Dissertations / Theses on the topic 'Multi-rate'

COORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
Inicialmente apresenta-se a estrutura de um sistema Multi- taxa, faz-se uma revisão teórica do mesmo, e descreve-se seu funcionamento. Posteriormente são apresentadas várias formas de implementar este sistema, como realizá-lo no domínio do tempo, parte no domínio do tempo e parte no domínio da freqüência e realizá-lo no domínio da freqüência. Nestas formas de implementação são considerados fatores como: emprego da técnica de overlap- save ou overlap-add para realização da convolução a ser implementada no sistema, e utilização de filtros do tipo IIR ou FIR para realizar o filtro de reconstrução. Nos sistemas implementados das diversas formas são analisados o atraso e a complexidade comparando-se os resultados teóricos obtidos. Nestas diferentes formas de implementação são mostrados sistemas com particularidades interessantes como: implementação da interpolação no domínio da freqüência e utilização de uma FFT inversa voltada para interpolação e decimação. Finalmente são apresentados resultados práticos dos sistemas realizados, sendo estes avaliados, comparados com os teóricos e comentados.
Firstly, a multi-rate system structure is presented, a theorical review is made and its behavior is described. Afterwards, many forms of its implementation are presented: in time domain, mixed time domain and frequency domain; and in the frequency domain only. In those implementation some factors are taken into account, such as the use of the overlap-save and overlap- add techniques for the convolution, and the utilization of IIR or FIR structures as reconstruction filters. In the system implemented, the delay and complexity are analised, by the comparing to the theorical results. Some interesting results are show, such as the implementation of the frequency domain interpolation and the use of an inverse FFT dedicated to decimation and interpolation. Finally, pratical results of the implemented system are presented. These are evaluated, compared to the theorical ones and commented upon.

[EN] This thesis deals with two characteristic problems in visual feedback robot control: 1) sensor latency; 2) providing suitable trajectories for the robot and for the measurement in the image. All the approaches presented in this work are analyzed and implemented on a 6 DOF industrial robot manipulator or/and a wheeled robot. Focusing on the sensor latency problem, this thesis proposes the use of dual-rate high order holds within the control loop of robots. In this sense, the main contributions are: - Dual-rate high order holds based on primitive functions for robot control (Chapter 3): analysis of the system performance with and without the use of this multi-rate technique from non-conventional control. In addition, as consequence of the use of dual-rate holds, this work obtains and validates multi-rate controllers, especially dual-rate PIDs. - Asynchronous dual-rate high order holds based on primitive functions with time delay compensation (Chapter 3): generalization of asynchronous dual-rate high order holds incorporating an input signal time delay compensation component, improving thus the inter-sampling estimations computed by the hold. It is provided an analysis of the properties of such dual-rate holds with time delay compensation, comparing them with estimations obtained by the equivalent dual-rate holds without this compensation, as well as their implementation and validation within the control loop of a 6 DOF industrial robot manipulator. - Multi-rate nonlinear high order holds (Chapter 4): generalization of the concept of dual-rate high order holds with nonlinear estimation models, which include information about the plant to be controlled, the controller(s) and sensor(s) used, obtained from machine learning techniques. Thus, in order to obtain such a nonlinear hold, it is described a methodology non dependent of the machine technique used, although validated using artificial neural networks. Finally, an analysis of the properties of these new holds is carried out, comparing them with their equivalents based on primitive functions, as well as their implementation and validation within the control loop of an industrial robot manipulator and a wheeled robot. With respect to the problem of providing suitable trajectories for the robot and for the measurement in the image, this thesis presents the novel reference features filtering control strategy and its generalization from a multi-rate point of view. The main contributions in this regard are: - Reference features filtering control strategy (Chapter 5): a new control strategy is proposed to enlarge significantly the solution task reachability of robot visual feedback control. The main idea is to use optimal trajectories proposed by a non-linear EKF predictor-smoother (ERTS), based on Rauch-Tung-Striebel (RTS) algorithm, as new feature references for an underlying visual feedback controller. In this work it is provided both the description of the implementation algorithm and its implementation and validation utilizing an industrial robot manipulator. - Dual-rate Reference features filtering control strategy (Chapter 5): a generalization of the reference features filtering approach from a multi-rate point of view, and a dual Kalman-smoother step based on the relation of the sensor and controller frequencies of the reference filtering control strategy is provided, reducing the computational cost of the former algorithm, as well as addressing the problem of the sensor latency. The implementation algorithms, as well as its analysis, are described.
[ES] La presente tesis propone soluciones para dos problemas característicos de los sistemas robóticos cuyo bucle de control se cierra únicamente empleando sensores de visión artificial: 1) la latencia del sensor; 2) la obtención de trayectorias factibles tanto para el robot así como para las medidas obtenidas en la imagen. Todos los métodos propuestos en este trabajo son analizados, validados e implementados utilizando brazo robot industrial de 6 grados de libertad y/o en un robot con ruedas. Atendiendo al problema de la latencia del sensor, esta tesis propone el uso de retenedores bi-frequencia de orden alto dentro de los lazos de control de robots. En este aspecto las principales contribuciones son: -Retenedores bi-frecuencia de orden alto basados en funciones primitivas dentro de lazos de control de robots (Capítulo 3): análisis del comportamiento del sistema con y sin el uso de esta técnica de control no convencional. Además, como consecuencia del empleo de los retenedores, obtención y validación de controladores multi-frequencia, concretamente de PIDs bi-frecuencia. -Retenedores bi-frecuencia asíncronos de orden alto basados en funciones primitivas con compensación de retardos (Capítulo 3): generalización de los retenedores bi-frecuencia asíncronos de orden alto incluyendo una componente de compensación del retardo en la señal de entrada, mejorando así las estimaciones inter-muestreo calculadas por el retenedor. Se proporciona un análisis de las propiedades de los retenedores con compensación del retardo, comparándolas con las obtenidas por sus predecesores sin compensación, así como su implementación y validación en un brazo robot de 6 grados de libertad. -Retenedores multi-frecuencia no lineales de orden alto (Capítulo 4): generalización del concepto de retenedor bi-frecuencia de orden alto con modelos de estimación no lineales, los cuales incluyen información tanto de la planta a controlar, como del controlador(es) y sensor(es) empleado(s), obtenida a partir de técnicas de aprendizaje. Así pues, para obtener dicho retenedor no lineal, se describe una metodología independiente de la herramienta de aprendizaje utilizada, aunque validada con el uso de redes neuronales artificiales. Finalmente se realiza un análisis de las propiedades de estos nuevos retenedores, comparándolos con sus predecesores basados en funciones primitivas, así como su implementación y validación en un brazo robot de 6 grados de libertad y en un robot móvil con ruedas. Por lo que respecta al problema de generación de trayectorias factibles para el robot y para la medida en la imagen, esta tesis propone la nueva estrategia de control basada en el filtrado de la referencia y su generalización desde el punto de vista multi-frecuencial. -Estrategia de control basada en el filtrado de la referencia (Capítulo 5): una nueva estrategia de control se propone para ampliar significativamente el espacio de soluciones de los sistemas robóticos realimentados con sensores de visión artificial. La principal idea es utilizar las trayectorias óptimas obtenidas por una trayectoria predicha por un filtro de Kalman seguido de un suavizado basado en el algoritmo Rauch-Tung-Striebel (RTS) como nuevas referencias para un controlador dado. En este trabajo se proporciona tanto la descripción del algoritmo como su implementación y validación empleando un brazo robótico industrial. -Estrategia de control bi-frecuencia basada en el filtrado de la referencia (Capítulo 5): generalización de la estrategia de control basada en filtrado de la referencia desde un punto de vista multi-frecuencial, con un filtro de Kalman multi-frecuencia y un Kalman-smoother dual basado en la relación existente entre las frecuencias del sensor y del controlador, reduciendo así el coste computacional del algoritmo y, al mismo tiempo, dando solución al problema de la latencia del sensor. La validación se realiza utilizando un barzo robot industria asi
[CAT] La present tesis proposa solucions per a dos problemes característics dels sistemes robòtics el els que el bucle de control es tanca únicament utilitzant sensors de visió artificial: 1) la latència del sensor; 2) l'obtenció de trajectòries factibles tant per al robot com per les mesures en la imatge. Tots els mètodes proposats en aquest treball son analitzats, validats e implementats utilitzant un braç robot industrial de 6 graus de llibertat i/o un robot amb rodes. Atenent al problema de la latència del sensor, esta tesis proposa l'ús de retenidors bi-freqüència d'ordre alt a dins del llaços de control de robots. Al respecte, les principals contribucions son: - Retenidors bi-freqüència d'ordre alt basats en funcions primitives a dintre dels llaços de control de robots (Capítol 3): anàlisis del comportament del sistema amb i sense l'ús d'aquesta tècnica de control no convencional. A més a més, com a conseqüència de l'ús dels retenidors, obtenció i validació de controladors multi-freqüència, concretament de PIDs bi-freqüència. - Retenidors bi-freqüència asíncrons d'ordre alt basats en funcions primitives amb compensació de retards (Capítol 3): generalització dels retenidors bi-freqüència asíncrons d'ordre alt inclouen una component de compensació del retràs en la senyal d'entrada al retenidor, millorant així les estimacions inter-mostreig calculades per el retenidor. Es proporciona un anàlisis de les propietats dels retenidors amb compensació del retràs, comparant-les amb les obtingudes per el seus predecessors sense la compensació, així com la seua implementació i validació en un braç robot industrial de 6 graus de llibertat. - Retenidors multi-freqüència no-lineals d'ordre alt (Capítol 4): generalització del concepte de retenidor bi-freqüència d'ordre alt amb models d'estimació no lineals, incloent informació tant de la planta a controlar, com del controlador(s) i sensor(s) utilitzat(s), obtenint-la a partir de tècniques d'aprenentatge. Així doncs, per obtindre el retenidor no lineal, es descriu una metodologia independent de la ferramenta d'aprenentatge utilitzada, però validada amb l'ús de rets neuronals artificials. Finalment es realitza un anàlisis de les propietats d'aquestos nous retenidors, comparant-los amb els seus predecessors basats amb funcions primitives, així com la seua implementació i validació amb un braç robot de 6 graus de llibertat i amb un robot mòbil de rodes. Per el que respecta al problema de generació de trajectòries factibles per al robot i per la mesura en la imatge, aquesta tesis proposa la nova estratègia de control basada amb el filtrat de la referència i la seua generalització des de el punt de vista multi-freqüència. - Estratègia de control basada amb el filtrat de la referència (Capítol 5): una nova estratègia de control es proposada per ampliar significativament l'espai de solucions dels sistemes robòtics realimentats amb sensors de visió artificial. La principal idea es la d'utilitzar les trajectòries optimes obtingudes per una trajectòria predita per un filtre de Kalman seguit d'un suavitzat basat en l'algoritme Rauch-Tung-Striebel (RTS) com noves referències per a un control donat. En aquest treball es proporciona tant la descripció del algoritme així com la seua implementació i validació utilitzant un braç robòtic industrial de 6 graus de llibertat. - Estratègia de control bi-freqüència basada en el filtrat (Capítol 5): generalització de l'estratègia de control basada am filtrat de la referència des de un punt de vista multi freqüència, amb un filtre de Kalman multi freqüència i un Kalman-Smoother dual basat amb la relació existent entre les freqüències del sensor i del controlador, reduint així el cost computacional de l'algoritme i, al mateix temps, donant solució al problema de la latència del sensor. L'algoritme d'implementació d'aquesta tècnica, així com la seua validaci
Solanes Galbis, JE. (2015). MULTI-RATE VISUAL FEEDBACK ROBOT CONTROL [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/57951
TESIS

