M. Tech. (Department of Information Technology, Faculty of Applied and Computer Sciences), Vaal University of Technology. / This research was initiated because of a global increase in congestion on roads and the consequent increase in the rate of fatalities on both national and international roads. Annually, 1.3 million people are killed on the roads globally, and millions are injured. It was estimated that 2.4 million people will be killed in road traffic accidents annually by 2030, and in South Africa, over 14 000 deaths were reported in 2016. A study undertaken by the American Automobile Association Foundation for Traffic Safety (AAAFTS), established in 1947 to conduct research and address growing highway safety issues, found that motorcar accidents, on average, cost the United States $300 billion per annum. In the same vain, the World Health Organisation (WHO) asserted in their 2013 Global Status Safety Report on Road Safety that by 2020, traffic accidents would become the third leading cause of death globally. In this organisation’s 2015 report, South Africa was listed as having one of the highest road fatality rates in the world, averaging 27 out of 100 000 people. Cognisance of these statistics that describe wanton loss of life and serious economic implications, among other reasons, led to the development of autonomous vehicles (AVs), such as Google and Uber’s driverless taxis and Tesla’s autonomous vehicle. Companies have invested in self-driving prototypes, and they bolster this investment with continuous research to rectify imperfections in the technologies and to enable the implementation of AVs on conventional roads. This research aimed to address issues surrounding the systems communication concept, and focused on a novel method of the routing facet of AVs by exploring the mechanisms of the virtual system of packet switching and by applying these same principles to route autonomous vehicles. This implies that automated vehicles depart from a source address and arrive at a pre-determined destination address in a manner analogous to packet switching technology in computer networking, where a data packet is allotted a source and destination address as it traverses the Open Systems Interconnection (OSI) model for open system interconnection prior to dissemination through the network. This research aimed to develop an IoT model that reduces road congestion by means of a cost effective and reliable method of routing AVs and lessen dependency on vehicle-to-vehicle (V2V) communication with their heavy and costly sensor equipment and GPS, all of which under certain conditions malfunction. At the same time, as safety remains the foremost concern, the concept aimed to reduce the human factor to a considerable degree. The researcher demonstrated this by designing a computer-simulated Internet of Things (IoT) model of the concept. Experimental research in the form of a computer simulation was adopted as the most appropriate research approach. A prototype was developed containing the algorithms that simulated the theoretical model of IoT vehicular technology. The merits of the constructed prototype were analysed and discussed, and the results obtained from the implementation exercise were shared. Analysis was conducted to verify arguments on assumptions to clarify the theory, and the outcome of the research (an IoT model encompassing vehicular wireless technologies) shows how the basic concept of packet switching can be assimilated as an effective mechanism to route large-scale autonomous vehicles within the IoT milieu, culminating in an effective commuter operating system. Controlled routing will invariably save the traveller time, provide independence to those who cannot drive, and decrease the greenhouse effect, whilst the packet switching characteristic offers greater overall security. In addition, the implications of this research will require a workforce to supplement new growth opportunities.

