Topicality of the problem. Wireless WAN technologies which can provide multimedia services to customer in most cases are implemented by the commercial providers of voice services. Thus technologies are expensive in development of the Hot-Spots, where volatile expanded concentration of customers may be observed. For such purposes the main alternative technologies are the IEEE 802.11. In modern telecommunications industry the expansion of the IEEE 802.11 networks is one of the fastest growing segment of the telecommunications market. This technology has quickly found a significant place and popularity to provide the typical services of Internet in business, home networking, and etc. Growing evolution of Internet technologies determines transmitted data flows to take a shape of specific real time multimedia flows features. For such conditions the IEEE 802.11 general technology was not adapted. It is important to develop the new operation methods based on IEEE 802.11 without changing main standard specification. This method lets to adopt an existing in market equipment of IEEE 802.11 for multimedia or voice flows. The methodology of IEEE 802.11 technological expenditures influence estimation, presented in dissertation, has not been used before. This estimation method allows to evaluate rationality of physical resource utilization and to predict protocol modification directions. Also, method of synchronous voice communication in customer access is proposed. This solution allows... [to full text] / Mokslo problemos aktualumas. Plačiajuostės licencijuojamų dažnių bevielės technologijos, kurios paprastai skirtos vartotojams teikti komercines multimedijos ir balso paslaugas, yra per brangios vystant prieigos tinklus, kuriuose sutinkama didelė vartotojų koncentracija. Dėl to šios technologijos dažniausiai naudojamos tik komercinių balso paslaugų tiekėjų. Labiausiai tinkama alternatyva – yra IEEE 802.11 technologijos, kurių naudojimas modernių telekomunikacijų tinklų išplėtimui įvairiose tipinėse sąlygose yra pastebimai auganti telekomunikacijų rinkos dalis. Ši technologija greitai išplito ir tapo populiari verslo, namų, „paskutinės mylios“ ir kituose tinklų vystymo sprendimuose. Modernėjant Interneto technologijoms, telekomunikacijų tinkluose įsivyrauja multimedijos požymių turintys srautai, kurių sukurtoms specifinėms sąlygoms IEEE 802.11 technologijos nėra pritaikytos. Todėl svarbu kurti naujus, ribines galimybes išnaudojančius, bet specifikacijos nekeičiančius protokolus, kurie leistų rinkoje esančią įrangą adaptuoti realaus laiko srautams. Disertacijoje naudojama IEEE 802.11 MAC protokolo technologinių sąnaudų įtakos vertinimo metodika nebuvo taikoma. Šis vertinimo būdas leidžia įvertinti fizinio resurso užėmimo racionalumą ir numatyti IEEE 802.11 protokolo modifikavimo kryptis. Pateiktas sinchroninis vartotojų prieigos adaptacijos balso perdavimams būdas leidžia racionaliai panaudoti IEEE 802.11 protokolą balsui adaptuotose vartotojų prieigose. Todėl, galima teigti... [toliau žr. visą tekstą]

Mokslo problemos aktualumas. Plačiajuostės licencijuojamų dažnių bevielės technologijos, kurios paprastai skirtos vartotojams teikti komercines multimedijos ir balso paslaugas, yra per brangios vystant prieigos tinklus, kuriuose sutinkama didelė vartotojų koncentracija. Dėl to šios technologijos dažniausiai naudojamos tik komercinių balso paslaugų tiekėjų. Labiausiai tinkama alternatyva – yra IEEE 802.11 technologijos, kurių naudojimas modernių telekomunikacijų tinklų išplėtimui įvairiose tipinėse sąlygose yra pastebimai auganti telekomunikacijų rinkos dalis. Ši technologija greitai išplito ir tapo populiari verslo, namų, „paskutinės mylios“ ir kituose tinklų vystymo sprendimuose. Modernėjant Interneto technologijoms, telekomunikacijų tinkluose įsivyrauja multimedijos požymių turintys srautai, kurių sukurtoms specifinėms sąlygoms IEEE 802.11 technologijos nėra pritaikytos. Todėl svarbu kurti naujus, ribines galimybes išnaudojančius, bet specifikacijos nekeičiančius protokolus, kurie leistų rinkoje esančią įrangą adaptuoti realaus laiko srautams. Disertacijoje naudojama IEEE 802.11 MAC protokolo technologinių sąnaudų įtakos