The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiver’s feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics based rate adaptation solution uses an on-demand incremental strategy for selecting a rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the route discovery process. The 802.11 mandates the use of different transmission rates for broadcast and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as ‘reachable neighbours’ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority queue are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result these factors are not considered which result in severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end delay and throughput.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada
Typical telemetry transmitter designs have focused on analog-circuit implementations, which suffer limitations when required to support multi-mode and multi-rate capabilities. In this paper, we introduce a transmitter design (and associated techniques) that employ an all-digital baseband line-up that utilizes only one single-rate clock. Thus, keeping the analog hardware to a minimum and providing the maximum possible flexibility through digital programmability, in order to efficiently support multi-mode (i.e., various modulation schemes) and multi-rate (i.e., various bit-rates) capabilities. The telemetry standard is defined in the IRIG 106-04 specification document published by the Range Commanders Council (RCC) government telemetry group [1]. The Telemetry standard supports several modulation schemes all of which fall under the general modulation family of continuous phase modulation (CPM). Out of such a family of modulation schemes, the work presented in this paper focuses on two modulation schemes as examples, namely, SOQPSK and the PCM/FM. However, this does not limit the scope of the ideas and techniques proposed in this paper. We present various design techniques as well as implementation considerations. We also present actual measured results using a test-bed and a synthesizer IC that have been developed in our laboratories. Finally, we compare the measured results with simulations in order to validate the performance of our implemented design.

Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2003.
Includes bibliographical references (leaves 132-137). Also available in electronic version. Access restricted to campus users.

