688 research outputs found

    Analysis and evaluation of in-home networks based on HomePlug-AV power line communications

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    [ESP] No hace mucho tiempo, las redes in-home (también denominadas redes domésticas) únicamente se utilizaban para interconectar los diferentes ordenadores de una vivienda, de manera que pudieran compartir una impresora entre ellos. Hoy en día, sin embargo, esta definición es mucho más amplia debido a la gran cantidad de dispositivos existentes en la vivienda con capacidad de conectarse a una red para transmitir y recibir información. En una red in-home actual, podemos encontrar desde teléfonos móviles equipados con conectividad WI-FI a dispositivos NAS (Network Attached Storage), utilizados para almacenar información, imágenes o videos en red, que a su vez pueden ser transferidos a televisiones de alta definición u ordenadores. A la hora de instalar una red de comunicaciones en una vivienda, se persiguen principalmente dos objetivos, reducir el coste de instalación y conseguir una gran flexibilidad de cara a futuras ampliaciones. Una red basada en tecnología PLC (Power Line Communications) cumple estos requisitos ya que, al utilizar la infraestructura de cableado eléctrico existente en la vivienda, es muy sencilla y económica de instalar y ampliar. Dentro de la tecnología PLC existen diferentes estándares, siendo HomePlug-AV (HomePlug Audio-Video o simplemente HPAV) el más extendido en la actualidad para la instalación de redes domésticas. Este estándar permite alcanzar velocidades de transmisión de hasta 200Mbps a través de los cables de baja tensión de una vivienda convencional. El objetivo principal de esta tesis doctoral es aportar nuevas ideas que mejoren las prestaciones de las redes in-home basadas en la tecnología PLC, utilizando como base el estándar Homeplug-AV. Estas redes utilizan una arquitectura centralizada, en la que la mayor parte de la inteligencia de red está concentrada en un coordinador central (CCo, por sus siglas en inglés). Por lo tanto, la mayor parte de las modificaciones propuestas irán encaminadas a mejorar dicho dispositivo, que podrá llegar a convertirse en un gestor de red capaz de manejar conjuntamente interfaces de diferentes tecnologías. En primer lugar, se presenta un análisis detallado del comportamiento del estándar en diferentes situaciones que se pueden producir de manera común en una red doméstica. Este análisis se realizó tanto con dispositivos reales como mediante simulación. Para el segundo tipo de medidas, se diseñó un simulador de la tecnología HomePlug que implementa el nivel físico y el nivel MAC de la misma, junto con modelos de los servicios más utilizados en entornos domésticos. Este simulador se utilizó tanto para estas medidas iniciales como para evaluar las diferentes modificaciones del estándar propuestas posteriormente en este trabajo. Este análisis proporcionó dos resultados significativos. En primer lugar, se comprobó que al introducir un modelo real de nivel físico al protocolo CSMA/CA utilizado a nivel MAC se producían resultados muy diferentes a los presentados en los modelos publicados hasta ese momento. Por ello, se propuso un modelo matemático que incorporaba dichos efectos. En segundo lugar, se identificaron diferentes áreas de la tecnología que eran susceptibles de mejora. El resto de la tesis se centró entonces en la mejora de dichos puntos débiles. El primero de estos puntos débiles está relacionado con las transmisión de datos unicast. El medio PLC es selectivo en frecuencia y muy dependiente del tiempo y de la localización de las estaciones. Incluso es posible que, en un mismo enlace, la capacidad de los enlaces ascendente y descendente sea distinta. En estos entornos, la utilización del protocolo de transporte TCP presenta serios problemas, ya que define gran parte de sus parámetros en función del Round Trip time (RTT) del enlace. Como alternativa se pensó en los códigos Fountain. Este tipo de codificación de fuente permite realizar transmisiones fiables de datos sin necesidad de utilizar un canal de retorno, evitando de esta forma los problemas derivados de las asimetrías de la red. Se realizaron varios experimentos comparando ambas soluciones, y se comprobó que las prestaciones de este tipo de codificaciones superan al protocolo TCP a la hora de transmitir ficheros de manera fiable a través de las redes PLC. Además, los códigos Fountain también se utilizaron para el diseño de otra aplicación. Es muy común que en un escenario doméstico haya disponible más de una tecnología (Wi-Fi, Ethernet, PLC, etc). Tenemos por tanto que una aplicación capaz de integrar interfaces de diferentes