Planejamento de redes de comunicação sem fio para ambiente indoor considerando os efeitos da polarização das antenas: abordagem baseada em medições

Uma das principais aplicações de ondas eletromagnéticas, na atualidade, na área de telecomunicações trata dos enlaces em sistemas móveis sem fio. Sejam estes terrestres (indoor/outdoor) ou via satélites, o projetista do sistema de telecomunicações tem que ser capaz de determinar os sistemas irradiantes, as potências envolvidas, a frequência de operação do sistema, a área de cobertura e os parâmetros de qualidade do serviço. O planejamento das novas redes de comunicações sem fio representa um grande desafio ao incluir serviços cada vez mais avançados com diferentes requisitos de qualidade, suporte a mobilidade, altas taxas de transmissão e capacidades elevadas de tráfego. Os diversos ambientes nos quais essas redes operam, os fenômenos associados produzem diversos efeitos no comportamento do sinal recebido e, consequentemente, uma variação no desempenho do enlace de comunicação entre os pontos de acesso, a rede e os usuários. Por conseguinte, esses efeitos devem ser avaliados corretamente, de tal forma que o dimensionamento da rede atenda aos requisitos de qualidade regulamentados. O presente trabalho objetiva estabelecer uma metodologia para o planejamento de redes de comunicação sem fio para ambientes indoor, considerando os parâmetros de qualidade de serviços e os efeitos da polarização das antenas. Foi proposto um modelo empírico para determinar a área de cobertura desse ambiente a partir de uma abordagem baseada em medições. Como resultado de campanhas de medições, foram identificados os principais parâmetros que interferem nas perdas no enlace de propagação, destacando-se os materiais envolvidos no ambiente bem como os efeitos da polarização das antenas transmissora, entre outros. Tais efeitos, avaliados corretamente, permitirão ao projetista da rede, de uma forma crítica e com base em dados obtidos em campo, definir a melhor configuração de parâmetros e critérios de projeto para a implantação de uma rede móvel de acesso sem fio. As medições para determinação dos parâmetros de cobertura e de qualidade de serviços foram realizadas no prédio do Laboratório de Engenharia Elétrica e de Computação e no prédio de aulas do Instituto de Tecnologia da Universidade Federal do Pará. Nas campanhas de medição foram utilizadas algumas frequências, escolhidas devido à importância dos serviços disponibilizados: 2,4 GHz - redes locais sem fio (WLAN’s); 3,5 GHz - Wimax licenciado; 5,85 GHz - Wimax livre e 10 GHz (a faixa de 9,8 a 10 GHz não está ainda regulamentada, de 10 - 10,15 GHz-radioamador (Resolução Anatel, Nº 452/2006 - D.O.U. de 20.12.2006) ou serviços de comunicações multimídias (SCM) para sistemas em banda larga). Os principais resultados obtidos com o modelo proposto foram avaliados e comparados com os principais modelos da literatura e mostraram que a metodologia adotada para o planejamento de redes de comunicação sem fio em ambientes indoor teve um bom desempenho.

Políticas públicas para a comunicação na Amazônia: o caso do Programa NavegaPará

O Programa NavegaPará, desenvolvido pelo Governo do Estado do Pará, desde 2007, configura-se como uma política pública com o objetivo de garantir acesso à Internet de forma gratuita nos municípios paraenses, através de uma ampla rede de fibra óptica própria. Observando além da infraestrutura básica, buscou-se compreender o NavegaPará acima de tudo como uma política de comunicação, baseando-se na discussão sobre comunicação, informação e incomunicação. À luz da Economia Política da Comunicação, buscou-se compreender o contexto e de que maneira a metodologia do programa é aplicada em três infocentros distintos na capital Belém, a partir da análise de seus condicionantes político-sociais, materiais, institucionais-metodológicos e ideológicos. O método de abordagem é indutivo de enfoque qualitativo, com aplicação de entrevistas semi-estruturadas a três grupos de agentes sociais pertencentes à dinâmica. A pesquisa encontrou despadronização na metodologia dos infocentros, contribuindo para que a questão cultural da comunicação fosse preterida em relação ao aspecto tecnicista do acesso aos microcomputadores e à Internet.