Doutoramento em Telecomunicações
Esta tese apresenta um estudo sobre alguns dos protocolos de cooperação MAC para redes sem fios utilizando o sistema IEEE 802.11 multi-débito. É proposto um novo modelo de arquitetura para a categorização e análise da cooperação em redes sem fios, tendo este modelo sido aplicado a protocolos cooperativos existentes para camada MAC. É investigado como as características do meio físico, assim como os requisitos de níveis superiores podem ser aplicados ao processo de cooperação, com vista a melhorar as características de funcionamento da rede de comunicações. Para este propósito são exploradas as métricas mais relevantes para o processo de cooperação. São igualmente estudados os limites impostos pelos protocolos da camada MAC e as limitações práticas impostas por protocolos da família de normas que compõem o IEEE 802.11. Neste trabalho foi criada uma métrica multicamada, que permite considerar os requisitos aplicacionais de performance e o tipo de tráfego, assim como a mobilidade dos dispositivos, no funcionamento dos mecanismos de cooperação. Como forma de validação, e para corretamente avaliar o impacto da métrica, um novo protocolo de cooperação foi desenvolvido e implementado. O seu funcionamento é descrito de forma analítica assim como validado através de a um ambiente de simulação. Os resultados obtidos mostram que a utilização de uma métrica multicamada é uma técnica robusta, fornecendo melhorias consistentes no contexto de redes IEEE 802.11. São igualmente demonstradas várias outras características de funcionamento com impacto para as comunicações. Estes dados fornecem uma visão real e encorajadora para a realização de mais pesquisas para a melhoria da performance dos protocolos cooperativos, assim como a sua utilização num variado número de aplicações futuras. No final do documento são apresentados alguns desafios para a continuação da investigação deste tópico.
This thesis presents a study on cooperative MAC protocols in Multi-rate IEEE 802.11 wireless networks. We proposed a novel architectural framework for cooperation algorithms in wireless network. This behavior model was considered for existing cooperative MAC protocols. A classification of these protocols was presented based on their cooperation objectives. We investigate how physical layer specifications and higher layer requirements can be applied in cooperation MAC protocols to enhance the overall network performance. For this purpose, we exploit the appropriate metrics which are consistent to the cooperation objectives. Performance bounds provided by MAC protocols and practical limitations posed by IEEE 802.11 standards have been also studied. A cross layer metric was achieved in cooperative MAC protocols to adapt cooperation performance to traffic service requirements and mobility scenario. In order to realize the impact of this metric, a new cooperative MAC protocol is designed and implemented. Analytical and simulation of this protocol was performed in different scenarios and environments. The obtained results have shown a robust technique in providing consistent cross layer optimization in context of IEEE 802.11 networks. A number of findings was experienced which are illustrated at the end. These observations would enhance and encourage potential research in the area and optimize the performance of cooperative protocols for a number of interesting applications in future. A summary of future research challenges is presented at the end.

Thesis (M.S. in Astronautical Engineering and Aeronautical and Astronautical Engineer) Naval Postgraduate School, June 2001.
Thesis advisor(s): Agrawal, Brij N. "June 2001." Includes bibliographical references (p. 109-110). Also available in print.

Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed December 13, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 85-88).

Packet switched wireless networks have become increasingly popular due to improvements in transmission speed, ease of deployment and mobility. Wireless technologies such as the IEEE 802.11 Wireless Local Area Networks provide transmission speeds capable of supporting multimedia applications. However, wireless channels suffer from short term effects such as interference and fading, and long term effects such as signal strength changes that are caused by user mobility. In multi-rate networks, stations can adapt to the channel variations by adjusting their physical transmission rates. This introduces resource management problems as resource usage depends on the application's bit rate as well as the physical transmission rate used. Multimedia applications demand consistent Quality of Service (QoS) performance from the network. This does not fit well with the dynamic nature of wireless networks. In this thesis, we propose a link layer resource manager to maintain application QoS requirements in multi-rate wireless networks. It consists of two components - Resource reservation and Medium Access Control (MAC) parameters selection. The resource reservation algorithm determines the current and future amount of channel resources required by a multimedia application and performs the function of admission control. This prevents any new traffic or physical transmission rate changes from degrading the QoS of the admitted traffic. The design of the MAC parameters selection algorithm is based on the IEEE 802.11e Enhanced Distributed Channel Access (EDCA) scheme. The algorithm enables the provision of QoS to individual multimedia applications with the prioritised service of EDCA. Analytical and simulation studies were performed to demonstrate the efficiency and effectiveness of the algorithms. The results highlighted the ability of the algorithms to mitigate the QoS provision problem in multi-rate wireless networks introduced by channel variations.

While the channel capacity of an isolated noise-limited wireless link is well-understood, the same is not true for the interference-limited wireless links that coexist in the same area and occupy the same frequency band(s). The performance of these wireless systems is coupled to each other due to the mutual interference. One such wireless scenario is modeled as a network of simultaneously communicating node pairs and is generally referred to as an interference channel (IC). The problem of characterizing the capacity of an IC is one of the most interesting and long-standing open problems in information theory. A popular way of characterizing the capacity of an IC is to maximize the achievable sum-rate by treating interference as Gaussian noise, which is considered optimal in low-interference scenarios. While the sum-rate of the single-band SISO IC is relatively well understood, it is not so when the users have multiple-bands and multiple-antennas for transmission. Therefore, the study of the optimal sum-rate of the multi-band MIMO IC is the main goal of this thesis. The sum-rate maximization problem for these ICs is formulated and is shown to be quite similar to the one already known for single-band MIMO ICs. This problem is reduced to the problem of finding the optimal fraction of power to be transmitted over each spatial channel in each frequency band. The underlying optimization problem, being non-linear and non-convex, is difficult to solve analytically or by employing local optimization techniques. Therefore, we develop a global optimization algorithm by extending the Reformulation and Linearization Technique (RLT) based Branch and Bound (BB) strategy to find the provably optimal solution to this problem. We further show that the spatial and spectral channels are surprisingly similar in a multi-band multi-antenna IC from a sum-rate maximization perspective. This result is especially interesting because of the dissimilarity in the way the spatial and frequency channels affect the perceived interference. As a part of this study, we also develop some rules-of-thumb regarding the optimal power allocation strategies in multi-band MIMO ICs in various interference regimes. Due to the recent popularity of Interference Alignment (IA) as a means of approaching capacity in an IC (in high-interference regime), we also compare the sum-rates achievable by our technique to the ones achievable by IA. The results indicate that the proposed power control technique performs better than IA in the low and intermediate interference regimes. Interestingly, the performance of the power control technique improves further relative to IA with an increase in the number of orthogonal spatial or frequency channels.
Master of Science

