Dissertations / Theses on the topic 'Transmission Spectrum'

The rapid development and deployment of wireless devices demand for the efficient spectrum usage to ensure quality of service. Thus, regulatory bodies opened new dimensions regarding the sharing of spectrum among the owners, keeping the respect of exclusive users as a primary objective. The main concern of secondary spectrum access is to protect primary licensed user from harmful interference of secondary devices. Accordingly, there are some rules to control interference aggregation to the primary victim, and this is accomplished by characterizing the aggregate interference. Statistical models of interference aggregation have been considered in previous studied. But, in real systems, secondary users do not follow the rules all the time and there might be erroneous transmission due to different reasons. In this thesis we developed a statistical model of aggregate interference when we take erroneous transmissions into account. In addition, probability distribution of the aggregate interference is approximated through its cumulants. The derived approximation shows a good agreement with Monte Carlo simulation result in tail region under specific conditions. It is also shown that even a single wrongdoer may dramatically degrade spectrum sharing opportunities particularly when it is relatively close to the primary receiver depending on the transmitted power to the victim receiver. Finally, impacts of erroneous transmission on the secondary access under variations in the density of opportunistic users and their probability of wrong transmission are investigated.

A serial search process achieved by reference code clock frequency offset suffers from a degraded autocorrelation function between the two codes because of the differing chip rates. In this thesis a computer simulation is used to investigate the code decorrelation, and the results are employed to obtain the mean acquisition time for the serial search process. The analysis is extended to include a CCD. type of matched filter following the integrate and dump detector, and to investigate the improvements in acquisition time that may be achieved over the simple serial search process if a search-lock strategy is employed. The effects of jitter and phase offset upon the error probability of the recovered data are investigated both theoretically and by measurement for the particular case of code modulation by sequence inversion keying. A tracking loop is presented that has been shown to maintain reference code phase offset to within ~ 0.01 chips under conditions where the noise on the communications link has made the recovered data unusable for most purposes. Finally, an application of spread spectrum techniques to small local area networks is presented, and a discussion of the effects of the crosscorrelation noise from the other user spreading codes upon the tracking loop's discriminator characteristic is given.

Spectrum sensing plays a key role for radio resource awareness in cognitive radio. To enhance the capabilities of cognitive radio nodes, exploiting the spatial resource in addition to frequency and time re-sources seems reasonable. This thesis investigates the possibility of exploiting the spatial resources during sensing and transmission using sector antennas which is also termed as directional spectrum sensing and transmission. The measured radiation patterns from fabricated antenna and radiation patterns obtained from analytical expressions representing circular array of dipole are used for performance analysis. A ray tracer tool is used for modelling the urban environment as well as for wave propagation simulation. The power angular profiles obtained at different locations are further processed in MATLAB using measured and analytical radiation patterns to evaluate the performance in terms of spatial opportunity and detection of weak primary signals. The results show that exploiting the spatial dimension in spectrum sensing using sector antennas increase the opportunities for secondary communication and also improves the detection of primary signals as compared with an omni-directional antenna. Additionally, directional sensing and trans-mission are studied together using analytical radiation patterns. The results show that the service probability as well as range of communica-tion increases with an increase in number of sectors but saturation is achieved when nine sectors are used, indicating that six sectors antenna is the optimum choice for exploring the spatial resource in cognitive radio in a typical multipath urban environment.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1988.
Title as it appears in M.I.T. Graduate List, June 1988: Imbedding data into television signals.
Bibliography: leaves 43-44.
by Tareq I. Hoque.
M.S.

GJ 436b is a prime target for understanding warm Neptune exoplanet atmospheres and a target for multiple James Webb Space Telescope (JWST) Guaranteed Time Observation programs. Here, we report the first space-based optical transmission spectrum of the planet using two Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) transit observations from 0.53 to 1.03 mu m. We find no evidence for alkali absorption features, nor evidence of a scattering slope longward of 0.53 mu m. The spectrum is indicative of moderate to high metallicity (similar to 100-1000x solar), while moderate-metallicity scenarios (similar to 100x. solar) require aerosol opacity. The optical spectrum also rules out some highly scattering haze models. We find an increase in transit depth around 0.8 mu m in the transmission spectra of three different sub-Jovian exoplanets (GJ 436b, HAT-P-26b, and GJ 1214b). While most of the data come from STIS, data from three other instruments may indicate this is not an instrumental effect. Only the transit spectrum of GJ 1214b is well fit by a model with stellar plages on the photosphere of the host star. Our photometric monitoring of the host star reveals a stellar rotation rate of 44.1 days and an activity cycle of 7.4 years. Intriguingly, GJ 436 does not become redder as it gets dimmer, which is expected if star spots were dominating the variability. These insights into the nature of the GJ 436 system help refine our expectations for future observations in the era of JWST, whose higher precision and broader wavelength coverage will shed light on the composition and structure of GJ 436b's atmosphere.

WASP-39b is a hot Saturn-mass exoplanet with a predicted clear atmosphere based on observations in the optical and infrared. Here, we complete the transmission spectrum of the atmosphere with observations in the near-infrared (NIR) over three water absorption features with the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) G102 (0.8-1.1 mu m) and G141 (1.1-1.7 mu m) spectroscopic grisms. We measure the predicted high-amplitude H2O feature centered at 1.4 mu m and the smaller amplitude features at 0.95 and 1.2 mu m, with a maximum water absorption amplitude of 2.4 planetary scale heights. We incorporate these new NIR measurements into previously published observational measurements to complete the transmission spectrum from 0.3 to 5 mu m. From these observed water features, combined with features in the optical and IR, we retrieve a well constrained temperature T-eq = 1030(20)(+30) K, and atmospheric metallicity 151(46) (+48) solar, which is relatively high with respect to the currently established mass-metallicity trends. This new measurement in the Saturn-mass range hints at further diversity in the planet formation process relative to our solar system giants.

Kyoto University (京都大学)
0048
新制・課程博士
博士(情報学)
甲第11908号
情博第180号
新制||情||40(附属図書館)
23688
UT51-2005-N742
京都大学大学院情報学研究科通信情報システム専攻
(主査)教授 吉田 進, 教授 酒井 英昭, 教授 佐藤 亨
学位規則第4条第1項該当

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2002.
Thesis advisor(s): Roberto Cristi, Joseph Rice. Includes bibliographical references (p. 129-130). Also available online.

GJ. 1214b is the most studied sub-Neptune exoplanet to date. Recent measurements have shown its near-infrared transmission spectrum to be flat, pointing to a high-altitude opacity source in the exoplanet 's atmosphere, either equilibrium condensate clouds or photochemical hazes. Many photometric observations have been reported in the optical by different groups, though simultaneous measurements spanning the entire optical regime are lacking. We present an optical transmission spectrum (4500-9260 angstrom) of GJ. 1214b in 14 bins, measured with Magellan/IMACS repeatedly over three transits. We measure a mean planet-to-star radius ratio of Rp R-s = 0.1146. 2 x 10(-4) and mean uncertainty of sigma(R-p/R-s) = 8.7 x 10(-4) in the spectral bins. The optical transit depths are shallower on average than observed in the near-infrared. We present a model for jointly incorporating the effects of a composite photosphere and atmospheric transmission through the exoplanet's limb (the CPAT model), and use it to examine the cases of absorber and temperature heterogeneities in the stellar photosphere. We find the optical and near-infrared measurements are best explained by the combination of (1) photochemical haze in the exoplanetary atmosphere with a mode particle size r = 0.1 mu m and haze-forming efficiency f(haze) = 10% and (2) faculae in the unocculted stellar disk with a temperature contrast Delta T= 354(-46)(+46) K, assuming 3.2% surface coverage. The CPAT model can be used to assess potential contributions of heterogeneous stellar photospheres to observations of exoplanet transmission spectra, which will be important for searches for spectral features in the optical.

Thesis (M.S. in material science and engineering)--Washington State University, May 2010.
Title from PDF title page (viewed on July 14, 2010). "School of Mechanical and Material Engineering." Includes bibliographical references (p. 90-92).

Given the ever-growing demand for radio spectrum, cognitive radio has recently emerged as an attractive wireless communication technology. This dissertation is concerned with developing spectrum sensing algorithms in cognitive radio networks where a single or multiple cognitive radios (CRs) assist in detecting licensed primary bands employed by single or multiple primary users. First, given that orthogonal frequency-division multiplexing (OFDM) is an important wideband transmission technique, detection of OFDM signals in low-signal-to-noise-ratio scenario is studied. It is shown that the cyclic prefix correlation coefficient (CPCC)-based spectrum sensing algorithm, which was previously introduced as a simple and computationally efficient spectrum-sensing method for OFDM signals, is a special case of the constrained generalized likelihood ratio test (GLRT) in the absence of multipath. The performance of the CPCC-based algorithm degrades in a multipath scenario. However when OFDM is implemented, by employing the inherent structure of OFDM signals and exploiting multipath correlation in the GLRT algorithm a simple and low-complexity algorithm called the multipath-based constrained-GLRT (MP-based C-GLRT) algorithm is obtained. Further performance improvement is achieved by combining both the CPCC- and MP-based C-GLRT algorithms. A simple GLRT-based detection algorithm is also developed for unsynchronized OFDM signals. In the next part of the dissertation, a cognitive radio network model with multiple CRs is considered in order to investigate the benefit of collaboration and diversity in improving the overall sensing performance. Specially, the problem of decision fusion for cooperative spectrum sensing is studied when fading channels are present between the CRs and the fusion center (FC). Noncoherent transmission schemes with on-off keying (OOK) and binary frequency-shift keying (BFSK) are employed to transmit the binary decisions to the FC. The aim is to maximize the achievable secondary throughput of the CR network. Finally, in order to reduce the required transmission bandwidth in the reporting phase of the CRs in a cooperative sensing scheme, the last part of the dissertation examines nonorthogonal transmission of local decisions by means of on-off keying. Proposed and analyzed is a novel decoding-based fusion rule for combining the hard decisions in a linear manner.

