Dissertations / Theses on the topic 'WLAN'

WLANs are become popular due to their different advantages. Beside all these advantages WLANs are also facing the major problem of the security, so that why lots of people are doing research on WLAN to improve the security because many companies want to transfer their sensible data over WLAN.

This report discusses the security issues of WLAN based on IEEE 802.11 standard, such type of networks are referred to as wifi network. WLAN is deployed as an extension of already existed wired LAN. Therefore it is necessary to provide the security of WLAN equals to Wired LAN.

We worked in a lab environment in order to configure the three different security solutions (WEP, WPA & WPA2 using IEEE 802.1X and RADIUS Server) on infrastructure mode for personnel and enterprise architecture of WLAN. For each security solution we used the backtrack as a security cracking tool, in order to break the WEP (64 and 128 bit long) security key of WLAN, make comparison between 64 and 128 bit long WEP key and also analyzed the different kind of attacks  and some drawbacks of using WEP security in WLAN. In the same way configure the WPA and WPA2 (using IEEE 802.1X and RADIUS Server) security solution in infrastructure mode of WLAN and use the same security cracking tool backtrack in order to break the security of the WLAN and analyze the different attacks on the network in these architecture and drawbacks of using WPA and WPA2 Security solutions. By using IEEE 802.1X and RADIUS Server we can improve the security of the enterprise network.

In the end we come with many conclusions and suggestions that will help in order to provide better security while deploying Wireless LAN.

Opponents: Ali Murtaza & Mansoor Ahmed

WLAN i form av standarden IEEE 802.11 används inte i större utsträckning i industriell miljö. Vi undersöker hur pass protokollet kan användas för datakommunikation i sådan miljö med avseende på störningskänslighet och datorkraftsbehov, i form av en empirisk undersökning. Dessa undersökningar har utförts på en industri med de tre vanligaste standarderna IEEE 802.11b/g/n. Syftet med denna uppsats är att kontrollera vad som stör signalerna samt om den nyaste standarden 802.11n har något nytt som kan revolutionera inriktningen. Tester och undersökningar har visat att 802.11b och 802.11n är bäst när det gäller signalstyrka med störningskällor i omgivningen. 802.11n är överlägsen när det gäller hög överföringshastighet.
WLAN in the form of IEEE 802.11 is not used to any wide extent in the industrial environment. We examine how the protocol can be used for data communication in such an environment with regard to noise immunity and computing power needs, in the form of an empirical investigation. These studies have been conducted in an industrial environment with the three most commonly used standards IEEE 802.11b/g/n. The purpose of this paper is to understand what it is in the environment that disturbs signals and if the newest standard IEEE 802.11n has something new to add to the table that could revolutionize the focus. Tests and studies have shown that 802.11b and 802.11n is the best in terms of signal strength with interference in the environment. 802.11n is superior in terms of high bit rate.

Rapporten täcker konstruktionen av en CAN-WLAN brygga från schemaritning ända till en nästintill konsumentfärdig produkt med inkapsling. Bryggan använder sig av mikroprocessorn AT90CAN128 tillsammans med WLAN-modulen WIZ610wi för att hantera kommunikation av CAN respektive WLAN. Bryggan är tänkt att monteras stationärt på en maskin/fordon som har en implementerad CAN-bus. Man kan sedan via smartphone eller bärbar dator avläsa informationen på CAN-bussen samt skicka ut CAN-paket. Allting sker via webbläsaren i den mobila enheten. Nätdel och kapsling har konstruerats av beställaren, Electrum. Resterande ingående delar har konstruerats från grunden och tas upp i denna rapport. Bryggan är generellt utformad för att klara alla typer av CAN-bussar med inställbara parametrar av hastighet, id-längd etc.
This report covers the construction of a CAN-WLAN bridge from a basic schematic all the way to a consumer ready product. The bridge uses the microprocessor AT90CAN128 and the WLAN module WIZ610wi which handles the communication of CAN and WLAN. The bridge is designed to be mounted stationary on a machine/vehicle which communicates through CAN. With a Smartphone or laptop you can then read the information on the CAN bus or send a CAN package. Everything is done through the web browser on the mobile device. Power supply and enclosure has been designed by the Electrum Automation. The remaining blocks have been designed from the ground up and is covered by this report. The bridge is generally designed to be able to communicate all types of CAN-busses with tunable parameters considering baud rate, id-length, etc.

Thesis (M.S.) -- University of Maryland, College Park, 2005.
Thesis research directed by: Dept. of Computer Science. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Wireless Interface for Sensors and Actuators (WISA) is ABB's proprietary wireless protocol for industrial automation on the factory floor. It operates in the 2.4GHz ISM band. Wireless Local Area Networks (WLANs), which typically occupy a fixed portion of the same 2.4GHz ISM band, are becoming more and more common on the factory floor. This raises a question of co-existence and how the performance of traffic over WLAN is affected when interfered by WISA. This report is a result of the development of a software tool and assembly of hardware that can aid the future testing of the effect WISA has on nearby WLANs. Together with the explanation of the usage of this software tool, this report will also investigate different arrangements of hardware components that are used to demonstrate and test the functionality of this new software tool. The software tool and the hardware components enable the measurement of important traffic metrics between two computers that communicate over a WLAN. The hardware components include a WISA Base Station (BS) that is configurable through the software tool and is used to cause interference on the WLAN.

This report evaluates various methods that can be used to position a smartphone running the Android platform, without the use of any special hardware or infrastructure and in conditions where GPS is unavailable or unreliable; such as indoors. Furthermore, it covers the implementation of such a system with the use of a deterministic fingerprinting method that is reasonably device independent, a method which involves measuring a series of reference points, called fingerprints, in an area and using those to locate the user. The project was carried on behalf of Sigma, a Swedish software consulting company.
Denna rapport evaluerar olika metoder för att bestämma positionen av en smartphone som använder sig av Android-plattformen. Metoden skall inte använda sig av någon speciell hårdvara eller infrastruktur samt kunna hantera förhållanden där GPS är otillgängligt eller opålitligt, som till exempel inomhus. Den beskriver också implementation av ett sådant system som använder sig av en deterministisk fingerprinting-metod som någorlunda väl kan hantera enheter av olika modeller, en metod som innebär att man mäter upp en mängd med referenspunkter, kallade fingerprints, och använder dessa för att placera användaren. Projektet utfördes på uppdrag av Sigma, ett svenskt mjukvarukonsultbolag.

This thesis deals with the investigation and assessment of communication standards LTE-Advance and WiFi (IEEE 802.11n/ac). The EVM error parameter is examined for each standard. To work with different standards a universal workplace have been proposed (testbed). This universal workplace serves for adjusting transmitting and receiving means and for processing signals transmitted and interpreted. Matlab was chosen for this work, through which only control devices such as generators and analyzers from Rohde & Schwarz. This workplace also measures the coexistence of these standards. At the conclusion of this thesis, different coexistence scenarios were designed and evaluated through testbed results.

The past few years have seen great increases in the use of portable devices like laptops, palmtops, etc. This has also led to the dramatic increase demand on wireless local area networks (WLAN) due to the flexibility and ease of use that it offers. Mobile IP and handover are important issues to be considered as these devices move within and between different networks and still have to maintain connectivity. It is, therefore, imperative to ensure seamless mobile IP handover for these devices as they move about.

In this thesis we undertake a survey to describe the real processes involved in mobile IP handover in WLAN environment for different scenarios. Our work also identifies individual sources of delay during the handoff process, the sum total of which makes up the total latency. Other factors that could militate against the aim of having a seamless handoff in an inter-subnet network roaming were also considered as well as some proposed solutions. These factors are security, packet loss and triangle routing.

This master’s thesis investigates the technology and security awareness associated with wireless networks (WLAN). It has been stated by the media and theories that many wireless networks are unprotected. This has sparked an interest to investigate the phenomenon in the Jonkoping region. The study is based on the following research questions:

- What security weaknesses are present with the WLAN-technology and how can these be avoided?

- How does the wireless infrastructure in the Jonkoping region look like?

- Why do companies implement the WLAN-technology?

- Are the companies aware of the risks involved with WLAN?

We conducted this study in three steps; the first step was to hack a wireless network in a controlled environment in order to investigate the weaknesses of the commonly used security measures. The second step of the study was to scan the wireless networks in Jonkoping, Gnosjo and Nassjo in order to create a picture of the wireless infrastructure of the region. The third step of the study was to contact companies that we found in the second step for interviews to investigate their awareness of the technology and its weaknesses.

