Control-theoretic approaches for efficient transmission on IEEE 802.11e wireless networks

With the increasing use of multimedia applications on the wireless network, the functionalities of the IEEE 802.11 WLAN was extended to allow traffic differentiation so that priority traffic gets quicker service time depending on their Quality of Service (QoS) requirements. The extended functionalities contained in the IEEE Medium Access Control (MAC) and Physical Layer (PHY) Specifications, i.e. the IEEE 802.11e specifications, are recommended values for channel access parameters along traffic lines and the channel access parameters are: the Minimum Contention Window CWmin, Maximum Contention Window CWmax, Arbitration inter-frame space number, (AIFSN) and the Transmission Opportunity (TXOP). These default Enhanced Distributed Channel Access (EDCA) contention values used by each traffic type in accessing the wireless medium are only recommended values which could be adjusted or changed based on the condition of number of associated nodes on the network. In particular, we focus on the Contention Window (CW) parameter and it has been shown that when the number of nodes on the network is small, a smaller value of CWmin should be used for channel access in order to avoid underutilization of channel time and when the number of associated nodes is large, a larger value of CWmin should be used in order to avoid large collisions and retransmissions on the network. Fortunately, allowance was made for these default values to be adjusted or changed but the challenge has been in designing an algorithm that constantly and automatically tunes the CWmin value so that the Access Point (AP) gives out the right CWmin value to be used on the WLAN and this value should be derived based on the level of activity experienced on the network or predefined QoS constraints while considering the dynamic nature of the WLAN. In this thesis, we propose the use of feedback based control and we design a controller for wireless medium access. The controller will give an output which will be the EDCA CWmin value to be used by contending stations/nodes in accessing the medium and this value will be based on current WLAN conditions. We propose the use of feedback control due to its established mathematical concepts particularly for single-input-single-output systems and multi-variable systems which are scenarios that apply to the WLAN

Timing Architecture for ESS

Programa Oficial de Doutoramento en Investigación en Tecnoloxías da Información. 5023V01[Resumo] O sistema de temporización é unha compoñente fundamental para o control e sincronización de instalacións industriais e científicas, coma aceleradores de partículas. Nesta tese traballamos na especificación e desenvolvemento do sistema de temporización para a European Spallation Source (ESS), a maior fonte de neutróns actualmente en construción. Abordamos este tra­ ballo a dous niveis: a especificación do sistema de temporización, e a imple­ mentación física de sistemas de control empregando circuítos reconfigurables. Con respecto á especificación do sistema de temporización, deseñamos e implementamos a configuración do protocolo de temporización para cumprir cos requirimentos do ESS e ideamos un modo de operación e unha aplicación para a configuración e control do sistema de temporización. Tamén presentamos unha ferramenta e unha metodoloxía para imple­ mentar sistemas de control empregando FPGAs, coma os nodos do sistema de temporización. ámbalas <lúas están baseadas en statecharts, unha repre­ sentación gráfica de sistemas que expande o concepto de máquinas de estados finitos, orientada a sistemas que necesitan ser reconfigurados rápidamente en múltiples localizacións minimizando a posibilidade de erros. A ferramenta crea automaticamente código VHDL sintetizable a partir do statechart do sistema. A metodoloxía explica o procedemento para implementar o state­ chart como unha arquitectura microprogramada en FPGAs.[Resumen] El sistema de temporización es un componente fundamental para el control y sincronización de instalaciones industriales y científicas, como aceleradores e partículas. En esta tesis trabajamos en la especificación y desarrollo el sistema de temporización para la European Spallation Source (ESS), la mayor fuente de neutrones actualmente en construcción. Abordamos este trabajo en dos niveles: la especificación del sistema de temporización, y la mplementación física de sistemas de control empleando circuitos reconfig­ rables. Con respecto a la especificación del sistema de temporización, diseñamos e implementamos la configuración del protocolo de temporización para cumplir on los requisitos de ESS e ideamos un modo de operación y una aplicación ara la configuración y control del sistema de temporización. También presentamos una herramienta y una metodología para imple­ entar sistemas de control empleando FPGAs, como los nodos del sistema e temporización. Ambas están basadas en statecharts) una representación gráfica de sistemas que expande el concepto de máquinas de estados fini­ os, orientada a sistemas que necesitan ser reconfigurados rápidamente en últiples localizaciones minimizando la posibilidad de errores. La her­ramienta crea automáticamente código VHDL sintetizable a partir del state­chart del sistema. La metodología explica el procedimiento para implemen­tar el statechart como una arquitectura microprogramada en FPGAs.[Abstract] The timing system is a key component for the control and synchronization of industrial and scientific facilities, such as particle accelerators. In this thesis we tackle the specification and development of the timing system for the European Spallation Source (ESS), the largest neutron source currently in construction. We approach this work at two levels: the specification of the timing system and the physical implementation of control systems using reconfigurable hardware. Regarding the specification of the timing system, we designed and imple­ mented the configuration of the timing protocol to fulfil the requirements of ESS and devised an operation mode andan application for the configuration and control of the timing system. We also present one too! and one methodology to implement control systems using FPGAs, such as the nodes of the timing system. Both are based on statecharts, a graphical representation of systems that expand the concepts of Finite State Machines, targeted at systems that need to be re­ configured quickly in multiple locations minimizing the chance of errors. The too! automatically creates synthesizable VHDL code from a statechart of the system. The methodology explains the procedure to implement the statechart as a microprogrammed architecture in FPGAs