Many different types of promising spectrum sensing algorithms for Cognitive Radio (CR) have already been developed. However, many of these algorithms lack robustness with respect to signal statistical parameters uncertainties, such as the noise variance or the shape of its distribution (often assumed to be simply Gaussian). In conjunction with the low Signal-to-Noise Ratio (SNR) requirements, this lack of robustness can often render interesting sensing algorithms impractical for real-life applications. In this thesis, we primarily focus on the impact of heavy-tail noise distributions on different CR detectors and the use of signal limiters (mostly the spatial sign function) to improve their robustness to such noise distributions. Introducing a non-linear transformation of the received signal prior to its processing by the detector fundamentally changes the signal distribution which in turn modifies the distribution of the detector statistic. In order to parametrize the detector and study its performance, it is then necessary to know the shape of the modified distribution. Three types of detectors are investigated: a generic second-order cyclic-feature detector, a Scaled-Largest Eigenvalue (SLE) detector studied in the context of stationary time-series and a new Sequential Likelihood Ratio Test (SLRT) detector. The analysis conducted for each detector revolves around the influence of its parameters, the distribution of the detector statistic and several comparisons with similar detectors for various detection scenarios. Our results indicate that at the cost of a moderate performance loss in a Gaussian noise environment, all the detectors fitted with a signal limiter become robust to impulsive noise and noise parameters uncertainties. We provide analytical approximations for the detectors statistical distribution that allow us to use the detectors in such configurations as well as to study their performance for different signal limiters and noise distributions.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

International Telemetering Conference Proceedings / October 29-November 02, 1990 / Riviera Hotel and Convention Center, Las Vegas, Nevada
Various PN codes for use in TTC spread-spectrum systems are considered. The evaluation is based on peak magnitudes and amplitude distributions of both the even and the odd autocorrelation and crosscorrelation functions. Furthermore the influence of the phase of a sequence on the correlation parameters is studied, multiple-access characteristics in terms of the total interference parameter are evaluated and synchronous as well as asynchronous code generation is considered.1

The radio spectrum is becoming increasingly congested everyday with emerging technologies and with the increasing number of wireless devices. Considering the limited bandwidth availability, accommodating the demand for higher capacity and data rates is a challenging task, requiring innovative technologies that can offer new ways of exploiting the available radio spectrum. Cognitive radio arises to be a tempting solution to the spectral crowding problem by introducing the notion of opportunistic spectrum usage. Because of its attractive features, orthogonal frequency division multiplexing (OFDM) has been successfully used in numerous wireless standards and technologies. We believe that OFDM will play an important role in realizing the cognitive radio concept as well by providing a proven, scalable, and adaptive technology for air interface. The goal of this dissertation is to identify and address some of the challenges that arise from the introduction of cognitive radio. Specifically, we propose methods for obtaining awareness about channel, spectrum, and waveform in OFDM-based cognitive radio systems in this dissertation. Parameter estimation for enabling adaptation, spectrum sensing, and OFDM system identification are the three main topics discussed. OFDM technique is investigated as a candidate for cognitive radio systems. Cognitive radio features and requirements are discussed in detail, and OFDM's ability to satisfy these requirements is explained. In addition, we identify the challenges that arise from employing OFDM technology in cognitive radio. Algorithms for estimating various channel related parameters are presented. These parameters are vital for enabling adaptive system design, which is a key requirement for cognitive radio. We develop methods for estimating root-mean-square (RMS) delay spread, Doppler spread, and noise variance. The spectrum opportunity and spectrum sensing concepts are re-evaluated by considering different dimensions of the spectrum which is known as multi-dimensional spectrum space. Spectrum sensing problem in a multi-dimensional space is addressed by developing a new sensing algorithm termed as partial match filtering (PMF). Cognitive radios are expected to recognize different wireless networks and have capability of communicating with them. Algorithms for identification of multi-carrier transmissions are developed. Within the same work, methods for blindly detecting transmission parameters of an OFDM based system are developed. Blind detection is also very helpful in reducing system signaling overhead in the case of adaptive transmission where transmission parameters are changed depending on the environmental characteristics or spectrum availability.

In this thesis, we first give an intensive review on the background of LTE-LAA technology, the research status of LTE-LAA and WiFi co-existence mechanisms and 3GPP Rel. 13 standardization on LTELAA. The existing co-existence designs focus on the time-domain, frequency-domain and power-domain to achieve fairness between two systems. Simultaneous transmissions are avoided to reduce collision probability. However, by exploiting the spatial domain, we discover the possibility of simultaneous LTE-LAA/WiFi transmission opportunities as long as the interference received at the WiFi receiver is well managed. We first show the feasibility of such simultaneous transmission opportunities considering AP/UE location diversity and various coverage overlap situations between LTE-LAA small cell and WiFi AP. Then, by utilizing multi-antenna beamforming capability, we propose a more practical co-existence scheme combing DoA estimation and null steering technologies. As the lack of direct communication link between LTE-LAA and WiFi systems, we also give our design of information exchange that requires minimal modifications on current WiFi standards and with little to none extra overhead. From the discussions and simulation results, we prove the existence of such simultaneous transmission opportunities that do not bring extra impact on WiFi networks. The channel occupancy time of LTE-LAA can be greatly improved. However, problems and challenges are also identified that require future investigations.

Mestrado em Engenharia Eletrónica e Telecomunicações
A recolha de energia do meio ambiente para alimentar dispositivos como forma de os tornar auto-sustentáveis tem vindo cada vez mais a suscitar interesse. Por outro lado, o crescimento contínuo do espectro resultante das telecomunicações constitui uma grande oportunidade para a colheita de energia. Assim sendo, neste trabalho e proposto um sistema altamente e ciente de recolha de energia de rádio-frequência que utiliza o sinal da televisão digital (D-TV) portuguesa e que converte-o em tenso que poder a ser reaproveitada. De forma a ser vantajoso, o sistema e otimizado para operar a baixos níveis de potência. Assim, o presente trabalho pretende também fornecer orientações para o correto desenvolvimento do sistema de colheita de energia para baixa potência de entrada, contribuindo para o desenvolvimento de projetos futuros. O sistema e dividido numa antena recetora e num retificador. Para o retificador são propostas três soluções distintas: um díodo série, um díodo paralelo e um duplicador de tensão. A eficiência obtida e semelhante para as três configurações - cerca de 54% para um sinal de entrada sinusoidal com um nível de potência de -10.5 dBm. Medições com o multiplicador de tensão e o sinal real da D-TV como entrada mostraram uma eficiência de 63% para o mesmo nível de potência. Relativamente à antena, e proposta uma patch com slots e com um elemento parasita que utiliza como substrato dielétrico FR-4. Esta configuração resulta da necessidade de melhorar a largura de banda da microstrip simples. Medições mostraram um aumento da largura de banda em cerca de 4 vezes quando em comparação com uma patch simples.
Collect energy from the surroundings is being biased to power-up devices in order to turn them self-sustainable. On the other hand, the spectrum resultant from the telecommunications tends to progressively increase and becomes wide-reaching, constituting an enormous opportunity to energy harvesting. Thus, in this work a high e ciency radio-frequency energy harvesting system is proposed that takes uses of the Portuguese Digital Television (D-TV) signal to obtain Direct Current (DC) power. To be useful, the system is optimized to operate at low power conditions. So, this work also aims to provide reliable guidelines in the design of energy harvesting systems with low-input power. The system is divided into an antenna and a recti er. For the recti er, three di erent solutions are presented: a single-series diode, a singleshunt diode and a voltage doubler con guration. The e ciency is similar for the three recti ers { around 54% with a sine-wave excitation and -10.5 dBm input power. Field measurements with the voltage doubler has proven 63% e ciency for the same input power. As receiver antenna is proposed a slotted patch with a stacked parasitic based on FR-4 substrate. This con guration results from the need to improve the bandwidth of the basic microstrip patch. Measurements have proven and enhancement around 4 times in comparison with a basic patch.

