With the transition towards renewable energy, and the deregulation of the electricity market, generation patterns and grid topology are changing. These changes increase the need for transfer capacity. One limiting factor, which sometimes leads to underutilization of the transmission grid, is interarea oscillations. These system-wide modes involve groups of generators oscillating relative to each other and are sometimes hard to control due to their scale and complexity. In this thesis we investigate how high-voltage direct current (HVDC) transmission can be used to attenuate interarea oscillations. The thesis has two main contributions. In the first contribution we show how the stability of two asynchronous grids can be improved by modulating the active power of a single interconnecting HVDC link. One concern with modulating HVDC active power is that the interaction between interarea modes of the two grids may have a negative impact on system stability. By studying the controllability Gramian, we show that it is always possible to improve the damping in both grids as long as the frequencies of their interarea modes are not too close. For simplified models, it is explicitly shown how the controllability, and therefore the achievable damping improvements, deteriorates as the frequency difference becomes small. The second contribution of the thesis is to show how coordinated control of two (or more) links can be used to avoid interaction between troublesome interarea modes. We investigate the performance of some multivariable control designs. In particular we look at input usage as well as robustness to measurement, communication, and actuator failures. Suitable controllers are thereby characterized. / Övergången till förnybar energi och avregleringen av elmarknaden leder till förändrade produktions-och överföringsmönster. Dessa förändringar medför behov av en ökad överföringskapacitet. En begränsande faktor, som kan leda till ett underutnyttjande av stamnätet, är interareapendlingar. Dessa systemövergripande pendlingar involverar grupper av generatorer som svänger i förhållande till varandra. Interareapendlingar är ibland svåra att styra på grund av deras skala och komplexitet. I denna avhandling undersöker vi hur förbindelser med högspänd likström, engleska high-voltage direct current (HVDC), kan användas för att dämpa interareapendlingar. Avhandlingen har två huvudbidrag. I det första bidraget visar vi hur stabiliteten hos två olika synkrona nät kan förbättras genom att modulera den aktiva effekten hos en enda HVDC-länk. Ett bekymmer med aktiv effektmodulering är att växelverkan mellan interareapendlingar hos de två näten kan ha en negativ inverkan på systemets stabilitet. Genom att studera styrbarhetsgramianen visar vi att det alltid är möjligt att förbättra dämpningen i båda näten så länge som frekvenserna hos deras interareapendlingar inte ligger för nära varandra. För förenklade modeller visas det uttryckligen hur styrbarheten och därmed de möjliga dämpningsförbättringarna, försämras då frekvensskillnaden blir liten. Avhandlings andra bidrag visar hur koordinerad styrning av två (eller fler) länkar kan användas för att undvika växelverkan mellan besvärliga interareapendlingar. Vi undersöker prestandan hos olika typer av flervariabla regulatorer. I synnerhet undersökers styrsignalsanvändning samt robusthet mot mät-, kommunikations- och aktuatorfel. Därigenom karakteriseras lämpliga regulatortyper. / <p>QC 20190308</p>

