La presente tesis doctoral contribuye a la incesante evolución de las comunicaciones inalámbricas. Se centra en el diseño de protocolos de acceso al medio (MAC) para redes ad hoc y redes inalámbricas cooperativas. En una primera parte introductoria se presenta un minucioso estado del arte y se establecen las bases teóricas de las contribuciones presentadas en la tesis. En esta primera parte introductoria se definen las principales motivaciones de la tesis y se plantean los objetivos. Después, las contribuciones de la tesis se organizan en dos grandes bloques, o partes. En la primera parte de esta tesis se diseña, analiza y evalúa el rendimiento de un novedoso protocolo MAC de alta eficiencia llamado DQMAN (Protocolo MAC basado en colas distribuidas para redes ad hoc). Este protocolo constituye la extensión y adaptación del protocolo DQCA, diseñado para redes centralizadas, para operar en redes sin infraestructura. En DQMAN se introduce un nuevo paradigma en el campo del acceso al medio para redes distribuidas: la integración de un algoritmo de clusterización espontáneo y dinámico basado en una estructura de master y esclavo junto con un protocolo MAC de alta eficiencia diseñado para redes centralizadas. Tanto el análisis teórico como las simulaciones por ordenador presentadas en esta tesis muestran que DQMAN mejora el rendimiento del actual estándar IEEE 802.11. La principal característica de DQMAN es que se comporta como un protocolo de acceso aleatorio cuando la carga de tráfico es baja y cambia automática y transparentemente a un protocolo de reserva a medida que el tráfico de la red aumenta. Además, su rendimiento es prácticamente independiente del número de usuarios simultáneos de la red, lo cual es algo deseable en redes que nacen para cubrir una necesidad espontánea y no pueden ser planificadas. El hecho de que algoritmo de clusterización se base en un acceso aleatorio permite la coexistencia e intercomunicación de usuarios DQMAN con usuarios basados en el estándar IEEE 802.11. Este estudio se presenta en esta primera parte de la tesis y es fundamental de cara a una posible explotación comercial de DQMAN. La metodología presentada en esta tesis mediante el cual se logra extender la operación de DQCA a entornos ad hoc sin infraestructura puede ser utilizada para adaptar cualquier otro protocolo centralizado. Con el objetivo de poner de manifiesto esta realidad, la primera parte de la tesis concluye con el diseño y evaluación de DPCF como una extensión distribuida del modo de coordinación centralizado (PCF) del estándar IEEE 802.11 para operar en redes distribuidas. La segunda parte de la tesis se centra en el estudio de un tipo específico de técnicas cooperativas: técnicas cooperativas de retransmisión automática (C-ARQ). La idea principal de las técnicas C-ARQ es que cuando un paquete de datos se recibe con bits erróneos, se solicita retransmisión, no a la fuente de datos, si no a cualquiera de los usuarios que escuchó la transmisión original. Estos usuarios se convierten en espontáneos retransmisores que permiten mejorar la eficiencia de la comunicación. A pesar de que este tipo de esquema puede obtener diversidad de cooperación, el hecho de implicar a más de un usuario en una comunicación punto a punto requiere una coordinación que hasta ahora ha sido obviada en la literatura, asumiendo que los retransmisores pueden coordinarse perfectamente para retransmitir uno detrás de otro. En esta tesis se analiza y evalúa el coste de coordinación impuesto por la capa MAC y se identifican los principales retos de diseño que las técnicas C-ARQ imponen al diseño de la capa MAC. Además, se presenta el diseño y análisis de dos novedosos protocolos MAC para C-ARQ: DQCOOP y PRCSMA. El primero se basa en DQMAN y constituye una extensión de este para operar en esquemas C-ARQ, mientras que el segundo constituye la adaptación del estándar IEEE 802.11 para poder ejecutarse en un esquema C-ARQ. El rendimiento de estos esquemas se compara en esta tesis tanto con esquemas no cooperativos como con esquemas ideales cooperativos donde se asume que el MAC es ideal. Los resultados principales muestran que el diseño eficiente de la capa MAC es esencial para obtener todos los beneficios potenciales de los esquemas cooperativos. / This thesis aims at contributing to the incessant evolution of wireless communications. The focus is on the design of medium access control (MAC) protocols for ad hoc and cooperative wireless networks. A comprehensive state of the art and a background on the topic is provided in a first preliminary part of this dissertation. The motivations and key objectives of the thesis are also presented in this part. Then, the contributions