tecnologías podría ser muy útil en estos entornos, ya que se podría conseguir un mayor ancho de banda, mayor tolerancia a errores, balanceo de carga, etc. El kernel de Linux dispone de un módulo denominado Bonding que permite agrupar diferentes interfaces Ethernet. Sin embargo, no está preparado para agrupar interfaces de diferentes tecnologías, y mucho menos para tecnologás de capacidad variable como es el caso de PLC o de las comunicaciones inalámbricas. Por ello, se realizó una modificación de dicho driver utilizando para ello los códigos Fountain, que solucionan los problemas que se pueden producir debido a las variaciones de capacidad. Por otra parte, con la actual versión del estándar HomePlug AV, las comunicaciones multicast presentan unas prestaciones muy pobres. Esto es debido a que, a pesar de que el canal PLC es broadcast, la naturaleza de la modulación OFDM (Ortogonal Frequency Division Multiplexing) que se utiliza a nivel físico es punto a punto. Esto hace que las transmisiones simultáneas a un grupo de receptores se traduzcan automáticamente en sucesivas transmisiones punto a punto a los diferentes miembros del grupo. Con esta técnica, la capacidad efectiva de transmisión multicast disminuye de manera muy importante a medida que aumenta el número de receptores. En este trabajo se han propuesto dos técnicas alternativas. La primera consiste en la utilización de un mapa de tonos común para todos los miembros del grupo multicast, asignado a estas comunicaciones los parámetros de modulación del cliente con las peores condiciones de canal. Este algoritmo ha sido tradicionalmente descartado en los sistemas OFDM por sus bajas prestaciones. Sin embargo, la correlación existente entre los diferentes canales de una red PLC hace que su comportamiento sea mucho mejor. Además, se propuso un segundo algoritmo que utilizaba técnicas de optimización para maximizar la tasa de comunicación multicast, obteniendo un mejor comportamiento cuando el número de clientes es elevado. Por último, en redes de capacidad física variable, como es el caso de las redes PLC, las técnicas cross-layer están despertando un gran interés. Este tipo de algoritmos están basado en la compartición de información entre diferentes capas de la estructura OSI para mejorar el comportamiento del sistema. En este trabajo se ha propuesto un algoritmo que modifica los parámetros del protocolo CSMA/CA de nivel MAC utilizando información de nivel físico y los requerimientos de QoS del servicio de niveles superiores. De esta forma se consigue dar prioridad en el acceso al medio a los clientes con problemas de QoS, mejorando de esta forma del comportamiento de la red. Este algoritmo ha sido evaluado mediante simulación en un escenario doméstico típico, comprobando que ofrece unos resultados muy prometedores. [ENG] Not very long time ago, in-home networks (also called domestic networks) were only used to share a printer between a number of computers. Nowadays, however, due to the huge amount of devices present at home with communication capabilities, this definition has become much wider. In a current in-home network we can find, from mobile phones with wireless connectivity, or NAS (Network Attached Storage) devices sharing multimedia content with high-definition televisions or computers. When installing a communications network in a home, two objectives are mainly pursued: Reducing cost and high flexibility in supporting future network requirements. A network based on Power Line Communications (PLC) technology is able to fulfill these objectives, since as it uses the low voltage wiring already available at home, it is very easy to install and expand, providing a cost-effective solution for home environments. There are different PLC standards, being HomePlug-AV (HomePlug Audio-Video, or simply HPAV) the most widely used nowadays. This standard is able to achieve transmission rates up to 200 Mpbs through the electrical wiring of a typical home. The main objective of this thesis is to provide new ideas to improve the performance of PLC technology based in-home networks, using as starting point the HPAV standard. A network based on this technology uses a centralized architecture, in which the most important part of the network intelligence is concentrated in a single device, the Central Coordinator (CCo). Hence, most of the modifications proposed in this work will try to improve this particular device, which can even become a multi-technology central manager, able to combine interfaces of different technologies to improve the network performance. Initially, it is presented a detailed analysis of HPAV performance in some scenarios typically found in a home environment. It was done