vertinimo metodika nebuvo taikoma. Šis vertinimo būdas leidžia įvertinti fizinio resurso užėmimo racionalumą ir numatyti IEEE 802.11 protokolo modifikavimo kryptis. Pateiktas sinchroninis vartotojų prieigos adaptacijos balso perdavimams būdas leidžia racionaliai panaudoti IEEE 802.11 protokolą balsui adaptuotose vartotojų prieigose. Todėl, galima teigti... [toliau žr. visą tekstą] / Topicality of the problem. Wireless WAN technologies which can provide multimedia services to customer in most cases are implemented by the commercial providers of voice services. Thus technologies are expensive in development of the Hot-Spots, where volatile expanded concentration of customers may be observed. For such purposes the main alternative technologies are the IEEE 802.11. In modern telecommunications industry the expansion of the IEEE 802.11 networks is one of the fastest growing segment of the telecommunications market. This technology has quickly found a significant place and popularity to provide the typical services of Internet in business, home networking, and etc. Growing evolution of Internet technologies determines transmitted data flows to take a shape of specific real time multimedia flows features. For such conditions the IEEE 802.11 general technology was not adapted. It is important to develop the new operation methods based on IEEE 802.11 without changing main standard specification. This method lets to adopt an existing in market equipment of IEEE 802.11 for multimedia or voice flows. The methodology of IEEE 802.11 technological expenditures influence estimation, presented in dissertation, has not been used before. This estimation method allows to evaluate rationality of physical resource utilization and to predict protocol modification directions. Also, method of synchronous voice communication in customer access is proposed. This solution allows... [to full text]

Dans cette thèse, nous examinons les aspects essentiels des réseaux locaux sans fil IEEE 802.11 (réseaux WiFi) en mode infrastructure, et identifions les problèmes qui peuvent affecter leurs performances. Après avoir étudié l'état de l'art, nous constatons que de nombreux efforts de recherche ont proposé des solutions diverses mais présentant des limitations qui empêchent leur déploiement dans les réseaux locaux sans fil existants. En outre, les utilisateurs de ces réseaux ont des attentes toujours croissantes de disponibilité, de fiabilité, de réponse instantanée et de sécurité de la part de leurs connexions sans fil. Motivés par ces défis, nous concevons et mettons en œuvre des solutions nouvelles et concrètes aux problèmes ouverts liés à la performance des réseaux locaux sans fil IEEE 802.11. Nous adoptons une approche centrée sur le point d'accès (Access Point), qui n'introduit pas de modifications côté client. Nous nous concentrons sur les aspects suivants des réseaux locaux sans fil : la mobilité des clients, la gestion des canaux, et la qualité de service, et nous explorons trois différents scénarios pour les déploiements les plus répandus : une entreprise, une ville (zone urbaine), et une résidence personnelle (maison ou appartement). Afin de fournir une base commune pour la mise en œuvre pratique de nouvelles solutions 802.11, nous introduisons un modèle de point d'accès intelligent, inspiré des techniques d'auto-gestion. Les contributions principales de cette thèse sont les suivantes : 1. Nous développons une solution de mobilité transparente pour la Voix sur IP (VoIP) dans les réseaux sans fil d'entreprise, appelée Multichannel Virtual Access Point (mVAP), qui n'introduit aucune modification côté client et reste compatible avec les appareils actuels. Nous mettons en œuvre et évaluons mVAP en utilisant du matériel 802.11 standard, et accomplissons une mobilité transparente sans interruption ni dégradation des communications en cours. 2. Nous étudions la possibilité d'exploiter la couverture WiFi existante dans les zones urbaines pour obtenir un accès mobile à Internet, grâce à des simulations réalisées à partir de données réelles collectées par des téléphones portables. Les résultats montrent que cette couverture WiFi est large et que la connectivité offerte peut être efficacement utilisée. Nous identifions des questions ouvertes concernant le déploiement effectif d'un tel réseau WiFi à l'échelle d'une ville, et les applications qui pourraient en bénéficier. 