Las redes ópticas de paquetes se han convertido en los últimos años en uno de los temas de vanguardia en el campo de las tecnologías de comunicaciones. El procesado de cabeceras es una de las funciones más importantes que se llevan a cabo en nodos intermedios, donde un paquete debe ser encaminado a su destino correspondiente. El uso de tecnología completamente óptica para las funciones de encaminamiento y reconocimiento de cabeceras reduce el retardo de procesado respecto al procesado eléctrico, disminuyendo de ese modo la latencia en el enlace de comunicaciones. Existen diferentes métodos de procesado de datos para implementar el reconocimiento de cabeceras. El objetivo de este trabajo es la propuesta de una nueva arquitectura para el procesado de cabeceras basado en el uso de puertas lógicas completamente ópticas. Estas arquitecturas tienen como elemento clave el interferómetro Mach-Zehnder basado en el amplificador óptico de semiconductor (SOA-MZI), y utilizan el efecto no lineal de modulación cruzada de fase (XPM) en los SOAs para realizar dicha funcionalidad. La estructura SOA-MZI con XPM es una de las alternativas más atractivas debido a las numerosas ventajas que presenta, como por ejemplo los requisitos de baja energía para las señales de entrada, su diseño compacto, una elevada relación de extinción (ER), regeneración de la señal y el bajo nivel de chirp que introducen. Este trabajo se ha centrado en la implementación de la funcionalidad lógica XOR. Mediante esta función se pueden realizar diversas funcionalidades en las redes ópticas. Se proponen dos esquemas para el reconocimiento de cabeceras basados en el uso de la puerta XOR. El primer esquema utiliza puertas en cascada. El segundo esquema presenta una arquitectura muy escalable, y se basa en el uso de un bucle de realimentación implementado a la salida de la puerta. Asimismo, también se presentan algunas aplicaciones del procesado de cabeceras para el encaminamiento de paquetes basadas en el uso d / Martínez Canet, JM. (2006). Photonic logic-gates: boosting all-optical header processing in future packet-switched networks [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1874

Tesis por compendio / La red en el chip (NoC) se han convertido en el elemento clave para la comunicación eficiente entre los núcleos dentro de los chip multiprocesador (CMP). Tanto el uso de aplicaciones paralelas en los CMPs como el incremento de la cantidad de memoria necesitada por las aplicaciones, ha impulsado que la red de comunicación gane una mayor importancia. La NoC es la encargada de transportar toda la información requerida por los núcleos. Además, el incremento en el número de núcleos en los CMPs impulsa las NoC a ser diseñadas de forma escalable, pero al mismo tiempo sin que esto afecte a las prestaciones de la red (latencia y productividad). Por tanto, el diseño de la red en el chip se convierte en crítico. Esta tesis presenta diferentes propuestas que atacan el problema de la mejora de las prestaciones de la red en tres escenarios distintos. Los tres escenarios en los que se centran nuestras propuestas son: 1) NoCs que implementan un algoritmo de encaminamiento adaptativo, 2) escenarios con necesidad de tiempos de acceso a memoria bajos y 3) sistemas con previsión de seguridad a nivel de aplicación. Las primeras propuestas se centran en el aumento de la productividad en la red utilizando algoritmos de encaminamiento adaptativos mediante un mejor uso de los recursos de la red, primera propuesta SUR, y evitando que se ramifique la congestión cuando existe tráfico intenso hacia un único destinatario, segunda propuesta EPC. La tercera y principal contribución de esta tesis se centra la problemática de reducir el tiempo de acceso a memoria. PROSA, mediante un diseño híbrido de conmutación de paquete y conmuntación de circuito, permite reducir la latencia de la red aprovechando la latencia de acceso a memoria para establecer circuitos. De esta forma cuando la información llega a la NoC, esta es servida sin retardos. Por último, la propuesta Token Based TDM se centra en el escenario con redes de interconexión seguras. En este tipo de NoC las aplicaciones esta divididas en dominios y la red debe garantizar que no existen interferencias entre los diferentes dominios para evitar de este modo la intrusión de posibles aplicaciones maliciosas. Token-based TDM permite el aislamiento de los dominios sin tener impacto en el diseño de los conmutados de la NoC. Los resultados obtenidos demuestran como estas propuestas han servido para mejorar las prestaciones de la red en los diferentes escenarios. La implementación y la simulación de las propuestas muestra como mediante el balanceado de la utilización de los recursos de la red, los CMPs con algoritmos de encaminamiento adaptativos son capaces de aumentar el tráfico soportado por la red. Además, el uso de un filtro para limitar el encaminamiento adaptativo en situaciones de congestión previene a los mensajes de la ramificación de la congestión a lo largo de la red. Por otra parte, los resultados demuestran que el