66 research outputs found

    COST EFFICIENT PROVISIONING OF MASS MOBILE MULTIMEDIA SERVICES IN HYBRID CELLULAR AND BROADCASTING SYSTEMS

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    Uno de los retos a los que se enfrenta la industria de las comunicaciones móviles e inalámbricas es proporcionar servicios multimedia masivos a bajo coste, haciéndolos asequibles para los usuarios y rentables a los operadores. El servicio más representativo es el de TV móvil, el cual se espera que sea una aplicación clave en las futuras redes móviles. Actualmente las redes celulares no pueden soportar un consumo a gran escala de este tipo de servicios, y las nuevas redes de radiodifusión móvil son muy costosas de desplegar debido a la gran inversión en infraestructura de red necesaria para proporcionar niveles aceptables de cobertura. Esta tesis doctoral aborda el problema de la provisión eficiente de servicios multimedia masivos a dispositivos móviles y portables utilizando la infraestructura de radiodifusión y celular existente. La tesis contempla las tecnologías comerciales de última generación para la radiodifusión móvil (DVB-H) y para las redes celulares (redes 3G+ con HSDPA y MBMS), aunque se centra principalmente en DVB-H. El principal paradigma propuesto para proporcionar servicios multimedia masivos a bajo coste es evitar el despliegue de una red DVB-H con alta capacidad y cobertura desde el inicio. En su lugar se propone realizar un despliegue progresivo de la infraestructura DVB-H siguiendo la demanda de los usuarios. Bajo este contexto, la red celular es fundamental para evitar sobre-dimensionar la red DVB-H en capacidad y también en áreas con una baja densidad de usuarios hasta que el despliegue de un transmisor o un repetidor DVB-H sea necesario. Como principal solución tecnológica la tesis propone realizar una codificación multi-burst en DVB-H utilizando códigos Raptor. El objetivo es explotar la diversidad temporal del canal móvil para aumentar la robustez de la señal y, por tanto, el nivel de cobertura, a costa de incrementar la latencia de la red.Gómez Barquero, D. (2009). COST EFFICIENT PROVISIONING OF MASS MOBILE MULTIMEDIA SERVICES IN HYBRID CELLULAR AND BROADCASTING SYSTEMS [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/6881Palanci