3. Nous proposons un mécanisme dynamique de sélection de canal pour les réseaux locaux sans fil personnels (maisons et appartements), qui utilise la charge de trafic variable dans le temps pour l'estimation d'interférences. Nous mettons en œuvre cette solution en utilisant du matériel 802.11 standard, et nous l'évaluons expérimentalement : les performances d'un tel réseau sont considérablement améliorées en choisissant le canal qui présente le moins d'interférences. / In this dissertation, we examine important aspects of infrastructure IEEE 802.11 Wireless Local Area Networks (WLANs) and identify issues that can affect their performance. Reviewing the state of the art, we observe that numerous research efforts have proposed diverse solutions with several limitations that impede their deployment in existing WLANs. Moreover, users have ever-increasing expectations of availability, reliability, instantaneous response and security from their wireless connections. Motivated by these challenges, we design and implement novel but practical solutions that address open issues affecting the performance of IEEE 802.11 WLANs. We adopt an Access Point (AP)-based approach, which does not require any modification in the clients. We focus on the following aspects of WLANs: client mobility, channel management, and quality of service, and explore three different scenarios for the most common deployments: an enterprise, a city (urban area), and a personal residence (home). To provide a common basis for practical implementation of new 802.11 solutions, we present a Smart AP model, inspired by self-management techniques. The main contributions of this thesis are: 1. We develop a seamless mobility solution for Voice over IP (VoIP) services in Enterprise WLANs, called Multichannel Virtual Access Points (mVAP), which requires no client modifications and is compatible with current devices. We implement and evaluate mVAP using commodity 802.11 hardware, and achieve transparent mobility without interruption or degradation of ongoing communications. 2. We investigate the feasibility of harnessing the existing WiFi coverage in urban areas for mobile Internet access, through trace-based simulations using real data collected by mobile phones. The results show that the WiFi coverage is large and the connectivity it offers can be effectively exploited. We identify open issues for the actual deployment of such a citywide WiFi network and the applications that could benefit from it. 3. We propose an adaptive traffic-aware channel selection mechanism for Home WLANs, that uses the time-varying traffic load for interference estimation. We implement this solution using commodity 802.11 hardware and experimentally evaluate it: the network performance is drastically improved by constantly picking the channel with the least interference.

在無線區域網路的範疇，IEEE 802.11是一個主要的媒介存取控制協定。然而在隨意式多跳接的網路中，IEEE 802.11面臨更嚴重的hidden terminal和exposed terminal problems，而這些問題主因都源自於過大的訊號干擾範圍與過大的訊號感應範圍。在這篇論文裡，我們提出一個可調式的媒介存取控制協定，針對IEEE 802.11 RTS/CTS handshake機制做簡單地修改，使得IEEE 802.11 devices可以依據週遭的傳收狀態動態調整自身的傳送和接收行為。實驗結果顯示我們的方法使原來的 802.11 減少了互相干擾的情形並且提升了系統的效能。 / The IEEE 802.11 standard is the most popular Medium Access Control (MAC) protocol for wireless local area networks. However, in multihop wireless ad hoc networks, the IEEE 802.11 MAC protocol will suffer from more serious hidden terminal and exposed terminal problems than those in single hop WLANs. More specifically, it is due to the large interference range and the large carrier sensing range. In this thesis, we propose an adaptive IEEE 802.11 MAC (AMAC) that makes two simple modifications of IEEE 802.11 RTS/CTS handshake to dynamically adjust the transmission and reception according to the shared medium status near transmitter and receiver, respectively. Simulation results show that our method can lessen interferences and increase system throughput as compared with IEEE 802.11 MAC.