Le portage et les infections à entérobactéries productrices de bêta-lactamase à spectre étendu (E-BLSE) touchent de plus en plus fréquemment les sujets communautaires. La prévalence de portage dans la communauté a été estimée à 30 et 70% respectivement en Afrique et en Asie alors qu’elle n’est que de 10% en Europe. Le fait de vivre ou de séjourner dans des zones de forte endémie constitue donc un facteur de risque élevé d’acquisition d’E-BLSE. La prévalence du portage d’entérobactéries résistantes dans les zones intertropicales et les facteurs de risque d’acquisition par un sujet individuel lors de l’exposition à de tels environnements ont été largement étudiés mais la question des transmissions secondaires à partir de ces cas index n’a pas été appréhendée alors qu’elle est essentielle, notamment pour comprendre son impact dans la diffusion des E-BLSE dans la communauté. Nous avons étudié l’acquisition et la transmission des E-BLSE au sein de deux cohortes de sujets vivant en zones de forte endémie et en promiscuité avec d’autres individus au moment de l’acquisition. Nous avons utilisé dans ce but des techniques de PCR et de séquençage de génome complet (WGS) associé à une fine analyse des single nucleotide polymorphisms (SNPs). La première cohorte était constituée de militaires en mission dans 3 régions différentes, l’Afghanistan, la Guyane et la Côte d’Ivoire. Les taux d'acquisition d'E-BLSE pendant la mission étaient variables selon les destinations : 88% en Afghanistan, 49% en Côte d’Ivoire et 5% en Guyane. La transmission d’E. coli BLSE entre les militaires, étudiée au sein de la compagnie afghane, n’a permis de mettre en évidence aucune transmission de souches dans cette compagnie. Les bonnes conditions d’hygiène dans le campement et le peu de contact avec la population locale suggéreraient que le fort taux d’acquisition observé pourrait être dû à une acquisition individuelle, à partir de repas achetés régulièrement auprès des nombreux vendeurs ambulants installés autour du campement. La deuxième cohorte était issue d’une étude contre placebo réalisée chez des enfants dénutris non hospitalisés vivant au Niger. Ce travail avait pour objectif de mesurer l’impact de l’amoxicilline administrée de façon systématique dans les protocoles de renutrition des enfants présentant une malnutrition sévère, sur la colonisation par des E-BLSE et sur la transmission des souches au sein desfratries. Nous avons observé que l’administration d’amoxicilline augmentait le risque d’acquisition d’E-BLSE chez l’enfant traité dans la semaine qui suivait sa prise en charge (54% vs 32%, p<0,001) ainsi que le risque de transmission d’une E-BLSE dans la fratrie (11.5% vs 3.8%, p=0.04). Au total, dans ces deux études nous avons pu montrer que la caractérisation complète des souches par WGS et l’analyse des SNPs apportait des informations incontournables pour comprendre la dynamique de partage des souches d’E-BLSE entre les sujets. Ces études apportent des éléments de réponses sur la transmission des E-BLSE dans la communauté et les facteurs de risques associés, mais d’autres facteurs de risques et d’autres situations restent encore à explorer avec ces nouveaux outils
Colonization and infection by extended spectrum bet a-lactamase producing enterobacteriaceae (ESBL-E) increasingly affect subjects in community. The prevalence of carriage in the community has been estimated at 30 and 70% respectively in Africa and Asia, while it is only 10% in Europe. Living or visiting areas with high endemicity is therefore a high risk factor for ESBL-E acquisition. ESBL-E prevalence carriage in intertropical areas and the risk factors for acquisition by an individual subject when exposed to such environments have been widely studied, but the issue of secondary transmissions from these index cases has not been addressed, although it is essential, in particular to understand its impact on the spread of ESBL-E in the community. We studied the acquisition and transmission of ESBL-E in two cohorts of subjects living in highly endemic areas in promiscuity, with other individuals at the time of acquisition. For this purpose, we used PCR and whole genome sequencing (WGS) techniques, combined with a fine analysis of single nucleotide polymorphisms (SNPs). The first cohort was composed of soldiers on mission in 3 different regions, Afghanistan, Guyana andCôte d'Ivoire. The ESBL-E acquisition rates during the mission varied depending on the destination: 88% in Afghanistan, 49% in Côte d'Ivoire and 5% in Guyana. The transmission of ESBL E. coli between soldiers, studied within the Afghan company, did not evidence any transmission of strains in this company. The good hygienic conditions in the camp and the limited contact with the local population would suggest that the high acquisition rate observed could be due to individual acquisition, based on meals purchased regularly from the many street vendors installed around thecamp. The second cohort was based on a placebo-controlled study on malnourished, outpatient children living in Niger. The objective of this work was to evaluate the impact of amoxicillin administered systematically in renutrition protocols for severely malnourished children, on ESBL-E colonization and on strain transmission in siblings. We observed that the administration of amoxicillin increased the risk of ESBL-E acquisition in the treated child within one week of treatment(54% vs. 32%, p<0.001) and the risk of ESBL transmission in the siblings (11.5% vs. 3.8%, p=0.04). In total, in these two studies, we showed that the complete characterization of strains by WGS and SNP analysis provided essential information to understand the dynamics of ESBL-E sharing between subjects.These studies provide some answers on the ESBL-E transmission in the community and the associated risk factors, but other risk factors and situations still need to be explored with these new tools

The next-generation wireless technologies are currently being researched to address the ever-increasing demands for higher data rates, massive connectivity, improved reliability, and extended coverage. Recently, massive multiple-input multiple-output (MIMO) has gained significant attention as a new physical-layer transmission technology that can achieve unprecedented spectral and energy efficiency gains via aggressive spatial multiplexing. Thus, massive MIMO has been one of the key enabling technologies for the fifth-generation and subsequent wireless standards. This dissertation thus focuses on developing a system, channel, and signal models by considering the practical wireless transmission impairments for massive MIMO systems, and ascertaining the viability of massive MIMO in fulfilling massive access, improved spectrum, enhanced security, and energy efficiency requirements. Specifically, new system and channel models, pilot sequence designs and channel estimation techniques, secure transmit/receive beamforming techniques, transmit power allocation schemes with enhanced security provisions, energy efficiency, and user fairness, and comprehensive performance analysis frameworks are developed for massive MIMO-aided non-orthogonal multiple access (NOMA), cognitive spectrum-sharing, and wireless relaying architectures.Our first work focuses on developing physical-layer transmission schemes for NOMA-aided massive MIMO systems. A spatial signature-based user-clustering and pilot allocation scheme is first formulated, and thereby, a hybrid orthogonal multiple access (OMA)/NOMA transmission scheme is proposed to boost the number of simultaneous connections. In our second work, the viability of invoking downlink pilots to boost the achievable rate of NOMA-aided massive MIMO is investigated. The third research contribution investigates the performance of underlay spectrum-sharing massive MIMO systems for reverse time division duplexing based transmission strategies, in which primary and secondary systems concurrently operate in opposite directions. Thereby, we show that the secondary system can be operated with its maximum average transmit power independent of the primary system in the limit of infinity many primary/secondary base-station antennas. In our fourth work, signal processing techniques, power allocation, and relay selection schemes are designed and analyzed for massive MIMO relay networks to optimize the trade-off among the achievable user rates, coverage, and wireless resource usage. Finally, the cooperative jamming and artificial noise-based secure transmission strategies are developed for massive MIMO relay networks with imperfect legitimate user channel information and with no channel knowledge of the eavesdropper. The key design criterion of the aforementioned transmission strategies is to efficiently combine the spatial multiplexing gains and favorable propagation conditions of massive MIMO with properties of NOMA, underlay spectrum-sharing, and wireless relay networks via efficient signal processing.

Le relayage cognitif multiple-input multiple-output (MIMO) hérite l’efficacité spectrale de la radiocognitive et les systèmes de relayage MIMO, apportant ainsi des gains prometteurs en termes de débit dedonnées et de fiabilité pour les futures communications sans fil et mobiles. Dans cette thèse, nous concevons et évaluons des schémas pratiques d’émetteurs et de récepteurs pour des systèmes de relayage MIMO cognitifs qui peuvent être mis en oeuvre à moindre coût. Tout d'abord, nous réduisons l'affaiblissement du débit du mode half-duplex du relayage MIMO amplify-and-forward non-orthogonale(NAF) large bande avec demande de répétition automatique (ARQ). Différemment des travaux de recherche existants, le protocole de relayage proposé ne nécessite que la durée de transmission d’un seul paquet sur des canaux sélectifs en fréquence. De plus, nous proposons une conception de réception itérative à complexité réduite pour cette classe de protocoles, entraînant ainsi une amélioration significative des performances de transmission de bout-en-bout. Deuxièmement, nous nous concentrons sur les systèmes de relayage cognitive de partage du spectre single-input multiple-output (SIMO) et évaluons l’impact des contraintes d’interférence instantanée et statistique sur la qualité de leur probabilité de coupure. Nos résultats révèlent que l’imposition d’une contrainte statistique sur la puissance d’émission du système secondaire est plus favorable que son adversaire consommatrice de spectre. Troisièmement, nous capitalisons sur notre deuxième contribution pour étudier les systèmes de relayage MIMO decode-and-forward (DF) cognitifs utilisant la sélection d'antenne à l’émission (TAS) ainsi que le maximum-ratio combining (MRC) à la réception. Basés sur la maximisation du rapport signal-sur-bruit (SNR) ou du rapport signal-sur-interférence-plus-bruit (SINR), nos résultats de probabilité de coupure nouvellement dérivés pour les deux stratégies proposées de TAS démontre l’optimalité du système de sélection d’antenne basé sur le SINR par rapport aux effets néfastes d’interférence mutuelle dans les systèmes de relayage MIMO DF cognitifs
Cognitive multiple-input multiple-output (MIMO) relaying inherits the spectrum usage efficiency from both cognitive radio and MIMO relay systems, thereby bearing promising gains in terms of data rate and reliability for future wireless and mobile communications. In this dissertation, we design and evaluate practical transmitter and receiver schemes for cognitive MIMO relay systems that can readily be implemented at a lower cost. First, we reduce the multiplexing loss due the half-duplex operation in non orthogonal amplify-and-forward (NAF) MIMO relay broadband transmissions with automatic repeat request(ARQ). Different from existing research works, the proposed relaying protocol requires only one packet duration to operate over frequency-selective block-fading relay channels. Further, we propose a low complexityiterative receiver design for this class of protocols which results in significant enhancement of the end-to-end transmission performance. Second, we focus on cognitive underlay single-input multiple-output (SIMO) relay systems and evaluate the impact of instantaneous and statistical interference constraints on their outage performance. Our results reveal that imposing a statistical interference constraint on the secondary system transmit power is most favored than its spectrum-consuming counter part. Third, we capitalize on our second contribution to investigate cost-effective transmission schemes for cognitive MIMO decode-and-forward (DF) relaying systems employing transmit-antenna selection (TAS) along with maximum-ratio combining (MRC) at the transmitter and receiver sides, respectively. Driven by maximizing either the received signal-to-noise ratio (SNR) or signal-to-interference-plus-noise ratio (SINR), our newly derived outage performance results pertaining to both proposed TAS strategies are shown to entail an involved derivation roadmap yet demonstrate the optimality of the SINR-driven TAS against the detrimental effect of mutual interference incognitive MIMO DF relay systems

Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 1990.
Thesis Advisor(s): Myers, Glen. Second Reader: Ha, Tri. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifiers: Direct sequence spread spectrum, data clocks, delay lock loops, sequence generators. Author(s) subject terms: Direct-sequence spread spectrum, communications, data clock recovery, M-sequence, delay-lock loop, spread spectrum, binary sequence generation. Includes bibliographical references (p. 40). Also available in print.

Given the ever increasing reliance of today’s society on ubiquitous wireless access, the paradigm of dynamic spectrum access (DSA) as been proposed and implemented for utilizing the limited wireless spectrum more efficiently. Orthogonal frequency division multiplexing (OFDM) is growing in popularity for adoption into wireless services employing DSA frame- work, due to its high bandwidth efficiency and resiliency to multipath fading. While these advantages have been proven for many wireless applications, including LTE-Advanced and numerous IEEE wireless standards, one potential drawback of OFDM or its non-contiguous variant, NC-OFDM, is that it exhibits high peak-to-average power ratios (PAPR), which can induce in-band and out-of-band (OOB) distortions when the peaks of the waveform enter the compression region of the transmitter power amplifier (PA). Such OOB emissions can interfere with existing neighboring transmissions, and thereby severely deteriorate the reliability of the DSA network. A performance-enhancing digital pre-distortion (DPD) technique compensating for PA and in-phase/quadrature (I/Q) modulator distortions is proposed in this dissertation. Al- though substantial research efforts into designing DPD schemes have already been presented in the open literature, there still exists numerous opportunities to further improve upon the performance of OOB suppression for NC-OFDM transmission in the presence of RF front-end impairments. A set of orthogonal polynomial basis functions is proposed in this dissertation together with a simplified joint DPD structure. A performance analysis is presented to show that the OOB emissions is reduced to approximately 50 dBc with proposed algorithms employed during NC-OFDM transmission. Furthermore, a novel and intuitive DPD solution that can minimize the power regrowth at any pre-specified frequency in the spurious domain is proposed in this dissertation. Conventional DPD methods have been proven to be able to effectively reduce the OOB emissions that fall on top of adjacent channels. However more spectral emissions in more distant frequency ranges are generated by employing such DPD solutions, which are potentially in violation of the spurious emission limit. At the same time, the emissions in adjacent channel must be kept under the OOB limit. To the best of the author’s knowledge, there has not been extensive research conducted on this topic. Mathematical derivation procedures of the proposed algorithm are provided for both memoryless nonlinear model and memory-based nonlinear model. Simulation results show that the proposed method is able to provide a good balance of OOB emissions and emissions in the far out spurious domain, by reducing the spurious emissions by 4-5 dB while maintaining the adjacent channel leakage ratio (ACLR) improvement by at least 10 dB, comparing to the PA output spectrum without any DPD.

The main goal of this thesis is to combine electron tomography and electron energy loss spectroscopy (EELS) in the TEM, in order to obtain chemical and electronic information in 3D in the nanoscale. Tomography in the TEM has been discussed and the advantages and disadvantages of HAADF STEM tomography have been analyzed. - A Fe3O4 nanocube sample has been considered to illustrate the acquisition, alignment, tilt axis assessment, reconstruction and visualization processes. - HAADF STEM tomography has been used to reconstruct the shape of a series of Cu2O nanoparticles. For one of the samples, the facets of the Cu2O nanoparticles, octahedral in shape, have been found to correspond to {111} planes. The physics and the data analysis methods of core-loss EELS have been briefly summarized. Two relevant contributions have been made: - The effects of beam precession on EELS have been investigated. A signal enhancement due to electron beam precession in the TEM when in zone axis conditions has been discovered for the first time. - A homemade software, Oxide Wizard, for valence state determination of transition metals has been developed and applied to map the Mn oxidation state of a MnOx/FeOy nanoparticle. EELS spectrum imaging and electron tomography have been combined to recover chemical information in 3D for FexCo(3-x)O4@Co3O4 mesoporous nanoparticles. - The samples have been first characterized by HAADF STEM tomography and EELS. - EELS chemical information is, of course, limited to 2D maps, while only structural information is be recovered in 3D form HAADF tomography. . An EELS-SI tilt series has been acquired at 80 kV and low acquisition times, resulting in a very noisy dataset. - Principal component analysis (PCA) has been used to separate the noise from the signal. - Quantifications of the O, Fe and Co signals have been reconstructed, and the shape of the particle recovered. - From the noise clean dataset, components with physical meaning (iron oxide, cobalt oxide and thickness) have been extracted using independent component analysis (ICA), and reconstructed in 3D. - A new kind of signal with chemical and thickness information has been obtained by combining the thickness component with the quantification results. This signal is able to properly reconstruct the chemical structure of the sample in 3D, detecting a higher presence of iron in the surface, and an even distribution of Fe inside of the particle. . Another EELS-SI tilt series has been acquired at 80 kV and low acquisition times with enough spatial resolution to resolve the porous structure. - The noise has been reduced using PCA. - Four signals extracted from the spectrum have been reconstructed: the integrated edge intensities for oxygen, iron and cobalt, and the integrated background prior to the oxygen edge. EELS-SI tomography has been applied to reconstruct CoFe2O4 (CFO) nanocolumns embedded in a BiFeO3 (BFO) matrix grown on LaNiO3 buffered LaAlO3 substrate (BFO-CFO//LNO/LAO). - The nanocomposite sample has been prepared in a nanoneedle shape by means of focused ion beam (FIB). This preparation has the advantage of keeping the thickness of the sample constant throughout the tilting experiment. The nanoneedle contains an island of CFO in a matrix of BFO, as well as the LNO/LAO substrate. - The noise has been discarded using PCA. - The oxygen, iron and lanthanum edges intensities have been extracted and reconstructed. A new kind of data hypercube, the Spectrum Volume, has been proposed. Just as a Spectrum Image contains a spectrum per pixel, a Spectrum Volume is to contain a spectrum per voxel. EELS-SI tomography has been applied to successfully acquire a spectrum volume (SV) of the (BFO-CFO//LNO/LAO) system. - PCA has been used to discard the noise and Bayesian linear unmixing (BLU) has been used to extract independent components (eigenspectra). - Each eigenspectrum has a 2D weighting map for each tilt; weighting maps have been reconstructed into 3D weighting volumes. - Full single spectra for any point in the reconstructed space can now be recovered as a weighed sum of eigenspectra, using the 3D weighting distributions. This approach is used to extract single spectra, spectrum lines and spectrum images from the inside of the sample. In the context of this thesis, tomography and EELS-SI have been combined to successfully recover chemical information in 3D at the nanoscale, and a new kind of data hypercube, the Spectrum Volume, has been proposed and experimentally recovered.
En el microscopi electrònic de transmissió (TEM), es poden obtenir imatges d’una mostra des de diferents angles i posteriorment reconstruir aquestes imatges en tres dimensions (3D). Per altra banda, les interaccions dels electrons del feix amb els electrons de la mostra poden ser analitzades mitjançant l’espectroscòpia de pèrdues d’energia dels electrons (EELS), obtenint així informació química de la mostra. L’objectiu d’aquesta tesi és la combinació de l’espectroscòpia EELS amb la tomografia electrònica per obtenir informació química en 3 dimensions a la nanoescala. S’han explicat les bases de la tomografia electrònica i el procediment de la reconstrucció ha estat il•lustrat amb una mostra de nanocubs d’òxid de ferro. Posteriorment, s’ha aplicat a una sèrie de nanopartícules de Cu2O per tal de descriure’n la forma. També s’ha explicat la física en què es basa l’EELS, fent especial atenció als llindars d’altes pèrdues d’energia. A continuació, s’ha mostrat l’augment del senyal obtingut amb precessió electrònica al TEM quan la mostra es troba en condicions d’eix de zona. Seguint amb les aplicacions d’EELS, s’ha explotat la possibilitat de caracteritzar els estats d’oxidació dels metalls de transició mitjançant un programa propi, escrit per a Digital Micrograph i anomenat Oxide Wizard. Una vegada la tomografia electrònica i l’espectroscòpia de pèrdues d’energia dels electrons han estat explicades, s’ha procedit a reconstruir informació extreta d’EELS en 3D. S’han realitzat una sèrie d’experiments amb partícules mesoporoses que han demostrat la utilitat d’aplicar l’anàlisi multivariable per tal de reduir el soroll de les dades i extreure’n els components. Finalment, s’ha dissenyat un experiment en el qual ha estat possible recuperar l’espectre corresponent a cada unitat d’espai com la combinació d’espectres propis en una mostra preparada en forma de nanoagulla. Els espectres recuperats corresponen a la contribució de cada unitat de volum als espectres projectats. Aquest nou tipus de dades permet extreure espectres de l’interior d’una mostra. Finalment, doncs, s’ha pogut combinar amb èxit la tomografia electrònica i EELS per obtenir informació química en tres dimensions a la nanoescala.