    무선 통신 네트워크 환경에서의 효과적인 비디오 스트리밍 기법 연구

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    학위논문 (박사)-- 서울대학교 대학원 : 전기정보공학부, 2013. 8. 최성현.오늘날 무선 네트워크 통신 기술의 발달로 인해 고품질의 비디오 스트리밍 서비스에 대한 요구가 급증하고 있다. 새로운 60~GHz 광대역 고속 무선 통신 기술은 기존의 무선 통신 기술에서는 불가능했던, 고품질의 무압축 비디오 스트리밍을 가능하게 한다. 제한된 무선 자원 환경에서 고품질의 비디오 서비스를 지원하기 위해 주어진 채널 환경에서 적절한 변조 및 코딩 기술을 선택하는 효율적인 링크 적응 기법이 필요하다. 비디오 스트리밍의 품질을 수치로 평가하는 ePSNR을 정의하고, 불평등 오류 보호 기법(UEP)을 추가로 도입하여 보다 세밀한 링크 적응 기법을 가능케 한다. 정의한 ePSNR을 기반으로 (1) 주어진 무선 자원에서 비디오 품질을 최대화, 혹은 (2) 목표 비디오 품질을 만족하는 무선 자원 사용을 최소화, 하는 두가지 링크 적응 기법들을 제안한다. 다양한 시뮬레이션 결과를 통해, 정의한 ePSNR이 비디오 품질을 잘 표현하고 있음을 확인하였다. 또한, 제안한 링크 적응 기법들이 비디오 스트리밍 서비스를 위한 적절한 품질을 제공하면서, 동시에 자원 효율성을 향상시킴을 검증하였다. 한편, 순방향 오류 정정 기법(FEC)은 무선랜 환경에서 고품질의 신뢰성있는 비디오 멀티캐스트를 지원한다. 무선랜 환경에서 복수개의 액세스포인트(AP)간의 조정을 통한 신뢰성있는 비디오 멀티캐스트 기법을 제시한다. 복수개의 AP간의 조정을 통해 각각의 AP들이 (1) 완전히 서로 다른, 혹은 (2) 부분적으로 서로 다른, 인코딩된 패킷들을 전송하게 하여, 공간 및 시간적 다양성을 멀티캐스트 유저에게 제공할 수 있다. 추가로, 제한된 무선 자원을 보다 효율적으로 사용하기 위해, 순방향 오류 정정 기법의 코딩 비율 적응 기법을 위한 자원 할당 알고리즘을 제안한다. 또한, FEC 디코딩 후의 비디오 패킷의 전송율를 예측할 수 있는 방법을 제안한다. 다양한 시뮬레이션과 실험을 통해 제안한 기법들의 우수성을 확인하였다. 멀티캐스트 전송은 기본적으로 무선 채널 오류로 인해 전송 실패가 발생할 가능성을 내포한다. 그러나 기존의 무선랜 표준에서는 멀티캐스트 환경에서 자동 반복 요청 기법(ARQ)을 통한 손실 조정 방법을 제공하지 않았다. 멀티캐스트 전송의 비신뢰성 문제를 해결하기 위해, 자동 반복 요청 기법(ARQ)과 순방향 오류 정정 기법(FEC)를 함께 고려한 신뢰성 있는 멀티캐스트 전송 기법을 제안한다. 신뢰성 있는 멀티캐스트 전송을 위한 피드백 교환의 오버헤드를 줄이기 위한 복수개의 효율적인 피드백 기법을 제시한다. 제안한 피드백 기법은 액세스포인트(AP)가 멀티캐스트 유저들의 손실된 패킷들의 복원을 위해 필요한 패리티(parity) 패킷의 개수를 쉽게 알 수 있도록 한다. 피드백 간의 충돌을 감안한 의도적인 동시 전송을 통해 피드백 오버헤드를 감소시킬 수 있다. 추가로, 효율적인 피드백 프로토콜을 활용하여, 변조 및 코딩 기법(MCS)의 폐쇄적 피드백 기반의 물리 전송 속도 적응 기법을 제안한다. 성능 검증을 통해 제안한 기법들이 효율적으로 피드백 오버헤드를 감소시키며, 동시에 신뢰성있는 멀티캐스트 전송을 보장함을 검증하였다.Today, along with the rapid growth of the network performance, the demand for high-quality video streaming services has greatly increased. The emerging 60 GHz multi-Gbps wireless technology enables the streaming of high-quality uncompressed video, which was not possible with other existing wireless technologies. To support such high quality video with limited wireless resources, an efficient link adaptation policy, which selects the proper Modulation and Coding Scheme (MCS) for a given channel environment, is essential. We introduce a new metric, called expected Peak Signal-to-Noise Ratio (ePSNR), to numerically estimate the video streaming quality, and additionally adopt Unequal Error Protection (UEP) schemes that enable flexible link adaptation. Using the ePSNR as a criterion, we propose two link adaptation policies with different objectives. The proposed link adaptation policies attempt to (1) maximize the video quality for given wireless resources, or (2) minimize the required wireless resources while meeting the video quality. Our extensive simulation results demonstrate that the introduced variable, i.e., ePSNR, well represents the level of video quality. It is also shown that the proposed link adaptation policies can enhance the resource efficiency while achieving acceptable quality of the video streaming. Meanwhile, Forward Error Correction (FEC) can be exploited to realize reliable video multicast over Wi-Fi with high video quality. We propose reliable video multicast over Wi-Fi networks with coordinated multiple Access Points (APs) to enhance video quality. By coordinating multiple APs, each AP can transmit (1) entirely different or (2) partially different FEC-encoded packets so that a multicast receiver can benefit from both spatial and time diversities. The proposed scheme can enlarge the satisfactory video multicast region by exploiting the multi-AP diversity, thus serving more multicast receivers located at cell edge with satisfactory video quality. We propose a resource-allocation algorithm for FEC code rate adaptation, utilizing the limited wireless resource more efficiently while enhancing video quality. We also introduce the method for