本研究で提案するマルチレート符号化法は、各ユーザが同じ通信路符号器を持つものの、符号器のパラメータ(Repeat Accumulate符号の繰り返し回数)と符号器に直列に連接する拡散列の長さを変化させることで、異なるレートの情報伝送を実現する、という方法である。通信路にガウス雑音が加算される場合、任意に低い誤り率の高信頼通信を可能にし、合計伝送レートを最大にする最適な通信路符号のパラメータと拡散長を理論解析で求める。
In this dissertation, the same encoder is employed for each user, and different rate transmissions is realized by adjusting the parameter of the encoder. We analyze the decoding performances of our coding schemes, and obtain the optimal coding parameters, which gives the maximum sum rates and approach the theoretical limits of the channel. The proposed coding schemes support multimedia services, and avoid employing multiple channel encoders to implement the multi-rate transmission.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University

L’objectif général de cette thèse est d’utiliser les connaissances en physique de la radiation, en programmation informatique et en équipement informatique à la haute pointe de la technologie pour améliorer les traitements du cancer. En particulier, l’élaboration d’un plan de traitement en radiothérapie peut être complexe et dépendant de l’utilisateur. Cette thèse a pour objectif de simplifier la planification de traitement actuelle en curiethérapie de la prostate à haut débit de dose (HDR). Ce projet a débuté à partir d’un algorithme de planification inverse largement utilisé, la planification de traitement inverse par recuit simulé (IPSA). Pour aboutir à un algorithme de planification inverse ultra-rapide et automatisé, trois algorithmes d’optimisation multicritères (MCO) ont été mis en oeuvre. Suite à la génération d’une banque de plans de traitement ayant divers compromis avec les algorithmes MCO, un plan de qualité a été automatiquement sélectionné. Dans la première étude, un algorithme MCO a été introduit pour explorer les frontières de Pareto en curiethérapie HDR. L’algorithme s’inspire de la fonctionnalité MCO intégrée au système Raystation (RaySearch Laboratories, Stockholm, Suède). Pour chaque cas, 300 plans de traitement ont été générés en série pour obtenir une approximation uniforme de la frontière de Pareto. Chaque plan optimal de Pareto a été calculé avec IPSA et chaque nouveau plan a été ajouté à la portion de la frontière de Pareto où la distance entre sa limite supérieure et sa limite inférieure était la plus grande. Dans une étude complémentaire, ou dans la seconde étude, un algorithme MCO basé sur la connaissance (kMCO) a été mis en oeuvre pour réduire le temps de calcul de l’algorithme MCO. Pour ce faire, deux stratégies ont été mises en oeuvre : une prédiction de l’espace des solutions cliniquement acceptables à partir de modèles de régression et d’un calcul parallèle des plans de traitement avec deux processeurs à six coeurs. En conséquence, une banque de plans de traitement de petite taille (14) a été générée et un plan a été sélectionné en tant que plan kMCO. L’efficacité de la planification et de la performance dosimétrique ont été comparées entre les plans approuvés par le médecin et les plans kMCO pour 236 cas. La troisième et dernière étude de cette thèse a été réalisée en coopération avec Cédric Bélanger. Un algorithme MCO (gMCO) basé sur l’utilisation d’un environnement de développement compatible avec les cartes graphiques a été mis en oeuvre pour accélérer davantage le calcul. De plus, un algorithme d’optimisation quasi-Newton a été implémenté pour remplacer le recuit simulé dans la première et la deuxième étude. De cette manière, un millier de plans de traitement avec divers compromis et équivalents à ceux générés par IPSA ont été calculés en parallèle. Parmi la banque de plans de traitement généré par l’agorithme gMCO, un plan a été sélectionné (plan gMCO). Le temps de planification et les résultats dosimétriques ont été comparés entre les plans approuvés par le médecin et les plans gMCO pour 457 cas. Une comparaison à grande échelle avec les plans approuvés par les radio-oncologues montre que notre dernier algorithme MCO (gMCO) peut améliorer l’efficacité de la planification du traitement (de quelques minutes à 9:4 s) ainsi que la qualité dosimétrique des plans de traitements (des plans passant de 92:6% à 99:8% selon les critères dosimétriques du groupe de traitement oncologique par radiation (RTOG)). Avec trois algorithmes MCO mis en oeuvre, cette thèse représente un effort soutenu pour développer un algorithme de planification inverse ultra-rapide, automatique et robuste en curiethérapie HDR.
L’objectif général de cette thèse est d’utiliser les connaissances en physique de la radiation, en programmation informatique et en équipement informatique à la haute pointe de la technologie pour améliorer les traitements du cancer. En particulier, l’élaboration d’un plan de traitement en radiothérapie peut être complexe et dépendant de l’utilisateur. Cette thèse a pour objectif de simplifier la planification de traitement actuelle en curiethérapie de la prostate à haut débit de dose (HDR). Ce projet a débuté à partir d’un algorithme de planification inverse largement utilisé, la planification de traitement inverse par recuit simulé (IPSA). Pour aboutir à un algorithme de planification inverse ultra-rapide et automatisé, trois algorithmes d’optimisation multicritères (MCO) ont été mis en oeuvre. Suite à la génération d’une banque de plans de traitement ayant divers compromis avec les algorithmes MCO, un plan de qualité a été automatiquement sélectionné. Dans la première étude, un algorithme MCO a été introduit pour explorer les frontières de Pareto en curiethérapie HDR. L’algorithme s’inspire de la fonctionnalité MCO intégrée au système Raystation (RaySearch Laboratories, Stockholm, Suède). Pour chaque cas, 300 plans de traitement ont été générés en série pour obtenir une approximation uniforme de la frontière de Pareto. Chaque plan optimal de Pareto a été calculé avec IPSA et chaque nouveau plan a été ajouté à la portion de la frontière de Pareto où la distance entre sa limite supérieure et sa limite inférieure était la plus grande. Dans une étude complémentaire, ou dans la seconde étude, un algorithme MCO basé sur la connaissance (kMCO) a été mis en oeuvre pour réduire le temps de calcul de l’algorithme MCO. Pour ce faire, deux stratégies ont été mises en oeuvre : une prédiction de l’espace des solutions cliniquement acceptables à partir de modèles de régression et d’un calcul parallèle des plans de traitement avec deux processeurs à six coeurs. En conséquence, une banque de plans de traitement de petite taille (14) a été générée et un plan a été sélectionné en tant que plan kMCO. L’efficacité de la planification et de la performance dosimétrique ont été comparées entre les plans approuvés par le médecin et les plans kMCO pour 236 cas. La troisième et dernière étude de cette thèse a été réalisée en coopération avec Cédric Bélanger. Un algorithme MCO (gMCO) basé sur l’utilisation d’un environnement de développement compatible avec les cartes graphiques a été mis en oeuvre pour accélérer davantage le calcul. De plus, un algorithme d’optimisation quasi-Newton a été implémenté pour remplacer le recuit simulé dans la première et la deuxième étude. De cette manière, un millier de plans de traitement avec divers compromis et équivalents à ceux générés par IPSA ont été calculés en parallèle. Parmi la banque de plans de traitement généré par l’agorithme gMCO, un plan a été sélectionné (plan gMCO). Le temps de planification et les résultats dosimétriques ont été comparés entre les plans approuvés par le médecin et les plans gMCO pour 457 cas. Une comparaison à grande échelle avec les plans approuvés par les radio-oncologues montre que notre dernier algorithme MCO (gMCO) peut améliorer l’efficacité de la planification du traitement (de quelques minutes à 9:4 s) ainsi que la qualité dosimétrique des plans de traitements (des plans passant de 92:6% à 99:8% selon les critères dosimétriques du groupe de traitement oncologique par radiation (RTOG)). Avec trois algorithmes MCO mis en oeuvre, cette thèse représente un effort soutenu pour développer un algorithme de planification inverse ultra-rapide, automatique et robuste en curiethérapie HDR.