Cette thèse propose un formalisme général pour modéliser la propagation des ondes acoustiques dans une multicouche composée de toute combinaison de couches liquides, solides élastiques isotropes et poro-élastiques isotropes, la méthode ayant la flexibilité d'être développée pour inclure d'autres natures de couches. Dans un premier lieu, un algorithme stable est développé, basé sur l'approche récursive de la matrice de rigidité, pour modéliser la propagation d'une onde plane incidente sur la multicouche en fonction de son angle d'incidence et de sa fréquence. Cet algorithme fusionne de manière récursive les matrices de rigidité des couches individuelles de la structure en une matrice de rigidité totale et permet ensuite le calcul des coefficients de réflexion et de transmission, ainsi que les composantes de déplacement et de contrainte à l'intérieur de la multicouche pour chaque direction d'incidence des ondes planes. Deuxièmement, pour modéliser la propagation d'un faisceau délimité d'ondes incidentes, la technique du spectre angulaire est utilisée, basée sur la décomposition de ce faisceau en un spectre d'ondes planes se propageant dans des directions différentes. Par la suite, le faisceau d'onde réfléchi dans le milieu d'incidence et le faisceau d'onde transmis dans le milieu de transmission, ainsi que la distribution des champs (composantes de déplacement et de contrainte) à l'intérieur de la multicouche sont obtenus en superposant la contribution de toutes les ondes planes se propageant dans les différentes directions. Comme application numérique, une tri-couche solide-poreuse-solide immergée dans l'eau est simulée. La réflexion et la transmission qui en résultent, ainsi que les composantes de déplacement et de contrainte dans la multicouche, correspondants à l’onde plane incidente et au faisceau limité incident, révèlent la stabilité du procédé et la continuité des déplacements et des contraintes aux interfaces
This thesis proposes a general formalism to model the acoustic wave propagation in a multilayer consisting of any combination of fluid, isotropic elastic solid, and isotropic poroelastic layers, the method having the flexibility to be extended to include other layer-natures. At a first stage, a stable algorithm is developed, based on the recursive stiffness matrix approach, to model the propagation of a plane wave incident on the multilayer as a function of its incidence angle and frequency. This algorithm merges recursively the structureindividual layers stiffness matrices into one total stiffness matrix and allows then the calculation of the reflection and transmission coefficients, as well as the displacement and stress components inside the multilayer for every incident plane wave direction. Secondly, to model the propagation of a bounded incident wave beam, the angular spectrum technique is used which is based on the decomposition of this beam into a spectrum of plane waves traveling in different directions. The corresponding reflected wave beam in the incidence medium, and the transmitted wave beam in the transmission medium, as well as the fields distributions (displacement and stress components) inside the multilayer are obtained by summing the contribution of all the plane waves traveling in different directions. As a numerical application, a three-layered solid-porous-solid structure immersed in water is simulated. The resulting reflection and transmission as well as the displacement and stress components in the multilayer corresponding to both, the incident plane wave in different directions and the incident bounded beam reveal the stability of the method and the continuity of the displacements and stresses at the interfaces

Orientador: Amir Ordacgi Caldeira
Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin
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Resumo: Este trabalho foi motivado por várias dificuldades encontradas no estudo do artigo de M. Ueda, Transmission Spectrum of a Tunneling Particle Interacting with Dynamical Fields: Real- Time Functional Integral Approach, Phys. Rev. B 54, 8676 (1996). Nesse artigo, num formalismo de tempo real, é descrito o tunelamento de uma partícula através de uma barreira utilizando tempos não reais de travessia através dessa barreira. No presente trabalho é proposto um formalismo mais amplo de tempo real para uma introdução mais natural de valores complexos do tempo na descrição do tunelamento de uma partícula cm interação com o ambiente. Esta proposta está baseada no chamado método do tempo complexo utilizado no caso do tunelamento de uma partícula sem interação com o ambiente estudado nos trabalhos de D. W. McLaughlin, J. Math. Phys. 13, 1099 (1972) c B. R. Holstein c A. R. Swift, Am. J. Phys. 50, 833 (1982). Seguindo o trabalho citado de Ueda, o ambiente da partícula é representado através de um conjunto, ou banho térmico, de osciladores harmônicos caracterizados por uma função de densidade espectral J(w). Utilizando o método de Feynman de integrais de trajetória, integramos sobre as coordenadas dos osciladores do banho c obtemos uma expressão exata para o espectro de transmissão da partícula para uma temperatura do banho T > O. Limitando-nos então ao caso mais simples T = O, estudamos o tunelamento dissipativo da partícula através da barreira. Considerando h um parâmetro pequeno (limite semiclássico), aproximamos o espectro de transmissão da partícula através da contribuição das trajetórias clássicas c suas trajetórias vizinhas. Nesta aproximação consideramos a variação da ação efetiva da partícula para tempos dados de duração das trajetórias c deste modo substituímos o procedimento variacional seguido no trabalho indicado de Ueda onde não é considerada a variação nos tempos de travessia da partícula através da barreira. Num segundo problema variacional nos tempos de duração das trajetórias clássicas de acordo com o método do tempo complexo e considerando também a variação nas posições iniciais c finais dessas trajetórias, obtemos as equações de movimento das chamadas trajetórias clássicas especiais. Este tratamento das coordenadas iniciais c finais das trajetórias clássicas substitui o procedimento seguido no trabalho de Ueda onde é considerc1da uma aceleração nula durante todo o trajeto de movimento incluindo o trajeto na região da barreira. Diferentemente do artigo citado de Ueda, no presente trabalho utilizamos pacotes de ondas relativamente bem localizados para descrever os estados inicial e final da partícula. Em consequência, aproximamos o espectro de transmissão da partícula através de trajetórias clássicas especiais com coordenadas iniciais c finais iguais ao valor médio da coordenada para esses pacotes de ondas. O procedimento seguido neste trabalho, baseado no método do tempo complexo, permite obter o fator ele acoplamento apropriado entre as duas trajetórias que descrevem a ação efetiva ela partícula substituindo assim o procedimento de tipo ad hoc seguido com este fim no trabalho indicado de Ueda. O método do tempo complexo permite obter também o termo ela diferença entre a ação efetiva da partícula c o expoente ele tunelamento, sendo que estas grandezas são tratadas como iguais no trabalho citado de Ueda. Considerando termos até primeira ordem num campo elétrico externo c na interação da partícula com o banho de osciladores, obtemos expressões gerais para o expoente de tunelamento, o espectro de transmissão, a taxa total de tunelamento c o tempo de travessia da partícula através da barreira, válidas para um banho de osciladores com uma função de densidade espectral arbitrária. Assim temos que a interação da partícula com um banho de osciladores com uma função de densidade espectral arbitrária diminui a taxa total de tunelamento. Adicionalmente, obtemos que a interação da partícula com os osciladores do banho com frequências ?a = ?C ~ 1.9 T , onde T0 é o tempo característico de travessia através da barreira no caso cm que não há interação da partícula com o banho de osciladores nem campo elétrico, não afeta o tempo característico de travessia através da barreira. Por outro lado, a interação da partícula com os osciladores do banho que têm frequências ?a < ?C (?a > ?C) diminui (aumenta) o tempo característico de travessia através da barreira. No caso de um banho de osciladores com uma única frequência w c uma constante de acoplamento com a partícula dada por Ca = Ca (wT)a , são identificados cinco comportamentos diferentes em função de w para o expoente característico de tunelamento e o tempo característico de travessia através da barreira. Estes comportamentos correspondem aos valores de s < 1, s = 1, 1 < s < 2, s = 2 e s > 2. No trabalho de M. Ueda, Phys. Rev. B 54, 8676 (1996), foi considerado somente o expoente característico de tunelamento no caso s = 1. No caso de um banho ôhmico de osciladores a temperatura zero, assim corno no caso de um banho de osciladores com uma única frequência, obtemos que o espectro de transmissão da partícula é zero para urna energia final característica da partícula maior que a energia inicial característica. Este resultado corrige o resultado correspondente no trabalho citado de Ueda, o qual não é consistente do ponto de vista físico, permitindo também obter de um modo mais coerente a corrente de tunelamento entre dois metais separados por um material isolante a temperatura zero. Obtém-se também que a interação da partícula com um banho ôhmico de osciladora não afeta o tempo característico de travessia através da barreira até primeira ordem nessa interação
Abstract: This work was motivated by several difficulties found when studying the article by M . Ueda, Transmission Spectrum of a Tunneling Particle Interacting with Dynamical Fields: Real-Time Functional-Integral Approach, Phys. Rev. B 54, 8676 (1996). In that paper, using a real-time formalism, a tunneling particle is described by complex traversal times of tunneling. In the present work we propose a broader real-time formalism that allows for a more natural introduction of complex values of time in the description of a tunneling particle interacting with the environment. This proposal is based on the well-known complex time method used in the case of a tunneling particle with no interaction with the environment studied in the works of D. W. McLaughlin, J. Math. Phys. 13, 1099 (1972) and B. R. Holstein and A. R. Swift, Am. J. Phys. 50, 833 (1982). Following the cited work of Ueda, the environment of the particle is represented by a set, or heat bath, of harmonic oscillators which is characterized by a spectral density function J(w). Using the Feynman path integrals method, we integrate out the coordinates of the bath oscillators and obtain an exact expression for the transmission spectrum of the particle for a bath temperature T > O. Limiting ourselves to the simpler case T = O, we study the case of a dissipative tunneling of the particle. Considering h a small parameter (semiclassical limit) we approximate the transmission spectrum of the particle by the contribution of the classical trajectories and its neighboring paths. In this approach we consider the variation of the effective action of the particle for given duration times of the paths and replace the variation procedure followed in the cited work of Ueda where the variation in the traversal times of tunneling is not considered. In a second variation problem for the duration times of the classical paths, according to the complex time method and considering also the variation in the initial and final positions of these paths, we obtain the equations of motion for the so-called special classical paths. This treatment of the initial and final coordinates of the classical paths replaces the procedure followed in the cited work of Ueda where an acceleration equal to zero is considered during the entire path of motion including the region under the barrier. Unlike the cited article of Ueda, we use in the present work wave packets relatively well localized to describe the init.ial and final statics of the particle. Conscqncnt.ly, we approximate the transmission spectrum of the particle through special classical paths with initial and final coordinates equal to the average value of the coordinate for those wave packets. The procedure followed in this work, based on the complex time method, gives the appropriate coupling factor between the two paths describing the effective action of the particle and thus replaces the ad hoc procedure followed for this purpose in the cited work of Ueda. The complex time method also allows us to obtain the difference term between the effective action of the particle and the tunneling exponent. These quantities are treated as equal in Ueda\'s work. Considering terms up to first order in an external electric field and the interaction of the particle with the bath of oscillators, we obtain general expressions for the tunneling exponent, transmission spectrum, total tunneling rate and traversal time of tunneling, which are valid for a bath of oscillators with an arbitrary spectral lenity function. We find that the interaction of the particle with a bath of oscillators with an arbitrary spectral density function decreases the total tunneling rate. Also, we find that the interaction of the particle with the bath oscillators with frequencies ?a = ?C ~ 1.9 T , where To is the characteristic traversal time of tunneling when there is no interaction of the particle with the bath of oscillators nor electric field. , does not affect the characteristic traversal time of tunneling. On the other hand, the interaction of the particle with the bath oscillators having frequencies ?a< ?c (?a: > ?c decreases (increases) the characteristic traversal time of tunneling. In the case of a bath of oscillators with a single frequency w and a coupling constant with the particle given by Ca = Ca (wT)a we identify five different behaviors deepening on w for the characteristic tunneling exponent and the characteristic traversal time of tunneling. These behaviors correspond to the values of s < 1, s = 1, 1 < s < 2, s = 2 and s > 2. In the work of M. Ueda, Phys. Rev. B 54, 8676 (1996), it was only considered the characteristic tunneling exponent in the case s = 1. In the case of an ohmic bath of oscillators at zero temperature, as well as in the case of a bath of oscillators with a single frequency, we obtain that the transmission spectrum of the particle is ;1,cro for a final characteristic energy of the particle greater than the initial characteristic energy. This result corrects the corresponding result in Ueda work, which is not consistent from a physical point of view, allowing also for a more coherent derivation of the tunneling current between two metals separated by an insulating material at zero temperature. It is also obtained that the interaction of the particle with an ohmic bath of oscillators does not affect the characteristic traversal time of tunneling up to first order in that interaction
Doutorado
Física
Doutor em Ciências