estimating the video packet delivery ratio after FEC decoding. The effectiveness of the proposed schemes is evaluated via extensive simulation and experimentation. The proposed schemes are observed to enhance the ratio of satisfied users by up to 37.1% compared with the conventional single AP multicast scheme. The multicast transmission is inherently unreliable due to the transmission failures caused by wireless channel errors, however, the error control with Automatic Repeat reQuest (ARQ) is not provided for the multicast transmission in legacy IEEE 802.11 standard. To overcome the unreliability of multicast transmission, finally, we propose the reliable multicast protocols considering both ARQ and packet-level FEC together. For the proposed reliable multicast protocol, to reduce the overheads of feedback messages while providing the reliable multicast service, the multiple efficient feedback protocols, i.e., Idle-time-based feedback, Slot-based feedback, Flash-based feedback, and Busy-time-based feedback, are proposed. The proposed feedback protocols let the AP know easily the number of requiring parity frames of the worst user(s) for the recovery of the lost packets. The feedback overheads can be reduced by intending the concurrent transmissions, which makes the collisions, between feedback messages. In addition, utilizing the efficient feedback protocols, we propose the PHY rate adaptation based on the close-loop MCS feedback in multicast transmissions. From the performance evaluations, the proposed protocols can efficiently reduce the feedback overheads, while the reliable multicast transmissions are guaranteed.1 Introduction 1 1.1 Video Streaming over Wireless Networks 1 1.1.1 Uncompressed Video Streaming over 60 GHz band 2 1.1.2 Video Multicast over IEEE 802.11 WLAN 3 1.2 Overview of Existing Approaches 5 1.2.1 Link Adaptation over Wireless Networks 5 1.2.2 Video Streaming over IEEE 802.11 WLAN 6 1.2.3 Reliable Multicast over IEEE 802.11 WLAN 8 1.3 Main Contributions 9 1.4 Organization of the Dissertation 11 2 Link Adaptation for High-Quality Uncompressed Video Streaming in 60 GHz Wireless Networks 12 2.1 Introduction 12 2.2 ECMA-387 and Wireless HDMI 17 2.2.1 ECMA-387 18 2.2.2 Wireless HDMI (HDMI PAL) 21 2.2.3 UEP Operations 22 2.2.4 ACK Transmissions for Video Streaming 23 2.2.5 Latency of Compressed and Uncompressed Video Streaming 24 2.3 ePSNR-Based Link Adaptation Policies 25 2.3.1 ePSNR 28 2.3.2 PSNR-based Link Adaptation 30 2.4 Performance Evaluation 33 2.4.1 Evaluation of ePSNR 34 2.4.2 Performance of Link Adaptation 40 2.5 Summary 45 3 Reliable Video Multicast over Wi-Fi Networks with Coordinated Multiple APs 47 3.1 Introduction 47 3.2 System Environments 50 3.2.1 Time-Slotted Multicast 50 3.2.2 FEC Coding Schemes 52 3.3 Reliable Video Multicast with Coordinated Multiple APs 52 3.3.1 Proposed Video Multicast 52 3.3.2 Video Multicast Procedure 55 3.4 FEC Code Rate Adaptation 58 3.4.1 Estimation of Delivery Ratio 59 3.4.2 Greedy FEC Code Rate Adaptation 61 3.5 Performance Evaluation 63 3.5.1 Raptor Code Performance 64 3.5.2 Simulation Results: No Fading 66 3.5.3 Simulation Results: Fading Channel 69 3.5.4 Simulation Results: Code Rate Adaptation 70 3.5.5 Experimental Results 74 3.5.6 Prototype Implementation 76 3.6 Summary 79 4 Reliable Video Multicast with Efficient Feedback over Wi-Fi 81 4.1 Introduction 81 4.2 Motivation 85 4.3 Proposed Feedback Protocols for Reliable Multicast 87 4.3.1 Idle-time-based Feedback 88 4.3.2 Slot-based Feedback 89 4.3.3 Flash-based Feedback 91 4.3.4 Busy-time-based Feedback 92 4.4 PHY Rate Adaptation in Multicast Transmission 93 4.5 Performance Evaluation 96 4.5.1 Performance evaluation considering feedback error 104 4.6 Summary 109 5 Conclusion and Future Work 110 5.1 Research Contributions 110 5.2 Future Research Directions 111 Abstract (In Korean) 121Docto