of the thesis are divided into two fundamental parts. The first part of the thesis is devoted to the design, analysis, and performance evaluation of a new high-performance MAC protocol. It is the Distributed Queueing MAC Protocol for Ad hoc Networks (DQMAN) and constitutes an extension and adaptation of the near-optimum Distributed Queueing with Collision Avoidance (DQCA) protocol, designed for infrastructure-based networks, to operate over networks without infrastructure. DQMAN introduces a new access paradigm in the context of distributed networks: the integration of a spontaneous, dynamic, and soft-binding masterslave clustering mechanism together with a high-performance infrastructure-based MAC protocol. Theoretical analysis and computer-based simulation show that DQMAN outperforms IEEE 802.11 Standard. The main characteristic of the protocol is that it behaves as a random access control protocol when the traffic load is low and it switches smoothly and automatically to a reservation protocol as the traffic load grows. In addition, its performance is almost independent of the number of users of a network. The random-access based clustering algorithm allows for the coexistence and intercommunication of stations using DQMAN with the ones just based on the legacy IEEE 802.11 Standard. This assessment is also presented in this first part of the dissertation and constitutes a key contribution in the light of the commercial application of DQMAN. Indeed, the rationale presented in this first part of the thesis to extend DQCA and become DQMAN to operate over distributed networks can be used to extend the operation of any other infrastructure-based MAC protocol to ad hoc networks. In order to exemplify this, a case study is presented to conclude the first part of the thesis. The Distributed Point Coordination Function (DPCF) MAC protocol is presented as the extension of the PCF of the IEEE 802.11 Standard to be used in ad hoc networks. The second part of the thesis turns the focus to a specific kind of cooperative communications: Cooperative Automatic Retransmission Request (C-ARQ) schemes. The main idea behind C-ARQ is that when a packet is received with errors at a receiver, a retransmission can be requested not only from the source but also to any of the users which overheard the original transmission. These users can become spontaneous helpers to assist in the failed transmission by forming a temporary ad hoc network. Although such a scheme may provide cooperative diversity gain, involving a number of users in the communication between two users entails a complicated coordination task that has a certain cost. This cost has been typically neglected in the literature, assuming that the relays can attain a perfect scheduling and transmit one after another. In this second part of the thesis, the cost of the MAC layer in C-ARQ schemes is analyzed and two novel MAC protocols for C-ARQ are designed, analyzed, and comprehensively evaluated. They are the DQCOOP and the Persistent Relay Carrier Sensing Multiple Access (PRCSMA) protocols. The former is based on DQMAN and the latter is based on the IEEE 802.11 Standard. A comparison with non-cooperative ARQ schemes (retransmissions performed only from the source) and with ideal CARQ (with perfect scheduling among the relays) is included to have actual reference benchmarks of the novel proposals. The main results show that an efficient design of the MAC protocol is crucial in order to actually obtain the benefits associated to the C-ARQ schemes.

The C2X Communication is of high interest to the automotive industry. Ongoing research on this topic mainly bases on the simulation of Vehicular Ad Hoc Networks. In order to estimate the necessary level of simulation details their impact on the results needs to be examined. This thesis focuses on different channel models as the freespace, shadowing, and Ricean model, along with varying parameters. For these simulations the network simulator ns-2 is extended to provide IEEE 802.11p compliance. However, the WAVE mode is not considered since it is still under development and not finally approved. Besides a more sophisticated packet error model than the existing implementation, as well as a link adaptation algorithm, is added. In this thesis several simulations examine specific details of wireless communication systems such as fairness of multiple access, interferences, throughput, and variability. Furthermore, the simulation points out some unexpected phenomena as starving nodes and saturation effects in multi hop networks. Those led to the conclusion that the IEEE 802.11 draft amendment does not solve known problems of the original IEEE 802.11 standard.

