Gotowa bibliografia na temat „Medium access controls (MAC) protocols”

This thesis proposes and studies a Medium Access Control (MAC) protocol for networks of tags deployed over an industrial machine using THz communications. Despite the great advantages of these frequencies, there are drawbacks that cannot be ignored, such as propagation delays that, even at small distances, are of the same order of magnitude as packet transmission times. For this reason, the mathematical models developed for Contention-Free and Contention-Based protocols take into account the propagation delay. The main focus of this thesis is on the CSMA/CA protocol, which introduces channel sensing to reduce collisions and increase performance. The performance of the protocol are compared with two benchmarks, based on Polling and Aloha, considering an industrial machine scenario and accounting for physical and MAC layers features.

In order to address the explosive demand for high-capacity and omnipresent wireless access, modern cell-based wireless networks are slowly adopting two major solution roadmaps. The first is the employment of small-cell formations in order to increase the overall spectral efficiency, whereas the second is the employment of higher frequency bands, such as the mm-wave 60GHz band, that offers vast amounts of bandwidth. Depending on the specific application, the above solutions inevitably require the installation and operational management of large amounts of Base Stations (BSs) or Access Points (APs), which ultimately diminishes the overall cost-effectiveness of the architecture. In order to reduce the system cost, Radio over Fiber (RoF) technology has been put forward as an ideal candidate solution, due to the fact that it provides functionally simple antenna units, often termed as Remote Antenna Units (RAUs) that are interconnected to a central managing entity, termed as the Central Office (CO), via an optical fiber. Although extensive research efforts have been dedicated to the development of the physical layer aspects regarding RoF technologies, such as CO/RAU physical layer design and radio signal transport techniques over fiber, very limited efforts have con-centrated on upper layer and resource management issues. In this dissertation, we are concerned with access control and resource management of RoF-based mm-wave network architectures targeting the exploitation of the dual medium and its centralized control properties in order to perform optimal optical/wireless/time resource allocation. In this dissertation, we propose a Medium-Transparent MAC (MT-MAC) protocol that concurrently administers the optical and wireless resources of a 60GHz RoF based network, seamlessly connecting the CO to the wireless terminals through minimal RAU intervention. In this way, the MT-MAC protocol forms extended reach 60GHz WLAN networks offering connectivity amongst wireless devices that are attached to the same or different RAUs under both Line of Sight (LOS) and non LOS conditions. The notion of medium-transparency relies on two parallel contention periods, the first in the optical domain and the second in the wireless frequency and time domains, with nested dataframe structures. The MT-MAC operation is based on a proposed RAU design that allows for wavelength selectivity functions, thus being compatible with completely passive optical distribution network implementations that are predominately used by telecom operators today. Two variants of the MT-MAC protocol are considered. The first offers dynamic wavelength allocation with fixed time windows, whereas the second targets fairness-sensitive applications by offering dynamic wavelength allocation with dynamic transmission opportunity window sizes, based on the number of active clients connected at each RAU. Both variants of the protocol are evaluated by both simulation and analytical means. For the latter part, this thesis introduces two analytical models for calculating saturation throughput and non-saturation packet delay for the converged MT-MAC protocol. Finally, this thesis presents an extensive study regarding the network planning and formation of 60GHz Gigabit WLAN networks when the latter are deployed over existing Passive Optical Network (PON) infrastructures. Three possible architectures where studied: i) the RoF approach, ii) the Radio & Fiber approach and iii) the hybrid RoF-plus-R&F approach that combines the properties of both the aforementioned architectures. During the elaboration of this thesis, one major key conclusion has been extracted. The work proposed in this thesis considers that there is a fundamental requirement for implementing new converged optical/wireless MAC protocols, that have the complete overview of both available resources in order to effectively administer the hybrid Radio-over-Fiber networks.