    Combined Time, Frecuency and Space Diversity in Multimedia Mobile Broadcasting Systems

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    El uso combinado de diversidad en el dominio temporal, frecuencial y espacial constituye una valiosa herramienta para mejorar la recepción de servicios de difusión móviles. Gracias a la mejora conseguida por las técnicas de diversidad es posible extender la cobertura de los servicios móviles además de reducir la infraestructura de red. La presente tesis investiga el uso de técnicas de diversidad para la provisión de servicios móviles en la familia europea de sistemas de difusión terrestres estandarizada por el prpoyecto DVB (Digital Video Broadcasting). Esto incluye la primera y segunda generación de sistemas DVB-T (Terrestrial), DVB-NGH (Handheld), y DVB-T2 (Terrestrial 2nd generation), así como el sistema de siguiente generación DVB-NGH. No obstante, el estudio llevado a cabo en la tesis es genérico y puede aplicarse a futuras evoluciones de estándares como el japonés ISDB-T o el americano ATSC. Las investigaciones realizadas dentro del contexto de DVB-T, DVB-H y DVBT2 tienen como objetivo la transmisión simultánea de servicios fijos y móviles en redes terrestres. Esta Convergencia puede facilitar la introducción de servicios móviles de TB debido a la reutilización de espectro, contenido e infraestructura. De acuerdo a los resultados, la incorporación de entrelazado temporal en la capa física para diversidad temporal, y de single-input multiple-output (SIMO) para diversidad espacial, son esenciales para el rendimiento de sistemas móviles de difusión. A pesar de que las técnicas upper later FEC (UL-FEC) pueden propocionar diversidad temporal en sistemas de primera generación como DVB-T y DVB-H, requieren la transmisión de paridad adicional y no son útiles para la recepción estática. El análisis en t�ñerminos de link budjget revela que las técnicas de diversidad noson suficientes para facilitar la provision de servicios móviles en redes DVB-T y DVB-T2 planificadas para recepción fija. Sin embargo, el uso de diversidad en redes planificadas para recepción portableGozálvez Serrano, D. (2012). Combined Time, Frecuency and Space Diversity in Multimedia Mobile Broadcasting Systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/16273Palanci

    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

    A hybrid packet loss recovery technique in wireless ad hoc networks

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    TCP utilization in wireless networks poses certain problems due to its inability to distinguish packet losses caused by congestion from those caused by frequent wireless errors, leading to degraded network performance. To avoid these problems and to minimize the effect of intensive channel contention in wireless networks, this work presents a new Hybrid ARQ technique for reliable and efficient packets transfer in static wireless ad hoc network. It is a combination of recent FEC based Raptor coding technique with ARQ based selective retransmission method, which outperforms purely ARQ based method. In contrast to most Hybrid ARQ techniques, which usually employ a byte level FEC, we mostly use packet level FEC in our simulations for the data transfer, on top of less frequent ARQ to recover the residual errors. Existing packet level FEC methods are mostly based on simple parity check codes or Reed Solomon codes with erasure decoding; in this work we use the recent raptor codes. We also introduce the notion of adaptive redundancy which helps to achieve better average network performance and to further improve the redundancy efficiency

    An Earth Orbiting Satellite Service and Repair Facility

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    A conceptual design was produced for the Geosynchronous Satellite Servicing Platform (GSSP), an orbital facility capable of repairing and servicing satellites in geosynchronous orbit. The GSSP is a man-tended platform, which consists of a habitation module, operations module, service bay and truss assembly. This design review includes an analysis of life support systems, thermal and power requirements, robotic and automated systems, control methods and navigation, and communications systems. The GSSP will utilize existing technology available at the time of construction, focusing mainly on modifying and integrating existing systems. The entire facility, along with two satellite retrieval vehicles (SRV), will be placed in geosynchronous orbit by the Advanced Launch System. The SRV will be used to ferry satellites to and from the GSSP. Technicians will be transferred from Earth to the GSSP and back in an Apollo-derived Crew Transfer Capsule (CTC). These missions will use advanced telerobotic equipment to inspect and service satellites. Four of these missions are tentatively scheduled per year. At this rate, the GSSP will service over 650 satelites during the projected 25 year lifespan

