Orientadores: Michel Daoud Yacoub, Omar Carvalho Branquinho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-08T18:59:46Z (GMT). No. of bitstreams: 1 Ferreira_DeboraMeyhofer_M.pdf: 1183194 bytes, checksum: 3c93692fbad066caa7e514b9442843d9 (MD5) Previous issue date: 2007 / Resumo: A Ethernet existe há mais de 20 anos e a ¿wireless ethernet¿ (ethernet sem fio), conhecida como o padrão 802.11, há mais de sete anos. Extensões do padrão original, tais como o 802.11g, foram criados para garantir maiores taxas de transmissão. No entanto, existem condições que afetam o seu desempenho. Um desses casos, conhecido como performance anomaly, ou anomalia de desempenho, ocorre quando em uma rede infraestruturada existem estações móveis (STAs) transmitindo com taxas diferentes. Nesse caso, uma STA a uma taxa baixa ocupa o canal por um longo período, degradando o desempenho das demais estações e comprometendo o funcionamento de toda a rede. Esse trabalho constata e quantifica essa anomalia e determina um método de priorizar as STAs com uma taxa de transmissão alta, objetivando a redução do efeito da anomalia. Essa priorização é feita alterando-se a janela de contenção de acordo com a relação sinal ruído da STA. O mecanismo é modelado matematicamente e avaliado através de simulação com o software Network Simulator / Abstract: Ethernet exists more than 20 years and the wireless Ethernet, known as IEEE 802.11, for more than seven years. Extensions of the original standard, as IEEE 802.11g, are been created to guarantee higher transmission rates. However, some conditions there are that affect the performance of the network. One of them, known as Performance Anomaly, occurs when in an infrastructured WLAN stations (STAs) operate at different rates. In such a case, the low rate STA rate captures the channel for a long time, penalizing the higher rate stations, thence degrading the performance of the network. This work substantiates and quantifies such an anomaly and proposes a method to mitigate the effect of it, prioritizating the higher STAs. This mitigation is is carried out using Signal to Noise Ratio as a criterion to control the Contention Window variation. The mechanism is modeled mathematically and evaluated by means of simulation using the software Network Simulator / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