We found that WLANs and their security measures have weaknesses. The commonly used WEP encryption can quite easily be broken and can lure users into a false sense of security. The study shows that companies are aware of this weakness, but use the encryption be-cause it offers a good level of usability and security. It is a compromise between usability and security. Usability is one of the major factors for companies when implementing wireless networks, companies strive for mobility, easy access and ease of use, which the WLAN technology offers. This has lead to an extended wireless infrastructure in cities within the region where one, with ease, can find wireless networks outside buildings. We have noticed an increase in the security awareness as our empirical findings differ from earlier research conducted in other cities. When these studies are compared you can see a trend where the number of unprotected networks decreases. Our contribution to increased wireless security is a checklist of possible security measures to minimize the security threats.

Denna magisteruppsats undersöker tekniken och säkerhetsmedvetandet gällande trådlösa nätverk (WLAN). Då det tidigare uppmärksammats i media och teori att många trådlösa nätverk står oskyddade har detta skapat intresse att undersöka fenomenet i Jönköpingsregionen. Studien baseras på följande frågeställningar:

- Vilka säkerhetsluckor finns i WLAN och hur kan dessa undvikas?

- Hur ser WLAN-infrastrukturen ut i Jönköpingsregionen?

- Varför implementerar företag WLAN-tekniken?

- Är företag medvetna om riskerna med trådlösa nätverk?

För att skapa en helhetsbild har vi genomfört studien i tre steg varav vi, i det första steget, genomfört dataintrång i en kontrollerad miljö för att undersöka svagheterna med säkerhetsfunktionerna som används i trådlösa nätverk. I det andra steget undersökte vi med hjälp av bärbar dator trådlösa nätverk i Jönköping, Gnosjö och Nässjö. Detta för att skapa oss en uppfattning om hur WLAN-infrastrukturen ser ut i dagsläget. Steg tre innebar intervjuer med företag som vi funnit i samband med steg två rörande deras medvetenhet om tekniken och dess brister.

Teorin och vår empiri gav oss underlag att dra slutsatser utifrån våra frågeställningar. Vi fann att WLAN och dess säkerhetsfunktioner har vissa sårbarheter. Den mest förekommande krypteringstekniken, WEP, kan dekrypteras tämligen enkelt och kan vagga in användarna i en falsk säkerhet. Studien visar att företagen är medvetna om detta, men att det handlar om en medveten kompromiss mellan användarvänlighet och säkerhet. Användarvänligheten står till grund för varför företagen väljer att implementera den trådlösa tekniken. Företag eftersträvar mobilitet, smidighet och enkel access, vilket den trådlösa tekniken erbjuder. Detta har lett till en utökad trådlös infrastruktur i städer runtom i regionen där man med lätthet kan hitta trådlösa nätverk utanför byggnader. Vi har noterat ett ökat säkerhetsmedvetande då våra empiriska resultat skiljer sig något från tidigare undersökningar i andra städer. När dessa ställs mot varandra anar man en trend där antalet oskyddade trådlösa nätverk minskar. Vårt bidrag till ökad trådlös säkerhet är en checklista med möjliga åtgärder för att minimera säkerhetsriskerna.

I datornätverk blir användandet av WLAN (trådlösa nätverk) allt vanligare tack vare sin smidighet. Det är framförallt bekvämare att använda trådlösa nätverk då man slipper allt kablage och ofta är oberoende av var man befinner sig för att använda nätverket. Trådlösa nätverk är dock inte helt problemfria. Den främsta anledningen till detta är att informationen färdas genom radiovågor istället för genom kablade nätverk. Detta gör att WLAN är i riskzonen för avlyssning, där informationen kan utsättas för obehörig åtkomst om den inte är väl skyddad. Detta problem är grunden till denna uppsats.

Den här uppsatsen är en utredning som har gått ut på att ta fram generella riktlinjer för hur myndigheter skall uppnå god säkerhet i WLAN. Anledningen till att vi ville ta fram generella riktlinjer åt myndigheter var på grund av en rapport vi fann genomförd av krisberedskapsmyndigheten (KBM) 2008. Denna uppmärksammade att myndigheter ofta hoppar på nya tekniker utan att ha tillräckligt kunskap nog om dem, och att säkerhetstänket ofta får låg prioritet vid införandet av nya system. Ytterligare en artikel skapade av KBM från 2007, pekar på att myndigheter även har bristande säkerhet i sina DNS-system.

Eftersom vi koncentrerade oss på WLAN funderade vi då på, om nu säkerhetstänket får så låg prioritet och är så dåligt ställt i myndigheternas DNS-system, hur är det då ställt med säkerheten i WLAN?

Vi konstaterade efter att vi gjort förfrågningar till flera myndigheter, att ytterst få myndigheter hade något WLAN eller planerade att införskaffa det. Anledning till detta tror vi var att myndigheter var skeptiska till att det går att få ett WLAN säkert och hade bristande kunskap inom området.

Vi tog fram de generella riktlinjerna genom en kvalitativ metodansats, där vi genomfört litteraturstudier, undersökning av myndigheters policys samt intervju av expert på WLAN.

Resultatet visade att myndigheter behöver både administrativa säkerhetsåtgärder, tekniska säkerhetsåtgärder samt en specifik fysisk säkerhetsåtgärd för att uppnå god säkerhet i WLAN.

The thesis seeks to improve the accuracy of indoor wireless local area network (WLAN) location detection. The main task of the project is the design and analysis of a solution, which utilizes the packets which are already emitted by WLAN devices. The system consists of a signal receiver and signal processing. The positioning system does not transmit, thus the detection is completely passive. The result of measurements on received frames is used to calculate the WLAN transmitter's position. It does not require any transmissions, thus the detection is completely passive. The result of the measurements can be used to calculate the WLAN transmitter’s position. Location systems are more and more viewed as a necessary element of a WLAN system. Positioning accuracy is the most important issue in location system, especial in the indoor WLAN location detection. Indoor location systems are affected by indoor environment both due to multi-path and man-made effects. To resist these problems, we introduce a way to detect the arrival of the first instance of the signal by detecting the signal header. In our experiment, we timestamp the arrival of an IEEE 802.11b header. In our prototype the logic necessary to do this is implemented in an FPGA, specifically that of the Ettus Research USRP. The additional logic is quite small and might easily be added to the receiver in an access point, thus reducing the deployment cost of a location system in a real network. The proposed solution was experimentally verified. From our experiments, the detection works without requiring any changes to the hardware or software of the mobile device. By exploiting existing IEEE 802.11b transmissions the cost and difficulty of deployment is simplified due to the wide usage of IEEE 802.11b in mobile devices. Additionally, the preamble has good correlation properties making it is easy to detect the arrival of a IEEE 802.11frame. Our implementation is based upon open source hardware and software making it possible to implement this solution. A relatively low cost FPGA can be used as the correlation and timestamp circuit is rather simple (in terms of numbers of gates), making this solution feasible for commercial implementation. The method, implementation, testing, and analysis are presented in detail in the thesis.
Avhandlingen syftar till att förbättra noggrannheten i inomhus trådlösa lokala nätverk (WLAN) placering upptäckt. Huvuduppgiften för projektet är design och analys av en lösning som utnyttjar paketen som redan avges av WLAN-enheter. Systemet består av en signal mottagare och signalbehandling. Det kräver inga transmissioner, alltså upptäckt är helt passiv. Resultatet av mätningarna kan användas för att beräkna WLAN-sändarens läge. Målet är att förbättra noggrannheten i inomhus plats uppskattning. Läge system alltmer ses som en nödvändig del av WLAN system. Positioneringsnoggrannheten ses som den viktigaste frågan i läge system, speciellt för inomhusbruk WLAN baserade location. Läge system påverkas mer av inomhusmiljöer än utemiljön, eftersom det finns mer multi-path fading och konstgjorda effekter. Att minska dessa problem, vi införa ett sätt att känna av signalen ankomst genom att förbättra upptäckten av ankomsten av IEEE 802.11-huvudet. Detta kan bidra till att besegra multipath effekt och enkla metoden skulle kunna minska kostnaderna för placering i framtiden kopplingspunkter. Den föreslagna lösningen har verifierats experimentellt. Från vårt experiment fungerar upptäckt utan att kräva några ändringar i hårdvara eller mjukvara för den mobila enheten. Genom att utnyttja befintliga IEEE 802.11b sändningar kostnaden och svårigheten att utbyggnaden är förenklad på grund av den breda användningen av IEEE 802.11b i mobila enheter. Dessutom "preamble" har god korrelation egenskaper som gör det lätt att upptäcka ankomsten av en IEEE 802.11-ramen. Vår genomfört bygger på öppen källkod maskin-och programvara som gör det möjligt att genomföra denna lösning. En relativt låg kostnad FPGA kan användas som korrelation och tidstämpel kretsen är ganska enkel (i termer av antalet logikelement), vilket gör denna lösning vara möjlig för kommersiell tillämpning. Metoden, implementation, testning och analys presenteras i detalj i avhandlingen.