Nature-Inspired Framework for Hyperspectral Band Selection

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Boca a boca on-line: um estudo sobre a Gestão da Comunicação na Internet

Researchs about consumer behavior show influences coming from a lot of fonts. Among them culture, social class, personal influence, family and consumer situation. Personal influence it’s the font object of this research. Personal influence can define what a consumer will buy or will not buy, especially with closer friends. Normally people got the information and transmit to him group, him family, making some difference in the opinion of this people. Ten years ago we were i………..by a dozen of friends. In these days, we have more facility to communicate and more facility to receiver information trough internet. Our personal influence extended from our closest friend to the world wide web group. That’s why company’s must to know what the consumer is speaking on internet

Governo eletrônico, democracia digital e comunicação pública: a presença do poder judiciário na internet

Pós-graduação em Comunicação - FAAC

Constrained least square pre-distortion scheme for multiuser ultra-wideband

The study proposes a constrained least square (CLS) pre-distortion scheme for multiple-input single-output (MISO) multiple access ultra-wideband (UWB) systems. In such a scheme, a simple objective function is defined, which can be efficiently solved by a gradient-based algorithm. For the performance evaluation, scenarios CM1 and CM3 of the IEEE 802.15.3a channel model are considered. Results show that the CLS algorithm has a fast convergence and a good trade-off between intersymbol interference (ISI) and multiple access interference (MAI) reduction and signal-to-noise ratio (SNR) preservation, performing better than time-reversal (TR) pre-distortion.

Study of silicon-on-insulator multiple-gate MOS structures including band-gap engineering and self heating effects

The progresses of electron devices integration have proceeded for more than 40 years following the well–known Moore’s law, which states that the transistors density on chip doubles every 24 months. This trend has been possible due to the downsizing of the MOSFET dimensions (scaling); however, new issues and new challenges are arising, and the conventional ”bulk” architecture is becoming inadequate in order to face them. In order to overcome the limitations related to conventional structures, the researchers community is preparing different solutions, that need to be assessed. Possible solutions currently under scrutiny are represented by: • devices incorporating materials with properties different from those of silicon, for the channel and the source/drain regions; • new architectures as Silicon–On–Insulator (SOI) transistors: the body thickness of Ultra-Thin-Body SOI devices is a new design parameter, and it permits to keep under control Short–Channel–Effects without adopting high doping level in the channel. Among the solutions proposed in order to overcome the difficulties related to scaling, we can highlight heterojunctions at the channel edge, obtained by adopting for the source/drain regions materials with band–gap different from that of the channel material. This solution allows to increase the injection velocity of the particles travelling from the source into the channel, and therefore increase the performance of the transistor in terms of provided drain current. The first part of this thesis work addresses the use of heterojunctions in SOI transistors: chapter 3 outlines the basics of the heterojunctions theory and the adoption of such approach in older technologies as the heterojunction–bipolar–transistors; moreover the modifications introduced in the Monte Carlo code in order to simulate conduction band discontinuities are described, and the simulations performed on unidimensional simplified structures in order to validate them as well. Chapter 4 presents the results obtained from the Monte Carlo simulations performed on double–gate SOI transistors featuring conduction band offsets between the source and drain regions and the channel. In particular, attention has been focused on the drain current and to internal quantities as inversion charge, potential energy and carrier velocities. Both graded and abrupt discontinuities have been considered. The scaling of devices dimensions and the adoption of innovative architectures have consequences on the power dissipation as well. In SOI technologies the channel is thermally insulated from the underlying substrate by a SiO2 buried–oxide layer; this SiO2 layer features a thermal conductivity that is two orders of magnitude lower than the silicon one, and it impedes the dissipation of the heat generated in the active region. Moreover, the thermal conductivity of thin semiconductor films is much lower than that of silicon bulk, due to phonon confinement and boundary scattering. All these aspects cause severe self–heating effects, that detrimentally impact the carrier mobility and therefore the saturation drive current for high–performance transistors; as a consequence, thermal device design is becoming a fundamental part of integrated circuit engineering. The second part of this thesis discusses the problem of self–heating in SOI transistors. Chapter 5 describes the causes of heat generation and dissipation in SOI devices, and it provides a brief overview on the methods that have been proposed in order to model these phenomena. In order to understand how this problem impacts the performance of different SOI architectures, three–dimensional electro–thermal simulations have been applied to the analysis of SHE in planar single and double–gate SOI transistors as well as FinFET, featuring the same isothermal electrical characteristics. In chapter 6 the same simulation approach is extensively employed to study the impact of SHE on the performance of a FinFET representative of the high–performance transistor of the 45 nm technology node. Its effects on the ON–current, the maximum temperatures reached inside the device and the thermal resistance associated to the device itself, as well as the dependence of SHE on the main geometrical parameters have been analyzed. Furthermore, the consequences on self–heating of technological solutions such as raised S/D extensions regions or reduction of fin height are explored as well. Finally, conclusions are drawn in chapter 7.