在使用者較為密集的場合中，常會碰到無線網路壅塞的問題，例如在一個大型會議廳中，常會在各個IEEE 802.11頻道上部署不同的WiFi AP（Access Point），來分散使用者的連線。但是由於IEEE 802.11的連線機制是屬於使用者主導（client driven），只能透過使用者去選定AP進行連線，對於使用者裝置來說,，連線到不同AP的優先順序，是依照接收到不同AP的信號強度（RSSI）作為排序指標。這種做法會讓在空間上使用者分佈不平均的環境中，造成多數使用者UE只連線到少數AP，而其餘AP資源閒置無用的情形。 本論文提出一個IEEE 802.11的負載平衡解決方案，結合藍牙低功耗（Bluetooth Low Energy，BLE）及IEEE 802.11成為一個智慧型AP架構。我們利用藍牙低功耗通訊協定GATT （Generic Attribute Profile）分派AP給不同使用者進行連線，再結合馬可夫鏈平穩狀態分佈（Markov Chains Stationary Distribution）演算法，依照使用者在AP網路拓樸中的歷史分佈紀錄，將多個AP的分派轉化為Erlang-C模型的排隊系統以計算AP分派規則，藉此達到系統的負載平衡。 / Usually, a user crowded space encounters wireless network congestion problem. For example, a large conference hall often deploys different wireless AP (Access Point) on each IEEE 802.11 channel to separate users’ connections. However, since the connection mechanism of IEEE 802.11 is client driven, the AP connection is selected by the user and the selection is according to the received signal strength (RSSI) from different APs. This conventional approach may result in most of the user devices connect to relatively limited number of APs, and the resource of the rest of the APs left unused. This paper proposes a smart AP architecture which is able to manage load balance for IEEE 802.11 Wireless LAN using Bluetooth Low Energy (BLE) GATT (Generic Attribute Profile) protocol in order to appropriately assign AP to different user devices. The core AP assignment algorithm is based on Markov chain stationary distribution. Simulation results show that the proposed BM-MS (BLE Management with Markov-Chains Stationary Load Balance) method outperforms RSSI based method in terms of system throughput and average user data rate.

M. Tech. Electrical Engineering. / Presents an IPv6-based mobility support scheme for vehicular scenarios. The focus of this study is on modelling of an efficient network layer handover scheme suitable for vehicular network environments. In order to achieve this, a Vehicular Fast handovers for Mobile IPv6 (VFMIPv6) network layer protocol has been proposed.

Le transport multicast est une solution efficace pour envoyer le même contenu à plusieurs récepteurs en même temps. Ce mode est principalement utilisé pour fournir des flux multimédia en temps réel. Cependant, le multicast classique de l'IEEE 802.11 n'utilise aucun mécanisme d'acquittement. Ainsi, l'échec de réception implique la perte définitive du paquet. Cela limite la fiabilité du transport multicast et impact la qualité des applications vidéo. Pour résoudre ce problème, 802.11v et 802.11aa sont définis récemment. Le premier amendement propose Direct Multicast Service (DMS). D'autre part, le 802.11aa introduit GroupCast with Retries (GCR). GCR définit deux nouvelles politiques de retransmission : Block Ack (BACK) et Unsolicited Retry (UR).Dans cette thèse, nous évaluons et comparons les performances de 802.11v/aa. Nos résultats montrent que tous les nouveaux protocoles multicast génèrent un overhead de transmission important. En outre, DMS a une scalabilité très limitée, et GCR-BACK n'est pas approprié pour des grands groupes multicast. D'autre part, nous montrons que DMS et GCR-BACK génèrent des latences de transmission importantes lorsque le nombre de récepteurs augmente. Par ailleurs, nous étudions les facteurs de pertes dans les réseaux sans fil. Nous montrons que l'indisponibilité du récepteur peut être la cause principale des pertes importantes et de leur nature en rafales. En particulier, nos résultats montrent que la surcharge du processeur peut provoquer un taux de perte de 100%, et que le pourcentage de livraison peut être limité à 35% lorsque la carte 802.11 est en mode d'économie d'énergie.Pour éviter les collisions et améliorer la fiabilité du transport multicast, nous définissons le mécanisme Busy Symbol (BS). Nos résultats montrent que BS évite les collisions et assure un taux de succès de transmission très important. Afin d'améliorer davantage la fiabilité du trafic multicast, nous définissons un nouveau protocole multicast, appelé Block Negative Acknowledgement (BNAK). Ce protocole opère comme suit. L'AP envoi un bloc de paquets suivi par un Block NAK Request (BNR). Le BNR permet aux membres de détecter les données manquantes et d'envoyer une demande de retransmission, c.