Along with playing an ever-increasing role in the integration of other communication networks and expanding in application diversities, the current Internet suffers from serious overuse and congestion bottlenecks. Efficient congestion control is fundamental to ensure the Internet reliability, satisfy the specified Quality-of-Service (QoS) constraints and achieve desirable performance in response to varying application scenarios. Active Queue Management (AQM) is a promising scheme to support end-to-end Transmission Control Protocol (TCP) congestion control because it enables the sender to react appropriately to the real network situation. Analytical performance models are powerful tools which can be adopted to investigate optimal setting of AQM parameters. Among the existing research efforts in this field, however, there is a current lack of analytical models that can be viewed as a cost-effective performance evaluation tool for AQM in the presence of heterogeneous traffic, generated by various network applications. This thesis aims to provide a generic and extensible analytical framework for analyzing AQM congestion control for various traffic types, such as non-bursty Poisson and bursty Markov-Modulated Poisson Process (MMPP) traffic. Specifically, the Markov analytical models are developed for AQM congestion control scheme coupled with queue thresholds and then are adopted to derive expressions for important QoS metrics. The main contributions of this thesis are listed as follows: • Study the queueing systems for modeling AQM scheme subject to single-class and multiple-classes Poisson traffic, respectively. Analyze the effects of the varying threshold, mean traffic arrival rate, service rate and buffer capacity on the key performance metrics. • Propose an analytical model for AQM scheme with single class bursty traffic and investigate how burstiness and correlations affect the performance metrics. The analytical results reveal that high burstiness and correlation can result in significant degradation of AQM performance, such as increased queueing delay and packet loss probability, and reduced throughput and utlization. • Develop an analytical model for a single server queueing system with AQM in the presence of heterogeneous traffic and evaluate the aggregate and marginal performance subject to different threshold values, burstiness degree and correlation. • Conduct stochastic analysis of a single-server system with single-queue and multiple-queues, respectively, for AQM scheme in the presence of multiple priority traffic classes scheduled by the Priority Resume (PR) policy. • Carry out the performance comparison of AQM with PR and First-In First-Out (FIFO) scheme and compare the performance of AQM with single PR priority queue and multiple priority queues, respectively.

In this thesis we address the problem of providing end-to-end quality of service (QoS) to real-time and data connections in a third generation (3G) cellular network based on the Universal Mobile Telecommunication System (UMTS) standard. Data applications usually use TCP (Transmission Control Protocol) and the QoS is a minimum guaranteed mean throughput. For this one first needs to compute the throughput of a TCP connection sending its traffic through the UMTS network (possibly also through the wired part of the Internet). Thus we obtain closed form expressions for a TCP throughput in a UMTS environment. For downloading data at a mobile terminal, the packets of each TCP connection are stored in separate queues at the base station (node B). These are fragmented into Protocol Data Units (PDU). The link layer uses ARQ (Automatic Repeat Request). Thus there can be significant random transmission/queueing delays of TCP packets at the node B. On the other hand the link may not be fully utilized due to the delays of the TCP packets in the rest of the network. In such a scenario the existing models of TCP may not be sufficient. Thus we provide new approximate models for TCP and also obtain new closed form expressions of mean window size. Using these we obtain the throughput of a TCP connection for the scenario where the queueing delays are non-negligible compared to the overall Round Trip Time (RTT) and also the link utilization is less than one. Our approximate models can be useful not only in the UMTS context but also else where. In the second half of the thesis, we use these approximate models of TCP to provide minimum mean throughput to data connections in UMTS. We also consider real-time applications such as voice and video. These can tolerate a little packet loss (~1%) but require an upper Bound on the delay and delay jitter (≤ 150 ms). Thus if the network provides a constant bandwidth and the received SINR is above a specified threshold ( with a certain probability), QoS for the real-time traffic will be satisfied. The 3G cellular systems are interference limited. Thus wise allocation of power is critical in these systems. Hence we consider the problem of providing end-to-end QoS to different users along with the minimization of the downlink power allocation.

