• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 3
  • 2
  • 1
  • Tagged with
  • 7
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Techniques in Secure Chaos Communication.

Lau, Yuu Seng, lauje@rocketmail.com January 2006 (has links)
In today's climate of increased criminal attacks on the privacy of personal or confidential data over digital communication systems, a more secure physical communication link is required. Chaotic signals which have bifurcation behavior (depending on some initial condition) can readily be exploited to enhance the security of communication systems. A chaotic generator produces disordered sequences that provide very good auto- and cross- correlation properties similar to those of random white noise. This would be an important feature in multiple access environments. These sequences are used to scramble data in spread spectrum systems as they can produce low co-channel interference, hence improve the system capacity and performance. The chaotic signal can be created from only a single mathematical relationship and is neither restricted in length nor is repetitive/ cyclic. On the other hand, with the progress in digital signal processing and digital hardware, there has been an increased interest in using adaptive algorithms to improve the performance of digital systems. Adaptive algorithms provide the system with the ability to self-adjust its coefficients according to the signal condition, and can be used with linear or non-linear systems; hence, they might find application in chaos communication. There has been a lot of literature that proposed the use of LMS adaptive algorithm in the communication arena for a variety of applications such as (but not limited to): channel estimation, channel equalization, demodulation, de-noising, and beamforming. In this thesis, we conducted a study on the application of chaos theory in communication systems as well as the application of adaptive algorithms in chaos communication. The First Part of the thesis tackled the application of chaos theory in com- munication. We examined different types of communication techniques utilizing chaos theory. In particular, we considered chaos shift keying (CSK) and mod- ified kind of logistic map. Then, we applied space-time processing and eigen- beamforming technique to enhance the performance of chaos communication. Following on, we conducted a study on CSK and Chaos-CDMA in conjunction with multi-carrier modulation (MCM) techniques such as OFDM (FFT/ IFFT) and wavelet-OFDM. In the Second Part of the thesis, we tried to apply adaptivity to chaos com- munication. Initially, we presented a study of multi-user detection utilizing an adaptive algorithm in a chaotic CDMA multi-user environment, followed by a study of adaptive beamforming and modified weight-vector adaptive beam- forming over CSK communication. At last, a study of modified time-varying adaptive filtering is presented and a conventional adaptive filtering technique is applied in chaotic signal environment. Twelve papers have been published during the PhD candidature, include two journal papers and ten refereed conference papers.
2

Analysis of noncoherent orthogonal modulation for mobile computing

Seet, Siong Leng Henry 12 1900 (has links)
Approved for public release; distribution is unlimited. / Wireless communication is employed to connect mobile computers in a networked environment for information exchange. In a tactical space, sensors and computers typically need to operate on-the-move while transmitting data over both short and long distances in different terrain and conditions. The wireless communication is thus susceptible to effects of Doppler shift and channel fading. In addition, when security and anti jamming features are required, such as frequency-hopping techniques, then coherent signal detection is difficult and noncoherent modulation is used instead. Our study will focus on the bit error rate (BER) performance analysis of noncoherent orthogonal modulation, specifically M-ary frequency-shift keying (MFSK) and code-shift keying (CSK) modulation, in both additive white Gaussian noise (AWGN) and for a Rayleigh fading channel with Doppler shift. The potential applications include communications between mobile computer-sensor devices, such as a mobile ground control station maintaining a datalink with UAV. / Civilian
3

Biologický význam fosforylace tyrosinu 90 v SH3 doméně kinázy Src / Biological relevance of the tyrosine 90 phosphorylation in SH3 domain Src kinase

Koudelková, Lenka January 2013 (has links)
Kinase Src plays an essential role in signal transduction from activated surface receptors. Src is involved in signal pathways that participate in the control of cell proliferation, differentiation or motility. That is why Src activation undergoes strict and complex regulation. Inactive conformation is maintained by intramolecular inhibitory interactions. SH3 domain associates with a polyprolin helix in CD linker whereas SH2 domain binds phosphorylated C-terminal tyrosine 527. Both regulatory domains maintain contacts with the lobes of a kinase domain thereby stabilizing an inactive conformation of the catalytic domain. Transition to an active state is accompanied by a disruption of these inhibitory interactions. Conformation changes are substantially influenced by the phosphorylation status of key tyrosines 416 and 527. Phosphoproteomic analysis revealed new Src tyrosine residue, which can be phosphorylated in vivo. It has been found, that tyrosine works as an additional regulator of Src activity. This is Tyr 90, which forms one of the hydrophobic pockets in the binding surface of Src SH3 domain. Based on the expression of phosphomimic mutant Src 90E in S. pombe or in SYF lineage, it has been observed, that Tyr 90 phosphorylation elevates Src kinase activity. The reason is that the phosphate...
4