The overall purpose of this thesis is to use the knowledge of radiation physics, computer programming and computing hardware to improve cancer treatments. In particular, designing a treatment plan in radiation therapy can be complex and user-dependent, and this thesis aims to simplify current treatment planning in high dose rate (HDR) prostate brachytherapy. This project was started from a widely used inverse planning algorithm, Inverse Planning Simulated Annealing (IPSA). In order to eventually lead to an ultra-fast and automatic inverse planning algorithm, three multi-criteria optimization (MCO) algorithms were implemented. With MCO algorithms, a desirable plan was selected after computing a set of treatment plans with various trade-offs. In the first study, an MCO algorithm was introduced to explore the Pareto surfaces in HDR brachytherapy. The algorithm was inspired by the MCO feature integrated in the Raystation system (RaySearch Laboratories, Stockholm, Sweden). For each case, 300 treatment plans were serially generated to obtain a uniform approximation of the Pareto surface. Each Pareto optimal plan was computed with IPSA, and each new plan was added to the Pareto surface portion where the distance between its upper boundary and its lower boundary was the largest. In a companion study, or the second study, a knowledge-based MCO (kMCO) algorithm was implemented to shorten the computation time of the MCO algorithm. To achieve this, two strategies were implemented: a prediction of clinical relevant solution space with previous knowledge, and a parallel computation of treatment plans with two six-core CPUs. As a result, a small size (14) plan dataset was created, and one plan was selected as the kMCO plan. The planning efficiency and the dosimetric performance were compared between the physician-approved plans and the kMCO plans for 236 cases. The third and final study of this thesis was conducted in cooperation with Cédric Bélanger. A graphics processing units (GPU) based MCO (gMCO) algorithm was implemented to further speed up the computation. Furthermore, a quasi-Newton optimization engine was implemented to replace simulated annealing in the first and the second study. In this way, one thousand IPSA equivalent treatment plans with various trade-offs were computed in parallel. One plan was selected as the gMCO plan from the calculated plan dataset. The planning time and the dosimetric results were compared between the physician-approved plans and the gMCO plans for 457 cases. A large-scale comparison against the physician-approved plans shows that our latest MCO algorithm (gMCO) can result in an improved treatment planning efficiency (from minutes to 9:4 s) as well as an improved treatment plan dosimetric quality (Radiation Therapy Oncology Group (RTOG) acceptance rate from 92.6% to 99.8%). With three implemented MCO algorithms, this thesis represents a sustained effort to develop an ultra-fast, automatic and robust inverse planning algorithm in HDR brachytherapy.
The overall purpose of this thesis is to use the knowledge of radiation physics, computer programming and computing hardware to improve cancer treatments. In particular, designing a treatment plan in radiation therapy can be complex and user-dependent, and this thesis aims to simplify current treatment planning in high dose rate (HDR) prostate brachytherapy. This project was started from a widely used inverse planning algorithm, Inverse Planning Simulated Annealing (IPSA). In order to eventually lead to an ultra-fast and automatic inverse planning algorithm, three multi-criteria optimization (MCO) algorithms were implemented. With MCO algorithms, a desirable plan was selected after computing a set of treatment plans with various trade-offs. In the first study, an MCO algorithm was introduced to explore the Pareto surfaces in HDR brachytherapy. The algorithm was inspired by the MCO feature integrated in the Raystation system (RaySearch Laboratories, Stockholm, Sweden). For each case, 300 treatment plans were serially generated to obtain a uniform approximation of the Pareto surface. Each Pareto optimal plan was computed with IPSA, and each new plan was added to the Pareto surface portion where the distance between its upper boundary and its lower boundary was the largest. In a companion study, or the second study, a knowledge-based MCO (kMCO) algorithm was implemented to shorten the computation time of the MCO algorithm. To achieve this, two strategies were implemented: a prediction of clinical relevant solution space with previous knowledge, and a parallel computation of treatment plans with two six-core CPUs. As a result, a small size (14) plan dataset was created, and one plan was selected as the kMCO plan. The planning efficiency and the dosimetric performance were compared between the physician-approved plans and the kMCO plans for 236 cases. The third and final study of this thesis was conducted in cooperation with Cédric Bélanger. A graphics processing units (GPU) based MCO (gMCO) algorithm was implemented to further speed up the computation. Furthermore, a quasi-Newton optimization engine was implemented to replace simulated annealing in the first and the second study. In this way, one thousand IPSA equivalent treatment plans with various trade-offs were computed in parallel. One plan was selected as the gMCO plan from the calculated plan dataset. The planning time and the dosimetric results were compared between the physician-approved plans and the gMCO plans for 457 cases. A large-scale comparison against the physician-approved plans shows that our latest MCO algorithm (gMCO) can result in an improved treatment planning efficiency (from minutes to 9:4 s) as well as an improved treatment plan dosimetric quality (Radiation Therapy Oncology Group (RTOG) acceptance rate from 92.6% to 99.8%). With three implemented MCO algorithms, this thesis represents a sustained effort to develop an ultra-fast, automatic and robust inverse planning algorithm in HDR brachytherapy.