Our work focuses on performance modelling of TCP-controlled file transfers in infrastructure mode IEEE 802.11 wireless networks, and application of the models in developing association schemes. A comprehensive set of analytical models is used to study the behaviour of TCP-controlled long and short file transfers in IEEE 802.11 WLANs. The results can provide insight into the performance of TCP-controlled traffic in 802.11 WLANs in a variety of different network environments. First, we consider several WLAN stations associated at rates r1, r2, ...,rk with an Access Point. Each station (STA) is downloading a long file from a local server, located on the LAN to which the AP is attached, using TCP. We assume that a TCP ACK will be produced after the reception of d packets at an STA. We model these simultaneous TCP-controlled transfers using a semi-Markov process. Our analytical approach leads to a procedure to compute aggregate download as well as per-STA throughputs numerically, and the results match simulations very well. Performance analysis of TCP-controlled long file transfers in a WLAN in infrastructure mode is available in the literature with one of the main assumptions being equal window size for all TCP connections. We extend the analysis to TCP-controlled long file uploads and downloads with different TCP windows. Our approach is based on the semi- Markov process considered in above work, but with arbitrary window sizes. We present simulation results to show the accuracy of the analytical model. Then, we obtain an association policy for STAs in an IEEE 802.11 WLAN by taking into account explicitly an aspect of practical importance: TCP controlled short file downloads interspersed with read times (motivated by web browsing). Our approach is based on two steps. First, we consider the analytical model mentioned above to obtain the aggregate download throughput. Second, we present a 2-node closed queueing network model to approximate the expected average-sized file download time for a user who shares the AP with other users associated at a multiplicity of rates. These analytical results motivate the proposed association policy, called the Estimated Delay based Association (EDA) policy: Associate with the AP at which the expected file download time is the least. Simulations indicate that for a web-browsing type traffic scenario, EDA outperforms other policies that have been proposed earlier; the extent of improvement ranges from 12.8% to 46.4% for a 9-AP network. We extend the performance model by considering _le sizes drawn from heavy-tailed distributions. We represent heavy-tailed distributions using a 1 mixture of exponential distributions (following Cox's method). We provide a closed queueing network model to approximate the expected average-sized file download time for a user who shares the AP with other users associated at a multiplicity of rates. Further, we analyze TCP-controlled bulk file transfers in a single station WLAN with nonzero propagation delay between the file server and the WLAN. Our approach is to model the flow of packets as a closed queueing network (BCMP network) with 3 service centres, one each for the Access Point and the STA, and the third for the propagation delay. The service rates of the first two are obtained by analyzing the WLAN MAC. We extend this work to obtain throughputs in multirate scenarios. Simulations show that our approach is able to predict observed throughputs with a high degree of accuracy.

The combination of hydrostatics and mechanical gearboxes cannot only improve system efficiency but also the usability of mobile machines. A possible solution could be a synchronized gearbox with two gears. Compared to the pure hydrostatic drivetrain, mobile machines with such a combination can have a larger drive torque with the first gear and higher efficiency at high speed. However, the calibration effort of this traditional drivetrain system is enormous; moreover, with a flow-based control, the degrees of freedom to achieve optimum shift performance in all conditions are limited. By adopting the primary torque control concept, we propose a novel hydrostatic-mechanical drivetrain control algorithm so that the holistic shift performance is better whilst the calibration effort is dramatically reduced by systematically adjusting only one hyper-parameter. Experienced engineers and machine operators validated the advantages mentioned here by a series of field experiments. Besides synchronized gearboxes, the controller proposed in this paper is also generalized to other kinds of mechanical transmissions.

When performing fingerprinting attacks against websites in a controlled environment astudy may achieve very promising results. However, these can be misleading as the closedworld setting may not accurately represent the real-world. This is a problem many priorworks have been critiqued for, the inability to transfer their results from the closed-worldsetting to the real-world. Being able to do so is of great importance to establish what thereal-world consequences would be of fingerprint attacks. If unable to apply one’s findingsoutside of a tightly controlled environment it is difficult to gauge if these attacks types posea real threat or not. Thereby, this thesis has, contrary to previous work, based its settingon a real-world scenario to provide tangible insights into vulnerabilities of news websites.Furthermore, it targeted internal pages of websites, something understudied by previousliterature. All of this while presenting a novel classifier that is lightweight and requireslittle training, and a framework for automatically collecting and labelling encrypted TCPtraffic without the use of a proxy.