    Cellular, Wide-Area, and Non-Terrestrial IoT: A Survey on 5G Advances and the Road Towards 6G

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    The next wave of wireless technologies is proliferating in connecting things among themselves as well as to humans. In the era of the Internet of things (IoT), billions of sensors, machines, vehicles, drones, and robots will be connected, making the world around us smarter. The IoT will encompass devices that must wirelessly communicate a diverse set of data gathered from the environment for myriad new applications. The ultimate goal is to extract insights from this data and develop solutions that improve quality of life and generate new revenue. Providing large-scale, long-lasting, reliable, and near real-time connectivity is the major challenge in enabling a smart connected world. This paper provides a comprehensive survey on existing and emerging communication solutions for serving IoT applications in the context of cellular, wide-area, as well as non-terrestrial networks. Specifically, wireless technology enhancements for providing IoT access in fifth-generation (5G) and beyond cellular networks, and communication networks over the unlicensed spectrum are presented. Aligned with the main key performance indicators of 5G and beyond 5G networks, we investigate solutions and standards that enable energy efficiency, reliability, low latency, and scalability (connection density) of current and future IoT networks. The solutions include grant-free access and channel coding for short-packet communications, non-orthogonal multiple access, and on-device intelligence. Further, a vision of new paradigm shifts in communication networks in the 2030s is provided, and the integration of the associated new technologies like artificial intelligence, non-terrestrial networks, and new spectra is elaborated. Finally, future research directions toward beyond 5G IoT networks are pointed out.Comment: Submitted for review to IEEE CS&

    Design and implementation of simulation tools, protocols and architectures to support service platforms on vehicular networks