WLAN/n är en attraktiv teknik då det ökar data genomströmningen och räckvidden med ökad effektivitet som ger mer bits per sekund. Utvecklingen inom 802.11n har ökat data raten och prestanda till högre nivåer. En teknik är att använda multipla antenner för sändare och mottagare för att sända multipla data strömmar genom MIMO system för n standarden. Mobila enheter i en cell kanske inte har fixerade positioner i cellen så utveckling av mer avancerade algoritmer som OFDM har också utvecklats och presenteras i den här rapporten. Interference för signalen är ett dilemma då den beräknade mängden av data tillverkare av wlan produkter har i sina specifikationer knappast stämmer med verkligheten när man mäter data genomströmning. Resultat från experimenten visar att störningar i vissa fall kan anses vara ett problem. Målet med den här rapporten är att besvara frågeställning kring olika tekniker inom WLAN teknologin och vilka typer av störningar och utveckling det finns för en stabilare och högre data genomströmning. Experimenten inkluderar WLAN nät i naturlig miljö med accesspunkt och laptop med nätverkskort.

Navigation and location technologies have been reaching in a major interest where Global Navigation Satellite System (GNSS) is mostly adopted. The limitation of this technology is that direct sky view is needed for reliable positioning. In indoor environments, however, it is difficult for GNSS technology to provide a reliable performance in positioning due to the signal attenuation and blocking caused by buildings and construction materials. For this reason, the growth in indoor applications has focused the research in new techniques for attempting mitigate the poor GNSS performance on this type of environments In the context of indoor positioning, multitude of emerging technologies for localization based on ultrasound, infrared, Ultra Wide Band (UWB), Zigbee, inertial navigation and other non-GNSS technologies have been proposed but special equipment is required and a large number of signal sources are needed. However, Wireless Local Area Network (WLAN) technology is widely used in indoor positioning. While the same requirements are also needed as the other technologies in order to improve the positioning accuracy, in terms of cost and ability, Wireless-based indoor location is widely used due to the already deployment of Anchor Points (AP) in urban and indoor areas. There are several methods for indoor positioning purposes e.g ToA (Time of Arrival), Received Signal Strength (RSS) measurements, AoA (Angle of Arrival), fingerprinting and so on. Most of the network-based location estimations use RSS measurements because almost all mobile devices are afforded to use this type of measurements. So, this thesis is centered in WLAN RSS-based positioning systems. The first step for indoor positioning is the distance estimation between the user and the AP. Theoretical and empirical propagation channel models are used to translate the difference between the transmitted and Received Signal Strength into an estimated range. A Propagation channel model built the radio map and also report changes in the environment. There are several models in the literature to characterize this channel. Indoor RSS-based localization has become a popular solution, but standard techniques still consider a time invariant simple single slope path loss channel model with a priori known constant channel parameters. While some contributions considered the RSS-based localization problem using a single path loss model with unknown parameters, the general solution that considersa generalized distance dependent measurement model is an important missing point. This thesis considers the two-slope channel model and proposes a robust indoor positioning solution based on a parallel architecture using a set of Interacting Multiple Models (IMM), each one involving two Extended Kalman filters (EKF) and dealing with the estimation of the distance to a given AP. Within each IMM, the two-slope path loss model parameters are sequentially estimated with Maximum Likelihood Estimate (MLE) to provide a robust solution. Finally, the set of distance estimates are fused into a standard EKF-based solution to mobile target tracking. In addition, the benchmarks derived in this thesis to evaluate the performance of our IMM-EKF algorithm are the Cramér Rao Lower Bound (CRLB) and the Posterior Cramér Rao Lower Bound (PCRLB) providing a guidance in the improvement of the experimental design. The CRLB is used to assess the estimation of model parameters and the PCRLB for tracking solution. This, combined with a path-loss exponent estimation, the channel calibration algorithm is validated with an online range estimation. The central theme throughout this thesis is to develop a completely online two-slope channel calibration and, simultaneously, a mobile target tracking algorithm. The performance of the method is assessed through realistic computer simulations and validated with real RSS measurements obtained from experimental tests in a typical office environment.
Las tecnologías en navegación y localización han estado obteniendo un gran interés en los últimos años donde el Sistema Global de Navegación por Satélite (GNSS) aparece como el más utilizado para estos fines. No obstante, una de las limitaciones del GNSS es la necesidad de tener una visión directa al cielo para así garantizar un posicionamiento bastante fiable. También, al utilizar solamente tecnología GNSS en espacios interiores (más conocidos en el mundo científico por entornos indoor), se es complicado conseguir un buen desempeño en términos de posicionamiento debido a la atenuación e interferencia de la señal causada por los edificios y materiales de construcción. Por esta razón, y debido al crecimiento en aplicaciones dentro de entornos indoor, la investigación de nuevas tecnologías para posicionamiento en interiores se ha centrado en intentar mitigar el mal desempeño de la tecnología GNSS en este tipo de ambientes. En el contexto de posicionamiento en interiores (indoor positioning), se han propuesto multitud de tecnologías emergentes para localización basadas en ultrasonido, infrarrojo, Banda Ultra Ancha (UWB), Zigbee,navegación inercial y otras tecnologías que no sean GNSS. Sin embargo, se requiere de equipo especial y un gran número de fuentes de señal. A pesar de ello, la tecnología en Redes de Área Local Inalámbricas (WLAN) es ampliamente utilizada en el posicionamiento en interiores. Aunque la tecnología WLAN tenga los mismos requerimentos que el resto de tecnologías, en términos de coste y practicidad, los sistemas de posicionamiento basados en redes inalámbricas se utilizan con mayor frecuencia debido al ya existente despliegue de estaciones base (AP) en áreas urbanas e interiores. Existen varias técnicas que sirven para fines de posicionamiento en interiores. Por ejemplo, utilizando el tiempo de llegada de la señal (TOA), las mediciones de la potencia de la señal recibida ( RSS), el ángulo de llegada (AoA), la técnica fingerprinting entre otras. Esta tesis está centrada en sistemas de posicionamiento basados en mediciones WLAN-RSS. Un modelo de canal de atenuación de interiores contruye un mapa de cobertura y también es capaz de reportar los cambios en el entorno indoor. El posicionamiento indoor basado en mediciones RSS se ha convertido en una solución bastante popular, pero las técnicas comunes consideran un modelo de pérdidas por trayectoria de una pendiente, invariante en el tiempo y con un conocimiento previo de los parámetros del canal que se consideran constantes. Esta tesis considera el modelo de pérdidas por trayectoria de pendiente dual y propone una solución robusta para posicionamiento en interiores basado en una arquitectura paralela conformada por un conjunto de algoritmos de Interacción de Múltiples Modelos (IMM) donde cada IMM involucra dos Filtros de Kalman Extendidos (EKF) para el proceso de estimación de la distancia entre el AP y el usuario. Dentro de cada IMM, los parametros del modelo de pérdidas por trayectoria de pendiente dual se estiman secuencialmente utilizando la estimación por máxima verosimilitud (MLE) y así proveer una solución robusta. Finalmente, el conjunto de distancias estimadas se fusionan en un EKF para tener una solución final de la posición del usuario. Además, las cotas de referencias que son derivadas en esta tesis y que sirven para evaluar el rendimiento del algoritmo IMM-EKF son la Cota Inferior de Cramér Rao (CRLB) y la Cota Inferior de Cramér Rao Posterior (PCRLB) que servirán de guía para el perfeccionamiento del diseño experimental. El tema central de esta tesis es desarrollar un algoritmo online para posicionamiento indoor que simultáneamente sea capaz de hacer la calibración del canal de propagación. El desempeño del método se evalúa mediante simulaciones por computadora que se validan con mediciones RSS reales obtenidas a partir de pruebas experimentales.

This thesis investigates how Ericsson AB should do to achieve fast and secure handover when roaming in a WLAN. It also provides a security analysis of the system that the wireless access point is part of. The reason for this is that Ericsson is selling an access point called the ABS 2200 aimed at the public hotspot market.

The premise was that they wanted a standardized way of handling the roaming issue. At the outset the 802.11F standard looked like a good alternative (in fact the only standardized alternative). Towards last stages of the work though, it was discovered that the 802.11F standard is no longer supported by IEEE.

Despite this fact, the conclusion is that secure and fast roaming can be attained if 802.11F is combined with the security standard 802.11i.