through simulation and by experimentation using real devices. To obtain the former results, it was designed a HPAV simulator which implements the physical (PHY) and medium access control (MAC) layers of the standard, together with a traffic modeling module which implements the services most commonly found in a home network. This simulation tool was used both in these initial measurements and to evaluate the standard modifications that are proposed in this work. This analysis provides two main results. Firstly, it was found that when a real PHY model is used together with the CSMA/CA MAC protocol the simulation results were very different to those obtained with previously presented mathematical models of this protocol. Hence, it was proposed a new model that considers these effects. Next, some areas of the technology which could be improved were identified. The rest of the thesis was then centered around proposing solutions to these weaknesses. The first weakness solved is related to unicast data transmission. PLC medium is frequency selective and time variant, and it presents a remarkable variation among locations or depending on the connected loads. Even in a single link, the channel capacities between transmitter and receiver can be very asymmetric. In such environments, the use of TCP as transport protocol presents serious problems, since it defines some of its parameters according to the Round Trip Time (RTT). Alternatively, the use of Fountain codes for reliable data transmission in these environments was proposed. These codes allow to transmit information without a feedback channel, overcoming in this way the problems related to the variability of the channel. Different experiments were performed comparing both solutions, concluding that in PLC based networks the performance achieved by Fountain codes outperforms the results obtained with a TCP-based application. In addition, Fountain codes were also used for another application. In home environments, it is very common to find more than one available technology to deploy a network (Wi-Fi, Ethernet, PLC, etc). Therefore, an application that makes possible the aggregation of different interfaces would be very useful, as it will provide higher bandwidth, fault tolerance and load balancing. The Linux Kernel contains a driver (Bonding) which allows Ethernet interfaces aggregation. However, it is not prepared for asymmetric interfaces aggregation and even less for variable capacity technologies like PLC or Wi-Fi. In this work, it is presented a modification of this driver which uses Fountain codes to solve the problems that may arise when asymmetric interfaces are aggregated. On another note, multicast communications in the actual HPAV standard versions presents serious problems. This is because, although PLC medium is broadcast by nature, the Orthogonal Frequency Division Multiplexing (OFDM) modulation used at PHY layer is always point to point. Therefore, multicast communications are carried out as successive point-to-point transmissions to the different members of the group. This technique clearly degrades the performance of multicast services as the number of receivers increases. In this work, they have been proposed two alternative algorithms. The first one consists of using a common tone map for all the multicast group members. This tone map corresponds to the modulation parameters obtained for the client with the worst channel conditions. This algorithm has been traditionally discarded in OFDM systems because of its poor performance. However, in contrast to other technologies (like wireless for example), channel responses in a given PLC network exhibit significant correlation among them. This reduces the differences among the users, improving the performance of this algorithm. In addition, another technique which uses an optimization algorithm to maximize the multicast bit rate is also evaluated, obtaining that its use can be suitable when the number of multicast clients is high. Finally, due to the properties of PLC medium, cross-layer technique are eliciting a big interest. These algorithms are based in the information sharing between adjacent layers in the OSI model to improve the system behavior. In this work, it has been proposed an extension of the HPAV CSMA/CA algorithm which modifies the protocol parameters using PHY layer information and the QoS requirements of the upper-layer services. In this way, priority access to the channel can be provided to the nodes with QoS problems, improving the whole network performance. This algorithm has been evaluated through simulation in a typical home environment with very promising results.Universidad Politécnica de Cartagen

