19 research outputs found

    Greediness control algorithm for multimedia streaming in wireless local area networks

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    This work investigates the interaction between the application and transport layers while streaming multimedia in a residential Wireless Local Area Network (WLAN). Inconsistencies have been identified that can have a severe impact on the Quality of Experience (QoE) experienced by end users. This problem arises as a result of the streaming processes reliance on rate adaptation engines based on congestion avoidance mechanisms, that try to obtain as much bandwidth as possible from the limited network resources. These upper transport layer mechanisms have no knowledge of the media which they are carrying and as a result treat all traffic equally. This lack of knowledge of the media carried and the characteristics of the target devices results in fair bandwidth distribution at the transport layer but creates unfairness at the application layer. This unfairness mostly affects user perceived quality when streaming high quality multimedia. Essentially, bandwidth that is distributed fairly between competing video streams at the transport layer results in unfair application layer video quality distribution. Therefore, there is a need to allow application layer streaming solutions, tune the aggressiveness of transport layer congestion control mechanisms, in order to create application layer QoE fairness between competing media streams, by taking their device characteristics into account. This thesis proposes the Greediness Control Algorithm (GCA), an upper transport layer mechanism that eliminates quality inconsistencies caused by rate / congestion control mechanisms while streaming multimedia in wireless networks. GCA extends an existing solution (i.e. TCP Friendly Rate Control (TFRC)) by introducing two parameters that allow the streaming application to tune the aggressiveness of the rate estimation and as a result, introduce fair distribution of quality at the application layer. The thesis shows that this rate adaptation technique, combined with a scalable video format allows increased overall system QoE. Extensive simulation analysis demonstrate that this form of rate adaptation increases the overall user QoE achieved via a number of devices operating within the same home WLAN

    Adaptive multimedia streaming control algorithm in wireless LANs and 4G networks

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    E-learning has become an important service offered over the Internet. Lately many users are accessing learning content via wireless networks and using mobile devices. Most content is rich media-based and often puts significant pressure on the existing wireless networks in order to support high quality of delivery. In this context, offering a solution for improving user quality of experience when multimedia content is delivered over wireless networks is already a challenging task. Additionally, to support this for mobile e-learning over wireless LANs becomes even more difficult. If we want to increase the end-used perceived quality, we have to take into account the users’ individual set of characteristics. The fact that users have subjective opinions on the quality of a multimedia application can be used to increase their QoE by setting a minimum quality threshold below which the connection is considered to be undesired. Like this, the use of precious radio resources can be optimized in order to simultaneously satisfy an increased number of users. In this thesis a new user-oriented adaptive algorithm based on QOAS was designed and developed in order to address the user satisfaction problem. Simulations have been carried out with different adaptation schemes to compare the performances and benefits of the DQOAS mechanism. The simulation results are showing that using a dynamic stream granularity with a minimum threshold for the transmission rate, improves the overall quality of the multimedia delivery process, increasing the total number of satisfied users and the link utilization The good results obtained by the algorithm in IEEE 802.11 wireless environment, motivated the research about the utility of the newly proposed algorithm in another wireless environment, LTE. The study shows that DQOAS algorithm can obtain good results in terms of application perceived quality, when the considered application generates multiple streams. These results can be improved by using a new QoS parameters mapping scheme able to modify the streams’ priority and thus allowing the algorithms decisions to not be overridden by the systems’ scheduler