Detta arbete beskriver och analyserar vilka förutsättningar som är viktiga att ta hänsyn till vid en installation av ett trådlöst nätverk hos SYSteam. Ämnet trådlösa nätverk är omfattande och komplext och många i branschen saknar idag kompetens inom området. Det finns en uppsjö av olika komponenter, krypteringar och tillvägagångssätt. Detta arbete har utförts i samarbete med SYSteam Network Center (SNC), som vill undersöka möjligheterna och vilka förutsättningar som krävs för att kunna erbjuda ett gemensamt trådlöst nätverk som uppfyller kraven att vara säkert, skalbart och centralt administrerbart från SNC. SNC vill skaffa sig en uppfattning om vilket behov som de olika bolagen hos SYSteam i Huskvarna har av ett trådlöst nätverk, och därmed få fram en gemensam bild av hur ett trådlöst nätverk bör utformas. Som en del av detta intervjuas personer inom respektive bolag. SNC önskar sedan kunna erbjuda SYSteams bolag i Huskvarna ett gemensamt trådlöst nätverk som beaktat samtligas intresse. Genom intervjuerna gick det att urskilja följande problem i SYSteams nuvarande nätverkslösning: Dagens struktur hämmar samarbete mellan bolag. Avsaknaden av en smidig gästaccess ger ett dåligt intryck på gäster. Gäster och personal är idag bundna till ett begränsat antal switchportar. Anslutna gäster får åtkomst till delar av SYSteams interna klientnät. Gästerna bör endast komma åt de delar som de absolut behöver. För att kunna behandla och bearbeta de olika problemen utförs en behovsanalys. Utifrån behovsanalysen studeras lämplig litteratur i syfte att förse SNC med en omfattande analys om tekniken, affärsnyttan och mervärden som ett trådlöst nätverk kan erbjuda, men också hur ett trådlöst nätverk bör administreras och säkras. Resultatet fokuserar även på vilka utmaningar och problem som kan förekomma i en trådlös miljö, samt ger förslag på hur SNC i Huskvarna bör utforma ett trådlöst nätverk. SNC står inför en stor utmaning med att erbjuda ett trådlöst nätverk som kan upplevas användarvänligt men som samtidigt måste uppfylla vissa säkerhetskrav. Arbetet visar att om man tar hänsyn till de utmaningar som finns och kartlägger de problem som finns så är det möjligt att utforma ett skalbart, säkert nätverk som samtidigt tar hänsyn till användarvänligheten. Ett gemensamt trådlöst nätverk kan erbjuda SYSteam i Huskvarna följande: Förbättrat samarbete mellan bolagen genom att medarbetarna blir mer mobila. Effektivare möten. En bättre miljö för projektgrupper – ökar deras rörlighet. Att kommunikationen internt mellan bolag kommer att underlättas och förbättras. Flexibiliteten ökar samt en ökning av motivationen bland personalen. Att professionaliteten höjs internt. Ett smidigt och användarvänligt gästnätverk vilket kommer förbättra bilden av SYSteam. Det ökar kundens upplevelse och tillfredställer kundens behov och kan resultera i att kundens lojalitet ökar. Kundkontakten kommer att underlättas. / This report describes and analyzes the requirements for a wireless network installation. The subject wireless network is both extensive and complex, and results of that many in the branch are missing the accurate qualifications. There is an abundance of different components, encryptions and procedures. This report has developed in cooperation with SYSteam Network Center (SNC), who wants to investigate the requirements and opportunities a common wireless network might provide. The common wireless network shall fulfill the need of security, scalability and to be centrally administrated. SNC wants knowledge about the different needs, that the internal SYSteam company in Huskvarna have about a common wireless network. And thereby be able to summarize a mutual image of how a wireless network should be designed. As a part of this, people from different companies at SYSteam where interviewed. SNC would like to offer the SYSteam companies situated in Huskvarna a common wireless network, which pays attention to everyone’s interests. The interviews gave the following notice that there were problem in the network solution used today: Today’s network structure restrains the cooperation between internal companies. The missing of a flexible guest access gives a bad impression to external guests. Today guests and staff are bound to a limited amount of switchports. Connected guests get access to parts of SYSteam internal clientnetwork. The guests should only get access to what they absolutely require. To be able to handle and process the problems a three-steep analyze have been made, primary to understand the requirement of the organization, to clearly define the problems and what opportunities a wireless network may have. From these three steps, proper literature have been studied in purpose to provide SNC with a comprehensive analyze about the technique, business considerations and what value a wireless network provides. The result focuses about what uprising challenge a wireless network may originate and the problems it could contain. In the conclusion, guide principles how a wireless network should be designed adjusted for SNC is formed. SNC is today facing a big challenge in order to offer a wireless network which shall meet the requirements of user-friendly and secured demands. The work shows, if consideration is taken to available challenges and survey existing problems, it’s possible to design a scalable, secured network which also provides user-friendly management. An example a common wireless network can offer SYSteam in Huskvarna can be one of the following: Cooperation improvements between companies, clients become even more mobile. Meetings become more efficient. Offer a better environment for project teams, due to increased mobility. Offer an ordinary guest access. The internal communication will facilitate and improve between companies.