<br>A fin de atender la demanda explosiva de alta capacidad y acceso inalámbrico omnipresente, las redes inalámbricas basadas en celdas están poco a poco adoptando dos principales guías de solución. La primera es el empleo de formaciones de celdas pequeñas con el fin de aumentar la eficiencia espectral global, mientras que la segunda es el empleo de bandas de frecuencia superior, como la banda de 60GHz, la cual ofrece una gran cantidad de ancho de banda. Dependiendo de la aplicación en específico, las soluciones anteriores inevitable-mente requieren de una instalación y una gestión operativa de grandes cantidades de Estaciones Base o Puntos de Acceso, que en última instancia disminuye la rentabilidad de la arquitectura. Para reducir el coste, la tecnología radioeléctrica por fibra (RoF) se presenta como una solución ideal debido al hecho de que proporciona unidades de antenas de sim-ple funcionamiento, a menudo denominadas Unidades de Antenas Remotas (RAUs), las cuales están interconectadas a una entidad central de gestión, denominada Oficina Central (CO), a través de la fibra óptica. A pesar de que se han dedicado muchos esfuerzos de investigación al desarrollo de varios aspectos de las capas física con respecto a las tecnologías RoF, muy pocos esfuerzos se han concentrado en la capa superior y cuestiones de gestión de recursos. En esta tesis, nos enfocando en el control de acceso y gestión de recursos de arquitecturas RoF y comunicaciones milimétricas, con el fin de aprovechar y explotar el medio dual y las propiedades para realizar una óptima asignación de los recursos ópticos, inalámbricos y temporales. Nosotros proponemos un protocolo Transparente al Medio MAC (MT-MAC) que simultáneamente administre los recursos ópticos e inalámbricos de una red RoF a 60GHz, conectando a la perfección el CO a los terminales inalámbricos a través de una mínima intervención RAU. El protocolo MT-MAC forma unas redes WLAN 60GHz de alcance extendido, ofreciendo así conectividad entre los dispositivos inalámbricos que están conectados al mismo o diferentes RAUs bajo con o sin Línea de Vista (condiciones LOS o NLOS) respectivamente. La noción de transparencia al medio se basa en dos períodos de contención para-lelos, el primero en el dominio óptico y el segundo en la frecuencia inalámbrica y dominio del tiempo, con estructuras de datos anidados. La operación MT-MAC se basa en proponer un diseño RAU que permita la selectividad de funciones de longitud de onda. Dos variantes del protocolo MT- MAC son considerados; el primer ofrece asignación de longitud de onda dinámica con ventanas de tiempo fijo, mientras que la segunda tiene como objetivo entornos de aplicaciones sensibles ofreciendo asignación de longitud de onda con tamaño de ventana de oportunidad de transmisión dinámico, basado en el número de clientes conectados en cada RAU. Ambas variantes del protocolo están evaluadas tanto por medios analíticos como de simulación. En la segunda parte, esta tesis introduce dos modelos analíticos para calcular el rendimiento de saturación y no saturación del retardo de paquetes para el protocolo MT-MAC convergente. Finalmente, esta tesis presenta un extenso estudio de la planificación de red y la formación de redes 60GHz Gigabit WLAN cuando esta se encuentra desplegada sobre las ya existente infraestructuras de Redes Ópticas Pasivas (PONs). Tres posibles arquitecturas han sido estudiadas: i) el enfoque RoF, ii) el enfoque Radio y Fibra , y iii) el enfoque híbrido, RoF más R&F el cual combina las propiedades de ambas arquitecturas anteriormente mencionadas. Durante la elaboración de esta tesis, se ha extraído una importante conclusión: hay un requerimiento fundamental para implementar nuevos protocolos ópticos/inalámbricos convergentes, que tengan una completa visión de ambos recursos disponibles para poder administrar efectivamente las redes de tecnología RoF.