    Handoff management for infotainment services over vehicular networks

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    Intelligent Transportation Systems (ITS) has impulsed the vehicular communications at the present time. The vehicular communications field is a hot research topic and is attracting a great interest in the automotive industry and telecommunications. There are essentially two main lines of work: (1) communication services related to road safety and traffic information; and (2) information and entertainment services, also named infotainment services. These latter services include both transmitting multimedia (voice over IP, streaming, on-line gaming, etc.) and classic data services (e-mail, access to private networks, web browsing, file sharing, etc.). In this thesis we will focus on these infotainment services because further research in this immature research field is necessary and, until nowadays, the main effort of the research community regarding vehicular communication has been focused on road safety and traffic information. Vehicular nodes need to be reached from the Internet and vice versa to be able to access to infotainment services. While vehicles move along the road infrastructure, they change their wireless point of attachment to the network. During this process, connectivity breaks down until the vehicle is connected again to a new road side unit in its area. This disconnection causes a disruption in the communications. Fast handoffs are a crucial requirement for vehicular networks to avoid long disruption times, since the high speed of vehicular nodes involves suffering a lot of handoffs during an Internet connection. This thesis is focused on Vehicular-to-Infrastructure (V2I) real-time infotainment services. The main contributions of this thesis are: i) a new testing framework for V2I communications to be able to test infotainment services in an easy way; ii) the analysis of the deployability of infotainment video services in vehicular networks using mobility protocols; and iii) the development of a new TCP architecture that will provide a better performance for all TCP-based infotainment services in a vehicular scenario with handoffs. In this thesis, firstly, we propose a new testing framework for vehicular infotainment applications. This framework is a vehicular emulation platform that allows testing real applications installed on Linux virtual machines. Using emulation, we are able to evaluate the performance of real applications with real-time requirements, so we can test multimedia applications used to offer infotainment services in vehicular scenarios in a straightforward way. Secondly, using the testing framework implemented in the first part of the thesis, we have done a performance evaluation of an infotainment service. Among these services, we think that video on demand services on highways will be interesting for users, and generate revenue to network operators. So we evaluated how network-layer handoffs can limit the deployment of a video streaming service. According to the results obtained, driving at high speeds will be an issue for a correct playback of video content, even using fast handoffs techniques. Finally, we developed a new TCP architecture to enhance performance during handoffs. Most of the non-safety services on ITS rely on the Transport Control Protocol (TCP), one of the core protocols of the Internet Protocol Suite. However there exists several issues related to TCP and mobility that can affect to TCP performance, and these issues are particularly important in vehicular networks due to its high mobility. Using new IEEE 802.21 MIH services, we propose a new TCP architecture that is able to anticipate handoffs, permitting to resume the communication after a handoff, avoiding long delays caused by TCP issues and adapting the TCP parameters to the new characteristics of the network. Using the architecture proposed, the performance of TCP is enhanced, getting a higher overall throughput and avoiding