Dissertação de Mestrado Integrado em Medicina Veterinária
ABSTRACT - Objective: This study aims to characterize the dynamics of antibiotic resistance gene transmission in dogs with skin and soft tissue infections (SSTI) and human beings co habiting with them. We also aim to evaluate the gut colonization of these individuals for the presence of extended spectrum beta-lactamases (ESBL’s) in Enterobacteriaceae and to assess the effect of antibiotherapy on the selection of MDR bacteria from human and canine gut microbiota. Methods: Two types of biological samples were gathered in a teaching veterinary hospital in Portugal, at the dermatology department, from twelve dogs diagnosed with SSTI and their household members. Collections included a swab from the infection site (ISS) and a faecal sample (FS). Gathering of samples was performed at two different times. The ISS were cultured and an AST was performed. The FS was also cultured, and the bacteria isolated subjected to molecular analysis. Antibiotic resistance patterns were obtained by disk diffusion antimicrobial susceptibility’s testing and Enterobactereaceae ESBL’s production was confirmed by amplification of the specific gene by PCR and sequencing. Results: High levels of Methicillin resistant Staphylococcus pseudintermedius (MRSP) were isolated, and high levels of other multidrug resistant bacteria (MDR) as well. One family was suspected of carrying the same E. coli clone, shared by two humans and one dog of the same household, with a blaCTX-M-15 gene. All of the isolated Enterobactereaceae displayed susceptibility to carbapenems. The most common ESBL genes found were from the blaCTX-M group, followed by blaOXA-1 and then blaTEM, no gene from the blaSHV gene was found. Conclusions: There is a high prevalence of ESBL-producing E. coli. Interspecies transmission of antimicrobial resistance is real. This issue should be addressed with introduction of antimicrobial stewardship strategies on a wider scale and better use of antimicrobials like chlorohexidine, especially in SSTI.
RESUMO - Esta dissertação enquadra-se nos objetivos de um projeto muito maior e ainda mais ambicioso, chamado PetRisk. Pretende-se analisar o impacto e as interações dos genes de resistência aos antibióticos, percebendo de que forma as barreiras interespécie podem ser ultrapassadas. Assim sendo, o estudante integrou o núcleo desse mesmo empreendimento em Portugal, o Laboratório de Resistência aos Antibióticos da FMV-UL, liderado pela Professora Doutora Constança Pomba. Objetivo: Este estudo teve como objetivo principal compreender a dinâmica de transmissão de genes de resistência aos antibióticos, entre cães com infeção de pele e tecidos moles e as pessoas com quem vivem em regime de co-habitação. Pretendeu-se avaliar a colonização do tubo digestivo desses mesmos indivíduos quanto à presença de Enterobactereacea produtoras de beta-lactamases de largo expectro e verificar o efeito da antibioterapia na seleção de estirpes multiresistentes da microbiota intestinal canina e humana. Outro obejtivo da realização deste trabalho é o de aumentar os recursos biológicos – com isto subentende-se, bactérias de diferentes agregados familiares e o seu perfil de resistência aos antimicrobianos – para o projeto mãe, o PetRisk. Métodos: Para tal, recolheram-se dois tipos de amostras biológicas no departamento de dermatologia do hospital veterinário escolar da FMV-ULisboa. A amostra inclui doze cães com infeções de pele e tecidos moles, assim como os restantes membros do seu agregado familiar. Os materiais recolhidos foram zaragatoas do local de infeção (ZLI) e amostras fecais (AF). As colheitas decorreram em dois tempos diferentes. Às ZLI após cultura microbiológica realizaram-se testes de suscetibilidade aos antibióticos de rotina. Os isolados provenientes das AF foram sujeitos a cultura microbiológica e análise molecular. Os padrões de resistência aos antibióticos foram obtidos pelo método de difusão de discos e a confirmação da produção das beta-lactamases de largo expectro pelas Enterobactereaceae por amplificação do respetivo gene por PCR e sequenciação. Resultados: Foram encontrados elevados níveis de Staphylococcus resistentes à meticilina, assim como a resistência a multiplos antibióticos. Também as nas Escherichia coli provenientes das AF foram encontrados elevados nívreis de resistência a múltiplos antibióticos. Uma familia foi suspeita de partilhar o mesmo clone de E.coli (duas pessoas e um cão) com o mesmo filogrupo e o gene blaCTX-M-15. Todas as Enterobactereaceae isoladas demonstraram suscetibilidade aos carbapenemos. Os genes de beta-lactamases de largo expectro detetados foram (da maior para a menor frequência): blaCTX-M , blaOXA-1 e blaTEM, com nenhum registo de blaSHV. Conclusões: Existe uma elevada prevalência de E. Coli produtoras de beta-lactamases de largo expetro. A transmissão de informação genética inter-espécies é uma realidade. A prática clínica beneficiaria de uma administração mais prudente e integrada de antibióticos, com uma equipa a trabalhar apenas para a gestão destes recursos num hospital, assim como maior atenção ao uso de antisséticos como a clorohexidina, especialmente em infeções de pele e tecidos moles onde os produtos disponivéis são de fácil aplicação.
N/A

The aim of this master´s thesis is an explanation of the problem of optical access networks with wavelength division multiplex, main purpose is to demonstrate the difference between simulation and real measurement. The thesis is divided into several basic thematic areas. At the beginning of thesis is outlined the basic division of multiplexing system, there are discussed the basic solutions of wavelength multiplexes and their possible combinations. The next chapter deals with the active elements, which are an essential part of xWDM systems such as optical lasers, detectors and amplifiers. The following chapter is focused on the passive elements, especially on the passive filters, which form a key part of the wavelength multiplex. Methods of measurement C/DWDM networks are discussed in the next part of thesis. The next chapter describes the topology used by active and passive optical networks. Penultimate part of this thesis consists of designs simulated models PON and WDM-PON networks and comparing their transmission parameters. The final part presents the results of practical measurements of experimental optical access network with wavelength division multiplex, the results are simultaneously compared with results of simulations.