uso combinado de la conmutación de paquete y conmutación de circuito reduce muy significativa de la latencia de red acceso a memoria, contribuyendo a una reducción significativa del tiempo de ejecución de la aplicación. Por último, Token-Based TDM incrementa las prestaciones de las redes TDM debido a su alta flexibilidad dado que no requiere ninguna modificación en la red para soportar una cantidad diferente de dominios mientras mejora la latencia de la red y mantiene un aislamiento perfecto entre los tráficos de las aplicaciones. / The Network on Chip (NoC) has become the key element for an efficient communication between cores within the multiprocessor chip (CMP). The use of parallel applications in CMPs and the increase in the amount of memory needed by applications have pushed the network communication to gain importance. The NoC is in charge of transporting all the data needed by the processors cores. Moreover, the increase in the number of cores pushes the NoCs to be designed in a scalable way, but at the same time, without affecting network performance (latency and productivity). Thus, network-on-chip design becomes critical. This thesis presents different proposals that attack the problem of improving the network performance in three different scenarios. The three scenarios in which our proposals are focused are: 1) NoCs with an adaptive routing algorithm, 2) scenarios with low memory access time needs, and 3) high-assurance NoCs. The first proposals focus on increasing network throughput with adaptive routing algorithms via the improvement of the network resources utilization, the first proposal SUR, and avoiding congestion spreading when an intense traffic to a single destination occurs, second proposal ECP. The third one and main contribution of this thesis focuses on the problem of reducing memory access latency. PROSA, through a hybrid circuit-packet switching architecture design, reduces the network latency by getting benefit of the memory access latency slack and to establishing circuits during that delay. In this way the information when arrives to the NoC is served without any delay. Finally, the proposal Token-Based TDM focuses on the scenario with high assurance networks on chips. In this type of NoCs the applications are divided into domains and the network must guarantee that there are no interferences between the different domains avoiding this way intrusion of possible malicious applications. Token-based TDM allows domain isolation with no design impact on NoC routers. The results show how these proposals improve the performance of the network in each different scenario. The implementation and simulations of the proposals show the efficient use of network resources in CMPs with adaptive routing algorithms which leads to an increasement of the injected traffic supported by the network. In addition, using a filter to limit the adaptivity of the routing algorithm under congested situations prevents messages from spreading the congestion along the network. On the other hand, the results show that the combined use of circuit and packet switching reduces the memory access latency significantly, contributing to a significant reduction in application execution time. Finally, Token-Based TDM increases network performance of TDM networks due to its high flexibility and efficient arbitration. Moreover, Token-Based TDM does not require any modification in the network to support a different number of domains while improving latency and keeping a strong traffic isolation from different domains. / La xarxa en el xip (NoC) s'ha convertit en un element clau per a una comunicació eficient entre els diferents nuclis dins d'un xip multiprocessador (CMP). Tant la utilització d'aplicacions paral·leles en el CMP com l'increment de la quantitat de memòria necessitada per les aplicacions, hi ha produït que la xarxa de comunicació tinga una major importància. La NoC és l'encarregada de transportar tota la informació necessària pels nuclis. A més, l'increment del nombre de nuclis dins del CMP fa que la NoC haja de ser dissenyada d'una forma escalable, sense que afecte les prestacions de la xarxa (latència i productivitat). Per tant, el disseny de la xarxa en el xip es converteix crític. Aquesta tesi presenta diferents propostes que ataquen el problema de la millora de les prestacions de la xarxa en tres escenaris distints. Els tres escenaris en els quals se centren les nostres propostes són: 1) NoCs que implementen un algoritme d'encaminament adaptatiu, 2) escenaris amb necessitat de temps baix d'accés a memòria i 3) sistemes amb previsió de seguretat en l'àmbit d'aplicació. Les primeres propostes se centren en l'augment de la productivitat en la xarxa utilitzant algoritmes d'encaminament adaptatiu mitjançant una millor utilització dels recursos de la xarxa, primera proposta SUR, i evitant que es ramifique la congestió quan existeix un trànsit intens cap a un únic destinatari, segona proposta EPC. La tercera i principal contribució d'aquesta tesi es basa en la problemàtica de reduir el temps d'accés a