Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores (Major em Telecomunicações). Faculdade de Engenharia. Universidade do Porto. 2009

Diss. (sammanfattning) Linköping : Linköpings universitet, 2006. / Härtill 6 uppsatser.

>Magister Scientiae - MSc / Wi-Fi authentication mechanisms include central authentication, dynamic and distributed authentication and some encryption methods. Most of the existing authentication methods were designed for single-hop networks, as opposed to multihop Wi-Fi mesh networks. This research endeavors to characterize and compare existing Wi-Fi authentication mechanisms to find the best secure connection mechanism associated with Wi-Fi mesh network fragmentation and distributed authentication. The methodology is experimental and empirical, based on actual network testing. This thesis characterizes five different types of Wrt54gl firmware, three types of Wi-Fi routing protocols, and besides the eight Wi-Fi mesh network authentication protocols related to this research, it also characterizes and compares 14 existing authentication protocols. Most existing authentication protocols are not applicable to Wi-Fi mesh networks since they are based on Layer 2 of the OSI model and are not designed for Wi-Fi mesh networks. We propose using TincVPN which provides distributed authentication, fragmentation, and can provide secure connections for backbone Wi-Fi mesh networks.

There has been an overwhelming interest in public Wi-Fi due to the increasing number of mobile users and a growing perception that Wi-Fi provides better connection experience at lower costs. Moreover, end users increasingly expect Wi-Fi to be free, thereby motivating a strong transition in leading markets to provide free-to-the-end-user Wi-Fi. Providing free internet to the users is a challenge as potential solutions must be self-sustainable and provide sufficient financial returns. Framework for Advertisement-based Community Wi-Fi access, called FRAC is a self-sustainable advertisement-based community network sharing framework which has the competence to provide significant financial returns. FRAC provides free internet access to its users by motivating Wi-Fi access point (AP) owners to share their internet service for benefits. FRAC builds on privately or commercially-owned, existing Wi-Fi infrastructure. The users accessing the internet using this framework provide a strong customer base for online marketing and advertising which provides the revenue to sustain this framework. This thesis describes the design and implementation of a prototype of the FRAC system. The design of key features of the framework such as user authentication, advertisement delivery, quality of service, messaging and security, are described, based on which an overall design of the framework is provided. The prototype developed includes a browser extension to support browser-based devices like laptops, netbooks and embeddable software that can be installed on wireless routers with Linux-based dd-wrt firmware. / Master of Science

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores (Major Telecomunicações). Faculdade de Engenharia. Universidade do Porto, INESC-Porto. 2010

The topic of Wi-Fi networks (Wireless Fidelity) is widely discussed currently as there is a big boom of this technology. The Wi-Fi refers to a method of modern technology that enables wireless transmission of data between devices such as printers and mobile phones. The main objectives of the thesis are focused on the development proposal to build a modern data network for an ISP (Internet Service Provider) in the technical area. Another aim was to process and analyze the results of the newly formed economic entity and their subsequent evaluation in recent years, i.e for the years 2008 - 2011. Business plan was designed in Branišov, which is a village near Czech Budejovice in 2001. Initially, it was the agreement of two local residents who believed that the offer of an Internet connection is not ideal for this location and started to develop some "small" wireless network. At the beginning, any professional equipment was not used in this network. When connected with an increasing number of customers (about five inhabitants of Branišov), professional antennas and access points began to be used. The above mentioned five customers manage to cover all operating costs created by the network. In subsequent years, i.e. 2004 ? 2007, there was a boom of the project. The number of connected users was growing constantly, even though not conducted any marketing or promotional activities. By the end of 2006, individual users began to demand greater guarantee of a stable connection. At the same time, it also proved to be absolutely necessary to establish a specific person responsible for the network. This person was supposed to maintain the network, develop it and manage it. In 2007, the initial non-commercial network was transformed into a commercial network model and brand new commercial entity ? a limited liability company ? was created. Currently, there is a continual development of this network, which already covers a total of 30 villages around České Budějovice and Vodňany and the signal spread through 115 broadcasting Access Points.

ZigBee based Wireless Sensor Networks (WSN) and Wireless Local Area Networks (WLAN) utilize the same un-licensed 2.4GHz frequency band. In our research, it is noticed that ZigBee could suffer serious performance degradation due to the collocated WLAN interference. After going through the available literature and combining with a thorough statistical analysis of our experimental results, several important factors that severely impact the ZigBee packet transmission performance have been identified. Motivated by these findings, novel techniques are designed to improve the performance of ZigBee packet transmission under WLAN interference. ACK with Interference Detection (ACK-ID) technique is developed to improve the delivery rate of ACK packets, and consequently reduce the number of redundant retransmissions. In order to improve the energy efficiency, Adaptive Transmit Power Adjustment (ATPA) is proposed to adaptively adjust the optimal transmit power while maintaining the predefined Packet Loss Rate (PLR) requirement. Time Aware Backoff and Transmission (TABTx) technique controls the time spent on each packet transmission attempt so as to avoid the Transmit First In First Out Byte Register (TXFIFO) overflow. Adaptive Preamble Padding with Retransmission Control (APPRC) is proposed to improve the transmission efficiency while satisfying the PLR requirement by determining the appropriate number of protective preamble padding bytes and whether or not to adopt packet retransmission. All these novel techniques have been implemented in the Crossbow MICAz motes and evaluated through extensive experimental measurements in the testbed.