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    Tesis por compendioProducts related with Intelligent Transportation Systems (ITS) are becoming a reality on our roads. All car manufacturers are starting to include Internet access in their vehicles and to integrate smartphones directly from the dashboard, but more and more services will be introduced in the near future. Connectivity through "vehicular networks" will become a cornerstone of every new proposal, and offering an adequate quality of service is obviously desirable. However, a lot of work is needed for vehicular networks to offer performances similar to those of the wired networks. Vehicular networks can be characterized by two main features: high variability due to mobility levels that can reach up to 250 kilometers per hour, and heterogeneity, being that various competing versions from different vendors have and will be released. Therefore, to make the deployment of efficient services possible, an extensive study must be carried out and adequate tools must be proposed and developed. This PhD thesis addresses the service deployment problem in these networks at three different levels: (i) the physical and link layer, showing an exhaustive analysis of the physical channel and models; (ii) the network layer, proposing a forwarding protocol for IP packets; and (iii) the transport layer, where protocols are proposed to improve data delivery. First of all, the two main wireless technologies used in vehicular networks where studied and modeled, namely the 802.11 family of standards, particularly 802.11p, and the cellular networks focusing on LTE. Since 802.11p is a quite mature standard, we defined (i) a propagation and attenuation model capable of replicating the transmission range and the fading behavior of real 802.11p devices, both in line-of-sight conditions and when obstructed by small obstacles, and (ii) a visibility model able to deal with large obstacles, such as buildings and houses, in a realistic manner. Additionally, we proposed a model based on high-level performance indicators (bandwidth and delay) for LTE, which makes application validation and evaluation easier. At the network layer, a hybrid protocol called AVE is proposed for packet forwarding by switching among a set of standard routing strategies. Depending on the specific scenario, AVE selects one out of four different routing solutions: a) two-hop direct delivery, b) Dynamic MANET On-demand (DYMO), c) greedy georouting, and d) store-carry-and-forward technique, to dynamically adapt its behavior to the specific situation. At the transport layer, we proposed a content delivery protocol for reliable and bidirectional unicast communication in lossy links that improves content delivery in situations where the wireless network is the bottleneck. It has been designed, validated, optimized, and its performance has been analyzed in terms of throughput and resource efficiency. Finally, at system level, we propose an edge-assisted computing model that allows reducing the response latency of several queries by placing a computing unit at the network edge. This way, traffic traversal through the Internet is avoided when not needed. This scheme could be used in both 802.11p and cellular networks, and in this thesis we decided to focus on its evaluation using LTE networks. The platform presented in this thesis combines all the individual efforts to create a single efficient platform. This new environment could be used by any provider to improve the quality of the user experience obtainable through the proposed vehicular network-based services.Los productos relacionados con los Sistemas Inteligentes de Transporte (ITS) se están transformando en una realidad en nuestras carreteras. Todos los fabricantes de coches comienzan a incluir acceso a internet en sus vehículos y a facilitar su integración con los teléfonos móviles, pero más y más servicios se introducirán en el futuro. La conectividad usando las "redes vehiculares" se convertirá en la piedra angular de cada nueva propuesta, y ofrecer una calidad de servicio adecuada será, obviamente, deseable. Sin embargo, se necesita una gran cantidad de trabajo para que las redes vehiculares ofrezcan un rendimiento similar al de las redes cableadas. Las redes vehiculares quedan definidas por sus dos características básicas: alto dinamismo, pues los nodos pueden alcanzar una velocidad relativa de más de 250 km/h; y heterogeneidad, por la gran cantidad de propuestas diferentes que los fabricantes están lanzando al mercado. Por ello, para hacer posible el despliegue de servicios sobre ellas, se impone la necesidad de hacer un estudio en profundidad de este entorno, y deben de proponerse y desarrollarse las herramientas adecuadas. Esta tesis ataca la problemática del despliegue de servicios en estas redes a tres niveles diferentes: (i) el nivel físico y de enlace, mostrando varios análisis en profundidad del medio físico y modelos derivados para su simulación; (ii) el nivel de red, proponiendo un protocolo de difusión de la información para los paquetes IP; y (iii) el nivel de transporte, donde otros protocolos son propuestos para mejorar el rendimiento del transporte de datos. En primer lugar, se han estudiado y modelado las dos principales tecnologías inalámbricas que se utilizan para la comunicación en redes vehiculares, la rama de estándares 802.11, en concreto 802.11p; y la comunicación celular, en particular LTE. Dado que el estándar 802.11p es un estándar bastante maduro, nos centramos en crear (i) un modelo de propagación y atenuación capaz de replicar el rango de transmisión de dispositivos 802.11p reales, en condiciones de visión directa y obstrucción por pequeños obstáculos, y (ii) un modelo de visibilidad capaz de simular el efecto de grandes obstáculos, como son los