memòria. PROSA, mitjançant un disseny híbrid de commutació de paquet i commutació de circuit, redueix la latència de la xarxa aprofitant la latència d'accés a memòria i establint els circuits durant aquesta latència. D'aquesta forma la informació quan arriba a la NoC pot ser enviada sense cap retràs. Per últim, la proposta Token-based TDM se centra en l'escenari amb xarxes d'interconnexió d'alta seguretat. En aquest tipus de NoC les aplicacions estan dividides en dominis i la xarxa deu garantir que no existeixen interferències entre els diferents dominis per a evitar d'aquesta forma la intrusió de possibles aplicacions malicioses. Token-based TDM permet l'aïllament dels dominis sense tindre impacte en el disseny dels encaminadors de la NoC. Els resultats demostren com aquestes propostes han servit per a millorar les prestacions de la xarxa en els diferents escenaris. La seua implementació i simulació demostra com mitjançant el balancejat de la utilització dels recursos de la xarxa, els CMP amb algoritmes d'encaminament adaptatiu són capaços d'augmentar el trànsit suportat per la xarxa. A més, l'ús d'un filtre per a limitar l'adaptabilitat de l'encaminament adaptatiu en situacions de congestió permet prevenir els missatges de la congestió al llarg de la xarxa. Per altra banda, els resultats demostren que l'ús combinat de la commutació de paquet i commutació de circuit redueix molt significativament de la latència d'accés a memòria, contribuint en una reducció significativa del temps d'execució de l'aplicació. Per últim, Token-based TDM incrementa les prestacions de les xarxes TDM debut a la seua alta flexibilitat donat que no requereix cap modificació en la xarxa per a suportar una quantitat diferent de dominis mentre millora la latència de la xarxa i mantén un aïllament perfecte entre els trànsits de les aplicacions. / Gorgues Alonso, M. (2018). Improving Network-on-Chip Performance in Multi-Core Systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107336 / Compendio

Road transport mobility continues to be a challenge to the City of Johannesburg (CoJ)’s economy in general. Traffic signals, their remote monitoring and control systems are the current implemented Intelligent Transport Systems (ITS), but daily systematic faults and maintenance uncertainties on such systems decrease the effectiveness of traffic engineers’ intersections optimization techniques. Inefficient electrical power supply to such ITS is a challenge, with conditional power cuts and fluctuations, uncertainties on traffic control system faults. Another factor leading to the problem is the communication channel which is using traditional modems which are not reliable. Reporting through both customer complaints and such unreliable remote monitoring systems makes maintenance to be ineffective. In this dissertation, the factors leading to the faults and uncertainties are considered. The proposed solution considers the important concerns of ITS, such as electrical power source performance optimization technique, road traffic control systems compatibility and communications systems / Electrical and Mining Engineering / M. Tech. (Electrical Engineering)

In this thesis we provide a model for a bufferless optical burst switching (OBS) and an optical packet switching (OPS) network. The thesis is divided in three parts. <p><p>In the first part we introduce the basic functionality and structure of OBS and OPS networks. We identify the blocking probability as the main performance parameter of interest. <p><p>In the second part we study the statistical properties of the traffic that will likely run through these networks. We use for this purpose a set of traffic traces obtained from the Universidad Politécnica de Catalunya. Our conclusion is that traffic entering the optical domain in future OBS/OPS networks will be long-range dependent (LRD). <p><p>In the third part we present the model for bufferless OBS/OPS networks. This model takes into account the results from the second part of the thesis concerning the LRD nature of traffic. It also takes into account specific issues concerning the functionality of a typical bufferless packet-switching network. The resulting model presents scalability problems, so we propose an approximative method to compute the blocking probability from it. We empirically evaluate the accuracy of this method, as well as its scalability. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