Wings in Orbit: Scientific and Engineering Legacies of the Space Shuttle, 1971-2010

The Space Shuttle is an engineering marvel perhaps only exceeded by the station itself. The shuttle was based on the technology of the 1960s and early 1970s. It had to overcome significant challenges to make it reusable. Perhaps the greatest challenges were the main engines and the Thermal Protection System. The program has seen terrible tragedy in its 3 decades of operation, yet it has also seen marvelous success. One of the most notable successes is the Hubble Space Telescope, a program that would have been a failure without the shuttle's capability to rendezvous, capture, repair, as well as upgrade. Now Hubble is a shining example of success admired by people around the world. As the program comes to a close, it is important to capture the legacy of the shuttle for future generations. That is what "Wings In Orbit" does for space fans, students, engineers, and scientists. This book, written by the men and women who made the program possible, will serve as an excellent reference for building future space vehicles. We are proud to have played a small part in making it happen. Our journey to document the scientific and engineering accomplishments of this magnificent winged vehicle began with an audacious proposal: to capture the passion of those who devoted their energies to its success while answering the question "What are the most significant accomplishments?" of the longestoperating human spaceflight program in our nation s history. This is intended to be an honest, accurate, and easily understandable account of the research and innovation accomplished during the era

High-throughput sperm cryopreservation of aquatic species

The goal of this dissertation was to integrate multiple disciplines for application of high-throughput sperm cryopreservation to aquatic species. The blue catfish Ictalurus furcatus was selected for research due to its role in production of hybrid catfish with eggs from channel catfish Ictalurus punctatus. A high-throughput cryopreservation pathway was developed by systematically evaluating each process factor and using automated processing systems. Large quantities of cryopreserved sperm produced from this protocol were evaluated in commercial-scale hatcheries in cooperation with aquaculture producers. To develop production for commercial requirements, quality characteristics of materials and products were identified and recorded during processing and analyzed using industrial engineering methods to regulate quality. More than 1 million channel catfish eggs from 300 females were fertilized with thawed sperm, which was larger than any previous large-scale fertilization trial performed in fish. This demonstrated that the fertilization capability of cryopreserved sperm was equivalent to fresh sperm in production of hybrid fry. Quality regulation was presented within a quality assurance plan designed specifically for this process using quality standards (specifications) and quality variation data (quality control). This quality assurance plan is potentially the first of its kind for cryopreserved sperm of any species. After being scaled up by automation and standardized by the quality assurance plan, the cryopreservation process produced reliable products for hatcheries. Proper use of these products (i.e., as a dose of 3704 eggs/straw) can provide a basis for industry standards for artificial spawning. A quantitative evaluation was developed based on the defined dose and the production efficiency. To increase the efficiency for large-scale production, simulation model computing was used to create a virtual process. The simulation model was validated based on the existing process, and provides a valuable tool for future improvements. This dissertation took the initiative to apply high-throughput cryopreservation in aquaculture and expand the process from planning to operation at the production line, to terminal use of products by customers. This enables cryopreserved sperm to become a practical form of genetic resources applicable for aquatic genetic improvement and conservation

Shuttle Ground Operations Efficiencies/Technologies (SGOE/T) study. Volume 2: Ground Operations evaluation

The Ground Operations Evaluation describes the breath and depth of the various study elements selected as a result of an operational analysis conducted during the early part of the study. Analysis techniques used for the evaluation are described in detail. Elements selected for further evaluation are identified; the results of the analysis documented; and a follow-on course of action recommended. The background and rationale for developing recommendations for the current Shuttle or for future programs is presented