à.d. un Block NAK Response (BNAK). Un BNAK est transmis en utilisant la procédure classique d'accès au canal afin d'éviter toute collision avec d'autres paquets. En plus, cette demande est acquittée. Sous l'hypothèse que 1) le récepteur est situé dans la zone de couverture du débit de transmission utilisé, 2) les collisions sont évitées et 3) le terminal a la bonne configuration, très peu de demandes de retransmission sont envoyées, et la bande passante est préservée. Nos résultats montrent que BNAK a une très grande scalabilité et génère des délais très limités. En outre, nous définissons un algorithme d'adaptation de débit pour BNAK. Nous montrons que le bon débit de transmission est sélectionné moyennant un overhead très réduit de moins de 1%. En plus, la conception de notre protocole supporte la diffusion scalable de lavvidéo. Cette caractéristique vise à résoudre la problématique de la fluctuation de la bande passante, et à prendre en considération l'hétérogénéité des récepteurs dans un réseau sans fil.

Most mobile nodes are operated using batteries, protocols which conserve energy are of interest. The Dynamic Directional Power Control Protocol (DDPC) is a protocol that dynamically varies the energy used in directional transmission to increase the battery life of the transmitter without sacrificing connectivity with the receiver. The advantage of DDPC is that it takes into account the remaining battery power of a node before changing its transmission power. DDPC can achieve a higher network lifetime when compared to a network where nodes use a fixed transmit power level. Meanwhile DDPC dynamically reduces the energy consumed by a node in transmission. It can also reach nodes far from the transmitter by using directional antennas.

This research investigates the denial of service problem, in the context of services provided over a network, and contributes to improved techniques for modelling, detecting, and preventing denial of service attacks against these services. While the majority of currently employed denial of service attacks aim to pre-emptively consume the network bandwidth of victims, a significant amount of research effort is already being directed at this problem. This research is instead concerned with addressing the inevitable migration of denial of service attacks up the protocol stack to the application layer. Of particular interest is the denial of service resistance of key establishment protocols (security protocols that enable an initiator and responder to mutually authenticate and establish cryptographic keys for establishing a secure communications channel), which owing to the computationally intensive activities they perform, are particularly vulnerable to attack. Given the preponderance of wireless networking technologies this research hasalso investigated denial of service and its detection in IEEE 802.11 standards based networks. Specific outcomes of this research include: - investigation of the modelling and application of techniques to improve the denial of service resistance of key establishment protocols; - a proposal for enhancements to an existing modelling framework to accommodate coordinated attackers; - design of a new denial of service resistant key establishment protocol for securing signalling messages in next generation, mobile IPv6 networks; - a comprehensive survey of denial of service attacks in IEEE 802.11 wireless networks; discovery of a significant denial of service vulnerability in the clear channel assessment procedure implemented by the medium access control layer of IEEE 802.11 compliant devices; and - design of a novel, specification-based intrusion detection system for detecting denial of service attacks in IEEE 802.11 wireless networks.