La tesi IMATGES DE LA FI va ser iniciada l'any 1990 a les envistes de la fi de l'anterior centúria i mil·lenni. La seva pretensió fou de constatar com les produccions artístiques últimes del segle XX venien poblades d'una iconografia abundosa d'escatologia, en la seva accepció més àmplia. Partint d'uns referents filosòfics i intel·lectuals al voltant del concepte del fi (fi de la filosofia, fi del paradigma clàssic, fi de la història, fi de l'art, fi de la modernitat, fi de la divinitat, fi dels temps...) i d'una renovació social dels antics temors mil·lenaristes, la tesi es proposa acollir un banc d'imatges, actituds i formalitzacions de l'art contemporani centrats bàsicament en l'ultima dècada del segle, fer-ne una agrupació temàtica i presentar-ne un corpus de lectures del paper de l'art d' "avantguarda" com a consciència crònica,o, encara més, anticipadora dels temps i com una praxis catàrquica i taumatúrgica.La tesi indaga en les formalitzacions de l'art i els artistes especialment de la dècada final de segle i en l'incipient s.XXI recolzant-se en algunes figures clau de mitjans de la centúria, personalitats i obres "frontissa" de l'avantguarda històrica (especialment Beuys i la seva obra "El final del segle XX", Warhol , Duchamp i altres...). No ha estat difícil trobar en l'art d'aquest període totes les gradacions iconogràfiques de l'horror, la barbàrie, la malaltia, el sofriment i la mort, unes icones d'apocalipsi contemporania que ens posen en connexió sensorial amb períodes remots de la història de l'art. La tesi posa èmfasi en la percepció que l'art de qualsevol període històric ha estat sempre cronista, que ha actuat de consciència col·lectiva, de ressort d'alarma o, per dir-ho en paraules del poeta Rimbaud, de parallamps que recull les energies circumdants. Què en fa l'art d'aquests símptomes mòrbids dels temps? Els posa a la consideració dels contemporanis. I ho fa ben sovint distorsionant, exagerant, provocant per a fer-se sentir, tal com diu el filòsof Gadamer. Per això tan sovint es mostra escatològic, agressiu, salvatge, sarcàstic, irreverent, descarnat, perquè així és la metodologia general de l'art de les últimes aportacions. Qui no compren això tampoc comprendrà l'art del passat i si tan sovint hi ha la percepció general que l'art ha mort, que ha arribat al seu final, és perquè sovint la mateixa vida que és qui ens sembla extingida en la seva capacitat generadora.La tesi parla de la mort de l'art, de l'anacronisme permanent davant l'ardidesa dels nous plantejaments, de les propostes últimes que semblen arraconar les precedents, parla de l'extrema fugacitat dels productes artístics, de la permanent reconsideració de tot allò fet. Qualsevol hipotètica fi de l'art serà el començament d'un art nou, ha dit Gadamer. Al llarg de la tesi veiem com l'art s'erigeix en imatge especular del món del final de segle XX. Hi veiem com aquest art es manifesta amb una àmplia voluntat inestètica o, des de l'estètica de la lletjor, Everithing is wrong, apunta una obra de l'artista Kakobsen, l'accepció, traduïda com a dolent, pecaminós, injust, equivocat, defectuós, inoportú, sense raó, culpable....podria ser la visió que els artistes tenen de l'actualitat del nostre món. Però una altra obra (del 1967), la de l'artista Bruce Nauman, incorpora el següent text en lletres lluminoses: el vertader artista ajuda el món a revelar les veritats místiques... Entre aquestes dues voluntats d'interpretació del món es mou l'art dels nostres dies. També la tesi inclou alguns dels treballs realitzats en escultura per l'autor, la temàtica dels quals s'insereixen en el discurs de diferents capítols.