Discrete Multitone is adopted in Digital Subscriber Line to offer high-speed data communication on the UTP channel. To combat the channel distortion, DMT system employed Time Domain Equalizer and Cyclic Prefix. In this thesis, we analyze different existing time domain equalizer design methods and their performances are compared based on our simulation results. Modification of the current method is proposed and significant performance improvement is obtained. Multi-rate equalization is studied theoretically, which enables us to achieve zero ISI channels that can be used not only in DMT system but also in all other communication systems. Our simulation results show that the new design method is superior and practical.

Adaptive mesh refinement (AMR) of hyperbolic systems allows us to refine the spatial grid of an initial value problem (IVP), in order to obtain better accuracy and improved efficiency of the numerical method being used. However, the solutions obtained are still limited to the local Courant-Friedrichs-Lewy (CFL) time-step restrictions of the smallest element within the spatial domain. Therefore, we look to construct a multi-rate time-integration scheme capable of solving an IVP within each spatial sub-domain that is congruent with that sub-domains respective time-step size. The primary objective for this research is to construct a multi-rate method for use with AMR. In this thesis we will focus on constructing a 2nd order, multi-rate partitioned Runge-Kutta (MPRK2) scheme, such that the non-uniform mesh is constructed with the coarse and fine elements at a two-to-one ratio. We will use general 2nd and 4th order finite differences (FD) methods for non-uniform grids to discretize the spatial derivative, and then use this model to compare the MPRK2 time-integrator against three explicit, 2nd order, single-rate time-integrators Adams-Bashforth 2 (AB2), Backward Differentiation Formula 2 (BDF2), and Runge-Kutta 2 (RK2).

Abstract. This thesis gives an overview of short-rate models in term structure modeling of interest rates. The focus is in simple preference-free models with affine term structures. The thesis also shows how these models can be extended to cover credit spreads over the risk-free interest rate. The empirical section analyzes how well these models can be applied to recent interest rate data. While short-rate models are still used, more recent market models have eclipsed them in pricing of complex derivatives. The previous literature in short-rate modeling has been mainly conducted before the financial crisis of 2007–08 and there is very little literature on comparing how well these models perform in the current market structure which features negative interest rates. The first chapters give an overview of arbitrage-free pricing methodology of contingent claims and short-rate modeling of interest rates and credit spreads. These chapters present analytical pricing formulas for zero-coupon bonds with and without credit risk and semi-analytical pricing method for options on zero-coupon bonds in simple preference-free affine multi-factor short-rate models. The main finding of the empirical study shows that single-factor models do not fit the recent market data. For multi-factors models, the results were not conclusive. The calibration of multi-factor models is very hard multi-dimensional optimization problem with heavy computational burden. While the quality of the multi-factor model calibrations was mostly lacking, the mixed results suggest that insufficient computing power might be cause. The rationale for this conclusion was that the calibration algorithm could not replicate previous calibration results when a different starting population was used in optimization. It seems that there were not enough computational resources to guarantee that stochastic optimization algorithm was able to find optimal parameter values. Based on the findings of the empirical study, it seems that multi-factor short-rate models with affine term structure can be used in term structure modeling but with caveats. The whole discount curve from over-night rate to the maturity of 30 years seems to be too complex for these models but shorter sections worked much better and optimization and the computational burden may not be ignored in a more serious calibration attempt.

In the uplink channel of the 3GPP long term evolution (LTE) and LTE-Advanced (LTE-A) systems, signal carrier frequency-division multiplexing access (SC-FDMA) transmission scheme is employed instead of orthogonal frequency-division multiplexing (OFDM) to reduce the peak-to-average power ratio (PAPR). However, compared to OFDM, SC-FDMA has lower channel throughput, since it suffers from inter-symbol interference (ISI). Multi-rate equalizer (MRE) is a novel low complexity and non-linear equalizer which can increase the channel throughput. The basic idea of the MRE is that it first decomposes the single ISI channel into two parallel sub-channels by employing multi-rate signal processing and successive interference cancellation (SIC). Then, this decomposition procedure can be executed recursively to further increase the number of sub-channels. The ISI decreases as the number of sub-channels increases. Meanwhile, since the MRE does not require pre-coding, it does not increase PAPR. The practical implementation of the MRE is not straightforward. An algorithm, which can recursively call each function block in the MRE and execute the entire decomposition processes is required. In this thesis, an algorithm is developed based on the construction pattern of the MRE to enable its realization. An LTE standard-compliant turbo code is simulated to evaluate the practical performance gains of the MRE concept. MATLAB is selected as the simulation environment. According to the simulation results, the channel throughput can be increased by employing the MRE together with LTE turbo code indeed. One time-invariant and one time-varying channel model are employed. Three kinds of MRE with binary modulation are considered. Those are the MRE with two, four and eight sub-channels. The increase in throughput is at least 25% and can reach 80% in highly frequency selective scenarios.

With the advent of the Global Position System (GPS), we now have the ability to determine absolute position anywhere on the globe. Although GPS systems work well in open environments with no overhead obstructions, they are subject to large unavoidable errors when the reception from some of the satellites is blocked. This occurs frequently in urban environments, such as downtown New York City. GPS systems require at least four satellites visible to maintain a good position â fixâ . Tall buildings and tunnels often block several, if not all, of the satellites. Additionally, due to Selective Availability (SA), where small amounts of error are intentionally introduced, GPS errors can typically range up to 100 ft or more. This thesis proposes several methods for improving the position estimation capabilities of a system by incorporating other sensor and data technologies, including Kalman filtered inertial navigation systems, rule-based and fuzzy-based sensor fusion techniques, and a unique map-matching algorithm.
Master of Science

This master thesis investigates the generic benchmark approach to measuring interest rate risk. First the background and market situation is described followed by an outline of the concept and meaning of measuring interest rate risk with generic benchmarks. Finally a single yield curve in an arbitrary currency is analyzed in the cases where linear interpolation and cubic interpolation technique is utilized. It is shown that in the single yield curve setting with linear interpolation or cubic interpolation the problem of finding interest rate scenarios can be formulated as convex optimization problems implying properties such as convexity and monotonicity. The analysis also shed light on the difference between linear interpolation and cubic interpolation technique for which scenario is generated and means to go about solving for the scenarios generated by the views imposed on the generic benchmark instruments. Further research on the topic of the generic benchmark approach that would advance the understanding of the model is suggested at the end of the paper. However at this stage it seems like using generic benchmark instruments for measuring interest rate risk is a consistent and computational viable option which not only measures the interest rate risk exposure but also provide a guidance in how to act in order to manage interest rate risk in a multi hierarchy paradigm

This thesis examines the fundamental relationship between a continuous-time system and its discrete-time models. This involves a study of the conditions that the state space realization of a model must satisfy in order to be valid. While such a study has been performed for models whose order equals that of the continuous-time system, this thesis also includes "higher order discrete-time models", that is, models whose order is higher than the continuous-time system. A strict mathematical definition for models is presented based upon the convergence in a certain sense of the time responses of the continuous-time system and its model. Theorems are also presented which can be used to prove the validity of models, and shown are that many common discretization techniques, such as mapping models and hold equivalent models, are valid. Using these theorems some of these discretization techniques can be generalized. However, the aim of this thesis is not to prove the validity of common discretization techniques, but to understand the conditions which a model must satisfy in order to be valid. Common discretization techniques simply provide convenient examples for this understanding.
The definition of models is later expanded to consider discrete-time time-varying and multi-rate system. It is with multi-rate systems that the importance of higher order models becomes particularly apparent. Depending on the particular ratio of sampling rates between the plant input and output, some multi-rate systems must include inherently discrete-time operations, resulting in a higher order, for these systems to be considered valid. Also shown is that it is possible for a discrete-time periodically-time-varying system to model a time-invariant continuous-time system.
Finally, using the developed model concept, the practical problem of the multi-rate implementation of an analogue control system is considered. The method presented is an extension of the plant input mapping method which is the only method capable of guaranteeing the stability of the digital closed-loop system provided the sampling period is nonpathological. Simulation examples illustrate the effectiveness of the proposed methods, even for very slow sampling periods.