La consommation d'énergie des centres de données est un enjeu majeur. Leurs communications internes représentent près du quart de cette consommation. Les technologies de commutation optique ont en principe une meilleure efficacité énergétique que les solutions actuelles. Ce travail porte sur les réseaux optiques en mode paquet pour des centres de données de petite et moyenne taille. Il s'est déroulé dans le cadre du projet EPOC (Energy Proportional and Opportunistic Computing) qui s'intéresse à la réduction de la consommation d'énergie d'un centre de données alimenté partiellement par des sources renouvelables. Une hypothèse clé est l'absence d'un réseau de stockage dédié réduisant ainsi la consommation des interconnexions. Par contre, afin de pouvoir éteindre certains serveurs selon la charge de travail et l'énergie disponible, le débit doit être de l'ordre de 100 Gbit/s. Après un état de l'art des réseaux optiques pour centre de données nous choisissons une solution reposant sur une infrastructure entièrement passive et des émetteurs rapidement accordables en longueur d'onde, proposée récemment dans la littérature (POPI).Nous étudions les limitations dues aux composants (pertes d'insertion, plage d'accord et espacement des canaux). Nous proposons une extension (E-POPI) qui permet d'augmenter le nombre de serveurs connectés en utilisant plusieurs plages de longueurs d'onde. Pour les centres de données de plus grande taille nous proposons un réseau à deux étages (intra- et inter-racks) opérant respectivement dans les bandes C et L, POPI+. La connexion entre étages se fait via une passerelle transparente dans un sens et opaque dans l'autre. Différentes solutions de contrôle des deux étages sont détaillées.Un des éléments essentiels de faisabilité de ces architectures est de concilier la montée en débit avec les pertes du réseau passif d'interconnexion. Les techniques cohérentes des transmissions longue distance ne sont pas actuellement envisageables pour un centre de données. Nous avons donc étudié les formats PAM 4 et 8, par simulation avec différents débits (jusqu'à 112 Gbit/s et récepteurs (PIN, APD et SOA-PIN) et aussi, expérimentalement, à 12 et 18 Gbit/s. Nous avons développé une méthode de compensation des distorsions générées par les différents composants qui procure un compromis entre précision de correction et temps de calcul.Ces résultats nous permettent de déterminer les pertes d'insertion tolérables. Nous les combinons avec les limitations liées à la plage d'accord des émetteurs et à l'encombrement spectral des canaux occupant des fenêtres multiples de 12,5 GHz pour dimensionner les différentes architectures. Les réseaux POPI, E-POPI et POPI+ permettent respectivement la connexion de 48, 99 et 2352 entités à 112 Gbit/s. Nos évaluations tiennent compte d'une possible dispersion des caractéristiques des principaux composants. / Data-center energy consumption is nowadays a major issue. Intra-data-center networking accounts almost for a quarter of the data-center total power consumption. Optical switching technologies could provide higher power efficiency than current solutions based on electrical-packet switching. This work focuses on optical-packet-switched networks for small- and medium-size data centers. It takes part of the EPOC (Energy-Proportional and Opportunistic Computing) project, which main interest consists on reducing the overall power consumption of a data center partially powered by renewable sources. A key assumption is that our data center does not rely on a dedicated storage network, in order to reduce the consumption of those interconnections. In addition, with the aim of being able to turn off some servers according to the workload and the available energy, the bit rate must be close to 100 Gbit/s. We have chosen, after studying the state of the art of data-center interconnects, a purely passive network architecture based on fast-wavelength-tunable transmitters under the name of POPI.We study POPI's limitations due to its components (insertion loss, tuning range and channel spacing). We then propose an extension called E-POPI that allows to increase the number of connected servers by using several transmission bands. For larger data centers, we propose POPI+, a two-stage infrastructure for intra- and inter-rack communications operating in the C and L bands, respectively. The connection between both stages is done via a transparent gateway in one direction and an opaque one in the other. We discuss different control solutions for both stages.The feasibility of these architectures depends on, among other factors, dealing with bit-rate increasing and power losses of a passive interconnect. Coherent long-distance-transmission techniques are not currently suited to data centers. We therefore studied PAM 4 and 8 modulation formats with direct detection. On one hand, by simulation, with different bit rates (up to 112 Gbit/s) and receivers (PIN, APD and SOA-PIN) and, on the other hand, experimentally, at 12 and 18 Gbit/s. We have developed a method for compensating the distortions generated by the different network components. Our method takes into account a good tradeoff between correction accuracy and computation time.Simulation results allow us to determine the amount of insertion loss that may be supported. We then combine these results with the limitations of transmitters-tuning range and channel spacing using multiple of 12.5 GHz slots for dimensioning the proposed architectures. POPI, E-POPI and POPI+ interconnects allow the connection of 48, 99 and 2352 entities, respectively, at 112 Gbit/s. Our assessments take into account a potential dispersion of the characteristics of the main architecture components.