The Enhanced Single-dish Control System and wide surveys of compact sources

The Italian radio telescopes currently undergo a major upgrade period in response to the growing demand for deep radio observations, such as surveys on large sky areas or observations of vast samples of compact radio sources. The optimised employment of the Italian antennas, at first constructed mainly for VLBI activities and provided with a control system (FS – Field System) not tailored to single-dish observations, required important modifications in particular of the guiding software and data acquisition system. The production of a completely new control system called ESCS (Enhanced Single-dish Control System) for the Medicina dish started in 2007, in synergy with the software development for the forthcoming Sardinia Radio Telescope (SRT). The aim is to produce a system optimised for single-dish observations in continuum, spectrometry and polarimetry. ESCS is also planned to be installed at the Noto site. A substantial part of this thesis work consisted in designing and developing subsystems within ESCS, in order to provide this software with tools to carry out large maps, spanning from the implementation of On-The-Fly fast scans (following both conventional and innovative observing strategies) to the production of single-dish standard output files and the realisation of tools for the quick-look of the acquired data. The test period coincided with the commissioning phase for two devices temporarily installed – while waiting for the SRT to be completed – on the Medicina antenna: a 18-26 GHz 7-feed receiver and the 14-channel analogue backend developed for its use. It is worth stressing that it is the only K-band multi-feed receiver at present available worldwide. The commissioning of the overall hardware/software system constituted a considerable section of the thesis work. Tests were led in order to verify the system stability and its capabilities, down to sensitivity levels which had never been reached in Medicina using the previous observing techniques and hardware devices. The aim was also to assess the scientific potential of the multi-feed receiver for the production of wide maps, exploiting its temporary availability on a mid-sized antenna. Dishes like the 32-m antennas at Medicina and Noto, in fact, offer the best conditions for large-area surveys, especially at high frequencies, as they provide a suited compromise between sufficiently large beam sizes to cover quickly large areas of the sky (typical of small-sized telescopes) and sensitivity (typical of large-sized telescopes). The KNoWS (K-band Northern Wide Survey) project is aimed at the realisation of a full-northern-sky survey at 21 GHz; its pilot observations, performed using the new ESCS tools and a peculiar observing strategy, constituted an ideal test-bed for ESCS itself and for the multi-feed/backend system. The KNoWS group, which I am part of, supported the commissioning activities also providing map-making and source-extraction tools, in order to complete the necessary data reduction pipeline and assess the general system scientific capabilities. The K-band observations, which were carried out in several sessions along the December 2008-March 2010 period, were accompanied by the realisation of a 5 GHz test survey during the summertime, which is not suitable for high-frequency observations. This activity was conceived in order to check the new analogue backend separately from the multi-feed receiver, and to simultaneously produce original scientific data (the 6-cm Medicina Survey, 6MS, a polar cap survey to complete PMN-GB6 and provide an all-sky coverage at 5 GHz).