<p>Wireless sensor networks offer easy implementation, flexibility and mobility of hand held </p><p>devices. Sensors consist of an internal power source, which is the great limitation for </p><p>the life time and the usage of sensor networks. To increase the life time, sensors should </p><p>stay in energy saving sleep mode as long as possible, because in sleep mode the radio is </p><p>either shut down or working with less energy. Better energy handling is implemented in </p><p>different power saving mechanism of common Medium Access Control protocols, which are </p><p>evaluated and analyzed and further extensions and ideas to improve the energy efficiency </p><p>are presented. Slotted PSM is simulated with the NS2 and compared to the WLAN 802.11 </p><p>PSM technology and the results show that energy efficiency and power consumption are </p><p>much better implemented and life time increases with the use of Slotted PSM.</p>

In recent years, the development of a large variety of mobile computing devices has led to wide scale deployment and use of wireless ad hoc and sensor networks. Wireless Sensor Networks consist of battery powered, tiny and cheap "motes", having sensing and wireless communication capabilities. Although wireless motes have limited battery power, communication and computation capabilities, the range of their application is vast. In the first part of the dissertation, we have addressed the specific application of Biomedical Sensor Networks. To solve the problem of data routing in these networks, we have proposed the Adaptive Least Temperature Routing (ALTR) algorithm that reduces the average temperature rise of the nodes in the in-vivo network while routing data efficiently. For delay sensitive biomedical applications, we proposed the Hotspot Preventing Routing (HPR) algorithm which avoids the formation of hotspots (regions having very high temperature) in the network. HPR forwards the packets using the shortest path, bypassing the regions of high temperature and thus significantly reduces the average packet delivery delay, making it suitable for real-time applications of in-vivo networks. We also proposed another routing algorithm suitable for being used in a network of id-less biomedical sensor nodes, namely Routing Algorithm for networks of homogeneous and Id-less biomedical sensor Nodes (RAIN). Finally we developed Biocomm, a cross-layer MAC and Routing protocol co-design for Biomedical Sensor Networks, which optimizes the overall performance of an in-vivo network through cross-layer interactions. We performed extensive simulations to show that the proposed Biocomm protocol performs much better than the other existing MAC and Routing protocols in terms of preventing the formation of hotspots, reducing energy consumption of nodes and preventing network congestion when used in an in-vivo network. In the second part of the dissertation, we have addressed the problems of habitat-monitoring sensor networks, broadcast algorithms for sensor networks and the congestion problem in sensor networks as well as one non-sensor network application, namely, on-chip communication networks. Specifically, we have proposed a variation of HPR algorithm, called Hotspot Preventing Adaptive Routing (HPAR) algorithm, for efficient data routing in Networks On-Chip catering to their specific hotspot prevention issues. A protocol similar to ALTR has been shown to perform well in a sensor network deployed for habitat monitoring. We developed a reliable, low overhead broadcast algorithm for sensor networks namely Topology Adaptive Gossip (TAG) algorithm. To reduce the congestion problem in Wireless Sensor Networks, we proposed a tunable cross-layer Congestion Reducing Medium Access Control (CRMAC) protocol that utilizes buffer status information from the Network layer to give prioritized medium access to congested nodes in the MAC layer and thus preventing congestion and packet drops. CRMAC can also be easily tuned to satisfy different application-specific performance requirements. With the help of extensive simulation results we have shown how CRMAC can be adapted to perform well in different applications of Sensor Network like Emergency Situation that requires a high network throughput and low packet delivery latency or Long-term Monitoring application requiring energy conservation.<br>Ph.D.<br>School of Electrical Engineering and Computer Science<br>Engineering and Computer Science<br>Computer Science PhD

Packet broadcast networks are in widespread use in modern wireless communication systems. Medium access control is a key functionality within such technologies. A substantial research effort has been and continues to be invested into the study of existing protocols and the development of new and specialised ones. Academic researchers are restricted in their studies by an absence of suitable wireless MAC protocol development methods. This thesis describes an environment which allows rapid prototyping and evaluation of wireless medium access control protocols. The proposed design flow allows specification of the protocol using the specification and description language (SDL) formal description technique. A tool is presented to convert the SDL protocol description into a C++ model suitable for integration into both simulation and implementation environments. Simulations at various levels of abstraction are shown to be relevant at different stages of protocol design. Environments based on the Cinderella SDL simulator and the ns-2 network simulator have been developed which allow early functional verification, along with detailed and accurate performance analysis of protocols under development. A hardware platform is presented which allows implementation of protocols with flexibility in the hardware/software trade-off. Measurement facilities are integral to the hardware framework, and provide a means for accurate real-world feedback on protocol performance.

It is widely accepted that low energy consumption is the most important requirement when designing components and systems for a wireless sensor network (WSN). The greatest energy consumer of each node within a WSN is the radio transceiver and as such, it is important that this component be used in an extremely energy e±cient manner. One method of reducing the amount of energy consumed by the radio transceiver is to turn it off and allow nodes to enter a sleep mode. The algorithms that directly control the radio transceiver are traditionally grouped into the Medium Access Control (MAC) layer of a communication protocol stack. This thesis introduces the emerging field of wireless sensor networks and outlines the requirements of a MAC protocol for such a network. Current MAC protocols are reviewed in detail with a focus on how they utilize this energy saving sleep mode as well as performance problems that they suffer from. A proposed new method of coordinating the use of this sleep mode between nodes in the network is specifed and described. The proposed new protocol is analytically compared with existing protocols as well as with some fundamental performance limits. The thesis concludes with an analysis of the results as well as some recommendations for future work.

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.<br>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.

Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2005. Directed by John Copeland.<br>Copeland, John, Committee Chair ; Owen, Henry, Committee Member ; Sivakumar, Raghupathy, Committee Member ; Lanterman, Aaron, Committee Member ; Dos Santos, Andre, Committee Member. Includes bibliographical references.