    DyMo: Dynamic Monitoring of Large Scale LTE-Multicast Systems

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    LTE evolved Multimedia Broadcast/Multicast Service (eMBMS) is an attractive solution for video delivery to very large groups in crowded venues. However, deployment and management of eMBMS systems is challenging, due to the lack of realtime feedback from the User Equipment (UEs). Therefore, we present the Dynamic Monitoring (DyMo) system for low-overhead feedback collection. DyMo leverages eMBMS for broadcasting Stochastic Group Instructions to all UEs. These instructions indicate the reporting rates as a function of the observed Quality of Service (QoS). This simple feedback mechanism collects very limited QoS reports from the UEs. The reports are used for network optimization, thereby ensuring high QoS to the UEs. We present the design aspects of DyMo and evaluate its performance analytically and via extensive simulations. Specifically, we show that DyMo infers the optimal eMBMS settings with extremely low overhead, while meeting strict QoS requirements under different UE mobility patterns and presence of network component failures. For instance, DyMo can detect the eMBMS Signal-to-Noise Ratio (SNR) experienced by the 0.1% percentile of the UEs with Root Mean Square Error (RMSE) of 0.05% with only 5 to 10 reports per second regardless of the number of UEs

    Models and Methods for Network Selection and Balancing in Heterogeneous Scenarios

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    The outbreak of 5G technologies for wireless communications can be considered a response to the need for widespread coverage, in terms of connectivity and bandwidth, to guarantee broadband services, such as streaming or on-demand programs offered by the main television networks or new generation services based on augmented and virtual reality (AR / VR). The purpose of the study conducted for this thesis aims to solve two of the main problems that will occur with the outbreak of 5G, that is, the search for the best possible connectivity, in order to offer users the resources necessary to take advantage of the new generation services, and multicast as required by the eMBMS. The aim of the thesis is the search for innovative algorithms that will allow to obtain the best connectivity to offer users the resources necessary to use the 5G services in a heterogeneous scenario. Study UF that allows you to improve the search for the best candidate network and to achieve a balance that allows you to avoid congestion of the chosen networks. To achieve these two important focuses, I conducted a study on the main mathematical methods that made it possible to select the network based on QoS parameters based on the type of traffic made by users. A further goal was to improve the computational computation performance they present. Furthermore, I carried out a study in order to obtain an innovative algorithm that would allow the management of multicast. The algorithm that has been implemented responds to the needs present in the eMBMS, in realistic scenarios

    Video QoS/QoE over IEEE802.11n/ac: A Contemporary Survey

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    The demand for video applications over wireless networks has tremendously increased, and IEEE 802.11 standards have provided higher support for video transmission. However, providing Quality of Service (QoS) and Quality of Experience (QoE) for video over WLAN is still a challenge due to the error sensitivity of compressed video and dynamic channels. This thesis presents a contemporary survey study on video QoS/QoE over WLAN issues and solutions. The objective of the study is to provide an overview of the issues by conducting a background study on the video codecs and their features and characteristics, followed by studying QoS and QoE support in IEEE 802.11 standards. Since IEEE 802.11n is the current standard that is mostly deployed worldwide and IEEE 802.11ac is the upcoming standard, this survey study aims to investigate the most recent video QoS/QoE solutions based on these two standards. The solutions are divided into two broad categories, academic solutions, and vendor solutions. Academic solutions are mostly based on three main layers, namely Application, Media Access Control (MAC) and Physical (PHY) which are further divided into two major categories, single-layer solutions, and cross-layer solutions. Single-layer solutions are those which focus on a single layer to enhance the video transmission performance over WLAN. Cross-layer solutions involve two or more layers to provide a single QoS solution for video over WLAN. This thesis has also presented and technically analyzed QoS solutions by three popular vendors. This thesis concludes that single-layer solutions are not directly related to video QoS/QoE, and cross-layer solutions are performing better than single-layer solutions, but they are much more complicated and not easy to be implemented. Most vendors rely on their network infrastructure to provide QoS for multimedia applications. They have their techniques and mechanisms, but the concept of providing QoS/QoE for video is almost the same because they are using the same standards and rely on Wi-Fi Multimedia (WMM) to provide QoS