Mass measurements on neutron-deficient nuclides at SHIPTRAP and commissioning of a cryogenic narrow-band FT-ICR mass spectrometer

The dissertation presented here deals with high-precision Penning trap mass spectrometry on short-lived radionuclides. Owed to the ability of revealing all nucleonic interactions, mass measurements far off the line of ß-stability are expected to bring new insight to the current knowledge of nuclear properties and serve to test the predictive power of mass models and formulas. In nuclear astrophysics, atomic masses are fundamental parameters for the understanding of the synthesis of nuclei in the stellar environments. This thesis presents ten mass values of radionuclides around A = 90 interspersed in the predicted rp-process pathway. Six of them have been experimentally determined for the first time. The measurements have been carried out at the Penning-trap mass spectrometer SHIPTRAP using the destructive time-of-fligh ion-cyclotron-resonance (TOF-ICR) detection technique. Given the limited performance of the TOF-ICR detection when trying to investigate heavy/superheavy species with small production cross sections (σ< 1 μb), a new detection system is found to be necessary. Thus, the second part of this thesis deals with the commissioning of a cryogenic double-Penning trap system for the application of a highly-sensitive, narrow-band Fourier-transform ion-cyclotron-resonance (FT-ICR) detection technique. With the non-destructive FT-ICR detection method a single singly-charged trapped ion will provide the required information to determine its mass. First off-line tests of a new detector system based on a channeltron with an attached conversion dynode, of a cryogenic pumping barrier, to guarantee ultra-high vacuum conditions during mass determination, and of the detection electronics for the required single-ion sensitivity are reported.

Sicurezza nelle reti di sensori wireless UWB: generazione di chiavi simmetriche da parametri fisici

Le reti di oggetti intelligenti costituiscono una realtà che si sta affermando nel mondo quotidiano. Dispositivi capaci di comunicare tra loro, oltre che svolgere la propria funzione primaria, possono comporre una nuvola che faccia riferimento al legittimo proprietario. Un aspetto fondamentale di questo scenario riguarda la sicurezza, in particolar modo per garantire una comunicazione protetta. Il soddisfacimento di questo requisito è fondamentale anche per altri punti come l'integrità dell'informazione condivisa e l'autenticazione. Lo strumento più antico e tutt'ora adatto alla riservatezza di una comunicazione è costituito dalla crittografia. Una tecnica crittografica è schematicamente composta da un algoritmo che, a seconda di una chiave e del messaggio in ingresso, restituisce in uscita un messaggio cifrato, il crittogramma. Questo viene poi inviato e al legittimo destinatario che, essendo in possesso della chiave e dell'algoritmo, lo converte nel messaggio originale. L'obiettivo è rendere impossibile ad un utente malevolo - non dotato di chiave - la ricostruzione del messaggio. L'assunzione che l'algoritmo possa essere noto anche a terze parti concentra l'attenzione sul tema della chiave. La chiave deve essere sufficientemente lunga e casuale, ma soprattutto deve essere nota ai due utenti che intendono instaurare la comunicazione. Quest'ultimo problema, noto come distribuzione della chiave, è stato risolto con il sistema RSA a chiave pubblica. Il costo computazionale di questa tecnica, specialmente in un contesto di dispositivi non caratterizzati da grandi potenze di calcolo, suggerisce però la ricerca di strade alternative e meno onerose. Una soluzione promettente ed attualmente oggetto di studio sembra essere costituita dalle proprietà del canale wireless. Un ponte radio è caratterizzato da una funzione di trasferimento che dipende dall'ambiente in cui ci si trova e, per il teorema di reciprocità, risulta essere lo stesso per i due utenti che l'hanno instaurato. Oggetto della tesi è lo studio ed il confronto di alcune delle tecniche possibili per estrarre una chiave segreta da un mezzo condiviso, come quello del canale wireless. Si presenterà il contesto in cui verrà sviluppato l'elaborato. Si affronteranno in particolare due casi di interesse, costituiti dalla attuale tecnologia di propagazione del segnale a banda stretta (impiegata per la maggior parte delle trasmissioni senza fili) per passare a quella relativamente più recente della banda Ultra-larga (UWB). Verranno poi illustrate delle tecniche per ottenere stringhe di bit dai segnali acquisiti, e saranno proposti dei metodi per la loro correzione da eventuali discordanze. Saranno infine riportate le conclusioni sul lavoro svolto e le possibili strade future.