En spectroscopie de perte d’énergie des électrons (EELS), l’échantillon à analyser est soumis à un faisceau d’électron et une détection de l’énergie perdue au cours de la traversée du matériau renseigne sur la composition chimique du composé. Pour des échantillons particulièrement sensibles aux dégâts d'irradiation électronique, comme par exemple des matériaux organiques, on cherche à limiter la dose totale d'électrons reçue par l'échantillon tout en obtenant un rapport signal-sur-bruit satisfaisant. Avec le développement récent de modules d’échantillonnage adaptés aux microscopes en transmission à balayage (STEM), l’acquisition initialement réalisée ligne par ligne est devenue hautement paramétrable. Ainsi, il est désormais possible de visiter un ensemble de positions spatiales quelconques au cours de l’acquisition. De nombreux travaux ont proposé de s’appuyer sur ces avancées techniques pour permettre une acquisition optimisée pour des échantillons sensibles. Pour une dose d’électron globale équivalente à un échantillonnage standard, ces stratégies consistent à visiter moins de positions spatiales, et donc à procéder à un échantillonnage partiel. Par conséquent, une dose d’électron par position spatiale plus élevée est autorisée, ce qui permet d’augmenter le rapport signal-sur-bruit de chaque spectre mesuré. En contrepartie, une étape de post-traitement est nécessaire pour reconstruire l’ensemble de l’image, en particulier les spectres associés aux positions spatiales non visitées au cours de l’acquisition. Parmi les techniques de reconstruction utilisées dans la littérature, les méthodes d’interpolation sont rapides mais peu précises ; elles sont d’un intérêt tout particulier pour visualiser l’image complète au cours de l’acquisition. Au contraire, les techniques par apprentissage de dictionnaire sont très performantes, mais coûteuses tant en mémoire qu’en temps de calcul, et sont donc privilégiées pour raffiner l’image reconstruite après l’expérimentation. En définitive, peu de travaux ont cherché à combler ce fossé. L’objectif principal de cette thèse est de proposer des algorithmes de reconstruction rapides et performants en imagerie EELS. Ils devront, comme pour les méthodes d’interpolation, être suffisamment rapides pour visualiser l’image reconstruite au cours de l’acquisition. D’autre part, ces méthodes devront également afficher de meilleures performances que celles données par l’interpolation, voire proches de celles des techniques par apprentissage de dictionnaire. Pour cela, des méthodes par moindres carrés régularisés sont envisagées dans le cas d’échantillons spatialement lisses et d’échantillons cristallins périodiques. Les algorithmes proposés sont ensuite testés en s’appuyant sur des données synthétiques et réelles. L’intérêt de l’approche par acquisition partielle et les performances par rapport à d’autres méthodes de reconstruction sont étudiés
In electron energy loss spectroscopy (EELS), the sample to be analyzed is exposed to an electron beam, and the measure of the energy loss after passing through the material informs about the chemical composition. For samples particularly sensitive to electronic irradiation damages, such as organic materials, the experimenter is constrained to reduce the total electron dose received by the sample while obtaining a satisfying signal-to-noise ratio. With the recent development of sampling modules adapted to scanning transmission electron microscopes (STEM), the initial raster acquisition (i.e., line-by-line) has become highly configurable. Henceforth, it is now possible to visit any set of spatial positions during the acquisition. Based on these technical advances, a lot of works proposed optimized acquisition schemes for preserving sensitive samples. For a global electron dose equivalent to standard sampling, these strategies consist in visiting less spatial positions, i.e., to perform partial sampling. As a consequence, a higher electron dose per spatial position is allowed, which permits to increase the signal-to-noise ratio for each sampled spectrum. Yet, a post-processing step is required to infer the missing spectra. Among the reconstruction techniques used in the literature, the interpolation methods are fast but rather inaccurate ; they are particularly efficient for displaying the full image along the acquisition process. On the contrary, the dictionary learning-based methods are very performant, but are memory and computation demanding. They are chosen in priority to refine the reconstructed image after experimenting. Finally, only a few works attempt to fill this gap. The main objective of this Ph.D. thesis is to propose fast and accurate reconstruction algorithms for STEM-EELS imaging. Similarly to the interpolation methods, they should be fast enough to visualize the reconstructed image along the acquisition. Meanwhile, they should also achieve better reconstruction performances than those reached by interpolation, close to those of dictionary learning-based methods. To that end, regularized least square methods are proposed in the context of spatially smooth samples or of periodic crystalline samples. The proposed algorithms are then tested based on synthetic as well as real data experiments. The interest of partial-sampling based methods and the performances with respect to other reconstruction methods are evaluated

Thesis (Ocean. E.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, and Woods Hole Oceanographic Institution, 1994.
Includes bibliographical references.
by Peter Traykovski.
Ocean.E.

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

Optofluidics is a relatively new and exciting field that includes the integration of optical waveguides into microfluidic platforms. The purpose of this field of study is to miniaturize previously developed optical systems used for biological and chemical analysis with the end goal of placing bench-top optics into microscopic packages. Mundane optical alignment and sample manipulation procedures would then be intrinsic to the platform and allow measurements to be completed quickly and with reduced human interaction. Biosensors based on AntiResonant Reflecting Optical Waveguides (ARROWs) consist of hollow-core waveguides used for fluid sample manipulation and analysis, as well as solid-core waveguides used in interfacing external components located at the chip edges. Hollow-core ARROWs are particularly useful for their ability to provide specifically tailored analyte volumes that are easily configurable depending upon the target experiment. Adaptations of standard planar microfabrication methods allow for complex integrated ARROW designs. Integrated spectral filtering with high rejection can be implemented on-chip, removing the need for additional off-chip components and increasing device sensitivity. Additional techniques to increase device sensitivity and utility, such as hybrid ARROW platforms and optical manipulation of samples, are also explored.

Bacteriorhodopsine, proteine membranaire, d'halobacterium halobium, est agregee dans des zones particulieres, possede un arrangement cristallin a deux dimensions. Elle utilise l'energie lumineuse absorbee par un chromophore endogene, pour le transport actif transmembranaire de protons. Methode de preparation de liposomes reconstitues de bacteriorhodopsine tres homogene est decrite. La bacteriorhodopsine subit un processus d'oligomerisation qui puisse rendre compte de la formation d'un reseau cristallin lors de l'agregation de la bacteriorhodopsine dans la membrane native. Le role des cations metalliques activateurs et inhibiteurs du transport de proton est etudie. Les sites de fixation de ces cations sont caracterises ainsi que leur influence sur l'activite photochimique de cette proteine

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Esta dissertação apresenta, de forma detalhada, um conjunto de metodologias e técnicas destinadas à análise de redes de energia elétrica como meio de transmissão de dados (power line communication - PLC). As características das redes elétricas que influenciam um sistema de comunicação de dados consideradas neste trabalho são as seguintes: a impedância de acesso à rede elétrica, a resposta ao impulso e o ruído. Para tanto, técnicas de processamento de sinais para estimação da resposta em frequência, estimação do comprimento efetivo da resposta ao impulso, detecção e segmentação de ruídos impulsivos e análise espectral de ruídos aditivos são propostas e discutidas na presente contribuição. Os desempenhos objetivos e a apreciação subjetiva das técnicas propostas, a partir de dados sintéticos e medidos, evidenciam a adequação destas técnicas para a análise em questão. Além disso, formulações matemáticas para a resposta ao impulso de canais PLC invariantes, variantes e periodicamente variantes no tempo, derivadas a partir do modelo de multi-propagação para canais PLC, são apresentadas. Tais formulações proporcionam de forma simples e objetiva a emulação dos possíveis comportamentos temporais de canais PLC reais e, portanto, podem se constituir como ferramentas de grande utilidade para o projeto e a avaliação de sistemas de comunicações baseados na tecnologia PLC.
This thesis addresses a set of methodologies and techniques for the analysis of electric grids as a medium for data communications (power line communications - PLC). The main features influencing a communication system that are considered in this work are the input impedance, the channel impulse response, and the noise. In this regards, signal processing-based techniques are investigated, proposed and analyzed for the estimations of the channel frequency response and the effective length of the channel impulse response; the detection and segmentation of impulsive noise; and the power spectral analysis of the additive noise at the channel output. The numerical performance and subjective analysis regarding the use of the proposed techniques in synthetic and measured data indicate that those techniques fit well in the thesis purposes. In addition, mathematical formulation for invariant, time-varying, and periodically time-varying PLC channel models, which are based on multi-path channel model approach, are presented. These formulations are simple and elegant ones for the emulation of possible temporal behavior of existing PLC channels and, as a result, can constitute a useful tool for the design and analysis of PLC systems.