The security analysis concludes that Denial Of Service is a major threat to WLAN hotspots. It also points out the link between the access point and authentication server is the weakest link in the system. The recommendation is that this link receives an additional layer of protection through IPsec withESP. The algorithm recommendations for ESP are AES for confidentiality and SHA-1 for integrity.

This thesis can also be used as a primer on security in WLAN and contains an extensive glossary making it useful as a reference when reading 802.11 standards.

Lately, researchers were trying to put a lot of efforts to enhance the performance of Wireless LANs. IEEE 802.11 algorithm, DCF, was an interesting subject for studies. Most studies were concentrating on avoiding collisions, packets loss, decreasing transmission delay and enhancing the overall performance of the network. Double Increment Double Decrement (DIDD) was introduced as a solution that enhance the performance by applying some changes in the algorithm. The main changes were applied on the Contention Window (CW). IEEE 802.11e introduced a new algorithm (EDCA) that introduces a QoS to the performance and though improves the overall performance of the WLAN This thesis aim is to study the performance of three different MAC algorithms by applying two different scenarios on legacy DCF, DIDD and EDCA. Analyzing different output results and checking the QoS of each algorithm. Simulations are implemented in Network Simulator 2 (ns-2) to simulate the network and communication procedures. By deducing and analyzing the output results of the main simulation, DIDD shows improvements that are slightly better than the legacy DCF, while EDCA shows better results from both DCF and DIDD. Though, EDCA shows a noticeable enhancement in the performance of the WLAN.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Recentemente, tem sido observado um crescimento explosivo na utilização de redes de acesso local sem fio (Wireless Local Area Networks - WLANs), utilizando equipamentos de nível de radiação restrito operando em bandas independentes de outorga de uso de rádio freqüência, tanto para uso corporativo como doméstico e para prover acesso pago em ambientes públicos como aeroportos, hotéis, centros de convenções, campi universitários e mesmo restaurantes e cafés. Se estas redes serão complementares ou competidoras das redes celulares de terceira e quarta gerações é ainda uma questão polêmica e aberta. Os objetivos deste trabalho são o desenvolvimento um modelo de propagação de sinais na faixa de freqüência de 2,4 GHz em ambientes fechados (indoor), para a previsão de cobertura de WLANs, e prover ao projetista de redes wireless uma metodologia um bom dimensionamento da rede. São apresentados os principais modelos semi-empíricos já existentes na literatura técnica e, a partir de medidas realizadas em diferentes ambientes, é proposto um ajuste de parâmetros de um modelo de propagação indoor bastante completo. As medidas realizadas incluem as perdas de penetração em paredes de diferentes materiais, o efeito de difração em quinas de paredes, efeito de movimentação de pessoas no ambiente, além do coeficiente de perda de propagação com a distância. Os modelos desenvolvidos foram implementados numa ferramenta de software para o planejamento de cobertura de redes wireless indoor que permite realizar o projeto a partir da planta baixa do ambiente disponibilizada em arquivos de imagem.
Recently, an explosive growth in the use of Wireless Local Area Networks - WLANs, using restricted radiation levels and operating in license exempted frequency bands, has been observed, not only for corporative domestic use but also to provide paid internet access in public environments such as airports, hotels, convention centers, university campus and even restaurants and coffee shops. The question if these networks will be complementary or will compete with third and forth generation of cellular networks, is still a controversial and opened. The objectives of this work are the development a model for propagation in closed environments (indoor) at the 2,4 GHz frequency band for the coverage planning of WLANs and to provide the wireless network designer with a complete project methodology . The most important semi-empirical models available in the technical literature are presented and, based on measurements carried out in different environments, a fairly complete model with fitted parameters is proposed. The measurements include losses of penetration in walls of different materials, the effect of diffraction at wall edges, the effect of movement of people in the environment and the rate of loss with distance coefficient. The developed models have been implemented in a software tool for coverage planning of wireless indoor networks that allows the development of the project starting from blue prints of the environment available as digital image files.

Location techniques that satisfy the requirements of advanced Location-Based Services (LBS) in environments where GPS fails are needed, therefore accurate indoor positioning is becoming increasingly important. This PhD Thesis is devoted to the research on location of mobile devices employing WLAN (IEEE 802.11). The use of this kind of wireless networks infrastructures for positioning enables a powerful synergy between communications and location and allows solutions with good performances at moderated costs. However the adopted WLAN location methods suffer from important limitations that prevents from applying them to some fields that need more flexible and robust solutions. The main objective of this PhD is exploring precise WLAN location methods that allow overcoming these limitations. The researched methods here are based on measuring the Time Of Arrival (TOA), which is the time that takes the signal propagating from the transmitter to the receiver. TOA-based location works in two stages: ranging and positioning. The ranging consists of estimating the distances between the targeted terminal and several WLAN access points, each distance obtained measuring the TOA and then multiplying it by the speed of the WLAN signal. After that, the positioning takes as inputs the estimated distances and the known coordinates of the involved access points and calculates the position of the terminal by means of a trilateration or tracking algorithm. The key problem is that the characteristics of the IEEE 802.11 protocols difficult to perform accurate TOA measurements. The main challenge that faces the research work reported here is demonstrating the feasibility of achieving this while keeping the modifications over standard WLAN consumer equipment at minimum. The objective of this work can be understood as exploring the current limits of TOA-based methods over WLAN, making contributions that form a complete TOA-based location method that goes a step forward with respect to the other existing proposals. First, research on TOA-based ranging -the key component of TOA-based location methods- is reported. The general adopted approach consists of performing Round Trip Time (RTT) measurements employing IEEE 802.11 MAC frames, taking the maximum advantage of the combination of IEEE 802.11 protocol and WLAN consumer devices mechanisms. After that, the performed research on trilateration/tracking -the second stage of TOA-based location methods- is explained. Finally some performed studies about the achieved location method are presented. Lloc i data Signatura
Actualment existeix la necessitat de disposar de tècniques de localització que satisfacin els requeriments de serveis avançats basats en localització en entorns on GPS no està disponible, de manera que el posicionament precís en interiors d’edificis és cada vegada més important. Aquesta tesi doctoral està dedicada a la investigació sobre la localització de dispositius mòbils que utilitzen WLAN (IEEE 802.11). L'ús d'aquest tipus de xarxes sense fils per al posicionament permet una profitosa sinèrgia entre les comunicacions i la localització i permet solucions amb un bon rendiment a un cost moderat. No obstant això, els mètodes basats WLAN proposats fins el moment pateixen de limitacions importants que impedeix la seva aplicació a alguns camps que requereixen solucions més flexibles i robustes. L'objectiu principal d'aquesta tesi és explorar mètodes de localització precisa WLAN que permetin superar aquestes limitacions. Els mètodes que s’han investigat durant la tesi es basen en la mesura del time of arrival (TOA), que és el temps que tarda el senyal en propagar-se des del transmissor fins al receptor. En les tècniques de posicionament basades en TOA s’hi poden diferenciar dues fases: ranging i posicionament. El ranging consisteix en l’estimació de distàncies entre el terminal a localitzar i diversos punts d'accés WLAN; cada estimació de distància s’obté mesurant el TOA i multiplicant-lo després per la velocitat de propagació del senyal IEEE 802.11. Un cop fet això, el posicionament pren com a inputs les distàncies estimades per a, conegudes les coordenades dels punts d'accés involucrats, calcular la posició del terminal per mitjà d'un algoritme de tracking o trilateració. El problema clau és que les característiques dels protocols IEEE 802.11 a dia d’avui fan difícil la realització de mesures precises de TOA d’una manera senzilla. El principal repte que afronta el present treball de recerca és demostrar la viabilitat d’això darrer, minimitzant en la major mesura possible les modificacions sobre els equips WLAN comercials. L'objectiu d'aquest treball pot ser entesa com l'exploració dels límits actuals dels mètodes de posicionament basats en TOA sobre WLAN, realitzant contribucions que conformen un mètode complet de localització basat en TOA que pretén anar un pas endavant respecte a les propostes existents. En primer lloc, la investigació sobre ranging basat en TOA -el component clau dels mètode de localització TOA- és explicada en detall. El mètode general adoptat per a calcular el TOA consisteix en la mesura del temps d'anada i tornada del senyal, round trip time (RTT), utilitzant trames MAC IEEE 802.11 per tal de treure el màxim profit de la combinació del protocol IEEE 802.11 i els mecanismes dels dispositius WLAN comercials. Després d'això, es detalla la investigació realitzada sobre trilateració i tracking, la segona etapa dels mètodes de localització basats en TOA. Finalment es descriuen alguns estudis realitzats sobre les prestacions, possibles millores i encaix en futurs estàndars del mètode de localització explorat.

