<p>The usage of Wireless Local Area Networks is increasing rapidly throughout the world. The technology today is not quality proof for the market’s demands. We want to be able to completely wireless perform our demands, such as confer via video or IP-telephony. This is what we call multimedia real-time traffic. It may be achieved over the physical infrastructure in some areas with good results. The goal of this Master’s Thesis is to analyze the possibilities and give solutions and suggestions to achieve multimedia over the wireless networks, with emphasis on the protocol Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). </p><p>This Master’s Thesis is a theoretical study and the suggested solutions have not been tested in an actual wireless network. Instead they have been tested by computer simulation to give an indication of improvements. Basic configurations are set to the same as in the IEEE 802.11 standard. </p><p>Different methods to reach possible improvements of a WLAN are studied, analyzed and simulated. Such methods are: priority, congestion management and multi-channel protocol. Simulations results show how the priority affects the wireless network and how a multi-channel protocol improves the latency and efficiency of the network. The simulation part is concentrated to show improvements of real-time traffic, which is time sensitive. With a multi- channel protocol the network can allow more users, i.e. more traffic. Also, the network will gain improvement in stability.</p>

El objetivo de la tesis es crear una herramienta de evaluación de prestaciones de redes de área local a nivel MAC para los mecanismos de acceso múltiple aleatorio y con control mediante paso de testigo. La metodología de evaluación se basa en la obtención de modelos analíticos y de simulación y su contratación con resultados experimentales. En acceso aleatorio se aportan modelos analíticos de características caudal-retardo explicitas para los protocolos CSMA/CD en función del concepto de persistencia del acceso.Del mecanismo de paso de testigo se estudia la dependencia estadística introducida por el mecanismo de acceso para los casos de estación sin almacenamiento y almacenamiento infinito.

Los microcontroladores están inmersos en nuestra forma de vida. Los encontramos en automóviles, lavarropas, celulares, reproductores MP3, agendas y en un sinfín de sitios en nuestra vida cotidiana. La capacidad de integración a muy alta escala (VLSI) -con crecimiento casi exponencial en los últimos años-, hace que estos dispositivos cada día contengan más y más funciones que antes eran impensadas. Debido a ello, una agrupación de estos dispositivos conectados en red, configura un sistema de control muy poderoso, que dotado de algún protocolo normalizado que permita su interconexión a Internet, le da un alcance prácticamente ilimitado y de gran escalabilidad. Por lo expuesto, en esta tesis se estudiará la implementación de una red de microcontroladores, definiendo funciones de Control y adquisición de datos, equivalentes a los sistemas de Control y Adquisición de Datos (SCADA) de gran escala. Sobre la definición efectuada, surgirá un protocolo de aplicación que permitirá así un desarrollo Top-Down del sistema. Sobre la base de la definición lograda, este primer capítulo describe en un modo general los alcances de la tesis, donde se estudiarán entre otros aspectos, los protocolos de capas de comunicaciones para llegar a dos de las implementaciones más populares utilizadas en los ambientes industriales: RS485 y Ethernet. Si bien la primera es mucho más antigua, sigue aún vigente y se ha potenciado a partir de la creación de interfaces compatibles, citando como ejemplo la inmunidad a ruido eléctrico que le provee una interfase transparente sobre fibra óptica. La segunda, más moderna, ya fija una tendencia debido a su ubicuidad y amplitud de prestaciones.

The dissertation thesis is focused on analysis, modeling and optimization of the medium access layer of power line communication. In the first part of the paper, the thesis briefly summarizes a basic information of power line communication. In the next sections, the objectives of the dissertation are placed. A simplification of current models of HomePlug and a optimalization of distribution function in back off procedure are one of the main goals of this work. A detailed analysis of HomePlug technology, which is widespread used in the broadband transmission, follows. The work is focused on analyzing of the MAC layer in this part. The discrete simulation models have been implemented in Matlab. The approximation discrete numerical model has been used for analysis of various distribution functions for HomePlug to optimalize backoff algorithm. The new optimalizations are suitable for large networks. The new approach of MAC modelling is introduced in last part of this work. The new model is not exact as Markov models but it is faster and easier for implementation. The analytical model desribes a system using probabilistic functions.

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No / Supported by the IEEE 802.15.4 standard, embedded sensor networks have become popular and been widely deployed in recent years. The IEEE 802.15.4 medium access control (MAC) protocol is uniquely designed to meet the desirable requirements of the low end-to-end delay, low packet loss, and low power consumption in the low rate wireless personal areas networks (LR-WPANs). This paper develops an analytical model to quantify the key performance metrics of the MAC protocol in LR-WPANs with bursty ONOFF traffic. This study fills the gap in the literature by removing the assumptions of saturated traffic or nonbursty unsaturated traffic conditions, which are unable to capture the characteristics of bursty multimedia traffic in sensor networks. This analytical model can be used to derive the QoS performance metrics in terms of throughput and total delay. The accuracy of the model is verified through NS-2 (http://www.isi.edu/nsnam/ns/) simulation experiments. This model is adopted to investigate the performance of the MAC protocol in LR-WPANs under various traffic patterns, different loads, and various numbers of stations. Numerical results show that the traffic patterns and traffic burstiness have a significant impact on the delay performance of LR-WPANs.

The idea of wireless distributed computing (WDC) is rapidly gaining recognition owing to its promising potential in military, public safety and commercial applications. This concept basically entails distributing a computationally intensive task that one radio device is assigned, among its neighboring peer radio devices. The added processing power of multiple radios can be harnessed to significantly reduce the time consumed in obtaining the results of the original complex task. Since the idea of wireless distributed computing depends on a radio device forming a network with its peers, it is imperative and necessary to have a medium access control (MAC) protocol for such networks which is capable of scheduling channel access by multiple radios in the network, ensuring reliable data transfer, incorporating rate adaptation as well as handling link failures. The thesis presented here elaborates the design and implementation of such a MAC protocol for WDC employed in a practical network of radio devices configurable through software. It also brings to light the design and implementation constraints and challenges faced in this endeavor and puts forward viable solutions. / Master of Science

Ultra-Wideband has recently gained great interest for high-speed short-range communications (e.g. home networking applications) as well as low-speed long-range communications (e.g. sensor network applications). Two flavors of UWB have recently emerged as strong contenders for the technology. One is based on Impulse Radio techniques extended to direct sequence spread spectrum. The other technique is based on Orthogonal Frequency Division Multiplexing. Both schemes are analyzed in this thesis and modifications are proposed to increase the performance of each system. For both schemes, the issue of simultaneously operating users has been investigated. Current MAC design for UWB has relied heavily on existing MAC architectures in order to maintain backward compatibility. It remains to be seen if the existing MACs adequately support the UWB PHY (Physical) layer for the applications envisioned for UWB. Thus, in this work we propose a new MAC scheme for an Impulse Radio based UWB PHY, which is based on a CDMA approach using a code-broker in a piconet architecture. The performance of the proposed scheme is compared with the traditional CSMA scheme as well as the receiver-based code assignment scheme. A new scheme is proposed to increase the overall performance of the Multiband-OFDM system. Two schemes proposed to increase the performance of the system in the presence of simultaneously operating piconets (namely Half Pulse Repetition Frequency and Time spreading) are studied. The advantages/disadvantages of both of the schemes are discussed. / Master of Science