en étudiant de manière détaillée l’interaction entre l’impulsion de bruit et le symbole. A partir de ces deux calculs, nous déduisons la capacité de coupure. Puis, nous proposons une approche qui maximise l’espérance mathématique du débit reçu. Finalement, nous présentons les résultats obtenus dans le cas particulier d’une transmission à haut débit sur PLC en présence de bruits impulsifs. / In recent years, the electrical network has become an essential candidate for high-speed data transmission inside buildings. Many solutions are currently underway in order to optimize these technologies known under the name of in-home Power-Line Communications (PLC). Multiple-Input Multiple-Output (MIMO) technique has recently been transposed into power-line networks for which different signal feeding possibilities can be considered between phase, neutral and earth wires. In this thesis, we propose two original contributions to indoor broadband PLC. The first contribution concerns the MIMO-PLC channel modeling. Based on a Single-Input Single-Output (SISO) parametric channel model presented in the literature, we propose a MIMO one by considering a new parameter which characterizes the spatial correlation. The proposed model enables an accurate description of the spatial correlation of European MIMO PLC field measurements. The second contribution is related to the impulsive noise present in power-line networks which constitutes a major problem in communications systems. We propose an outage capacity approach in order to optimize the average data rate in Orthogonal Frequency Division Multiplexing (OFDM) systems affected by impulsive noise. First, we study the channel capacity as a function of a noise margin provided to the transmitted symbols. Then we determine the analytical expression of the outage probability of an OFDM symbol in terms of the noise margin, by studying in detail the interaction between the noise impulse and the symbol. Based on the two aforementioned relations, we deduce the outage capacity. Then we propose an approach that enables to maximize the average system data rate. Finally, we present the results in the particular case of indoor broadband PLC in the presence of impulsive noise.

The objective of this dissertation is to investigate the performance of the recently proposed MIMO technology in real indoor environments based on channel measurements centered at 5.8 GHz. First, a MIMO channel measurement system is implemented based on the virtual antenna array infrastructure. This measurement testbed can acquire the wideband channel matrices of MIMO systems with arbitrary array geometries. The measurement system structure and measurement procedure are described in detail in the first part. The second part is about MIMO channel modeling. Two novel number-of-sources detection algorithms, which are more robust and suitable for practical applications than traditional methods, are proposed. The MIMO path parameters, including delay, DOA, and DOD are estimated from measured data by several estimation schemes based on the ESPRIT algorithm. The accuracies of these estimation schemes are evaluated in terms of the estimation error between the capacities of the directly measured and the reconstructed channels. Moreover, based on ray tracing and measurement results, the spherical wave model is suggested to replace conventional plane wave model in order to prevent the capacity underestimation of short-range MIMO channels. An important observation is that short-range MIMO can achieve full capacity in free space channel. A threshold distance is derived to determine whether the spherical wave model is necessary. In the final part, measurements conducted in the Residential Laboratory are used to investigate the impact of element spacing, LOS, interference, spatial correlation between the interfering and data links, and stream control. A capacity enhancement scheme, which improves the performance by adapting the element locations, is implemented using our measurement system. Finally, the performances of beam selection and antenna selection in combination with MIMO technologies are compared in both narrowband and wideband channels.