Este trabalho apresenta uma análise completa da qualidade de voz esperada em serviços de VoIP quando prestados sobre a plataforma WLAN IEEE 802.11g. Diferentemente da maior parte da literatura, este estudo complementa as informações de atraso, variação do atraso e taxa de perda dos pacotes, com um modelo analítico de avaliação de qualidade de voz proposto pela ITU-T, o Modelo E. Desta forma, todos os fatores modelados como perceptíveis pelos usuários do serviço telefônico são considerados simultaneamente, gerando, por fim, resultados correspondentes à escala de avaliação subjetiva da qualidade de voz MOS, que qualifica a opinião média em: “muito satisfeitos”, “satisfeitos”, “alguns insatisfeitos”, “muitos insatisfeitos”, “quase todos insatisfeitos” e “não recomendado”. O código do simulador NS-2 foi expandido para prover todas as funcionalidades requeridas neste trabalho. Com ele, diferentes cenários de aplicação foram simulados utilizando três dos codificadores de voz mais utilizados atualmente, o G.723.1, o G.729a e o G.711 (com e sem PLC). A funcionalidade centralizada da camada MAC IEEE 802.11, o PCF, também foi estudada, tendo os parâmetros referentes ao período entre repetições do CFP e à máxima duração do mesmo analisados e ajustados de modo a prover o melhor desempenho. Experimentos similares foram realizados para a função DCF, permitindo então uma comparação direta entre os dois modos de operação do nível MAC. Além disso, ensaios considerando outros tráfegos menos prioritários (estações de dados) foram realizados com o intuito de caracterizar a capacidade dos sistemas em diferenciar ambos os tráfegos. / This work is intended to provide a complete evaluation of the voice quality obtained in IEEE 802.11g WLAN environments. In contrast to the major literature, this dissertation complements the traditional network metrics, as delay, jitter and loss rate, with an analytical model for voice quality evaluation created by ITU-T, named E Model. With this model, all factors able of affecting the user’s perception of quality in a telephony service are simultaneously considered to reflect the subjective voice quality scale MOS, which rates the mean opinion as follow: “very satisfied”, “satisfied”, “some user satisfied”, “many users dissatisfied”, “nearly all user dissatisfied” and, “not recommended”. An extension to the NS-2 simulator source code has been developed to provide all the features required by this study. With this ‘customized simulator’, several scenarios have been analyzed considering three of the most important vocoders in the market today, G.723.1, G.729a, and G.711 (with and without PLC). Moreover, the centralized scheme for the IEEE 802.11 MAC, called PCF, has been studied to show the effect of the CFP repetition interval and the CFP maximum duration on its upper bound limit of simultaneous voice calls. Similar experiments have been carried out for the DCF MAC functionality, allowing these medium access modes to have their performance directly compared against each other. Finally, scenarios with low priority traffic (data traffic) have been created to help describing the ability of both MAC functions to deal with traffic differentiation.

Este trabalho apresenta uma análise completa da qualidade de voz esperada em serviços de VoIP quando prestados sobre a plataforma WLAN IEEE 802.11g. Diferentemente da maior parte da literatura, este estudo complementa as informações de atraso, variação do atraso e taxa de perda dos pacotes, com um modelo analítico de avaliação de qualidade de voz proposto pela ITU-T, o Modelo E. Desta forma, todos os fatores modelados como perceptíveis pelos usuários do serviço telefônico são considerados simultaneamente, gerando, por fim, resultados correspondentes à escala de avaliação subjetiva da qualidade de voz MOS, que qualifica a opinião média em: “muito satisfeitos”, “satisfeitos”, “alguns insatisfeitos”, “muitos insatisfeitos”, “quase todos insatisfeitos” e “não recomendado”. O código do simulador NS-2 foi expandido para prover todas as funcionalidades requeridas neste trabalho. Com ele, diferentes cenários de aplicação foram simulados utilizando três dos codificadores de voz mais utilizados atualmente, o G.723.1, o G.729a e o G.711 (com e sem PLC). A funcionalidade centralizada da camada MAC IEEE 802.11, o PCF, também foi estudada, tendo os parâmetros referentes ao período entre repetições do CFP e à máxima duração do mesmo analisados e ajustados de modo a prover o melhor desempenho. Experimentos similares foram realizados para a função DCF, permitindo então uma comparação direta entre os dois modos de operação do nível MAC. Além disso, ensaios considerando outros tráfegos menos prioritários (estações de dados) foram realizados com o intuito de caracterizar a capacidade dos sistemas em diferenciar ambos os tráfegos. / This work is intended to provide a complete evaluation of the voice quality obtained in IEEE 802.11g WLAN environments. In contrast to the major literature, this dissertation complements the traditional network metrics, as delay, jitter and loss rate, with an analytical model for voice quality evaluation created by ITU-T, named E Model. With this model, all factors able of affecting the user’s perception of quality in a telephony service are simultaneously considered to reflect the subjective voice quality scale MOS, which rates the mean opinion as follow: “very satisfied”, “satisfied”, “some user satisfied”, “many users dissatisfied”, “nearly all user dissatisfied” and, “not recommended”. An extension to the NS-2 simulator source code has been developed to provide all the features required by this study. With this ‘customized simulator’, several scenarios have been analyzed considering three of the most important vocoders in the market today, G.723.1, G.729a, and G.711 (with and without PLC). Moreover, the centralized scheme for the IEEE 802.11 MAC, called PCF, has been studied to show the effect of the CFP repetition interval and the CFP maximum duration on its upper bound limit of simultaneous voice calls. Similar experiments have been carried out for the DCF MAC functionality, allowing these medium access modes to have their performance directly compared against each other. Finally, scenarios with low priority traffic (data traffic) have been created to help describing the ability of both MAC functions to deal with traffic differentiation.