L'utilisation de la communication sans fil dans les applications de contrôle offre de nombreux avantages comme la mobilité. Toutefois, la communication sans fil souffre de nombreux inconvénients tels que la perte d'information, délais aléatoires. Ces problèmes sont essentiellement induits par le non déterministe du comportement de la communication sans fil qui peut avoir un impact négatif sur la performance du système. L'objectif de ce travail porte sur l'amélioration des performances de Systèmes Discrets Contrôlés via un Réseau Sans fil. Ses systèmes sont caractérisés par une commande logique distribuée sur des automates programmables et des boîtiers d'entrées/sorties déportés communiquant via un réseau de communication sans fil, IEEE 802.11. L'approche proposée repose sur un processus de co-conception basé : un, sur une modélisation conjointe des comportements de la commande et du réseau au travers de modèles SED déterministes pour la commande et stochastiques pour le réseau, et sur la simulation pour évaluer les performances des SDCR sans fil et notamment leur temps de réponse. Deux, la proposition d'un algorithme qui alloue dynamiquement les priorités définies par l'IEEE 802.11e sur les trafics de communication en fonction des besoins et des états de la commande; cet algorithme est évalué sur un cas d'étude, pour lequel la communication sans fil induit des risques de collision entre des équipements d'une installation industrielle, en utilisant l'environnement de simulation précédemment défini. Les simulations montrent une amélioration de la performance du système surtout dans des cas où le réseau est très chargé / Using wireless communication in the control system introduces many advantages like reduced wiring costs but also many drawbacks such as the delays, packet losses... which may disturb the system performance. The objective of this thesis is to improve the performance of a Wireless Networked Discrete Control System. This kind of system is characterized with a logic command distributed among PLC and plant part communicating through a wireless network, IEEE 802.11. The proposed approach is based on a co-design concept by simultaneously modeling the behavior of the command part (deterministic), and network part (non deterministic). Simulation tools do not cope with this co-design point of view because they are generally either ?control design? or ?network analysis? dedicated. Two solutions are explored: first, by integrating the network model into a control-oriented tool, Matlab-Truetime library and second, by integrating the discrete control system behavior into a network-oriented tool, OPNET. Comparisons between these tools confirm the possibility of modeling a WNDCS using Matlab-Truetime (with some modifications) and OPNET. Moreover, an algorithm is proposed to improve the global system performance; it dynamically allocates IEEE 802.11e priorities to the communication traffic with regard to the control requirements and the current state of the system, but also by taking into account the current quality of service provided by the network. Simulations of a case study performed using OPNET have highlighted the efficiency of the proposed algorithm

En esta tesis se estudia la tecnología 802.11n, detallando las modificaciones realizadas en la capa MAC y Física respecto de las tecnologías legadas. Así mismo, cuales serán los resultados como solución de acceso en redes de área local y como podría influir esta tecnología como solución de enlaces punto a punto y punto multipunto de banda ancha en zonas no urbanas. Para esto se analizarán las condiciones de adaptación que deben ser consideradas para lograr los escenarios propuestos en zonas no urbanas de difícil acceso. Finalmente siguiendo los parámetros del último draft se determinará si esta tecnología podría ser en un futuro una solución paralela a otras tecnologías para realizar un enlace de banda ancha de larga distancia. / Tesis

Se plantea la posibilidad de migrar a IEEE 802.16 (WiMAX) en los lugares donde se usa WiFi como solución tecnológica ya que la primera es una tecnología inalámbrica diseñada para redes MAN que no solo permite conectividad inalámbrica sino también velocidades de banda ancha; lográndose llenar los vacíos que deja WiFi. De esta manera se estaría fomentando el acceso universal el cual es un componente en la estrategia del desarrollo de las telecomunicaciones en el Perú. / Tesis