TCP fairness issues between users.Els Sistemes de Transport Intel·ligents (ITS) han impulsat les comunicacions vehiculars en l'actualitat. Les comunicacions vehiculars és un camp d'investigació de moda, i està atraient un gran interès en la indústria automobilística i de les telecomunicacions. En el camp de les comunicacions vehiculars, hi ha principalment dues línies de treball: (1) serveis de comunicacions relacionats amb la seguretat viària i la informació del trànsit; i (2) serveis d'informació i entreteniment, també anomenats serveis d'infotainment. Aquests últims inclouen tant serveis multimèdia (veu sobre IP, streaming, jocs on-line, etc.), com serveis clàssics de dades (correu electrònic, accés a xarxes privades, navegació web, compartir arxius, etc.). En aquesta tesi ens centrarem en aquests serveis d'infotainment ja que és necessari aprofundir en la investigació per aquests tipus de serveis, ja que, fins avui, els esforços de la comunitat científica en el camp de les comunicacions vehiculars s'ha centrat en els serveis relacionats amb la seguretat viària i la informació del trànsit. Els nodes vehiculars necessiten tenir connexió a Internet per a poder tenir accés als serveis d'infotainment. Mentre els vehicles estan en moviment a través de la xarxa viària, els vehicles han d'anar canviant el punt de connexió sense fils amb la xarxa. Durant aquest procés de canvi de punt de connexió, anomenat handoff, es perd la connectivitat fins que el vehicle es reconnecta a un altre punt de connexió viària prop de la seva àrea. Aquesta desconnexió causa interrupcions en les comunicacions. Uns handoffs ràpids són bàsics a les xarxes vehiculars per a evitar llargs períodes d'interrupció durant les comunicacions, ja que la gran velocitat a la que es mouen els nodes vehiculars significa un gran nombre de handoffs durant una connexió a Internet. Aquesta tesi es centra en serveis d'infotaiment en temps real per a comunicacions Vehicle-a-Infraestructura (V2I). Les principals contribucions d'aquesta tesi son: i) un nou marc de proves per a les comunicacions (V2I) per a poder provar serveis d'infotainment d'una manera fàcil; ii) l'anàlisi de la viabilitat del desplegament de serveis d'infotainment de vídeo en xarxes vehiculars utilitzant protocols de mobilitat IP; i iii) el desenvolupament d'una nova arquitectura TCP que proporciona un millor funcionament per a tots aquells serveis d'infotainment basats en el protocol TCP en un escenari vehicular amb handoffs. En aquesta tesi, primer proposem un nou marc de proves per a aplicacions vehiculars d'infotainment. Aquest marc és una plataforma d'emulació vehicular que permet provar aplicacions reals instal·lades en màquines virtuals Linux. Utilitzant l'emulació, som capaços d'avaluar el rendiment d'aplicacions reals amb característiques de temps real. D'aquesta manera es poden avaluar aplicacions multimèdia utilitzades per oferir serveis d'infotainment d'una forma senzilla en escenaris vehiculars. Segon, utilitzant el marc de prova implementat en la primera part de la tesi, hem avaluat el rendiment d'un servei d'infotainment. Entre aquest tipus de servei, creem que els serveis de vídeo sota demanda en autopistes/autovies serà interessant pels usuaris i generarà beneficis per als operadors de la xarxa. Per tant, hem avaluat com els handoffs a nivell de la capa de xarxa poden limitar el desplegament d'un servei de streaming de vídeo sota demanda. D'acord amb els resultats obtinguts, conduir a grans velocitats podria ser un problema per a poder reproduir un vídeo correctament, tot i utilitzar tècniques de handoffs ràpids. Finalment, hem desenvolupat una nova arquitectura TCP per a millorar el rendiment del protocol durant els handoffs. La majoria dels serveis d'infotainment utilitzen el Protocol de Control de Transport (TCP), un dels principals protocols de la pila de protocols d'Internet. Però existeixen forces problemes relacionats amb l'ús de TCP i la mobilitat que n'afecta el rendiment, i aquests problemes són particular