O controle de congestionamento padrão do TCP apresenta vários problemas; ele não consegue distinguir se o pacote foi perdido por falha no enlace ou por descarte de pacotes devido a um congestionamento de rede (se a falha foi no enlace não há necessidade de ativar os mecanismos de controle de congestionamento); e o correto ajuste de sua taxa de transmissão requer informação de perdas de pacotes. Neste trabalho é apresentado o new generalized window advertising (NGWA), que é um novo esquema de controle de congestionamento para o TCP. O NGWA traz informações da banda disponível da infraestrutura de rede para os pontos finais da conexão TCP. Seu desempenho foi comparado com TCP New Reno, RED e o TCP padrão via simulações com o software NS-3, considerando topologias de rede largamente citadas na literatura. O NGWA foi, também, implementado e testado no Linux (versão 2.6.34). O novo método demonstrou ser superior aos comparados, apresentando uma operação mais estável, melhor justiça e menor taxa de perda de pacotes, considerando o elenco de testes realizados. / The TCP congestion control mechanism in standard implementations presents several problems; he cannot distinguish if the packet was lost by link failure or by congestion in the net (if the fault was in the link there is no need to active congestion control mechanisms); and the right adjust of your transmission rate requires information from packet loss. This work presents the new generalized window advertising (NGWA), which is a new congestion control scheme for TCP. The NGWA provides information considering the available bandwidth of the network infrastructure to the endpoints of the TCP connection. Results obtained by the NGWA approach were compared with those from TCP New Reno, RED, and standard TCP (using the network simulator NS-3), considering network topologies widely cited in the literature. A NGWA Linux implementation is also presented. The new method proved to be superior when compared with the traditional approaches, presenting a more stable operation, better fairness and lower packet loss, considering the set of tests carried out.

Fundação Araucária / O gerenciamento do tráfego na Internet tornou-se essencial devido à grande utilização de serviços em rede nos últimos anos. Assim, para executar alguns serviços que demandam um certo grau de qualidade é necessário otimizar o uso de recursos existentes. Organizações mantenedoras de backbones são responsáveis por rotear o tráfego, utilizando protocolos que encaminham dados da origem ao destino. Um dos protocolos de roteamento mais utilizados mundialmente é o Open Shortest Path First (OSPF). A qualidade das rotas oferecidas pelo protocolo OSPF depende dos pesos atribuídos pelo operador de rede às ligações (enlaces). A determinação destes pesos depende dos critérios técnicos ou econômicos considerados necessários por parte da empresa provedora de serviços telemáticos. Nesta dissertação aborda-se o problema de rotear a demanda de tráfego na rede com o objetivo de oferecer uma qualidade de serviço satisfatória por meio de uma atribuição inteligente de pesos aos enlaces. O problema de atribuição de pesos (WSP), consiste em encontrar um conjunto de pesos OSPF que otimiza o desempenho da rede. Para solução deste problema, a literatura científica apresenta algoritmos que, na sua maioria, buscam equilibrar o tráfego na rede pelo ajuste correto da carga de cada enlace. Essa dissertação visa solucionar o WSP propondo uma nova abordagem que leva em consideração a perda de pacotes em caminhos origem-destino e a sobrecarga gerada em cada enlace. Também uma formulação estendida é proposta, permitindo a obtenção de um conjunto de pesos operacionais em ambientes normais e em ambientes onde ocorrem falhas de nós. A aplicação de duas heurísticas conhecidas, Simulated Annealing e Harmony Search, a este problema permite encontrar soluções satisfatórias para os critérios de desempenho especificados. / Internet traffic management becomes essential due the large use of the Internet the past decades. Balancing the use of existing IP resources improves the performance of services. Backbone manteiners are responsible for routing data that are sent along the network links from a source to a destination host. A routing protocol is used to perform this task. One of the most commonly used internal routing protocol is OSPF (Open Shortest Path First). The quality of the routes offered by the OSPF protocol mainly depends on weights that are assigned by the network operator to the links. The determination of these weights depends on technical or economic criteria deemed necessary by the ISPs. This master dissertation addresses the routing problem aiming at providing network quality of service by optimizing the weights assigned to links. The weight setting problem (WSP) corresponds to find a set of OSPF weights that optimize network performance. To solve this problem, the literature shows algorithms that mostly seek to balance the network traffic by correctly setting link loads. This work aims at solving WSP proposing a new approach that takes into account packet losses over origin-destination paths and link overhead. Also an extended formulation is proposed, to obtain a set of operating weights in normal environments and in environments where node failures can occur. The application of two well known heuristics, Simulated Annealing and Harmony Search, to this problem allows to find satisfactory solutions to the performance criteria specified.