Along with playing an ever-increasing role in the integration of other communication networks and expanding in application diversities, the current Internet suffers from serious overuse and congestion bottlenecks. Efficient congestion control is fundamental to ensure the Internet reliability, satisfy the specified Quality-of-Service (QoS) constraints and achieve desirable performance in response to varying application scenarios. Active Queue Management (AQM) is a promising scheme to support end-to-end Transmission Control Protocol (TCP) congestion control because it enables the sender to react appropriately to the real network situation. Analytical performance models are powerful tools which can be adopted to investigate optimal setting of AQM parameters. Among the existing research efforts in this field, however, there is a current lack of analytical models that can be viewed as a cost-effective performance evaluation tool for AQM in the presence of heterogeneous traffic, generated by various network applications. This thesis aims to provide a generic and extensible analytical framework for analyzing AQM congestion control for various traffic types, such as non-bursty Poisson and bursty Markov-Modulated Poisson Process (MMPP) traffic. Specifically, the Markov analytical models are developed for AQM congestion control scheme coupled with queue thresholds and then are adopted to derive expressions for important QoS metrics. The main contributions of this thesis are listed as follows: iii ¿ Study the queueing systems for modeling AQM scheme subject to single-class and multiple-classes Poisson traffic, respectively. Analyze the effects of the varying threshold, mean traffic arrival rate, service rate and buffer capacity on the key performance metrics. ¿ Propose an analytical model for AQM scheme with single class bursty traffic and investigate how burstiness and correlations affect the performance metrics. The analytical results reveal that high burstiness and correlation can result in significant degradation of AQM performance, such as increased queueing delay and packet loss probability, and reduced throughput and utlization. ¿ Develop an analytical model for a single server queueing system with AQM in the presence of heterogeneous traffic and evaluate the aggregate and marginal performance subject to different threshold values, burstiness degree and correlation. ¿ Conduct stochastic analysis of a single-server system with single-queue and multiple-queues, respectively, for AQM scheme in the presence of multiple priority traffic classes scheduled by the Priority Resume (PR) policy. ¿ Carry out the performance comparison of AQM with PR and First-In First-Out (FIFO) scheme and compare the performance of AQM with single PR priority queue and multiple priority queues, respectively.

This thesis develops dynamic models for the two-mode FWD EVT, develops a control system based on those models that is capable of meeting driver torque demands and performing synchronous mode shifts between different EVT modes while also accommodating preferred engine operating points. The two-input two-output transmission controller proposed herein incorporates motor-generator dynamics, is based on a general state-space integral control structure, and has feedback gains determined using linear quadratic regulator (LQR) optimization. Dynamic modeling of the vehicle is categorized as dynamic modeling of the mechanical and electrical subsystems where the mechanical subsystem consists of the planetary gear sets, the transmission and the engine whereas the electrical subsystem consists of the motor-generator units and the battery pack. A discussion of load torque is also considered as part of the mechanical subsystem. With the help of these derived dynamic models, a distinction is made between dynamic output torque and steady-state output torque. The overall control system consisting of multiple subsystems such as the human driver, power management unit (PMU), friction brakes, combustion engine, transmission control unit (TCU) and motor-generator units is designed. The logic for synchronous mode shifts between different EVT modes is also detailed as part of the control system design. Finally, the thesis presents results for responses in individual operating modes, EVT mode shifting and a full UDDS drive cycle simulation.