edifcios, de una manera realista. Además, proponemos un modelo basado en indicadores de rendimiento de alto nivel (ancho de banda y retardo) para LTE, que facilita la validación y evaluación de aplicaciones. En el plano de red, se propone un protocolo híbrido, llamado AVE, para el encaminamiento y reenvío de paquetes usando un conjunto de estrategias estándar de enrutamiento. Dependiendo del escenario, AVE elige entre cuatro estrategias diferentes: a) entrega directa a dos saltos, b) Dynamic MANET On-demand (DYMO) c) georouting voraz, y d) una técnica store-carry-and- forward, para adaptar su comportamiento dinámicamente a cada situación. En el plano de transporte, se propone un protocolo bidireccional de distribución de contenidos en canales con pérdidas que mejora la entrega de contenidos en situaciones en las que la red es un cuello de botella, como las redes inalámbricas. Ha sido diseñado, validado, optimizado, y su rendimiento ha sido analizado en términos de productividad y eficiencia en la utilización de recursos. Finalmente, a nivel de sistema, proponemos un modelo de computación asistida que permite reducir la latencia en la respuesta a muchas consultas colocando una unidad de computación en el borde de la red, i.e., la red de acceso. Este esquema podría ser usado en redes basadas en 802.11p y en redes celulares, si bien en esta tesis decidimos centrarnos en su evaluación usando redes LTE. La plataforma presentada en esta tesis combina todos los esfuerzos individuales para crear una plataforma única y eficiente. Este nuevo entorno puede ser usado por cualquier proveedor para mejorar la calidad de la experiencia de usuario en los servicios desplegados sobre redes vehiculares.Els productes relacionats amb els sistemes intel · ligents de transport (ITS) s'estan transformant en una realitat en les nostres carreteres. Tots els fabri- cants de cotxes comencen a incloure accés a internet en els vehicles i a facilitar- ne la integració amb els telèfons mòbils, però en el futur més i més serveis s'hi introduiran. La connectivitat usant les xarxes vehicular esdevindrà la pedra angular de cada nova proposta, i oferir una qualitat de servei adequada serà, òbviament, desitjable. No obstant això, es necessita una gran quantitat de treball perquè les xarxes vehiculars oferisquen un rendiment similar al de les xarxes cablejades. Les xarxes vehiculars queden definides per dues característiques bàsiques: alt dinamisme, ja que els nodes poden arribar a una velocitat relativa de més de 250 km/h; i heterogeneïtat, per la gran quantitat de propostes diferents que els fabricants estan llançant al mercat. Per això, per a fer possible el desplegament de serveis sobre aquestes xarxes, s'imposa la necessitat de fer un estudi en profunditat d'aquest entorn, i cal proposar i desenvolupar les eines adequades. Aquesta tesi ataca la problemàtica del desplegament de serveis en aquestes xarxes a tres nivells diferents: (i) el nivell físic i d'enllaç , mostrant diverses anàlisis en profunditat del medi físic i models derivats per simular-lo; (ii) el nivell de xarxa, proposant un protocol de difusió de la informació per als paquets IP; i (iii) el nivell de transport, on es proposen altres protocols per a millorar el rendiment del transport de dades. En primer lloc, s'han estudiat i modelat les dues principals tecnologies sense fils que s'utilitzen per a la comunicació en xarxes vehiculars, la branca d'estàndards 802.11, en concret 802.11p; i la comunicació cel · lular, en partic- ular LTE. Atès que l'estàndard 802.11p és un estàndard bastant madur, ens centrem a crear (i) un model de propagació i atenuació capaç de replicar el rang de transmissió de dispositius 802.11p reals, en condicions de visió directa i obstrucció per petits obstacles, i (ii) un model de visibilitat capaç de simular l'efecte de grans obstacles, com són els edificis, d'una manera realista. A més, proposem un model basat en indicadors de rendiment d'alt nivell (ample de banda i retard) per a LTE, que facilita la validació i l'avaluació d'aplicacions. En el pla de xarxa, es proposa un protocol híbrid, anomenat AVE, per a l'encaminament i el reenviament de paquets usant un conjunt d'estratègies estàndard d'encaminament. Depenent de l'escenari , AVE tria entre quatre estratègies diferents: a) lliurament directe a dos salts, b) Dynamic MANET On-demand (DYMO) c) georouting voraç, i d) una tècnica store-carry-and- forward, per a adaptar-ne el comportament dinàmicament a cada situació. En el pla de transport, es proposa un protocol bidireccional de distribució de continguts en canals amb pèrdues que millora el lliurament de continguts en situacions en què la xarxa és un coll de botella, com les xarxes sense fils. Ha sigut dissenyat, validat, optimitzat, i el seu rendiment ha sigut analitzat en termes de productivitat i eficiència en la utilització de recursos. Finalment, a nivell de sistema, proposem un model de computació assistida que permet reduir la latència en la resposta a moltes consultes col · locant una unitat de computació a la vora de la xarxa, és a dir, la xarxa d'accés. Aquest esquema podria ser usat en xarxes basades en 802.11p i en xarxes cel · lulars, si bé en aquesta tesi decidim centrar-nos en la seua avaluació usant xarxes LTE. La plataforma presentada en aquesta tesi combina tots els esforços indi- viduals per a crear una plataforma única i eficient. Aquest nou entorn pot ser usat per qualsevol proveïdor per a millorar la qualitat de l'experiència d'usuari en els serveis desplegats sobre xarxes vehiculars.Báguena Albaladejo, M. (2017). Design and implementation of simulation tools, protocols and architectures to support service platforms on vehicular networks [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/85333TESISCompendi
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