The convergence of future networks relies on the evolution of technology that enables seamless roaming abilities across non-heterogenous networks for mobile clients. This thesis presents an experimental study of a GPRS-WLAN integration scenario where the objective is to analyze various aspects of the issues related to charging, mobility, roaming and security between GPRS and WLAN networks. The mainly discussed integration scenario in this thesis is loosely coupled systems working on RADIUS platforms, which together with MobileIP and IPSec provides the mobile client with a secure and access-technology independent network access platform.

In order to accommodate GPRS client authentication for WLAN operators, there is a prominent need for the incorporation of necessary GPRS functionality into present AAA servers. RADIUS has been studied as the initial target for the implementation of a GPRS interface towards SMS-Cs and HLRs.The authentication of a mobile client is performed against a HLR/AuC in a GPRS network, either over SS7 links or through the incorporation of SIGTRAN protocols over SCTP. SIGTRANsolutions has the ability to join WLAN networks in a SS7 resource sharing model where the SS7 authentication signalling traffic is transported over IP networks to a Signalling Gateway acting as the logical interface against SS7 networks.

GPRS-WLAN accounting may be solved through direct roaming agreements between mobile operators and in such a case transport CDR’s over FTP between their billing systems. If roaming agreements does not exist, it may be viable to establish relationships between WLANs and brokers as well as mobile operators and brokers. The brokering model provides a scalable model that allows easier exchange of charging and billing information on an infrastructure based on WLAN and GPRS billing systems. Standardised transmission protocols for accounting information such as GTP’/TAP3 may be utilised in order to provide a generic billing exchange format between billing systems and operators.

Furthermore, different network architectures may have different requirements in order to accommodate GPRS clients with WLAN access. A few network architectures has been analysed, and the developed GPRS AAA Interface Daemon (GAID) has been put into context in order to present a generic GPRS-WLAN systems integration solution for WLAN operators.

The analysed solutions in this thesis give various possibilities for WLAN operators to setup wireless services for bypassing mobile clients. The implementational work provides a RADIUS platform, which can be enhanced with functionality that enables communication over any interface in the future.

The background for this masters thesis is the threat of session hijacking in public wireless networks. A public wireless network in this context is a network such as Wireless Trondheim where users with WLAN enabled devices can connect for a small fee for a given period of time. These kind of networks relies on having a high degree of user friendliness to reach users with average knowledge in computers and wireless networks. There is always a struggle between user friendliness and security and the downside to the user friendliness in these kind of networks is poor security. Many of these networks only use the unique identifier (MAC address) of the network device to identify users and grant them access. A person with some technical knowledge about wireless networks and less then honest intentions may exploit this weak security barrier and impersonate the legitimate user by duplicating the MAC address. The practical part of this master thesis starts with the setup of a test bench with three computers, an attacker, a legitimate client and a passive monitor. A MAC spoofing attack was performed on the production network to prove that this kind of attack is easy to perform. The attack was first done with Backtrack which is a specialized penetration testing OS and the same type of attack was done in Windows to also prove that it does not require specialized tools. The attacker was able to gain access to the Internet without going through the web page for authentication. The thesis also proposes some countermeasures against this kind of attack. They are session ID, MAC sequence number tracking and monitoring physical properties such as received signal strength and RTS-CTS handshake round trip times. The thesis presents some thoughts on how they can be implemented in the wireless Trondheim network and what the major difficulties of each of them might be. The thesis also makes an evaluation of how well each of them fit with Wireless Trondheims requirements for countermeasures against the attacks done in this thesis.

I forbindelse med denne masteroppgaven har det blitt designet, implementert og testet en nettsentrert lokaliseringsløsning for WLAN. Løsningen baserer seg på innsamling av lokasjonsdata i form av lokasjonsfingeravtrykk. Ved å benytte lokasjonsfingeravtrykk har det blitt oppnådd en universell lokaliseringsløsning som vil kunne fungere i alle trådløse nettverk, og som baserer seg på allerede eksisterende trådløs infrastruktur. I tidligere forskning på lokaliseringsløsninger basert på fingeravtrykk, har det blitt tatt i bruk relativt begrensede dekningsområder. Samtidig har innsamlingen av lokasjonsdata og testingen av lokaliseringsløsningen blitt gjennomført med den samme mobile enheten. Det har heller ikke blitt fokusert på tiden lokasjonssystemet behøver for å gjennomføre et lokasjonsestimat. Lokaliseringsløsningen utviklet i forbindelse med denne masteroppgaven skiller seg fra tidligere forskning ved at det er studert et mer helhetlig lokasjonssystem. Det har blitt identifisert hvordan en slik lokaliseringsløsning vil fungere i et omfattende dekningsområde, og det har blitt tilrettelagt for bruk av ulike mobile enheter. Samtidig har det blitt fokusert på hvordan en bruker av lokasjonstjenesten vil oppfatte systemets ytelse. Det har derfor blitt vektlagt at et lokasjonsestimat skal gjennomføres så raskt som mulig. Hensikten med oppgaven har vært å undersøke hvorvidt en slik lokaliseringsløsning vil være en fornuftig måte å implementere et innendørs lokasjonssystem i store bygninger, slik som ved NTNU campus. Lokasjonsløsningen har et omfattende dekningsområde i EL-bygget ved NTNU Gløshaugen på 856 kvadratmeter, fordelt over to etasjer. Kjernen av lokaliseringsløsningen er en server som estimerer lokasjoner basert på lokasjonsdata mottatt fra klienter. For klientene er lokaliseringsløsningen utelukkende programvare basert. Alle klienter med WLAN-støtte, og mulighet for å kjøre programvare, vil kunne benytte seg av lokasjonstjenesten. På denne måten har det blitt skapt et lokasjonssystem som vil fungere for ulike mobile enheter, uavhengig av underliggende hardware og plattform. Dette har blitt bevist ved at det er implementert klientløsninger for to ulike smarttelefon-plattformer, iPhone OS og Android. Ulike mobile enheter vil oppfatte signalstyrker fra WLAN-aksesspunkt forskjellig for samme lokasjon. Dette gjør det til en krevende oppgave for lokasjonsserveren å estimere riktig lokasjon, uavhengig av hva slags mobil enhet som benyttes. Euklids avstand har tidligere blitt ansett som en svært egnet lokasjonsbestemmende algoritme i lokaliseringsløsninger basert på fingeravtrykk. I denne oppgaven har det blitt bevist at når lokaliseringsløsningen skal gi støtte for bruk av ulike mobile enheter, gir Euklids avstand ikke lenger til- fredsstillende resultater med hensyn på nøyaktighet. For å øke nøyaktigheten av lokasjonssystemet har det derfor blitt utviklet en alternativ lokasjonsbestemmende algoritme. Denne algoritmen benytter et vektingssystem, basert på forholdet mellom mottatt signalstyrke fra ulike aksesspunkt, for å estimere klientenes lokasjon. I etterkant av implementasjonen har lokaliseringsløsningen blitt testet for å identifisere ytelsen med hensyn nøyaktighet og tidsbruk. Testene ble utført ved hjelp av en iPhone og den Android-baserte HTC Hero. Den gjennom- snittlige tiden det tar å estimere en lokasjon for Android-telefonen er 1104 millisekunder, mens en det i gjennomsnitt tar 1343 millisekunder å estimere en lokasjon for iPhone. Nøyaktigheten av et lokasjonsestimat har blitt funnet ved å måle avvik i luftlinje mellom estimert og reell lokasjon. Det gjennomsnittlige avviket mellom estimert og reell lokasjon ble for iPhonen funnet til å være 3,46 meter, mens for Android-telefonen var dette 4,62 meter. Selv om vektingsalgoritmen økte lokasjonssystemets ytelse med hensyn på nøyaktighet, anses nøyaktigheten fortsatt ikke som tilfredsstillende. Det har derfor blitt forsøkt å identifisere en måte en vil kunne øke nøyaktigheten av lokaliseringsløsningen ytterligere. Det vil oppleves en større fluktuering i mottatt signalstyrke for sterke signaler, sammenliknet med svake signaler. Dette tilsier at det er mer egnet å benytte svake signalstyrker i en lokaliseringsløsning basert på fingeravtrykk. Det har derfor blitt forsøkt å identifisere et intervall for signalstyrker som vil være ideelle å benytte i en lokaliseringsløsning. Intervallet ble identifisert til å strekke seg fra -75 dBm til -65 dBm. Ved å benytte flere fingeravtrykk for å definere en lokasjon i serverens database, vil det være flere signalstyrkeforhold å sammenlikne for vektingsalgoritmen. Det antas derfor at ved å øke antallet fingeravtrykk, og samtidig danne fingeravtrykk ut i fra signalstyrker som finner seg innenfor det identifiserte signalstyrkeintervallet, vil en kunne øke nøyaktigheten av lokaliseringsløsningen.