    A Comprehensive Survey of the Tactile Internet: State of the art and Research Directions

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    The Internet has made several giant leaps over the years, from a fixed to a mobile Internet, then to the Internet of Things, and now to a Tactile Internet. The Tactile Internet goes far beyond data, audio and video delivery over fixed and mobile networks, and even beyond allowing communication and collaboration among things. It is expected to enable haptic communication and allow skill set delivery over networks. Some examples of potential applications are tele-surgery, vehicle fleets, augmented reality and industrial process automation. Several papers already cover many of the Tactile Internet-related concepts and technologies, such as haptic codecs, applications, and supporting technologies. However, none of them offers a comprehensive survey of the Tactile Internet, including its architectures and algorithms. Furthermore, none of them provides a systematic and critical review of the existing solutions. To address these lacunae, we provide a comprehensive survey of the architectures and algorithms proposed to date for the Tactile Internet. In addition, we critically review them using a well-defined set of requirements and discuss some of the lessons learned as well as the most promising research directions

    Provision Quality-of-Service Controlled Content Distribution in Vehicular Ad Hoc Networks

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    By equipping vehicles with the on-board wireless facility, the newly emerged vehicular networking targets to provision the broadband serves to vehicles. As such, a variety of novel and exciting applications can be provided to vehicular users to enhance their road safety and travel comfort, and finally raise a complete change to their on-road life. As the content distribution and media/video streaming, such as Youtube, Netflix, nowadays have become the most popular Internet applications, to enable the efficient content distribution and audio/video streaming services is thus of the paramount importance to the success of the vehicular networking. This, however, is fraught with fundamental challenges due to the distinguished natures of vehicular networking. On one hand, the vehicular communication is challenged by the spotty and volatile wireless connections caused by the high mobility of vehicles. This makes the download performance of connections very unstable and dramatically change over time, which directly threats to the on-top media applications. On the other hand, a vehicular network typically involves an extremely large-scale node population (e.g., hundreds or thousandths of vehicles in a region) with intense spatial and temporal variations across the network geometry at different times. This dictates any designs to be scalable and fully distributed which should not only be resilient to the network dynamics, but also provide the guaranteed quality-of-service (QoS) to users. The purpose of this dissertation is to address the challenges of the vehicular networking imposed by its intrinsic dynamic and large-scale natures, and build the efficient, scalable and, more importantly, practical systems to enable the cost-effective and QoS guaranteed content distribution and media streaming services to vehicular users. Note that to effective- ly deliver the content from the remote Internet to in-motion vehicles, it typically involves three parts as: 1.) an infrastructure grid of gateways which behave as the data depots or injection points of Internet contents and services to vehicles, 2.) protocol at gateways which schedules the bandwidth resource at gateways and coordinates the parallel transmissions to different vehicles, and 3.) the end-system control mechanism at receivers which adapts the receiver’s content download/playback strategy based on the available network throughput to provide users with the desired service experience. With above three parts in mind, the entire research work in this dissertation casts a systematic view to address each part in one topic with: 1.) design of large-scale cost-effective content distribution infrastructure, 2.) MAC (media access control) performance evaluation and channel time scheduling, and 3.) receiver adaptation and adaptive playout in dynamic download environment. In specific, in the first topic, we propose a practical solution to form a large-scale and cost-effective content distribution infrastructure in the city. We argue that a large-scale infrastructure with the dedicated resources, including storage, computing and communication capacity, is necessary for the vehicular network to become an alternative of 3G/4G cellular network as the dominating approach of ubiquitous content distribution and data services to vehicles. On addressing this issue, we propose a fully distributed scheme to form a large-scale infrastructure by the contributions of individual entities in the city, such as grocery stores, movie theaters, etc. That is to say, the installation and maintenance costs are shared by many individuals. In this topic, we explain the design rationale on how to motivate individuals to contribute, and specify the detailed design of the system, which is embodied with distributed protocols and performance evaluation. The second topic investigates on the MAC throughput performance of the vehicle-to- infrastructure (V2I) communications when vehicles drive through RSUs, namely drive-thru Internet. Note that with a large-scale population of fast-motion nodes contending the chan- nel for transmissions, the MAC performance determines the achievable nodal throughput and is crucial to the on-top applications. In this topic, using a simple yet accurate Marko- vian model, we first show the impacts of mobility (characterized by node velocity and moving directions) on the nodal and system throughput performance, respectively. Based on this analysis, we then propose three enhancement schemes to timely adjust the MAC parameters in tune with the vehicle mobility to achieve the maximal the system throughput. The last topic investigates on the end-system design to deliver the user desired media streaming services in the vehicular environment. In specific, the vehicular communications are notoriously known for the intermittent connectivity and dramatically varying throughput. Video streaming on top of vehicular networks therefore inevitably suffers from the severe network dynamics, resulting in the frequent jerkiness or even freezing video playback. To address this issue, an analytical model is first developed to unveil the impacts of network dynamics on the resultant video performance to users in terms of video start-up delay and smoothness of playback. Based on the analysis, the adaptive playout buffer mechanism is developed to adapt the video playback strategy at receivers towards the user-defined video quality. The proposals developed in the three topics are validated with the extensive and high fidelity simulations. We believe that our analysis developed in the dissertation can provide insightful lights on understanding the fundamental performance of the vehicular content distribution networks from the aspects of session-level download performance in urban vehicular networks (topic 1), MAC throughput performance (topic 2), and user perceived media quality (topic 3). The protocols developed in the three topics, respectively, offer practical and efficient solutions to build and optimize the vehicular content distribution networks