Thesis (S.B. and M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1999.
Includes bibliographical references (leaf 40).
by John L. Benko.
S.B.and M.Eng.

碩士
元智大學
電機工程學系
106
A multi-rate filtered PWM(MRFPWM) is proposed in this thesis to improve the harmonics distortion and the switching loss of the voltage source inverters(VSIs). In the traditional CBPWM, although we can reduce the harmonics distortion by increasing the switching frequency, such a method also leads to more switching loss. Therefore, we develop the MRFPWM, which can reduce the harmonics distortion by increasing the calculative frequency rather than switching frequency, to reduce the current harmonics distortion. Pratically the current signal is used to control the pulse-width modulation. Therefore, we have to adopt a PI current controller in the PWM structure to make sure MRFPWM can be used to control a motor. Further, an experimental platform of five-phase VSI drive is built . As validate the effectiveness of MRFPWM for comparing with traditional CBPWM, both simulations and experiments reducing the current harmonics distortion.

碩士
元智大學
電機工程學系
104
A multi-rate filtered PWM (MRFPWM) is proposed to improve both baseband harmonics distortion and the switching loss of the voltage source inverters (VSIs). In the conventional SVPWM, it is a tradeoff to select between a lower harmonics distortion or a lower switching loss. In the proposed scheme, the dependency of harmonics distortion and switching loss is alleviated by separating the modulator into two blocks with different operating frequencies -- optimal filter block that operates at calculative frequency and switching generation block that switches at carrier frequency. Therefore, the harmonics components are attenuated by increasing the calculative frequency and the switching loss is reduced with low carrier frequency. Two simulations are done in this work. The first one drives the ideal five-phase VSI by using SVPWM and the proposed multi-rate FPWM in Matlab. Time/frequency domain analysis of the produced phase voltages under various carrier frequencies are shown. Second, the proposed modulator is applied to the five-phase VSI built by PSIM with deadtime 2us. Further, a experimental platform of five-phase VSI drive is built. Comparing with conventional SVPWM, both simulations and experiments confirm the ability of current harmonics attenuation of the proposed MRFPWM under lower carrier frequency.

碩士
國立交通大學
電信工程研究所
101
The IEEE 802.11e Enhanced Distributed Channel Access (EDCA) provides a class-based differentiated quality of service (QoS) to IEEE 802.11 WLANs. But since EDCA mechanism only takes single-rate network environment into account, when it equipped in the multi-rate network it can’t function well. That’s because the 802.11e standard provide time fairness among the high priority access category which may influence the QoS performance of the low speed users. And among the low priority access category, 802.11e provides same probability of channel access to all users. That means when the users are transmitting large frame, the low-rate users will occupy more channel slots then the high-rate users do. This characteristic not only causes the compression to the channel transmission time of the high-rate users but also affect the total system throughput of the network. Regarding of the defect above, we propose a new fairness mechanism for two purposes: 1. Reducing the transmission time of the low speed non-QoS users to enhance the total throughput. 2. Providing same bandwidth guarantee to all QoS requirement stream regardless of the user’s transmission rate. Finally, we simulate the improvement between new fairness mechanism and original EDCA function.

碩士
國立清華大學
動力機械工程學系
96
第三代蜂巢式行動通訊系統要能支援許多服務，如語音、資料及影像傳輸。換句話說，用戶會以多種傳輸速率來傳輸訊號。在這份論文中，我們選擇以直接序列(direct sequence)展頻技術調變之分碼多工存取系統，來設計一個多速率的通訊系統。我們使用MC及MPG技術來實踐多速率傳輸。在MC系統中，高傳輸速率使用者會使用多個展頻碼(spreading sequence)。在MPG系統中，所有訊號都被調變成相同的頻寬，但高速率使用者的展頻增益(processing gain)及符號區間(symbol duration)會小於低速率的使用者，如此高速率使用者才能在固定時間內傳輸較多的符號。 分碼多工系統中之主要缺點之一為多重存取干擾（MAI）。這是由於在此系統中，多位使用者同時在相同的頻帶上傳送訊息所造成。另一個形成干擾的原因則為多路徑干擾。此兩原因降低了系統的效能，為了要抑制干擾，數種多用戶偵測器曾被提出，其中包括了平行干擾消除偵測器（PIC）。平行干擾消除偵測器的結構是由多個傳統的匹配濾波器（matched filter）一層層組成，藉由層級上的疊代而改善傳統匹配濾波器的效能。在此論文裡，我們提出與干擾投影法相互結合之平行干擾消除偵測器。藉由應用干擾投影法於平行干擾消除偵測器中，我們可以估測出每個使用者的傳輸振幅，並能預期分碼多工存取系統在多速率多路徑情況下能有更佳的效能。

博士
國立臺灣大學
電信工程學研究所
94
Multi-carrier multiplexing and Code-Division-Multiple-Access are two promising signaling technologies in wireless frequency-selective-fading channels. In this dissertation, their combination, Multi-Carrier CDMA (MC-CDMA) transmission, is studied to support wireless multimedia communications in broadband wireless channels. Two multi-rate MC-CDMA transmission schemes based on Multi-Code (MC) and Variable-Spreading-Length (VSL) concepts are proposed and the related system issues and reception problems are investigated. Multiuser detections supporting MC/VSL dual mode receptions are proposed to solve the inherent distortion of spreading code orthogonality in uplink channels due to spread spectrum over multiple carriers, which yields effective reception of MC/VSL MC-CDMA for uplink applications. To optimize the efficiency of radio resource utilization in multimedia applications, the allocations of transmission rate, power, and sub-carriers are investigated to minimize the total power consumption and practical allocation algorithms are proposed. Since mobility is a critical challenge of future wireless communication systems, a reception technique that enhances the reception performance of MC-CDMA against Doppler Effect in mobile channels is applied to improve the capability of mobile multimedia transmissions. Finally, a re-configurable system architecture is constructed, which not only leads to a programmable platform capable of MC/VSL hybrid MC-CDMA access but also promises system integration with various major OFDM-CDMA systems as Software Define Radio to provide hardware adaptation for system diversity toward seamless communication access. The design and direction to future wireless multimedia communication systems are investigated in this dissertation.