Verktyg för att analysera Karlstad Centralsjukhus värme & kylproduktion / A tool for analyzing Karlstad Central Hospital heating & cooling production

Hammar, Martin January 2012 (has links)
Världens energipriser har ökat drastiskt sedan 1970-talet. Detta skapar incitament för investeringar för att sänka sina energikostnader, vilket det satsas på inom industri-, transport- och bebyggelsesektorn. Karlstad Centralsjukhus är inget undantag gällande dessa investeringar och med en lokalyta motsvarande 26 fotbollsplaner med aktivitet dygnen runt förbrukas här stora mängder energi, om inte annat bara för att värma och kyla sjukhuset till ett behagligt klimat. För tillfället sker ombyggnationer över hela sjukhuset för att minska dess energianvändning. Efter ombyggnationer som färdigställdes september 2010 ändrades sjukhusets energiproduktion. Det installerades då sex värmepumpar, två kopplade mot sjukhusets kylsystem för återvinna värme och fyra stycken mot 81 nya borrhål och Klarälven, som rinner förbi sjukhuset. Fjärrvärme används som reserv- och spetskraft när inte värmepumparna klarar leverera hela värmebehovet. Sjukhusets kyla produceras genom de två värmepumparna, kylmaskiner samt frikyla från berget. I projekteringen av anläggningen var värmepumparna dimensionerade att lösa värmeenergibehovet till -4°C resten skulle täckas upp av fjärrvärme. Berget skulle ge möjlighet att säsongslagra energi mellan årstiderna. Drift av anläggningen har dock visat att verkligheten skiljer sig från projekteringen. Värmepumparna har inte kunnat användas fullt ut vintertid då varken berg eller älv har fungerat sig som tänkt. Den driftstrategi som togs fram vid projekteringen stämmer därmed inte utan en ny måste tas fram. Detta examensarbete är ett steg i detta arbete, projektets mål var att i samarbete med Centralsjukhusets driftpersonal ta fram ett verktyg för att kunna analysera sjukhusets drifthistorik. Verktygets målgrupp är sjukhusets driftpersonal så dess utformning måste vara lättförstådd för dessa varför en testperiod gjordes av dessa innan slutgiltig överlämning. Verktyget som togs fram gjordes i Microsoft Exel och det skapar fyra stycken varaktighetsdiagram av drifthistoriken för varje år. Två som visar värme- respektive kyleffekten i kW under ett år och vad som producerat denna effekt. De andra två visar kostnaden per månad i tusen kronor för dessa effekter. Detta gör verktyget genom att bearbeta data som samlas in effekt och temperaturmätare som finns installerade i anläggningen och samlas in genom övervakningsprogrammet Citec och statistikprogrammet WebEss. Genom att jämföra effektdiagrammet för värme och kostnadsdiagrammet går det då att se exempelvis vad värmepumparna producerat och hur mycket denna produktion kostat. Ett ledord i arbetet har varit enkelhet för de senare användarna. Verktyget skulle vara smidigt och snabbt att uppdatera och enkelt att förstå. Vilket även uppnåddes. Efter en veckas testperiod hade driftgruppen inga önskade ändringar varav verktyget lämnades över slutgiltigt. Det överlämnades även fyra rekommendationer till landstinget för att få bättre kontroll på sina energikostnader. / The Worlds energy usage has dramatically increased since the 1970's and as a consequence also the prices for energy. This creates incentives for investments with the purpose to decrease energy costs, which is a development you can see in the industry, transport and building sectors. Karlstad Central Hospital is no exception with a floorspace equivalent of 26 football fields and activity around the clock. Just to heat and cool the hospital to a pleasant climate consumes a large amount of energy. Currently the parts of the hospital is being rebuilt to reduce its energy consumption. In September 2010 the hospital's energy production changed . When six heatpumps were installed, two linked to hospital cooling system to recover heat and four to geothermal heat by 81 boreholes and the river Klarälven, which runs past the hospital. Long-distance heating is used for peak loads and in reserve when the heat pumps cannot supply all heating needs. The hospital's cooling is produced by the two heat pumps, three cooling machines and free cooling from the geothermal connection. When designing the new energy production it was meant that the heat pumps should produce the heat required to -4 ° C, the rest would be covered by long-distance heating. The boreholes would make possible to storage energy between seasons. But operation of the plant has shown that reality differs from the theory. The heatpumps have not been fully utilized during the winter when neither the geothermal or the river behaved as intended. The operating strategy that was developed during project planning valid and therefore needs to be revised. This thesis is a step in that effort. The project's objectives was to produce a tool to analyze the hospital's operating history in cooperation with the Central Hospital's engineering staff. The tools users is meant to be the same staff so its design must be easily understood for those. A trialperiod took place therefore before the final handover. The tool was developed in Microsoft Excel and it creates four graphs showing the operational history of each year. Two of them are showing the heat- or cold-output in kilowatts for a year and what produces this output. The other two shows the cost in thousand swedish crowns to produce these effects. The tool calculates thus by collecting data from power and temperatur gauges installed in the hospitol and is collected by the monitoring program Citec och statistics program WebEss. By comparing the power and cost graph for heat it can be seen for example what heat pumps produced and how much the production cost. A key word in the development of the tool has been simplicity for the users. The tool should be easy and fast to update and simple to understand, which was achieved. After a week's trial had been running the staff had no wanted changes so the tool was handed over.
5