    Quality of service based distributed control of wireless networks

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    Support of resource-aware vertical handovers in WLAN hotspots

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    Endgeräte wie Smartphones oder Tablets bieten häufig eine Vielfalt drahtloser Zugänge zum Internet an. Üblicherweise schließt dies die 802.11 WLANs und auch Technologien drahtloser Weitverkehrsnetze (WWANs) aus dem Bereich LTE oder WiMAX ein. Aufgrund dieser Optionen haben sich die Endanwender daran gewöhnt, überall und zu jeder Zeit auf ihre Internetdienste zuzugreifen. Damit hat auch der Datenverkehr pro Anwender zugenommen, was eine Herausforderung insbesondere für die Betreiber von WWANs ist. Soweit verfügbar, favorisieren Endanwender heutzutage eher einen drahtlosen Zugang zum Internet über WLANs als über WWANs. Des Weiteren haben die 3GPP-Standardisierungsgremien Ansätze erarbeitet, die zusätzlich Verkehr aus WWANs in Netze mit geringerer Abdeckung wie WLAN- oder Femto-Zellen abgeben. Solche Ansätze werden auch als "Traffic Offloading" bezeichnet und haben das Ziel, die WWANs zu entlasten. Dabei werden jedoch eher einfache Strategien verfolgt, die auf der Nutzung zusätzlicher Kapazitäten heterogener Netze beruhen und dann angewendet werden, wenn ein alternatives Zugangsnetz für ein Endgerät verfügbar ist. Im Rahmen dieser Arbeit zeigen wir Gewinne auf, die entstehen, wenn man die Auswahl der Endgeräte für ein WLAN-Netz stattdessen auf Basis der von ihnen belegten Ressourcen durchführt. In diesem Kontext schlagen wir vor, Geräte mit stark negativem Einfluss auf die WLAN-Kapazität wieder zurück in das WWAN zu reichen, was wir als "Onloading" bezeichnen. Ein solches "Onloading" zieht Herausforderungen in unterschiedlichen Richtungen mit sich. Die fortschreitende Miniaturisierung hat in den letzten Jahren zu dem Trend geführt, die Anzahl der Netzwerkkarten (NICs) in Endgeräten zu reduzieren. Wir bezeichnen eine NIC als multimodal, wenn sie mehrere Funktechnologien unterstützt, aber zu einem bestimmten Zeitpunkt immer nur eine davon genutzt werden kann. Deswegen stellt für eine multimodale NIC das "Onloading" während einer laufenden Verbindung eine Herausforderung dar. Wir schlagen einen Ansatz vor, der vorbereitende Mechanismen für ein "Onloading" als auch eine laufende Verbindung im WLAN über eine solche NIC ermöglicht. Des Weiteren ist es wichtig, in einem WLAN Hotspot zu entscheiden, welche Geräte einen negativen Einfluss auf die Kapazität des Netzes haben. Dafür haben wir eine Metrik entwickelt, die eine Entscheidungsgrundlage für das Onloading bildet. Diese Metrik basiert rein auf einer Beobachtung des Netzes und seiner Geräte, ermöglicht jedoch keine Entscheidung für sich neu assoziierende Geräte im WLAN. Erschwerend kommt hinzu, dass viele Eigenschaften der NICs durch herstellerabhängige Implementierungen geprägt werden. Solche Algorithmen bieten eine zusätzliche Herausforderung, da ihre internen Abläufe üblicherweise unbekannt sind. Ein bekanntes Beispiel für solche Algorithmen stellt die Anpassung der WLAN-Link-Datenraten dar. Diese Algorithmen wählen die jeweiligen Modulations- und Kodierungsschemata (MCSs) für die drahtlosen Übertragungen aus. Robuste MCSs resultieren dabei in geringere Link-Datenraten und haben somit einen starken Einfluss auf die Kapazität einer WLAN-Zelle. Aus diesem Grund fokussieren wir uns auf eine Abschätzung der Datenratenwahl eines Endgerätes. Damit lassen sich im Vorfeld Aussagen treffen, ob ein Gerät starken Einfluss auf die WLAN-Kapazität haben wird, so dass