Antipodal random sequences with prescribed second-order statistics: application to Compressive Sensing and UWB system based on DS-CDMA

It is usual to hear a strange short sentence: «Random is better than...». Why is randomness a good solution to a certain engineering problem? There are many possible answers, and all of them are related to the considered topic. In this thesis I will discuss about two crucial topics that take advantage by randomizing some waveforms involved in signals manipulations. In particular, advantages are guaranteed by shaping the second order statistic of antipodal sequences involved in an intermediate signal processing stages. The first topic is in the area of analog-to-digital conversion, and it is named Compressive Sensing (CS). CS is a novel paradigm in signal processing that tries to merge signal acquisition and compression at the same time. Consequently it allows to direct acquire a signal in a compressed form. In this thesis, after an ample description of the CS methodology and its related architectures, I will present a new approach that tries to achieve high compression by design the second order statistics of a set of additional waveforms involved in the signal acquisition/compression stage. The second topic addressed in this thesis is in the area of communication system, in particular I focused the attention on ultra-wideband (UWB) systems. An option to produce and decode UWB signals is direct-sequence spreading with multiple access based on code division (DS-CDMA). Focusing on this methodology, I will address the coexistence of a DS-CDMA system with a narrowband interferer. To do so, I minimize the joint effect of both multiple access (MAI) and narrowband (NBI) interference on a simple matched filter receiver. I will show that, when spreading sequence statistical properties are suitably designed, performance improvements are possible with respect to a system exploiting chaos-based sequences minimizing MAI only.

Progetto elettromagnetico di antenne per tag eco-compatibili a banda ultra-larga

Questo lavoro si è occupato della ricerca e progettazione di un'antenna UWB per la realizzazione di un tag RFID e si colloca all'interno del progetto GRETA (GREen TAgs), finanziato dal MIUR. Le principali caratteristiche richieste al green tag sono: dimensioni complessive di massimo 4-5 cm, assenza di batterie e compatibilità con l'ambiente. L'eco-compatibilità viene garantita tramite la realizzazione dell'antenna al di sopra di un substrato di carta; i limiti derivanti dall'assenza di batterie vengono invece sopperiti tramite realizzazione di energy harvesting, al fine di raggiungere una completa autonomia energetica. Viene sfruttata la tecnica UWB per la comunicazione nella banda (3.1-4.8 GHz); l'energy harvesting si effettua invece a 868 MHz. Sono infine stati ricavati alcuni primi risultati relativi alla potenza rettificabile con la soluzione proposta, tramite realizzazione di un opportuno circuito rettificatore.

Studio di fattibilità di applicazione di radar UWB per controlli non distruttivi

Studio di fattibilità sull'utilizzo della tecnologia radar Ultra Wideband per il controllo non distruttivo di manufatti in materiale composito in fibra di carbonio. La tecnologia radar UWB permette, a differenza dei radar convenzionali, una maggiore risoluzione e un maggior quantitativo di informazioni estraibili dal segnale ricevuto come eco. Nella prima parte del lavoro ci si è concentrati sulla individuazione dell'eventuale presenza del difetto in lastre di materiale composito di differenti dimensioni. Le lastre vengono "illuminate" da un fascio di onde radar UWB dal cui eco si estraggono le informazioni necessarie per determinare la presenza o meno del difetto. Lo scopo è progettare le basi di un algoritmo che, qualora la lastra in esame presenti una certa difettologia, informi l'utente della presenza dell'anomalia. Nella seconda parte si è passati a scansionare la lastra con un radar UWB in modo tale da costruire un'immagine della stessa grazie alle informazioni ricevute dai segnali eco. Per fare questo è stata necessaria dapprima la costruzione di un movimentatore ad hoc in grado di muovere il radar lungo due dimensioni (per permetterne la scansione del piano della lastra). Il movimentatore, autocostruito, è gestibile da Matlab attraverso cavo USB. L'algoritmo di controllo gestisce sia la movimentazione che l'acquisizione dei segnali ricevuti e quindi la creazione del database, punto di partenza per la creazione dell'immagine della lastra. Rispetto alla prima fase del lavoro dove si cercava di sapere se ci fosse o meno il difetto, ora, si è in grado di determinare dimensione e posizione dello stesso.