The deployment of heterogeneous wireless networks in the same spectrum space introduces the need for dynamic spectrum access so as to increase the utilization of the available wireless resources. Dynamic spectrum access needs to be controlled in order avoid interference between the users of different systems. Different schemes can be used in order to avoid the mutual interference between the systems: orthogonality in space, frequency or time. In this thesis we address the problem with a solution based on time orthogonality, in which the coexisting wirless systems are a WLAN and WSN. Due to the high power asymmetry it is necessary to implement a cognitive capability in the most affected system, i.e. the WSN, which will predict the behaviour of the WLAN spectrum usage and take advantage of the white spaces left for WSN interference-free communication. For this, it is necessary to model the traffic of the WLAN system. The applicability of two different semi-Markovian models has been studied in the scope of this thesis: one represents an ideal case in which the sensors have unlimited sensing capabilities and a second, more realistic, approach in which the sensor view is limited by hardware and resources. In this project we investigate whether and when the proposed models are suitable to be used in order to model, estimate and predict realistic WLAN channel usage; for that we consider a measurement-based, multi-layer WLAN traffic workload model. Different experiments have been developed to test different traffic scenarios in which we apply our prediction model. The experiments show that the WLAN usage estimation process is robust, i.e. insensitive to irregularities introduced by the packet level randomization and the underlying protocols in the WLAN. An almost perfect fitting is achieved in a wide range of cases between the distributions to model the active and idle periods and the empirically derived channel usage functions. In addition, we study different usage load regions in which we apply our model and the results show that it can be applied with high success in a region of 10 to 30% of load. On the other hand, the realistic model, based on partial observation of WLAN trafic, shows higher variations between different traffic conditions, increasing the performance of the estimation process in cases of higher WLAN load.

Switch Nordic Green AB (Nordic Green Energy) is an energy company with about 40 employees. The customer service department is in-house and a lot of the work, by all departments, is done by programs running on remote servers.  Today most of the network traffic is through a wired local area network, although there is a wireless guest network which is very unstable. While planning a move to a smaller office the company is planning to implement a more extensive wireless local area network. This bachelor thesis will provide a basis for implementing the local area network and wireless local area network for the company's new office. The thesis will also establish the network platform for an eventual move of a department within the company located in Finland. This documentation will enable the company to save both time and money.  With a local area network, designed and implemented for the new office, the employees will have the best possibility to improve their work and it will also increase the efficiency of the company.
Switch Nordic Green AB (Nordic Green Energy) är ett elbolag med cirka 40 anställda. Kundtjänsten sköts internt och mycket av arbetet, även på de andra avdelningarna, sker mot fjärrservrar. Idag ligger majoriteten av nätverkstraffien på ett trådat lokalt nätverk, men det finns även ett trådlöst gästnätverk, som dock är väldigt instabilt. När företaget ska flytta till ett mindre kontor planerar de att implementera ett mer omfattande trådlöst nätverk. Den här kandidatexamenauppsatsen kommer användas som grund för implementationen av både trådat och trådlöst lokalt nätverk på det nya kontoret. Uppsatsen ska upprätta en nätverksplattform som kan användas vid en eventuell framtida flytt av företagets kontor i Finland. Med denna dokumentation tillgänglig kan företaget spara både tid och pengar.  Med ett lokalt nätverk som är designat och implementerat för det nya kontoret har de anställda möjlighet att förbättra sin arbetainsats och företagets effektivitet.

Un des principaux défis majeurs des prochaines générations des systèmes de communication sans fil serait d'utiliser les ressources limitées des réseaux de communications d'une manière efficace à l'effet d'obtenir une qualité et une capacité qui soient suffisantes pour faire face à des demandes sans cesse croissante de services. En effet, les besoins en bande passante des utilisateurs ont augmenté en raison des résultats satisfaisants relevés des différentes applications telles que la vidéo et la navigation sur Internet. Ceci a permit à plusieurs technologies de voir le jour et qui ne cessent de s'améliorer afin de répondre aux besoins des utilisateurs. C'est notamment le cas des réseaux hétérogènes qui servent à interconnecter les réseaux WIFI, GSM/UMTS et Satellitaires. Ce progrès va permettre de répondre à la demande des utilisateurs en leurs offrants une très grande mobilité dans le monde et une connexion n'importe où et n'importe quand. L'objectif de ce présent mémoire de maîtrise est d'étudier la problématique de gestion de mobilité entre les deux réseaux et de combiner ces techniques afin d'exploiter au mieux les avantages inhérents à ces deux réseaux : cellulaire (UMTS) et local sans fil (WLAN) et de pouvoir intégrer ces deux technologies de telle sorte que le changement de technologie soit transparent. Dans le cadre de la première partie de ce mémoire, nous avons traité particulièrement les aspects de gestion de mobilité. Les deux différentes architectures d'interconnexion au contexte des réseaux hétérogènes UMTS/WLAN sont relatées ainsi que différents algorithme sont également mis en évidence principalement l'algorithme RSS, SNR et SINR La plupart des contributions faites dans ce contexte prennent en considération juste la maximisation du débit à travers les deux réseaux. Par contre la minimisation de nombre de handoff durant un appel ou transfert de données joue un rôle très prépondérant, afin d'éviter tout handoff inutile et d'éliminer par voie de conséquence l'effet ping-pong qui dégrade la qualité de service. C'est pourquoi, dans la seconde partie de notre mémoire, nous avons proposé une nouvelle stratégie intégrant pour la réalisation d'un handoff vertical des utilisateurs mobiles entre les deux réseaux tout en minimisant le nombre de handoff la probabilité de perdre des paquets et d'atteindre un débit plus élevé avec meilleur prix conespondant. Dans ce cadre nous avons présenté et nous avons testé plusieurs algorithmes de handoff et nous avons comparé ces algorithmes avec notre solution proposée. Tous les algoritlmies entrepris ont été validés et évalués par des simulations.

碩士
國立清華大學
資訊工程學系
91
A SIM-based authentication is preferable for GPRS operators for the integrated GPRS-WLAN networks. It requires WLAN system process the GPRS-based authentication and transport the GPRS authentication messages back to the GPRS networks. This thesis presents an alternative WLAN-centric approach based on the perspective of WLAN providers. The proposed WLAN-centric authentication instead leverages the widely used WLAN-based authentication and requires the GPRS operator install an AAA (Authentication, Authorization, and Accounting) server. The proposed approach is based on loose coupling architecture. In addition, it assumes that the GPRS and WLAN systems are two parallel networks and work independently. Scenarios for GPRS subscribers and WLAN users roaming between two systems are detailed. The proposed approach is implemented in a GPRS and WLAN testbed, which comprises most of the components in GPRS and WLAN systems. Performance analysis based on empirical experiments is also discussed.

No
A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes.

碩士
國立臺灣大學
資訊工程學研究所
95
Over the past few years, there has been a tremendous growth in the market of mobile computing devices exemplified by the laptop computers. Also the ease of installation and low cost of IEEE 802.11 network, contribute to the enormous growth in the adoption of WLAN. Amid this trend, High-Density WLAN has emerged, which comprises of a large number of Access Points (APs). However, with the current connection architecture, we select an AP among such High-Density WLAN only base on signal strength, which can lead to bad performance due to its ignorance of the load at different APs. Moreover, due to existences of noise and interferences, frame errors occur quite often which makes the performance suffers and current architecture only uses rate adaptation to improve the performance. In this thesis, we propose a new connection architecture, which use monitor mode to collect environment information for AP selection, also adopt rate adaptation and dynamic fragment threshold to improve the performance while condition getting worse. Furthermore, we use estimated bandwidth as a criterion of condition awareness. We use three access points, and four notebooks and a cordless phone as interference to setup practical scenario. Our experiments show that the proposed architecture works well and has better performance than original architecture.

碩士
大同大學
通訊工程研究所
97
In this thesis, two unique approaches are respectively applied to design a CPW-fed circularly and a linearly polarized antenna. For the circularly polarized antenna, center conductor of the CPW is bended into a semi-circular shape and two ground branches of the CPW are connected together to form an open-aperture. We may consider that center conductor of the CPW is modified to form the first type and is protruded into the aperture. By keeping this aperture, the center conductor of the CPW can be modified into the second type. The second type results in the linearly polarized antenna by extending and widening the width of the center conductor of the CPW. The CP antenna is designed and implemented for WLAN standards of 2.4 GHz and WiMAX standard of 2.5 GHz (2.5-2.69GHz). The measured 10-dB return loss bandwidth is 22.04 %( 2.22-2.77GHz), the 3dB axial ratio is 17.4% (2.35-2.8GHz), and the in-band antenna gain lies between 1~4.5 dBic. The LP antenna is designed to cover 2.5/3.5/5.5 GHz of WiMAX bands and 5.8 GHz of WLAN bands. The measured 10-dB return loss bandwidth is 44.6% (2.42-3.81GHz) and 16.33% (5.38-6.351GHz), and the in-band antenna gain is around 0.15~4.4 dBi. The latter one may further improve the reception ability.