Cette these est consacre l'etude mathematique de la
propagation non-linaire d'ondes haute-frequence, dans des milieux
inhomognes constitues de deux matriaux d'indice de refraction constant et
separes par une interface plane. La presence de l'interface ncessite
de decrire les phnomenes de reflexion-transmission a la traverse de la
discontinuite. L'approche choisie releve de l'optique gometrique.
L'exemple typique, etudie, est le systeme d'quations Maxwell-Lorentz
complete de diverses quations dcrivant la polarisation de chaque milieux.

La nouveaute de ce travail vient du caractere dispersif des quations
et de la prise en compte des quations de bord exactes.
Dans ce cadre la relation de dispersion ou variete caractristique n'est pas
homogne ce qui implique une reelle dpendance des vitesses de groupe
vis-a-vis de la taille des frequences et pas seulement de leur direction.
Au niveau du probleme limite ceci a pour consquence la creation de
nouvelles phases caracterisriques issues des intractions
non-lineaires des phases existentes avec le bord.

Le premier chapitre re-situe la problematique dans un contexte
historique et mathematique. Il y est egalement donne un resume des
trois autres chapitres. Le second chapitre, coeur de la these,
concerne l'analyse de l'Optique Gomtrique pour le problme de
transmission avec des dveloppements assymptotiques tous ordres. Il
contient une analyse precise de la generation non-linaire des phases
au bord et justifie rigoureusement l'approximation du
developpement. Il donne galement un nouveau traitement des modes evanescents.

Dans le meme contexte geomtrique, le troisime chapitre aborde le
probleme de l'Optique Diffractive avec la recherche de solutions
assymptotiques approchees a tous ordres pour des temps de propagation plus long.

Enfin, dans un quatrieme chapitre sont construits et testes des shemas
numriques 1D quasi linairement exacts pour simuler la propagation (en variable
d'espace) en temps long d'ondes issues d'un bord.

Orientadores: Aldário Chrestani Bordonalli, Júlio César Rodrigues Fernandes de Oliveira
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
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Resumo: Uma das alternativas para os sistemas de transmissão óptica de próxima geração é o uso de múltiplos subcanais ópticos densamente multiplexados em frequência (supercanais) com alta eficiência espectral. Supercanais ópticos empregam o processamento paralelo de sinais para alcançar taxas de transmissão além dos limites da eletrônica. Atualmente, as técnicas CO-OFDM e Nyquist WDM são vistas como as principais para a implementação de supercanais ópticos. Neste trabalho, estudam-se abordagens para aumentar a capacidade de transmissão dos sistemas ópticos por meio da realização de supercanais. A implementação em laboratório, análise de desempenho e comparativo entre as técnicas CO-OFDM e Nyquist WDM são realizadas para sistemas operando a 400 Gb/s e 1 Tb/s por canal, com modulação DP-16QAM e eficiências espectrais que chegam a 6 b/s/Hz e acima. Os principais desafios e soluções para a implementação de sistemas de transmissão óptica de próxima geração baseados em supercanais são identificados
Abstract: One of the options for the next generation of optical transmission systems is the use of multiple optical subchannels densely multiplexed in frequency (superchannels) with high spectral efficiency. Optical superchannels employ parallel signal processing to achieve transmission rates beyond the limits of electronics. Currently, CO-OFDM and Nyquist WDM are seen as the main techniques to the implementation of optical superchannels. In this work, different ways to increase the capacity of the current optical systems by the realization of superchannels are studied. The experimental implementation, performance analysis, and comparison between CO-OFDM and Nyquist WDM techniques are performed for systems operating at 400 Gb/s and 1 Tb/s per-channel with DP-16QAM modulation and spectral efficiencies of 6 b/s/Hz and beyond. The main challenges and solutions for the implementation of next generation optical transmission systems based on superchannels are identified
Mestrado
Telecomunicações e Telemática
Mestre em Engenharia Elétrica

This thesis presents experimental and theoretical work on optical fibre communication systems covering dispersion compensation, short pulse generation and high speed transmission. The focus of this thesis is on dispersion compensation using the midspan spectral inversion (MSSI) technique. Experimental investigation and theoretical studies on an MSSI system suggest potential compensation of both fibre chromatic dispersion as well as fibre nonlinearity. The performance of MSSI systems is found to be limited by a few effects that cannot be compensated for by phase conjugation and a different approach has to be employed in order to overcome these factors. Optical phase conjugators are essential elements of MSSI transmission systems. Dispersion shifted fibre (DSF) and semiconductor optical amplifiers (SOA) are two of the most important nonlinear media for phase conjugation. A comparison of these two types of phase conjugator has been carried out. By using fibre Bragg grating based filters, the noise performance of the conjugators could be optimised. Computer numerical models of various optical components have been developed which could simulate the basic function of erbium-doped fibre amplifiers, optical band pass filters, optical fibres and fibre gratings. Signal transmission in single mode fibre is modelled using the split-step Fourier method to solve the nonlinear Schrödinger equation (NLSE). These numerical models can be programmed to suit different experimental setups and allow the study of various system experiment configurations. The theoretical results help to explain and provide estimated limitations to the experimental results. Experiments carried out in the laboratories have finally culminated in a 10 Gbit/s MSSI field trial in Italy. Successful transmission of 6 picosecond pulses at 10 Gbit/s over 140 km of standard installed fibre was demonstrated. The field trial proved not only the feasibility of 40 Gbit/s MSSI transmission in the final field trial but also an implication on upgradability of currently installed links around the world. A novel polarisation insensitive optical phase conjugation configuration is proposed and demonstrated. With the use of all-fibre DFB lasers as FWM pumps, the first all fibre optical phase conjugator is realised. This configuration can achieve polarisation insensitive operation with great simplicity compared to conventional methods, which are complex and of high component count. Moreover, the same configuration can be applied to an SOA with equally good performance. We have demonstrated wideband and polarisation independent phase conjugation using a highly nonlinear DSF and a long SOA. High bit-rate operation up to 40 Gbit/s and MSSI transmission over 204 km of standard fibre using these devices has also been experimentally investigated.

La majeure partie des communications mondiales est transportée par des systèmes transocéaniques à fibre optique. Il est estimé que d'ici 2020 le trafic de données atteindra 4.3 ZB par an. Afin de faire face à cette demande, différentes technologies sont actuellement étudiées pour augmenter la capacité des systèmes de transmission très longue distance. Avec l'avènement des circuits intégrés à haute vitesse, des formats de modulation avancés et des techniques de traitement de signal numérique (DSP) peuvent être utilisés pour maximiser l'efficacité spectrale de transmission. Par ailleurs, la capacité des systèmes modernes est fortement limitée par les effets non-linéaires de type Kerr dans la fibre. Ainsi, la première partie de ce travail est axée sur l’étude de la performance et des gains réalisables par des techniques DSP à faible complexité pour mitiger les effets non-linéaires monocanal. En outre, l’utilisation des formats de modulation multiniveaux à haute efficacité spectrale au-delà de 16QAM a pris de l'ampleur pour augmenter le débit de transmission des systèmes, notamment avec l’introduction des formats QAM avec mise en forme probabiliste (PCS-QAM), plus performants que les formats QAM classiques. La deuxième partie de ce travail présente donc une comparaison théorique ainsi qu’expérimentale du format PCS-64QAM avec d’autres formats à haute efficacité spectrale pour les distances transatlantiques. La mise en œuvre d’un format PCS-64QAM conçu pour les distances transpacifiques est également abordée. Enfin, la dernière partie de ce travail concrétise les résultats des travaux menés dans les deux sections précédentes en présentant plusieurs records de transmission
Global data traffic is expected to reach up to 4.3 ZB per year by 2020. With the majority of the global communications being transported on submarine point-to-point fiber-optic systems, different cutting-edge technologies have been under research to cope with this unprecedented traffic growth. Continuous advances in high-speed integrated circuits have allowed the use of advanced modulation formats and digital signal processing (DSP) techniques to maximize the transmission spectral efficiency. With mitigation of fiber linear effects efficiently carried out by DSP with relative low-complexity, the capacity of modern fiber optic systems rests limited by fiber nonlinearities. To this extent, in the first part of this work, the performance and achievable benefits of low-complexity DSP techniques aiming to mitigate fiber Kerr nonlinear effects are investigated. Besides nonlinear compensation techniques, the use of multi-level modulation formats beyond 16QAM and high symbol rate channels have gained momentum to increase the system spectral efficiency. One of the major breakthroughs in the recent years, has been the introduction of QAM-based probabilistic constellation shaping (PCS-QAM), which has proven to outperform regular QAM formats. In this sense, in the second part of this work, the practical achievable rate increase brought by PCS-QAM for transoceanic distances is investigated. A theoretical and experimental comparison with other high-capacity formats is performed, and the design of a PCS-QAM for trans-Pacific distances is addressed. Finally, in the last section, several transmission records using the two above techniques are reported