Optimization of demodulation performance of the GPS and GALILEO navigation messages / Optimisation de la performance de démodulation des messages de navigation GPS et GALILEO

Garcia Peña, Axel Javier 08 October 2010 (has links)
La performance de démodulation des signaux GNSS existants, GPS L1 C/A, L2C ou L5, est satisfaisante en environnements ouverts où le C/N0 disponible est assez élevé. Cependant, en milieu urbain, le niveau de C/N0 du signal reçu est souvent très bas et est affecté de variations rapides qui peuvent nuire la démodulation des messages GNSS. Donc, car les applications du marché de masse sont appelées à être déployées dans ces environnements, il est nécessaire d'étudier et de chercher des méthodes de démodulation/décodage qui améliorent la performance de démodulation des messages GNSS dans ces environnements. Il est aussi nécessaire de considérer les nouveaux signaux GPS L1C et GALILEO E1. Ces signaux doivent fournir un service de positionnement par satellite dans tout type d'environnement, et spécifiquement en milieu urbain. Ainsi, cette thèse analyse aussi les performances de démodulation des nouveaux signaux GNSS tels que définis dans les documents publics actuels. De plus, de nouvelles structures de message GALILEO E1 sont proposées et analysées afin d'optimiser la performance de démodulation ainsi que la quantité d'information diffusée. En conséquence, le but principal de cette thèse est d'analyser et améliorer la performance de démodulation des signaux GNSS ouverts au public, spécifiquement en milieu urbain, et de proposer de nouvelles structures de messages de navigation pour GALILEO E1. La structure détaillée des chapitres de cette thèse est donnée ci-après. En premier lieu, le sujet de cette thèse est introduit, ses contributions originales sont mises en avant, et le plan du rapport est présenté. Dans le 2ième chapitre, la thèse décrit la structure actuelle des signaux GNSS analysés, en se concentrant sur la structure du message de navigation, les codages canal implantés et leurs techniques de décodage. Dans le 3ième chapitre, deux types de modèles de canal de propagation sont présentés pour deux différents types de scénarios. D'un côté, un canal AWGN est choisi pour modéliser les environnements ouverts. De l'autre côté, le modèle mathématique de Perez-Fontan d'un canal mobile est choisi pour représenter les environnements urbains et indoor. Dans le 4ième chapitre, une tentative pour effectuer une prédiction binaire d'une partie du message de navigation GPS L1 C/A est présentée. La prédiction est essayée en utilisant les almanachs GPS L1 C/A, grâce à un programme de prédiction à long terme fourni par TAS-F, et des méthodes de traitement du signal: estimation spectrale, méthode de PRONY et réseau de neurones. Dans le 5ème chapitre, des améliorations à la performance de démodulation du message de GPS L2C et L5 sont apportées en utilisant leur codage canal de manière non traditionnelle. Deux méthodes sont analysées. La première méthode consiste à combiner les codages canal internes et externes du message afin de corriger davantage de mots reçus. La deuxième méthode consiste à utiliser les probabilités des données d'éphémérides afin d'améliorer le décodage traditionnel de Viterbi. Dans le 6ième chapitre, la performance de démodulation des messages de GPS L1C et du Open Service GALILEO E1 est analysée dans différents environnements. D'abord, une étude de la structure de ces deux signaux est présentée pour déterminer le C/N0 du signal utile reçu dans un canal AWGN. Puis, la performance de démodulation de ces signaux est analysée grâce à des simulations dans différents environnements, avec un récepteur se déplaçant à différentes vitesses et avec différentes techniques