Hybrid Networks employing wireless communication technologies have nowadays brought closer the vision of communication “anywhere, any time with anyone”. Such communication technologies consist of various standards, protocols, architectures, characteristics, models, devices, modulation and coding techniques. All these different technologies naturally may share some common characteristics, but there are also many important differences. New advances in these technologies are emerging very rapidly, with the advent of new models, characteristics, protocols and architectures. This rapid evolution imposes many challenges and issues to be addressed, and of particular importance are the interoperability issues of the following wireless technologies: Wireless Fidelity (Wi-Fi) IEEE802.11, Worldwide Interoperability for Microwave Access (WiMAX) IEEE 802.16, Single Channel per Carrier (SCPC), Digital Video Broadcasting of Satellite (DVB-S/DVB-S2), and Digital Video Broadcasting Return Channel through Satellite (DVB-RCS). Due to the differences amongst wireless technologies, these technologies do not generally interoperate easily with each other because of various interoperability and Quality of Service (QoS) issues. The aim of this study is to assess and investigate end-to-end interoperability issues and QoS requirements, such as bandwidth, delays, jitter, latency, packet loss, throughput, TCP performance, UDP performance, unicast and multicast services and availability, on hybrid wireless communication networks (employing both satellite broadband and terrestrial wireless technologies). The thesis provides an introduction to wireless communication technologies followed by a review of previous research studies on Hybrid Networks (both satellite and terrestrial wireless technologies, particularly Wi-Fi, WiMAX, DVB-RCS, and SCPC). Previous studies have discussed Wi-Fi, WiMAX, DVB-RCS, SCPC and 3G technologies and their standards as well as their properties and characteristics, such as operating frequency, bandwidth, data rate, basic configuration, coverage, power, interference, social issues, security problems, physical and MAC layer design and development issues. Although some previous studies provide valuable contributions to this area of research, they are limited to link layer characteristics, TCP performance, delay, bandwidth, capacity, data rate, and throughput. None of the studies cover all aspects of end-to-end interoperability issues and QoS requirements; such as bandwidth, delay, jitter, latency, packet loss, link performance, TCP and UDP performance, unicast and multicast performance, at end-to-end level, on Hybrid wireless networks. Interoperability issues are discussed in detail and a comparison of the different technologies and protocols was done using appropriate testing tools, assessing various performance measures including: bandwidth, delay, jitter, latency, packet loss, throughput and availability testing. The standards, protocol suite/ models and architectures for Wi-Fi, WiMAX, DVB-RCS, SCPC, alongside with different platforms and applications, are discussed and compared. Using a robust approach, which includes a new testing methodology and a generic test plan, the testing was conducted using various realistic test scenarios on real networks, comprising variable numbers and types of nodes. The data, traces, packets, and files were captured from various live scenarios and sites. The test results were analysed in order to measure and compare the characteristics of wireless technologies, devices, protocols and applications. The motivation of this research is to study all the end-to-end interoperability issues and Quality of Service requirements for rapidly growing Hybrid Networks in a comprehensive and systematic way. The significance of this research is that it is based on a comprehensive and systematic investigation of issues and facts, instead of hypothetical ideas/scenarios or simulations, which informed the design of a test methodology for empirical data gathering by real network testing, suitable for the measurement of hybrid network single-link or end-to-end issues using proven test tools. This systematic investigation of the issues encompasses an extensive series of tests measuring delay, jitter, packet loss, bandwidth, throughput, availability, performance of audio and video session, multicast and unicast performance, and stress testing. This testing covers most common test scenarios in hybrid networks and gives recommendations in achieving good end-to-end interoperability and QoS in hybrid networks. Contributions of study include the identification of gaps in the research, a description of interoperability issues, a comparison of most common test tools, the development of a generic test plan, a new testing process and methodology, analysis and network design recommendations for end-to-end interoperability issues and QoS requirements. This covers the complete cycle of this research. It is found that UDP is more suitable for hybrid wireless network as compared to TCP, particularly for the demanding applications considered, since TCP presents significant problems for multimedia and live traffic which requires strict QoS requirements on delay, jitter, packet loss and bandwidth. The main bottleneck for satellite communication is the delay of approximately 600 to 680 ms due to the long distance factor (and the finite speed of light) when communicating over geostationary satellites. The delay and packet loss can be controlled using various methods, such as traffic classification, traffic prioritization, congestion control, buffer management, using delay compensator, protocol compensator, developing automatic request technique, flow scheduling, and bandwidth allocation.

The project to design a CD transport (CD player) in conjunction with Perreaux Industries came about from the need for a source component in their Silhouette series of products. This project describes the design a high quality CD player, at a low price, to compliment Perreaux's Silhouette series. A CD drive is selected over a proprietary optical pickup due to the former's low cost and the standardisation of the interface. The control circuitry includes a micro controller and discrete logic to provide the correct data and clock signals to the SPDIF transmitter and DAC circuits. These two circuits provided a high quality analogue output, and facilitate an upgrade path by connecting the SPDIF output to an external DAC. After three board iterations, a final production ready revision was achieved. The design includes a high quality toroidal transformer, low jitter crystal oscillator, and a very high quality SPDIF pulse transformer output. The design also allows a remote input to control the player, and an optional digital cable via an RJ45 connector to provide synchronisation with a future design of the SXD2 DAC module, or to transmit SPDIF to a remote location. The specifications of the final design were higher than expectations. The digital output boasts equal or superior performance to competitive products in the same price range, with the analogue output attaining exceptionally high performance.