es für ein "Onloading" in Frage kommt.End-user devices such as smart phones and tablets have become very popular as they offer a variety of wireless Internet accesses ranging from the WLAN standards to WWAN technologies such as LTE or even WiMAX. Due to these different wireless access options and new emerging applications—e.g., from the areas of video streaming, social networks, as well as Internet clouds—people are increasingly connecting to the Internet with their de- vices while being on the move. In line with this, the number of devices as well as the traffic demand of end users have been reported to increase rapidly over the last years which imposes a strong challenge especially for the operators of WWANs. Thereby, end users frequently tend to use settings that favor a connectivity to the Internet whenever possible rather over WLAN than over WWAN access. Further, the cellular standardization bodies of the 3GPP envision solutions to hand over on-going wireless sessions from cellular to other small cell accesses such as WLANs or femto cells. This is also known as traffic offloading essentially freeing capacity in terms of users with a certain service in the cellular accesses. Nevertheless this offloading follows a rather simple strategy to utilize additional capacity of heterogeneous accesses such as WLANs whenever being available for a given device. This thesis shows that stronger gains can be expected if the selection of devices to be served in WLANs is conducted in a resource-aware fashion including an evaluation of the WLAN traffic in terms of the channel occupation time and MAC overhead as result of contention, interference, and fluctuating channels. In this context, this thesis envisions to onload unfavorable devices negatively affecting the WLAN capacity back to WWAN accesses. A support of such an onloading imposes challenges in different dimensions. From the hardware design of devices, there is a strong trend to limit the number of separate network interface cards (NICs) due to space and cost issues. We refer to a multi-mode NIC if it covers multiple technologies, while at a given time only access to one technology is possible. Thus, smoothly onloading a device with such a NIC is by far not trivial. We present an approach that conducts handover preparation mechanisms, while also allowing a continuous WLAN communication over a multi-mode NIC. Further, it is by far not trivial to judge which subset of associated devices is negatively affecting the capacity of a WLAN hotspot. Thus, a careful evaluation of devices regarding a selection for an onloading back to WWAN accesses imposes a challenge yet. In this direction, we present a performance metric that identifies devices degrading the WLAN capacity. While our performance metric tackles a reactive selection, it falls short to support a predictive evaluation, e.g., of devices which just joined the WLAN cell. Even worse, proprietary algorithms inside a WLAN stack impose a severe challenge as their internal routines are usually not conveyed via typical management interfaces. A well-known example for this category of algorithms are the link data rate adaptation schemes, with which WLAN devices adjust the modulation and coding scheme (MCS) for their transmissions. As MCSs resulting in low link data rates may specifically degrade the capacity of a WLAN cell, we focus on an estimation regarding the data rate selection of a device as a third contribution of this thesis. This estimation enables to select devices that will likely degrade the capacity of the WLAN hotspot for an onloading in advance