    Video streaming over the internet using application layer multicast

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    Multicast is a very important communication paradigm. However, the deployment of multicast at IP layer is very slow, due to development and deployment issues such as ISPs' lack of incentives to update routers and inter-operability among multicast routing protocols. Application Layer Multicast (ALM) is a good alternative, where participating peers organize themselves into a logical overlay network atop the physical links and data is \tunneled" to each other via unicast links. The distinctive feature between IP multicast and ALM is that in ALM, data replication and forwarding functionalities are performed by participating peers (a.k.a. end systems), rather than the routers in Internet Protocol (IP) multicast. This fundamental difference enables ALM to be able to circumvent the development and deployment issues of IP multicast, by exploiting the resources (e.g., CPU cycles, storage, and access bandwidth) at the edge of the network. Nevertheless, it also raises other challenges, as peers are not as stable as routers since they may join and depart the on-going session at will. In this thesis, we address some of the challenges and they are summarized as follows: First, most current P2P or ALM streaming systems are equipped with a non-scalable membership management algorithm, greatly hindering their applicability to large-scale implementations over the Internet: they either rely on a central entity to handle group membership, or simply assume that all group members are visible to each other and flooding is the main mechanism used to disseminate membership-related updates to all participating group members. This implies that they are only applicable to small groups. Second, one of ALM's prominent features, flexility, has not been fully exploited: moving the multicast functionalities from lower layer (IP layer) to higher layer (Application layer) can greatly facilitate the integration of Quality-of-Service (QoS) support. The end-to-end philosophy states that it is better to leave those functionalities to higher layers because the heterogeneity among users' requirements can be handled much better by end users, rather than the network. However, QoS, and in particular, reliability has not been thoroughly addressed in existing ALM schemes. Third, admission control algorithms are essential to the success of any ALM system, due to the fact that in ALM, each peer acts as both a client as well as a server. On the other hand, the heterogeneity among peers, in terms of their computational power, storage capacity, and access bandwidth, further complicates the design of a good admission control. Several contributions are made to address the aforementioned research challenges, and they are outlined as follows: The first contribution is a devised gossip-based membership management algorithm that is able to collect and disseminate membership-related information under high rate of churn, using relatively low communication overheads. The second contribution is a reliability-centric multicast tree construction algorithm that greatly enhance peers' perceived reliability. The third contribution is a QoS-aware tree construction algorithm that accommodates the heterogeneity among peers, such as access bandwidth, network distance, and reliability. The last contribution is the identification of the admission control problem in this overlay video streaming

    Framework for Content Distribution over Wireless LANs

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    Wireless LAN (also called as Wi-Fi) is dominantly considered as the most pervasive technology for Intent access. Due to the low-cost of chipsets and support for high data rates, Wi-Fi has become a universal solution for ever-increasing application space which includes, video streaming, content delivery, emergency communication, vehicular communication and Internet-of-Things (IoT). Wireless LAN technology is defined by the IEEE 802.11 standard. The 802.11 standard has been amended several times over the last two decades, to incorporate the requirement of future applications. The 802.11 based Wi-Fi networks are infrastructure networks in which devices communicate through an access point. However, in 2010, Wi-Fi Alliance has released a specification to standardize direct communication in Wi-Fi networks. The technology is called Wi-Fi Direct. Wi-Fi Direct after 9 years of its release is still used for very basic services (connectivity, file transfer etc.), despite the potential to support a wide range of applications. The reason behind the limited inception of Wi-Fi Direct is some inherent shortcomings that limit its performance in dense networks. These include the issues related to topology design, such as non-optimal group formation, Group Owner selection problem, clustering in dense networks and coping with device mobility in dynamic networks. Furthermore, Wi-Fi networks also face challenges to meet the growing number of Wi Fi users. The next generation of Wi-Fi networks is characterized as ultra-dense networks where the topology changes frequently which directly affects the network performance. The dynamic nature of such networks challenges the operators to design and make optimum planifications. In this dissertation, we propose solutions to the aforementioned problems. We contributed to the existing Wi-Fi Direct technology by enhancing the group formation process. The proposed group formation scheme is backwards-compatible and incorporates role selection based on the device's capabilities to improve network performance. Optimum clustering scheme using mixed integer programming is proposed to design efficient topologies in fixed dense networks, which improves network throughput and reduces packet loss ratio. A novel architecture using Unmanned Aeriel Vehicles (UAVs) in Wi-Fi Direct networks is proposed for dynamic networks. In ultra-dense, highly dynamic topologies, we propose cognitive networks using machine-learning algorithms to predict the network changes ahead of time and self-configuring the network
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