Investiga-se uma forma de energy harvesting que consiste em recuperar a energia do sinal eletromagnético de rádio frequência (RF), processo que também é conhecido como transferência de energia sem fio. Aplica-se o protocolo time switching (TS) para coordenar o processo de energy harvesting, o qual divide o período de envio de um pacote em dois blocos, o primeiro é dedicado à transferência de energia e o segundo ao envio de informação. A fração do tempo dedicada a cada tarefa, dada pelo parâmetro TS, tem grande impacto no desempenho do sistema. Esta dissertação mostra a investigação do uso do protocolo TS em conjunto com esquemas de retransmissão (HARQ) para o envio da informação. Os resultados mostram que os esquemas HARQ melhoram o desempenho do sistema para a alta relação sinal-ruído (SNR). Essa melhoria é ainda maior quando o destino aplica combinação de Chase entre as diversas cópias do quadro recebido. / We investigate a form of energy harvesting consisting of gathering energy from the radio frequency (RF) electromagnetic waves, also known as wireless power transfer. We employ a time switching (TS) protocol to coordinate the harvesting process, which separates a time slot into two parts, one devoted to wireless energy transfer and the other to wireless information transmission. The fraction of time devoted to each task, the TS parameter, has great impact on the overall performance. This thesis presents an investigation on the usage of the TS protocol, including the numerical optimization of the TS parameter, when hybrid automatic repeat request (HARQ) schemes are used for information transmission. Our results demonstrate that HARQ schemes can improve the system performance for high SNR. This improvement is even better if the destination applies Chase combining among the previously received copies of a frame.

O controle de congestionamento padrão do TCP apresenta vários problemas; ele não consegue distinguir se o pacote foi perdido por falha no enlace ou por descarte de pacotes devido a um congestionamento de rede (se a falha foi no enlace não há necessidade de ativar os mecanismos de controle de congestionamento); e o correto ajuste de sua taxa de transmissão requer informação de perdas de pacotes. Neste trabalho é apresentado o new generalized window advertising (NGWA), que é um novo esquema de controle de congestionamento para o TCP. O NGWA traz informações da banda disponível da infraestrutura de rede para os pontos finais da conexão TCP. Seu desempenho foi comparado com TCP New Reno, RED e o TCP padrão via simulações com o software NS-3, considerando topologias de rede largamente citadas na literatura. O NGWA foi, também, implementado e testado no Linux (versão 2.6.34). O novo método demonstrou ser superior aos comparados, apresentando uma operação mais estável, melhor justiça e menor taxa de perda de pacotes, considerando o elenco de testes realizados. / The TCP congestion control mechanism in standard implementations presents several problems; he cannot distinguish if the packet was lost by link failure or by congestion in the net (if the fault was in the link there is no need to active congestion control mechanisms); and the right adjust of your transmission rate requires information from packet loss. This work presents the new generalized window advertising (NGWA), which is a new congestion control scheme for TCP. The NGWA provides information considering the available bandwidth of the network infrastructure to the endpoints of the TCP connection. Results obtained by the NGWA approach were compared with those from TCP New Reno, RED, and standard TCP (using the network simulator NS-3), considering network topologies widely cited in the literature. A NGWA Linux implementation is also presented. The new method proved to be superior when compared with the traditional approaches, presenting a more stable operation, better fairness and lower packet loss, considering the set of tests carried out.