d'estimation de la phase porteuse du signal. / The demodulation performance achieved by any of the existing GPS signals, L1 C/A, L2C or L5, is satisfactory in open environments where the available C/N0 is quite high. However, in indoor/urban environments, the C/N0 level of the received signal is often very low and suffers fast variations which can further affect the GNSS messages demodulation. Therefore, since the mass-market applications being designed nowadays are aimed at these environments, it is necessary to study and to search alternative demodulation/decoding methods which improve the GNSS messages demodulation performance in these environments. Moreover, new GNSS signals recently developed, such as GPS L1C and GALILEO E1, must also be considered. These signals aim at providing satellite navigation positioning service in any kind of environment, giving special attention to indoor and urban environments. Therefore, the demodulation performances of the new GNSS signals as they are defined in the current public documents is also analysed. Moreover, new GALILEO E1 message structures are proposed and analysed in order to optimize the demodulation performance as well as the quantity of broadcasted information. Therefore, the main goal of this dissertation is to analyse and to improve the demodulation performance of the current open GNSS signals, specifically in indoor and urban environments, and to propose new navigation message structures for GALILEO E1. A detailed structure of this dissertation sections is given next. First, the subject of this thesis is introduced, original contributions are highlighted, and the outline of the report is presented. Second, this dissertation begins by a description of the current structure of the different analysed GNSS signals, paying special attention to the navigation message structure, implemented channel code and their decoding techniques. In the third section, two types of transmission channel models are presented for two different types of environments. On one hand, an AWGN channel is used to model the signal transmission in an open environments. On the other hand, the choice of a specific mobile channel, the Perez-Fontan channel model, is chosen to model the signal transmission in an urban environment. In the fourth section, a tentative to make a binary prediction of the broadcasted satellite ephemeris of the GPS L1 C/A navigation message is presented. The prediction is attempted using the GPS L1 C/A almanacs data, a long term orbital prediction program provided by TAS-F, and some signal processing methods: spectral estimation, the PRONY method, and a neural network. In the fifth section, improvements to the GPS L2C and GPS L5 navigation message demodulation performance are brought by using their channel codes in a non-traditional way. Two methods are inspected. The first method consists in sharing information between the message inner and outer channel codes in order to correct more received words. The second method consists in using the ephemeris data probabilities in order to improve the traditional Viterbi decoding. In the sixth section, the GPS L1C and GALILEO E1 Open Service demodulation performance is analysed in different environments. First, a brief study of the structure of both signals to determine the received C/N0 in an AWGN channel is presented. Second, their demodulation performance is analysed through simulations in different environments, with different receiver speeds and signal carrier phase estimation techniques.
6

On ultra-wideband over fiber transmission systems employing semiconductor optical amplifiers / Etude de systèmes de transmission à bande ultra large sur fibre utilisant des amplificateurs optiques à semiconducteurs