碩士
國立高雄應用科技大學
電子工程系碩士班
102
It is almost everyone has a smart phone due to rapid advance of technologies in recent years. The GPS (Global Position Services), Wi-Fi and other wireless communication devices had become standard equipment. This leads to more and more location-based services (Location Based Services, LBS). As visiting popular tourist attractions, people often share their location and photos with their friends with handheld devices. Wi-Fi is encouraged and even deployed by government policies, such as Taipei City Government's TPE-FREE. The makes Wi-Fi AP (Access Points) easy to access anywhere and anytime. In view of this, this study examines the possibility of traffic load estimation using WLAN infrastructure. A Wi-Fi AP broadcast beacon packet every 100ms to announce its existence for the neighborhood. The geographical locations of individual APs are known in advance. As a mobile client travel along the urban areas, it will experience the beacon signals of different APS. With a prior knowledge on the AP’s geographical locations, a reliable estimation on the moving speed can then be obtained, without excessive additional speed measurement equipment. This sort of information is essential for the entire intelligent transportation management system. Simulation tools, including NS-2, SUMO, and MOVE, are used in our study. Experiment results reveal that the proposed approach can be an effective approach for traffic estimation is urban area.

碩士
國立臺灣大學
資訊工程學研究所
93
Along with the progressing of technology, wireless Internet is becoming popular. Users can use the Internet everywhere with wireless Internet. There are many solutions about wireless Internet. We try to find out the best way that can be applied to the current environment and combine most advantages of existing wireless solutions. There are many applications of smart card, such as bankcards, credit cards, health card, certificate cards, and SIM cards especially. Nowadays mobile phones have become a daily necessity. Since it is safer for users to do authentication through mobile phone, we try to authenticate the wireless users by mobile phones. The main points of this paper are to increase the authentication security and charges wireless LAN and mobile phone in only one bill.

碩士
國立中興大學
電機工程學系
92
The development of wireless communication systems for high data-rate transmission has become one of important researches. In this thesis, design of the baseband transmitter is simulated and verified in MATLAB environment. The result shows that functional blocks of the transmitter can meet the standard specifications. FIR filters are often used in signal processing and spectral analysis. The digital FIR filter plays an important role. In the thesis, a Nyquist digital filter, i.e., a raised cosine filter, for IEEE 802.11a of WLAN BBP will be implemented. The shaping filter is a typical FIR Filter whose passband shape is set by the tap coefficients. Based on 20MHz system operation, the FIR filters are compared with different architectures, such as direct form, folded direct form(symmetric), and Canonical Signed Digit. We use ASIC design flow to do hardware simulation and verification. The filters are implemented by using UMC0.18μm CMOS technology and the supply voltage is 1.8V. The results show that the implemented raised cosine filter can meet IEEE 802.11a standard.

碩士
國立臺灣大學
電機工程學系
85
In an indoor radio environment plagued by the severe spatial fading and temporal fading effects of multipath, diversity schemes usually required. This thesis proposes a flat diversity antenna, consisting of two cross-polarized dipole antennas selectly excited by a PIN diode at the feeding point, to reduce the fading effects in the indoor environment. Results presented here provide a comparison between measurement and simulation results of input impedance and radiation pattern. Parameters studies of the antennas are also presented. To verify the diversity effects of this antenna, measurement for propagation characteristics was made in one of NTU EE laboratories at 2.4 GHz. The diversity gain is forward to be at least 3dB at 99% signal availability.

碩士
義守大學
機械與自動化工程學系碩士班
93
With the prevalence and development of the Internet, the network infrastructure begins to extend from the original wired network to the wireless network. In recent years, the development of wireless network attracts much attention in various applications. Due to the widespread use of the wireless network. One of the applications is personal or device locating service of location. With the increasing demand of the positioning service, people pay much attention to the indoor wireless positioning system based on Wireless Local Area Networks (WLAN). Nowadays, GPS is the most extensively used for locating service in outdoor environment but GPS deployment is not cost-effective. This research describes the development and implementation of an indoor wireless positioning systems based on IEEE 802.11x wireless network. We developed programs to obtain the values of signal strength transmitted from various Access Points (AP) in the wireless network. As the distance between transmitter and receiver changes, the received signal strength changes accordingly. This research aims to use the variations of signal strength combined with the probabilistic model of indoor wireless channels to calculate the position of the mobile terminal and to design a digital filter to improve positioning accuracy.

碩士
中華大學
電機工程學系(所)
94
Since the WLAN was invented, information that transmitted through WLAN gradually increase and standards for high-speed WLAN are weeded through the old to bring forth the new continuously. Form the early IEEE Std 802.11-1997, IEEE Std 802.11b-1999 and IEEE Std 802.11a-1999 to the hottest WLAN standard, IEEE Std 802.11g™-2003, the speed of WLAN is up to 54 Mbit/s. Standards referred above will be introduced and implemented on software platform one by one. First, specification for each system would be introduced. Then, baseband transceivers, implemented with SIMULINK® and verified by the curve of BER (Bit Error Rate), would be performed. Next, performance of systems versus fading channel would be analyzed using transceivers constructed early. Finally, simulation of adaptive modulation controlling for IEEE Std 802.11a-1999 system would be performed under a principle estimated by the curve of system performance acquired early.

碩士
中華大學
電機工程學系碩士班
90
For the rapidly increasing requirements of wireless data communications, the orthogonal frequency division multiplexing (OFDM) techniques have been heavily developed in recent years. In July 1998, the IEEE standardization group decided to select OFDM as the basic multiplexing technique for their new 5-GHz wireless local area network (WLAN) standard, and this new standard is the first one to use OFDM in packet-based communications, while the use of OFDM was limited to continuous transmission systems before. In this thesis, basic OFDM principles, the effects of synchronization errors, and important parameters of IEEE 802.11a are described. Besides, a preamble receiver is proposed for the wireless LAN. It provides the smoothing algorithm to resist time-dispersive channels and uses the short preamble for the carrier frequency offset acquisition. The short preamble format, which has a shorter period, is more robust to the delay spread and helpful for the channel estimation in long preamble, even though the short preamble is used for a coarse frequency offset estimation in IEEE 802.11a proposal.

碩士
國立臺北科技大學
光電工程系所
97
This paper will discuss for Wireless Local Access Network (WLAN) system measurement. With Multi-Input Multi-output (MIMO) technology and modify system parameters, we also enhance system performance to reach commercial use purpose. First at all, we setup a WLAN transmission environment which comply IEEE 802.11b/g standard in the Lab with standard antenna and accessories. With the Spectrum analyzer, reference RF card and Network analyzer, we can calculate the basic performance parameters for this WLAN system. Then we propose the upgrade plan for existing system. We can replace standard accessories by high performance antenna, low loss RF cable and connector to increase EIRP. And changing the antenna lambdas and related system parameters to extend cover area and maintain transmission performance. Finally, we successfully deploy the 2.4GHz commercial Public WLAN network and come out positive consultation. We successful extend WLAN signal covery area and can still maintain excellent throughput, BER and packet jitter to provide Internet and video transmission service. This system can also extend more that 50% network cover area than Hata Model.

The need for higher data rates in WLANs boosts drastically because tremendous consumer interest in emerging multimedia applications, such as HDTV, has been increased. Currently, the IEEE 802.11a/b/g WLANs provide a limited data rate for the current user application requirements. In order to overcome substantial limitations of the existing WLANs, the next generation of WLANs, IEEE 802.11n, is in the course of development and expected to support higher throughput, larger coverage area and better QoS. The high performance IEEE 802.11n WLAN can improve data rate significantly by using smart antenna systems in the physical layer to take advantage of multi-path fading of wireless channels. In this thesis, an analytical model is developed to study the MAC performance and the underlying smart antenna technologies used in multi-path fading channels. Multiple antennas employed in the AP arise two popular approaches to provide a significant performance improvement, diversity and multiplexing. Considering the diversity gain of multiple antennas at the AP in which the AP with multiple antennas serves one user at a time, the capacity and throughput can be obtained. In addition, the AP is possible to serve multiple users in the downlink, by exploiting the multiplexing gain of the wireless channel. We investigate the maximum network throughput when the traffic intensity of the AP approaches to one. Unlike most of previous research which focus on either the physical or the MAC layer performance, our analytical model jointly considers the MAC protocol and the smart antenna technology.