This thesis addresses the problem of `efficient' broadcast in a multi-radio multi-channel multi-rate wireless mesh network (MR$^2$-MC WMN). In such a MR$^2$-MC WMN, nodes are equipped with multiple radio network interface cards, each tuned to an orthogonal channel, that can dynamically adjust transmission rate by choosing a modulation scheme appropriate for the channel conditions. We choose `broadcast latency', defined as the maximum delay between a packet's network-wide broadcast at the source and its eventual reception at all network nodes, as the `efficiency' metric of broadcast performance. The problem of constructing a broadcast forwarding structure having minimal broadcast latency is referred to as the `minimum-latency-broadcasting' (MLB) problem. While previous research for broadcast in single-radio single-rate wireless networks has highlighted the wireless medium's `\emph{wireless broadcast advantage}' (WBA); little is known regarding how the new features of MR$^2$-MC WMN may be exploited. We study in this thesis how the availability of multiple radio interfaces (tuned to orthogonal channels) at WMN nodes, and WMN's multi-rate transmission capability and WBA, might be exploited to improve the `broadcast latency' performance. We show the MLB problem for MR$^2$-MC WMN to be NP-hard, and resort to heuristics for its solution. We divide the overall problem into two sub-problems, which we address in two separate parts of this thesis. \emph{In the first part of this thesis}, the MLB problem is defined for the case of single-radio single-channel multi-rate WMNs where WMN nodes are equipped with a single radio tuned to a common channel. \emph{In the second part of this thesis}, the MLB problem is defined for MR$^2$-MC WMNs where WMN nodes are equipped with multiple radios tuned to multiple orthogonal channels. We demonstrate that broadcasting in multi-rate WMNs is significantly different to broadcasting in single-rate WMNs, and that broadcast performance in multi-rate WMNs can be significantly improved by exploiting the availability of multi-rate feature and multiple interfaces. We also present two alternative MLB broadcast frameworks and specific algorithms, centralized and distributed, for each framework that can exploit multiple interfaces at a WMN node, and the multi-rate feature and WBA of MR$^2$-MC WMN to return improved `broadcast latency' performance.

碩士
逢甲大學
資訊工程所
97
In IEEE 802.11, the transmission rate of the data signals is different from the transmission rate of control signals. The different transmission rate causes the different signals coverage. Usually the control signals coverage is 4 to 6 times bigger than data signals coverage. There are two problems occur in different signals coverage. One is the communication pair has finished handshaking but they can’t transmit data packet. Because of the data signals can’t reach the communication receiver nodes. The other is all the nodes in control signal coverage they can’t communicate with other nodes. In fact, the data signals coverage is smaller than control signals coverage. The nodes in control signals coverage but not in data signals coverage can communicate with other nodes. However, they set their status in NAV (Network Allocation Vector). Our purposed method is to increase the communicate nodes. We expect the nodes in control signals but not in data signals not to set their status in NAV, the control signals and data signals not interfere with each other. We separate the Channel into Multiple Channels (control channel, data channel and ACK channel). Furthermore, the bad bandwidth allocation strategy will decrease network throughput. We proposed the optimal bandwidth allocation strategy to increase network throughput. To estimate our method, we compare IEEE 802.11 DCF with ours in throughput and collision number. Our method increase 30 to 40 percent network throughput and decrease 60 to 70 percent collision number. According to our simulation results, our method increase network throughput and decrease collision number efficiently.

碩士
國立交通大學
電信工程研究所
103
Due to increasing requirements of wireless network, users’ requirements of performance in wireless network also increase. To provide better Qos (Quality of Service), we have to provide good performance in multi-rate and multiple APs scenario. Here we discuss throughput and delay for performance, and use IEEE 802.11 standard for wireless network in the following discussion and analysis. Consider that there are many APs in the system, each client can choose which station to connect now, and different connections affect throughput and delay of system. This is a network selection problem of multi-rate system. In this problem, we want to find a configuration such that the system performance is maximal, which means maximal throughput and minimal delay. We can solve the network selection problem in optimization, and use utility function to represent real performance in this problem. With utility function, we can find optimal configuration which causes maximal performance by using iterative method of utility function optimization in multi-rate network selection problem. After design of iterative algorithm, it is ensure the method can get or close to optimal configuration, and has the best performance than other methods. To decide utility function, consider there are one AP in the system, find the variables which affect performance. In addition, different distances from client to AP cause different transmission rate. In multi-rate environment, we can divide the stations by transmission rate into different groups, so it reduces the reduction of throughput if high rate stations and low rate stations transmit together. The method is called grouping. The analysis of the variables effect on multi-rate system are used to utility function. After design of iterative algorithm, we compare this method with other methods in different configurations. Iterative method is the best method which is the closest to optimal performance even if changing client number in the system or changing arrival rate. Also, the performance is higher than other methods by 15% in the best case.

碩士
義守大學
資訊工程學系
92
The wireless mobile ad hoc networks (MANET) are becomes increasing popular. By connecting a cluster of mobile hosts, the applications of MANET appear in places where pre-deployment of network infrastructure is difficult or unavailable and emerging communication is required (e.g., natural disasters, battle fields, history building, and festival field grounds). Due to the ratification of standards, wireless devices can transmit at high data rate. IEEE 802.11a operates in the 5GHzband at data rate up to 54Mbps. IEEE 802.11b operates in the 2.4GHz band at 5.5 and 11 Mbps. In a MANET, one essential issue is Medium Access Control (MAC) protocol in the diversified environment with high mobility of the mobile hosts and fading channels. In this paper, we focus on develop a robust MAC protocol for a MANET with multi-channel and multi-rate in the fading channels by dynamically allocating channel and dynamically modulating the data rate. Through a dynamic channel allocation algorithm, two devices can negotiate the transmission data rate for the fading environment. This project has great challenge when we intend to consider the diversified environment with multi-channel and multi-rate in the fading channels. It is a difficult job even considering single condition. Hence, we develop a simulator on Network Simulator version 2 (NS2) to evaluate the influence of each technique used in our MAC protocol.

碩士
國立臺灣大學
資訊工程學研究所
97
Wireless Mesh Networks(WMNs) provide cost-effective broadband access for users. Multi-Channel Multi-Radio Wireless Mesh Networks has been one of the most important research topic. In WMNs, much attention has been paid to the problem that how to efficiently utilize multiple orthogonal channels and multiple communication radios to enhance the aggregate throughput. Most of prior works on the channel assignment problem assume that all transmission links use the basic rate and do not consider the presence of multiple bit-rates. However, in multi-rate wireless net- works, the achievable throughput of high-rate links is severely affected by low-rate links when they share the same physical channel. This problem is called multi-rate sharing problem. To address the problem, we proposed a Distributed Rate-Loss Based Channel Assignment, which can efficiently alleviate the multi-rate sharing problem. We also proposed a Rate-Loss function to support our channel assignment, where the Rate-Loss value represents the total rate degradation of all links using the channel when the current link chooses this channel. The simulation results shows that our algorithm outperforms existing schemes and is suitable for unstable environment.