Gao Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 70-73). / Abstracts in English and Chinese. / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Literature Survey and Background --- p.6 / Chapter 2.1 --- Capacity of Wireless Networks --- p.6 / Chapter 2.2 --- Physical Layer Techniques --- p.8 / Chapter 2.2.1 --- Radio Propagation Models --- p.8 / Chapter 2.2.2 --- Multiple Access Techniques --- p.11 / Chapter 2.3 --- MAC layer --- p.13 / Chapter 2.3.1 --- An Introduction to the IEEE 802.11 protocol --- p.13 / Chapter 2.3.2 --- Performance Analysis of the IEEE 802.11 protocol in single cell networks --- p.15 / Chapter 3 --- Model and Methodology --- p.18 / Chapter 3.1 --- System Model --- p.18 / Chapter 3.1.1 --- DCF Model --- p.19 / Chapter 3.1.2 --- The Problems of Hidden Node --- p.21 / Chapter 3.2 --- A Methodology to Compute Throughput Capacity --- p.23 / Chapter 3.2.1 --- Constructing a Contention Graph --- p.24 / Chapter 3.2.2 --- Determining the Link Capacity Ei --- p.27 / Chapter 3.2.3 --- Determining the Channel Idle Probability zi --- p.30 / Chapter 3.2.4 --- Detennining the Collision Probability γi --- p.32 / Chapter 3.3 --- Throughput Analysis of a Chain network --- p.35 / Chapter 4 --- Applications of the Proposed Methodology --- p.38 / Chapter 4.1 --- Application 1: Determining the End-to-End Throughput Capacity in Multi-hop Networks --- p.38 / Chapter 4.1.1 --- Routing Optimization --- p.40 / Chapter 4.1.2 --- Offered Load Control --- p.45 / Chapter 4.2 --- Application 2: Determining the Equilibrium Throughput of onehop Networks --- p.47 / Chapter 4.2.1 --- Throughput Capacity of One-Hop Networks --- p.49 / Chapter 4.3 --- Application 3: Optimal Hop Distance in Multi-hop Networks --- p.51 / Chapter 4.3.1 --- Analysis of Regular One-Dimension Network --- p.51 / Chapter 4.3.2 --- Optimal Hop Distance --- p.53 / Chapter 5 --- Simulation and Validation --- p.55 / Chapter 5.1 --- Simulation Environment --- p.55 / Chapter 5.2 --- MAC layer Collisions --- p.56 / Chapter 5.3 --- Single Flow Capacity: --- p.58 / Chapter 5.4 --- Neighboring Traffic Effect: --- p.59 / Chapter 5.5 --- Routing Optimization: --- p.60 / Chapter 5.6 --- Optimal Offered Load Control: --- p.62 / Chapter 5.7 --- Optimal Hop Distance --- p.63 / Chapter 5.7.1 --- One-Source ROD Network --- p.63 / Chapter 5.7.2 --- Two-Source ROD Network --- p.64 / Chapter 5.7.3 --- Simulation Investigation on Hop Distance --- p.65 / Chapter 6 --- Related Work --- p.68 / Chapter 7 --- Conclusion --- p.69

" IEEE 802.11 wireless access points (APs) act as the central communication hub inside homes, connecting all networked devices to the Internet. Home users run a variety of network applications with diverse Quality-of-Service requirements (QoS) through their APs. However, wireless APs are often the bottleneck in residential networks as broadband connection speeds keep increasing. Because of the lack of QoS support and complicated configuration procedures in most off-the-shelf APs, users can experience QoS degradation with their wireless networks, especially when multiple applications are running concurrently. This dissertation presents CATNAP, Classification And Treatment iN an AP , to provide better QoS support for various applications over residential wireless networks, especially timely delivery for real-time applications and high throughput for download-based applications. CATNAP consists of three major components: supporting functions, classifiers, and treatment modules. The supporting functions collect necessary flow level statistics and feed it into the CATNAP classifiers. Then, the CATNAP classifiers categorize flows along three-dimensions: response-based/non-response-based, interactive/non-interactive, and greedy/non-greedy. Each CATNAP traffic category can be directly mapped to one of the following treatments: push/delay, limited advertised window size/drop, and reserve bandwidth. Based on the classification results, the CATNAP treatment module automatically applies the