Unmanned Aerial Vehicles (UAVs) recently enabled a myriad of new applications spanning domains from personal entertainment and industrial inspection, to criminal surveillance and forest monitoring. A combination of sensor collection, wireless communication and path planning between multiple distributed agents is the natural way to support applications. Several small UAVs working collaboratively can rapidly provide extended reach, at low cost, and efficiently stream sensor information to operators on a ground station. A significant amount of previous work has addressed each of these topics independently, but in this dissertation we propose a holistic approach for joint coordination of networking and topology (placement of mobile nodes). Our thesis is that this approach improves user-interactive control of UAVs for live-streaming applications in terms of throughput, delay and reliability. In order to defend these claims, this dissertation begins by experimentally evaluating and modeling the wireless link between two UAVs, under different conditions. Due to limited link range, and the need for wide-area operation, the model is extended to encompass a multi-hop topology. We show that the performance of such networks using COTS devices is typically poor, and solutions must rely on coordination of network protocol and topology, simultaneously. At the network layer, we introduce a novel Time-division Multiple Access (TDMA) scheme called Distributed Variable Slot Protocol that relies on adaptive slot-length. We prove its convergence as well as its meliorated performance experimentally validated, namely 50% higher packet delivery. In terms of network topology, we show that without node placement control overall performance of the network is severely penalized, due to natural link asymmetries. We propose a novel protocol, named Dynamic Relay Placement, that is able to do both online link quality model-estimation and in a distributed fashion decide the best location for each network node, increasing throughput by 300%. Finally, we demonstrate the end-to-end system in a multi-vehicle monitoring mission. We show that coordination of multiple UAVs increases the sensor sampling rate up to 7 times in wide areas when compared to a naive approach. This work considers environmental constraints such as wind, as well as the intrinsic limitations of the vehicles such as maximum acceleration.

IEEE 802.11 (a.k.a. WiFi) is a popular wireless LAN specification. This thesis documents implementation of this standard within the experimental operating system HelenOS which differs from conventional operating systems with its microkernel-based design. First, the basic concepts of WiFi technology are described. Description of external tools used during development is following. Together with that, the chosen method of integrating the wireless framework into existing system is depicted. In the next chapter we analyse the implementation details of the work. There is thoroughly explained the structure of the driver for selected WiFi device and also the functionality of resulting IEEE 802.11 library. In the end of the thesis there is an evaluation of the features of final work and comparison of enclosed implementation with existing solutions.

The diploma thesis is focused on exploring the possibility of VoIP service in a wireless network of University of Economics, Prague. This thesis describes the basic principles of VoIP and related wireless technologies necessary for its quality and stable operation. Subsequently, different configurations of wireless network and end clients are tested and compared, including its impact on ordinary users, in a laboratory environment with idle and fully utilized frequency band. Finally, a roaming operation with the use of several advanced 802.11 standards is tested in the real environment of the Old building in Žižkov. In conclusion, the ideal settings for all telecommunication devices are recommended in order to maximize the quality of VoIP operation and to minimize the negative impact on ordinary users.

A local call admission control (CAC) algorithm for third generation wireless networks was designed and implemented, which allows for the simulation of network throughput for different spreading factors and various mobility scenarios. A global CAC algorithm is also implemented and used as a benchmark since it is inherently optimized; it yields the best possible performance but has an intensive computational complexity. Optimized local CAC algorithm achieves similar performance as global CAC algorithm at a fraction of the computational cost. Design of a dynamic channel assignment algorithm for IEEE 802.11 wireless systems is also presented. Channels are assigned dynamically depending on the minimal interference generated by the neighboring access points on a reference access point. Analysis of dynamic channel assignment algorithm shows an improvement by a factor of 4 over the default settings of having all access points use the same channel, resulting significantly higher network throughput.

This master’s thesis deals with analysis of security in wireless networks. There are desc- ribed various methods of security systems, such as WEP, TKIP and CCMP. There is also realization of attacks against the wireless network and there is analysis of security weaknesses. Then there are discussed possible defense mechanisms. Part of this work was also analysis of local security in certain areas and evaluation of their security.

This master’s thesis is about concept of gateway connection a water heater controller to a cloud through a home Wi-Fi network. In the first part, possible solutions of Wi-Fi gateway are described. The next part describes development of the gateway and its realization.

This master’s thesis is about concept of gateway connection a water heater controller to a cloud through a home Wi-Fi network. In the first part, possible solutions of Wi-Fi gateway are described. The next part describes development of the hardware and software of gateway and its realization.

This work deals with wireless standard 802.11, primaly about security algorithms used in them. Further there is made analysis of algorithms WEP, WPA and WPA2. This algorithms are described how coding by them works and for easier understandig are added block schemes of their principles. In practical part is realized algorithms WEP, WPA and WPA2 in program Matlab simulink. Model is complemented by graphs which shows how data changes when comming throught this systems.