The number of smartphones in use is overwhelmingly increasing every year. These devices rely on connectivity to the Internet for the majority of their applications. The ever-increasing number of deployed 802.11 wireless access points and the relatively high cost of other data services make the case for opportunistic communication using free WiFi hot-spots. However, this requires effective management of the WLAN interface, because by design the energy cost of WLAN scanning and interface idle operation is high and energy is a primary resource on mobile devices. This thesis studies the WLAN interface management problem on mobile devices. First, I consider the hypothetical scenario where future knowledge of wireless connectivity opportunities is available, and present a dynamic programming algorithm that finds the optimal schedule for the interface. In the absence of future knowledge, I propose several heuristic strategies for interface management, and use real-world user traces to evaluate and compare their performance against the optimal algorithm. Trace-based simulations show that simple static scanning with a suitable interval value is very effective for delay-tolerant, background applications. I attribute the good performance of static scanning to the power-law distribution of the length of the WiFi opportunities of mobile users, and provide guidelines for choosing the scanning interval based on the statistical properties of the traces. I improve the performance of static scanning, by 46% on average, using a local cache of previous scan results that takes advantage of the location hints provided by the set of visible GSM cell towers.

碩士
樹德科技大學
電腦與通訊研究所
93
Abstract Focal point that communication science and technology still develop for various countries so far, the business opportunity brought by it is limitless, setting-up of the mobile communication system, have driven the development of the wireless local area network, What each mobile communication company puts into the large-scale base station of WLAN laying, in some public service organizations, such as the school, publicly-owned and private organ, station , coffee shop , department store , restaurant ,etc, have already erected the small-scale base station of WLAN, make the network wireless, can surf the Net and obtain information through the WLAN always in any time, IEEE802.11g 2.4GHz supreme transmitting rate of materials can reach 54Mbps at present, the restriction of the transmit distance, the distance of transmission under the space without hitch is smaller than 100 meters, the transmission distance under having obstacle space is smaller than several dozen meters, although IEEE802.11g have high-speed transmitting rate, but it is unable to cover the communication area effectively, Cause user's transmitting rate to slacken, even make signal break off, if erect more Access Point and adapter in order to improve the containing rate, increased the huge cost too at the same time . Develop its WLAN 802.11b/g booster in this thesis, Its frequency range is ISM frequency band of 2.4~4835 GHz, transmitting gain can get up to 29dB, the Receive gain also having 11dB , Noise Figure less than 3.7dB, data rate keep on 15Mbps, output power less than 1W, so not only increase bi-directional gain, but also can compensate for RF cable losses, and then extend wireless transmitted distance , and install the cost of the Access Point in reducing by a wide margin , improve existing communication quality, no matter transmitting or receiving, also can reduce Frame Error Rate.

碩士
國立中央大學
通訊工程研究所碩士在職專班
96
Purpose that thesis study this is it discuss which kind of antenna is it apply to 802.11n WLAN AP most to make up to lie in, and design the antenna in analysis according to this. Introduction of WLAN, is it analyses why it will be antenna demand of system this to go on then from the beginning, and then design, improve from various kinds of parameter characteristics of the antenna, and then after the verification of the electromagnetic simulation software, entering and proving and testing in fact, get an intact antenna of associations finally, its characteristics of various fields all accord with this thesis to plan and set up, and compared with known antenna, there is progress by a wide margin, among them the efficiency of the antenna has been improved by more than 35%, the average gain of azimuth plane has improved and exceeded 4dB by a wide margin even more, the average gain of azimuth plane is higher than 0dBi, at the same time this antenna was made up great diversity also on the space, polarization and radiation patterns, really become suitable for 802.11n WLAN AP.

碩士
靜宜大學
資訊管理學系研究所
92
Nowadays, many advantages of wireless have been discussed such as high movement and easy to use, and more and more places equip wireless network for customers to use. At present, the commercial WLANs charge the subscribers in “time-prepaid” mode or “time-used” mode. In this thesis, we proposed a billing system that supports four billing modes in the underlying WLAN. The billing system adopts FreeRADIUS to be the Authentication Server, the Cisco 1231 Access Point (NAS build-in) to be the Authenticator, and builds a Web-based Application Server by PHP and MySQL.

碩士
國立臺北科技大學
電腦與通訊研究所
99
Wireless communication technology has changed our lives during the passing decades. Wireless local area networks (WLAN) is one of the most important applications of the wireless communication technology. The demand for WLAN is becoming popular throughout the world in a greater extent, since it provides high speed connectivity and easy access to networks without wiring. The study mainly focuses on the current trends in development of compact and low profile Wi-Fi PDA and smart mobile phone and provides a wideband monopole antenna design suitable for application in wireless LAN communication system in the near future. The proposed antennas are applicable for wireless 802.11a/b/g/n and VoIP/WiFi wireless systems applications. The antennas with various shapes and arrangement of folded wire and metal patch radiator are for the applications and have bandwidths of about 200MHz with center frequency at 2.35GHz (2.25-2.45GHz) and 1,000MHz with center frequency at 5.375GHz (5-6GHz). The bandwidths specification can effectively cover the operation range as prescribed by IEEE 802.11a (5.15-5.35GHz and 5.47-5.825GHz), IEEE 802.11b (2.4-2.485GHz), IEEE 802.11g (2.4-2.485GHz) and IEEE 802.11n (2.4-2.485GHz, 5.15-5.35GHz and 5.47-5.825GHz).

碩士
國立臺北科技大學
電腦與通訊研究所
102
In the design of wireless access point radio frequency circuit, harmonic distortion, noise interference, antenna isolation electromagnetic interference are key issues. In this paper, we analyze and provide solutions during the design phase. The non-linearity of power amplifier will cause harmonic distortion and impact the EMI/EMC safety, therefore we use the filters to suppress. (2) Using the cavity resonance to suppress the high order mode harmonic distortion of wireless radio chip, and also find out the tuning variable to improve the performance. (3) DDR(Double Data Rate Synchronous Dynamic Random Access Memory, DDR) and CPU(Central Processing Unit, CPU) communication traffic will induce in-band noise, and it will impact throughput performance once the antenna received. We used two solutions to solve it, and provide measurement results. (4) Antenna isolation is the key point when designing smaller housing. In this paper, we use two structures to improve antenna isolation and provide measurement throughput results for the reference.

碩士
國立臺灣大學
電信工程學研究所
94
In this thesis, coupling-of-modes (COM) approach and equivalent circuit model (ECM) are applied to design surface-acoustic wave (SAW) filters for various applications. A ladder-type SAW filter at IEEE 802.11a WLAN band is designed and the chip size is 214 × 115 μm2. An RF filter for unlicensed band of WiMAX and 802.11b WLAN is proposed and the chip size is 431 × 145 μm2. A miniaturized low-loss SAW duplexer has been developed for the WiMAX band and the chip size is 295 × 226.5 μm2. A six-channel low-loss switchable SAW filter bank is designed for the WiMAX system. It has the insertion loss of less than 1.8 dB, channel bandwidth of 20 MHz, stopband rejection of more than 35 dB, and the chip size is 3 × 1.7 mm2. Those SAW filters are designed on 42 YX-LiTaO3 substrate with aluminum (Al) electrodes. Sensitivity study has also been conducted. i

碩士
國立臺灣大學
電信工程學研究所
93
In this thesis, the design and test of IEEE 802.11b WLAN circuits are described. The circuit blocks consist of baseband processor RF3002, IF and RF transceiver RF2958, power amplifier RF5189, RF filter, RF switches, IF SAW filter and regulators. The circuits are fabricated with four-layer PCB process. The implemented wireless LAN card can provide four kinds of data rates which are 1Mbps(DSSS), 2Mbps(DSSS), 5.5Mbps(CCK), and 11Mbps(CCK) based on IEEE802.11b specification. For the software implementation, the C language code compiled by Keil is downloaded to the microprocessor by the USB interface to control and coordinate the functions between the circuit blocks of WLAN card. The introduction of IEEE 802.11 WLAN standard is presented in Chapter 1. Chapter 2 describes the specification of the 802.11b WLAN physical layer and circuit system design. The circuit design consisted of baseband processor, IF and RF transceiver, power amplifier, front-end circuit, dc power circuits, PHY interface circuits, MAC control circuits, and link budget are described in Chapter 3. Chapter 4 gives the circuit layout to realize the designed circuit on a four layer PCB. Chapter 5 describes the test results of each circuit and demonstrates the data transmitting and receiving of the developed WLAN cards. Finally, the conclusion is given in the Chapter 6.