    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

    LTE Optimization and Resource Management in Wireless Heterogeneous Networks

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    Mobile communication technology is evolving with a great pace. The development of the Long Term Evolution (LTE) mobile system by 3GPP is one of the milestones in this direction. This work highlights a few areas in the LTE radio access network where the proposed innovative mechanisms can substantially improve overall LTE system performance. In order to further extend the capacity of LTE networks, an integration with the non-3GPP networks (e.g., WLAN, WiMAX etc.) is also proposed in this work. Moreover, it is discussed how bandwidth resources should be managed in such heterogeneous networks. The work has purposed a comprehensive system architecture as an overlay of the 3GPP defined SAE architecture, effective resource management mechanisms as well as a Linear Programming based analytical solution for the optimal network resource allocation problem. In addition, alternative computationally efficient heuristic based algorithms have also been designed to achieve near-optimal performance

    Contribution to quality of user experience provision over wireless networks

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    The widespread expansion of wireless networks has brought new attractive possibilities to end users. In addition to the mobility capabilities provided by unwired devices, it is worth remarking the easy configuration process that a user has to follow to gain connectivity through a wireless network. Furthermore, the increasing bandwidth provided by the IEEE 802.11 family has made possible accessing to high-demanding services such as multimedia communications. Multimedia traffic has unique characteristics that make it greatly vulnerable against network impairments, such as packet losses, delay, or jitter. Voice over IP (VoIP) communications, video-conference, video-streaming, etc., are examples of these high-demanding services that need to meet very strict requirements in order to be served with acceptable levels of quality. Accomplishing these tough requirements will become extremely important during the next years, taking into account that consumer video traffic will be the predominant traffic in the Internet during the next years. In wired systems, these requirements are achieved by using Quality of Service (QoS) techniques, such as Differentiated Services (DiffServ), traffic engineering, etc. However, employing these methodologies in wireless networks is not that simple as many other factors impact on the quality of the provided service, e.g., fading, interferences, etc. Focusing on the IEEE 802.11g standard, which is the most extended technology for Wireless Local Area Networks (WLANs), it defines two different architecture schemes. On one hand, the infrastructure mode consists of a central point, which manages the network, assuming network controlling tasks such as IP assignment, routing, accessing security, etc. The rest of the nodes composing the network act as hosts, i.e., they send and receive traffic through the central point. On the other hand, the IEEE 802.11 ad-hoc configuration mode is less extended than the infrastructure one. Under this scheme, there is not a central point in the network, but all the nodes composing the network assume both host and router roles, which permits the quick deployment of a network without a pre-existent infrastructure. This type of networks, so called Mobile Ad-hoc NETworks (MANETs), presents interesting characteristics for situations when the fast deployment of a communication system is needed, e.g., tactics networks, disaster events, or temporary networks. The benefits provided by MANETs are varied, including high mobility possibilities provided to the nodes, network coverage extension, or network reliability avoiding single points of failure. The dynamic nature of these networks makes the nodes to react to topology changes as fast as possible. Moreover, as aforementioned, the transmission of multimedia traffic entails real-time constraints, necessary to provide these services with acceptable levels of quality. For those reasons, efficient routing protocols are needed, capable of providing enough reliability to the network and with the minimum impact to the quality of the service flowing through the nodes. Regarding quality measurements, the current trend is estimating what the end user actually perceives when consuming the service. This paradigm is called Quality of user Experience (QoE) and differs from the traditional Quality of Service (QoS) approach in the human perspective given to quality estimations. In order to measure the subjective opinion that a user has about a given service, different approaches can be taken. The most accurate methodology is performing subjective tests in which a panel of human testers rates the quality of the service under evaluation. This approach returns a quality score, so-called Mean Opinion Score (MOS), for the considered service in a scale 1 - 5. This methodology presents several drawbacks such as its high expenses and the impossibility of performing tests at real time. For those reasons, several mathematical models have been presented in order to provide an estimation of the QoE (MOS) reached by different multimedia services In this thesis, the focus is on evaluating and understanding the multimedia-content transmission-process in wireless networks from a QoE perspective. To this end, firstly, the QoE paradigm is explored aiming at understanding how to evaluate the quality of a given multimedia service. Then, the influence of the impairments introduced by the wireless transmission channel on the multimedia communications is analyzed. Besides, the functioning of different WLAN schemes in order to test their suitability to support highly demanding traffic such as the multimedia transmission is evaluated. Finally, as the main contribution of this thesis, new mechanisms or strategies to improve the quality of multimedia services distributed over IEEE 802.11 networks are presented. Concretely, the distribution of multimedia services over ad-hoc networks is deeply studied. Thus, a novel opportunistic routing protocol, so-called JOKER (auto-adJustable Opportunistic acK/timEr-based Routing) is presented. This proposal permits better support to multimedia services while reducing the energy consumption in comparison with the standard ad-hoc routing protocols.Universidad Politécnica de CartagenaPrograma Oficial de Doctorado en Tecnologías de la Información y Comunicacione
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