Taki, Haidar 25 September 2017 (has links)
La technologie Ultra WideBand (UWB) sur fibre est une solution prometteuse pour répondre aux enjeux des futurs réseaux de communication WLAN/WPAN. Les caractéristiques de la fibre, incluant son énorme bande passante, offrent la possibilité d'une bonne qualité de service à longue portée. La propagation sans-fil UWB doit être réalisée sous des contraintes de densité spectrale de puissance particulières, imposées par l'autorité de régulation (FCC pour les Etats-Unis). La nouveauté de notre travail provient de I' exploitation des avantages d'un amplificateur optique à semi-conducteurs (SOA) afin d'obtenir une extension de portée à un coût et une complexité limités. Cependant, les effets non linéaires et le bruit d'émission spontanée amplifiée (ASE), intrinsèques à ce type de composant, sont susceptibles de dégrader la performance du système. La réduction de ces effets indésirables a donc été d'une importance centrale dans cette étude. Les non-linéarités du SOA ont été compensées en appliquant une solution de pré-distorsion analogique des formes d'ondes électriques. Un traitement basé sur phaser a également été proposé pour réduire simultanément I' influence de I'ASE et linéariser les caractéristiques du SOA, grâce à des opérations de chirping réparties entre l'émetteur et le récepteur. Avec la transmission Impulse Radio, en raison des propriétés temporelles des formats de modulation, des raies spectrales apparaissent, ce qui peut violer la limite FCC ou réduire I' efficacité énergétique. Une nouvelle technique de randomisation de formes d'ondes a été étudiée, qui s'est révélée efficace pour supprimer ces pics spectraux. Les trois approches ont montré un grand potentiel avec les formats On Off Keying et Pulse Position Modulation, à longue portée optique. Les performances d'une modulation différentielle Chaos Shift Keying ont finalement été examinées; une probabilité d'erreur inférieure a été obtenue expérimentalement en comparaison avec d'autres modulations non cohérentes. / Ultra WideBand (UWB) over fiber is a promising technology for meeting the demands of future wireless local-area networks (WLANs) and wireless personal-area networks (WPANs). Thanks to the enormous bandwidth and fiber characteristics, a high communication quality may be established at long reach. UWB wireless propagation must be achieved with special power and spectral constraints fixed by the regulatory bodies (e.g. US Federal Communication Commission). The novelty of our work originates from exploiting the benefits of a Semiconductor Optical Amplifier (SOA) so as to get a reach extension at limited cost and complexity. However, the inherent nonlinear effects and Amplified Spontaneous Emission (ASE) noise associated to such device may affect the system performance.Overcoming these impairments has been of central importance in this study. SOA nonlinearities have been mitigated by applying analog pre-distortion in electrical domain. Phaser-based processing was also proposed to simultaneously reduce ASE influence and linearize SOA characteristics, thanks to up/down chirping performed on the transmitter/receiver sides. With Impulse Radio UWB transmission, due to the time properties of modulation patterns, discrete lines arise in the corresponding spectrum, which may violate FCC limit or reduce the power efficiency. A new shape randomization technique has been investigated, which proved to be effective in suppressing these spectral spikes. The three approaches have shown a great potential with On Off Keying and Pulse Position Modulation formats at long optical reach.The performance of Differential Chaos Shift Keying was finally examined in the over fiber system, a lower error probability was experimentally achieved in comparison with other non-coherent modulations.
7

Regulační úlohy proteinů PAG a CSK v FcɛRI signalizaci žírných buněk / Regulatory roles of PAG and CSK in FcɛRI signaling of mast cells

Potůčková, Lucie January 2017 (has links)
8 1 ABSTRACT (EN) This thesis is focused mainly on understanding mechanisms of regulatory roles of C-terminal Src kinase (CSK) and phosphoprotein associated with glycosphingolipid- enriched microdomains (PAG) in the high-affinity IgE receptor (FcɛRI)-mediated signaling of murine mast cells. FcɛRI activation is initiated by aggregation of the receptor by complexes of multivalent antigen with IgE, followed by activation and enhanced activities of protein tyrosine kinases, phosphatases, adaptor proteins and number of other signal transduction molecules. The signaling events result in mast cell degranulation and release of variety of proinflammatory mediators, responsible for initiation of allergy and other inflammatory diseases. Understanding the function of key regulatory molecules controlling FcεRI-mediated mast cell activation, degranulation, and cytokines production could have therapeutic impact. CSK is a major negative regulator of Src family tyrosine kinases (SFKs) that play a critical role in various immunoreceptor signaling events. However, its function in mast cell activation has not been completely understood. Because of its cytoplasmic localization, CSK was assumed to be brought to the vicinity of the plasma membrane- bound SFKs via binding to membrane-bound adaptors and PAG was a major candidate....

Page generated in 0.0412 seconds