Orientador: Nelson Luis Saldanha da Fonseca / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação / Made available in DSpace on 2018-08-13T10:35:13Z (GMT). No. of bitstreams: 1 Santi_Julianade_M.pdf: 1658984 bytes, checksum: 8a9f078587406a06815484e4fe057f7d (MD5) Previous issue date: 2008 / Resumo: A utilização eficiente da banda passante em redes de alta velocidade e grandes atrasos, denominadas redes com produto banda-atraso elevado (PBA), tornou-se um grande desafio. Isto ocorre devido aos ajustes do protocolo Transmission Control Protocol (TCP). O High Speed TCP (HSTCP), uma variante do TCP para redes com PBA elevado, emprega ajustes mais agressivos permitindo, assim, que a utilização da banda seja escalável. As políticas de Gerenciamento Ativo de Filas ou Active Queue Management (AQM), monitoram o nível de ocupação das filas nos roteadores e notificam o congestionamento incipiente aos emissores TCP através do descarte/marcação de pacotes. O sistema de controle de congestionamento apresenta natureza de retroalimentação, na qual a taxa de transmissão dos nós fontes é ajustada em função do nível de ocupação da fila. Os controladores AQM determinam a probabilidade de descarte/marcação para maximizar a vazão e minimizar perdas, garantindo, assim, a estabilidade do tamanho da fila independentemente das variações das condições da rede. Neste trabalho, define-se a política de gerenciamento ativo de filas HSTCP-H2 para redes com PBA elevado que utilizam o protocolo HSTCP. Para a derivação de HSTCP­H2: são utilizadas técnicas de Teoria de Controle Ótimo. A principal característica desta política é considerar o atraso do sistema o que permite melhor utilização dos recursos disponíveis. A estabilidade e os objetivos de desempenho do sistema são expressos e solu­cionados através de Desigualdades Matriciais Lineares, permitindo que os parâmetros do controlador possam ser calculados através da solução de um problema convexo simples. Diferentes controladores foram derivados considerando-se diferentes objetivos de de­sempenho, os quais consideram as características de redes com produto banda-atraso elevado. Através de simulações, os desempenhos dos controladores derivados são avalia­dos e a eficácia do controlador que apresentou o melhor desempenho foi comparado com o desempenho da política de AQM RED. São considerados cenários com enlace gargalo único e com múltiplos gargalos. / Abstract: The efficient utilization of bandwidth in high speed and large delay networks, called high bandwidth-delay product networks (BDP), has become a major challenge. This is due to adjustments of the Transmission Control Protocol (TCP). The High Speed TCP HSTCP): a TCP variant to high BDP networks, employs more aggressive adjustments, allowing scalable bandwidth utilization. The Active Queue Management (AQM) policies monitor the queue length in the routers and notify incipient congestion to TCP source by marking or dropping packets. The congestion control system presents intrinsic feedback nature, where the transmission rates of the sources are adjusted according to the level of congestion inferred by the queue occupancy. The AQM controllers determine the dropping marking probability values to maximize throughput and minimize losses, giving guarantees to stabilize the queue length independent of network conditions. In this work, it is defined HSTCP-H2, an active queue management policy to high BDP networks, which adopt the HSTCP as their transport protocol. Optimal control theory is used to conceive HSTCP-H2. The novelty of the proposed approach lies in consider the delay of the system which allows better use of available resources. Furthermore, in the proposed approach, stability and performance objectives are completely expressed as Linear Matrix Inequalities (LMIs), thus requiring the solution of a single convex problem for the computation of the controller parameters. Different controllers are derived considering different design goals, which take into ac­count the characteristics of the high bandwidth-delay product networks. The performance produced by different optimal controllers was investigated. The efficacy of the control­ler with the best performance was then compared to the performance of RED policy. The simulation experiments were carried out using topologies with single and multiple bottleneck. / Mestrado / Redes de Computadores / Mestre em Ciência da Computação

<p dir="ltr">Evidence for climate change-related impacts and risks is already widespread globally, affecting not only the ecosystems but also the economy and health of our communities. Data-driven predictive modeling approaches such as machine learning and deep learning have emerged to be powerful tools for interpreting large and complex non-linear datasets such as meteorological variables from weather stations or the distribution of infectious droplets produced in a cough. However, the strength of these data-driven models can be further optimized by complementing them with foundational knowledge of the physical processes they represent. By understanding the core physics, one can enhance the reliability and accuracy of predictive outcomes. The effectiveness of these combined approaches becomes particularly feasible and robust with the recent advancements in the High-Performance Computing field. With improved processing speed, algorithm design, and storage capabilities, modern computers allow for a deeper and more precise examination of the data. Such advancements equip us to address the diverse challenges presented by climate change more effectively.</p><p dir="ltr">In particular, this document advances research in mitigating and preventing the consequences of global warming by implementing data-driven predictive models based on statistical, machine learning, and deep learning methods via two phases. In the first phase, this dissertation proposes frameworks consisting of machine and deep learning algorithms to increase the resilience of small-scale renewable energy systems, which are essential for reducing greenhouse gas emissions in the ecosystems. The second phase focuses on using data from physics-based models, i.e., computational fluid dynamics (CFD), in data-driven predictive models for improving the design of air cleaning technologies, which are crucial to reducing the transmission of infectious diseases in indoor environments. </p><p dir="ltr">Specifically, this work is an article-based collection of published (or will be published) research articles. The articles are reformatted to fit the thesis's structure. The contents of the original articles are self-contained. </p>