Design and experimental characterization of antennas and wireless systems for innovative wearable and implantable ultra low–power applications

The present PhD thesis exploits the design skills I have been improving since my master thesis’ research. A brief description of the chapters’ content follows. Chapter 1: the simulation of a complete front–end is a very complex problem and, in particular, is the basis upon which the prediction of the overall performance of the system is possible. By means of a commercial EM simulation tool and a rigorous nonlinear/EM circuit co–simulation based on the Reciprocity Theorem, the above–mentioned prediction can be achieved and exploited for wireless links characterization. This will represent the theoretical basics of the entire present thesis and will be supported by two RF applications. Chapter 2: an extensive dissertation about Magneto–Dielectric (MD) materials will be presented, together with their peculiar characteristics as substrates for antenna miniaturization purposes. A designed and tested device for RF on–body applications will be described in detail. Finally, future research will be discussed. Chapter 3: this chapter will deal with the issue regarding the exploitation of renewable energy sources for low–energy consumption devices. Hence the problem related to the so–called energy harvesting will be tackled and a first attempt to deploy THz solar energy in an innovative way will be presented and discussed. Future research will be proposed as well. Chapter 4: graphene is a very promising material for devices to be exploited in the RF and THz frequency range for a wide range of engineering applications, including those ones marked as the main research goal of the present thesis. This chapter will present the results obtained during my research period at the National Institute for Research and Development in Microtechnologies (IMT) in Bucharest, Romania. It will concern the design and manufacturing of antennas and diodes made in graphene–based technology for detection/rectification purposes.

Band structure of Heusler compounds studied by photoemission and tunneling spectroscopy

Heusler compounds are key materials for spintronic applications. They have attracted a lot of interest due to their half-metallic properties predicted by band structure calculations.rnThe aim of this work is to evaluate experimentally the validity of the predictions of half metallicity by band structure calculations for two specific Heusler compounds, Co2FeAl0.3Si0.7 and Co2MnGa. Two different spectroscopy methods for the analysis of the electronic properties were used: Angular Resolved Ultra-violet Photoemission Spectroscopy (ARUPS) and Tunneling Spectroscopy.rnHeusler compounds are prepared as thin films by RF-sputtering in an ultra-high vacuum system. rnFor the characterization of the samples, bulk and surface crystallographic and magnetic properties of Co2FeAl0.3Si0.7 and Co2MnGa are studied. X-ray and electron diffraction reveal a bulk and surface crossover between two different types of sublattice order (from B2 to L21) with increasing annealing temperature. X-ray magnetic circular dichroism results show that the magnetic properties in the surface and bulk are identical, although the magnetic moments obtained are 5% below from the theoretically predicted.rnBy ARUPS evidence for the validity of the predicted total bulk density of states (DOS) was demonstrated for both Heusler compounds. Additional ARUPS intensity contributions close to the Fermi energy indicates the presence of a specific surface DOS. Moreover, it is demonstrated that the crystallographic order, controlled by annealing, plays an important role on brodening effects of DOS features. Improving order resulted in better defined ARUPS features.rnTunneling magnetoresistance measurements of Co2FeAl0.3Si0.7 and Co2MnGa based MTJ’s result in a Co2FeAl0.3Si0.7 spin polarization of 44%, which is the highest experimentally obtained value for this compound, although it is lower than the 100% predicted. For Co2MnGa no high TMR was achieved.rnUnpolarized tunneling spectroscopy reveals contribution of interface states close to the Fermi energy. Additionally magnon excitations due to magnetic impurities at the interface are observed. Such contributions can be the reason of a reduced TMR compared to the theoretical predictions. Nevertheless, for energies close to the Fermi energy and for Co2MnGa, the validity of the band structure calculations is demonstrated with this technique as well.