treatment policy to provide better QoS support. CATNAP is implemented with the NS network simulator, and evaluated against DropTail and Strict Priority Queue (SPQ) under various network and traffic conditions. In most simulation cases, CATNAP provides better QoS supports than DropTail: it lowers queuing delay for multimedia applications such as VoIP, games and video, fairly treats FTP flows with various round trip times, and is even functional when misbehaving UDP traffic is present. Unlike current QoS methods, CATNAP is a plug-and-play solution, automatically classifying and treating flows without any user configuration, or any modification to end hosts or applications. "

Cheung Cheuk Lun. / Thesis submitted in: July 2004. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (leaves 109). / Abstracts in English and Chinese. / Abstract --- p.1 / Chapter 1 --- Introduction --- p.3 / Chapter 1.1 --- Differentiation from existing products --- p.6 / Chapter 1.2 --- Problems --- p.6 / Chapter 1.3 --- Assumption --- p.9 / Chapter 2 --- Study of bulk transfer --- p.10 / Chapter 2.1 --- Simple wireless solution --- p.10 / Chapter 2.2 --- Problems of the simple wireless solution --- p.10 / Chapter 2.2.1 --- Low performance due to header overhead --- p.12 / Chapter 2.2.2 --- Low performance due to unnecessary packets --- p.12 / Chapter 2.2.3 --- Model derivation --- p.12 / Chapter 2.2.4 --- Performance study --- p.17 / Chapter 2.3 --- Packed wireless solution --- p.19 / Chapter 2.3.1 --- Example --- p.19 / Chapter 2.3.2 --- Solved problems --- p.21 / Chapter 2.3.3 --- Model derivation --- p.22 / Chapter 2.3.4 --- Performance study --- p.24 / Chapter 2.3.4 --- Performance study on the effect of the value of n --- p.25 / Chapter 2.4 --- Controllable packed wireless solution --- p.27 / Chapter 2.4.1 --- Problem --- p.27 / Chapter 2.4.2 --- Analysis --- p.27 / Chapter 2.4.3 --- Solution --- p.29 / Chapter 2.4.4 --- Model derivation --- p.33 / Chapter 2.4.5 --- Performance study --- p.35 / Chapter 2.4.6 --- Performance study on the effect of the sliding window size --- p.36 / Chapter 2.5 --- Summary of performance study --- p.41 / Chapter 2.5.1 --- Comparison of the throughput between four cases --- p.41 / Chapter 2.5.2 --- Study of how the throughput-varies with the processing time --- p.44 / Chapter 2.6 --- Simulation --- p.47 / Chapter 2.6.1 --- Measuring the packet loss rate and the throughput --- p.49 / Chapter 2.6.2 --- Studying the throughput against the distance --- p.50 / Chapter 2.6.3 --- Studying the throughput against the packet loss rate --- p.53 / Chapter 2.7 --- Conclusion --- p.54 / Chapter 3 --- Study of interrupt transfer --- p.55 / Chapter 3.1 --- Problem --- p.55 / Chapter 3.2 --- Solution --- p.56 / Chapter 3.2.1 --- Remote polling --- p.56 / Chapter 3.3 --- Feasibility of the solution --- p.58 / Chapter 3.4 --- The problem of Distributed Coordination Function collision --- p.60 / Chapter 3.5 --- Collision avoidance --- p.60 / Chapter 3.6 --- Model derivation --- p.61 / Chapter 3.6.1 --- Wired case --- p.61 / Chapter 3.6.2 --- Wireless solution (remote polling) --- p.62 / Chapter 3.7 --- Maximum allowed request generation frequency --- p.64 / Chapter 3.7.1 --- More than one interrupt transfer --- p.64 / Chapter 3.7.2 --- More than one bulk transfer --- p.64 / Chapter 3.7.3 --- Maximum allowed request generation frequency --- p.65 / Chapter 3.8 --- Conclusion --- p.65 / Chapter 4 --- System architecture issues --- p.66 / Chapter 4.1 --- USB network --- p.66 / Chapter 4.1.1 --- Problems --- p.66 / Chapter 4.1.2 --- Solution --- p.66 / Chapter 4.1.3 --- Conclusion --- p.69 / Chapter 4.2 --- Security --- p.70 / Chapter 4.2.1 --- Suggested solution --- p.70 / Chapter 4.2.2 --- Conclusion --- p.72 / Chapter 4.3 --- Cost --- p.72 / Chapter 4.4 --- Power supply --- p.73 / Chapter 5 --- Conclusion --- p.75 / Appendix --- p.77 / Chapter A. --- Wireless USB (WUSB) --- p.77 / Chapter B. --- Introduction of USB --- p.83 / Chapter C. --- Framing details of 802.11 --- p.99 / Chapter D. --- A case study of a USB device --- p.102 / Chapter E. --- Reference of notations used in figures --- p.106 / Chapter F. --- Values of all symbols --- p.107 / Reference i --- p.109