Este trabalho apresenta uma análise completa da qualidade de voz esperada em serviços de VoIP quando prestados sobre a plataforma WLAN IEEE 802.11g. Diferentemente da maior parte da literatura, este estudo complementa as informações de atraso, variação do atraso e taxa de perda dos pacotes, com um modelo analítico de avaliação de qualidade de voz proposto pela ITU-T, o Modelo E. Desta forma, todos os fatores modelados como perceptíveis pelos usuários do serviço telefônico são considerados simultaneamente, gerando, por fim, resultados correspondentes à escala de avaliação subjetiva da qualidade de voz MOS, que qualifica a opinião média em: “muito satisfeitos”, “satisfeitos”, “alguns insatisfeitos”, “muitos insatisfeitos”, “quase todos insatisfeitos” e “não recomendado”. O código do simulador NS-2 foi expandido para prover todas as funcionalidades requeridas neste trabalho. Com ele, diferentes cenários de aplicação foram simulados utilizando três dos codificadores de voz mais utilizados atualmente, o G.723.1, o G.729a e o G.711 (com e sem PLC). A funcionalidade centralizada da camada MAC IEEE 802.11, o PCF, também foi estudada, tendo os parâmetros referentes ao período entre repetições do CFP e à máxima duração do mesmo analisados e ajustados de modo a prover o melhor desempenho. Experimentos similares foram realizados para a função DCF, permitindo então uma comparação direta entre os dois modos de operação do nível MAC. Além disso, ensaios considerando outros tráfegos menos prioritários (estações de dados) foram realizados com o intuito de caracterizar a capacidade dos sistemas em diferenciar ambos os tráfegos. / This work is intended to provide a complete evaluation of the voice quality obtained in IEEE 802.11g WLAN environments. In contrast to the major literature, this dissertation complements the traditional network metrics, as delay, jitter and loss rate, with an analytical model for voice quality evaluation created by ITU-T, named E Model. With this model, all factors able of affecting the user’s perception of quality in a telephony service are simultaneously considered to reflect the subjective voice quality scale MOS, which rates the mean opinion as follow: “very satisfied”, “satisfied”, “some user satisfied”, “many users dissatisfied”, “nearly all user dissatisfied” and, “not recommended”. An extension to the NS-2 simulator source code has been developed to provide all the features required by this study. With this ‘customized simulator’, several scenarios have been analyzed considering three of the most important vocoders in the market today, G.723.1, G.729a, and G.711 (with and without PLC). Moreover, the centralized scheme for the IEEE 802.11 MAC, called PCF, has been studied to show the effect of the CFP repetition interval and the CFP maximum duration on its upper bound limit of simultaneous voice calls. Similar experiments have been carried out for the DCF MAC functionality, allowing these medium access modes to have their performance directly compared against each other. Finally, scenarios with low priority traffic (data traffic) have been created to help describing the ability of both MAC functions to deal with traffic differentiation.