A Simulation Tool for Evaluating Video Streaming Architectures in Vehicular Network Scenarios

An integrated simulation tool called Video Delivery Simulation Framework over Vehicular Networks (VDSF-VN) is presented. This framework is intended to allow users to conduct experiments related to video transmission in vehicular networks by means of simulation. Research on this topic requires the use of many independent tools, such as traffic and network simulators, intermediate frameworks, video encoders and decoders, converters, platform-dependent scripting languages, data visualisation packages and spreadsheets, and some other tasks are performed manually. The lack of tools necessary to carry out all these tasks in an integrated and efficient way formed the motivation for the development of the VDSF-VN framework. It is managed via two user-friendly applications, GatcomSUMO and GatcomVideo, which allow all the necessary tasks to be accomplished. The first is primarily used to build the network scenario and set up the traffic flows, whereas the second involves the delivery process of the whole video, encoding/decoding video, running simulations, and processing all the experimental results to automatically provide the requested figures, tables and reports. This multiplatform framework is intended to fill the existing gap in this field, and has been successfully used in several experimental tests of vehicular network

Evaluating the Use of QoS for Video Delivery in Vehicular Networks

In a near future, video transmission capabilities in intelligent vehicular networks will be essential for deploying high-demanded multimedia services for drivers and passengers. Applications and services like video on demand, iTV, context-aware video commercials, touristic information, driving assis-tance, multimedia e-call, etc., will be part of the common multimedia service-set of future transportation systems. However, wireless vehicular networks introduce several constraints that may seriously impact on the final quality of the video content delivery process. Factors like the shared-medium communication model, the limited bandwidth, the unconstrained delays, the signal propagation issues, and the node mobility, will be the ones that will degrade video delivery performance, so it will be a hard task to guarantee the minimum quality of service required by video applications. In this work, we will study how these factors impact on the received video quality by using a detailed simulation model of a urban vehicular network scenario. We will apply different techniques to reduce the video quality degradation produced by the transmission impairments like (a) Intra-refresh video coding modes, (b) frame partitioning (tiles/slices), and (c) quality of service at the Medium Access Control (MAC) level. So, we will learn how these techniques are able to fight against the network impairments produced by the hostile environment typically found in vehicular network scenarios. The experiments were carried out with a simulation environment based on the OMNeT++, Veins and SUMO simulators. Results show that the combination of the proposed techniques significantly improves the robustness of video transmission in vehicular networks, paving the way, with a wise collaboration with other techniques, to achieve a robust video delivery system that supports multimedia applications in future intelligent transportation systems

Simulation Framework for Evaluating Video Delivery Services over Vehicular Networks

Vehicular Ad-hoc Networks contribute to the Intelligent Transportation Systems by providing a set of services related to traffic, mobility, safe driving, and infotainment applications. One of the most challenging applications is video delivery, since it has to deal with several hurdles typically found in wireless communications, like high node mobility, bandwidth limitations and high loss rates. In this work, we propose an integrated simulation framework that will provide a multilayer view of a particular video delivery session with a bunch of simulation results at physical (i.e., collisions), MAC (i.e., packet delay), application (i.e.,%of lost frames), and user levels (i.e., perceptual video quality). With this tool, we can analyze the performance of video streaming over vehicular networks with a high level of detail, giving us the keys to better understand and, as a consequence, improve video delivery services

Optimizing the Transmission of Multimedia Content over Vehicular Networks

The multi channel operation mechanism of the IEEE 1609.4 protocol, used in vehicular networks, may impact network performance if applications do not care about its details. Packets delivered from the application layer to the MAC layer during a Control Channel time slot have to wait to be transmitted until the following Service Channel time slot arrives. The accumulation of packets at the beginning of this time slot may introduce additional delays and higher collision rates when packets are transmitted. In this work we propose a method, which we call SkipCCH, that deals with this issue in order to make a better use of the wireless channel and, as a consequence, increase the overall network performance. With our proposal, streaming video in vehicular networks will provide better reconstructed quality at the receiver side under the same network conditions. Furthermore, this method has particularly proven its benefits when working with QoS techniques, not only by increasing the received video quality, but also because it avoids starvation of the lower priority traffic

A Simulation Tool for Evaluating Video Streaming Architectures in Vehicular Network Scenarios

An integrated simulation tool called Video Delivery Simulation Framework over Vehicular Networks (VDSF-VN) is presented. This framework is intended to allow users to conduct experiments related to video transmission in vehicular networks by means of simulation. Research on this topic requires the use of many independent tools, such as traffic and network simulators, intermediate frameworks, video encoders and decoders, converters, platform-dependent scripting languages, data visualisation packages and spreadsheets, and some other tasks are performed manually. The lack of tools necessary to carry out all these tasks in an integrated and efficient way formed the motivation for the development of the VDSF-VN framework. It is managed via two user-friendly applications, GatcomSUMO and GatcomVideo, which allow all the necessary tasks to be accomplished. The first is primarily used to build the network scenario and set up the traffic flows, whereas the second involves the delivery process of the whole video, encoding/decoding video, running simulations, and processing all the experimental results to automatically provide the requested figures, tables and reports. This multiplatform framework is intended to fill the existing gap in this field, and has been successfully used in several experimental tests of vehicular networks

Aplicación de técnicas para la mejora de la transmisión de contenido multimedia en entornos de redes vehiculares

La transmisión de contenido multimedia en entornos de redes vehiculares, o Vehicular Ad-hoc NETworks (VANETs), puede tener un gran número de aplicaciones. Sin embargo, el uso de un canal inalámbrico compartido por todos los nodos de la red y el alto requerimiento de ancho de banda para el envío de vídeo pueden hacer que la calidad del vídeo recibido no sea aceptable, sobre todo en aplicaciones en tiempo real (p. ej., video streaming), donde se requiere, además, un bajo retardo y una variación de retardo acotada. A todos estos problemas se les añaden los continuos cambios en la topología debido a la movilidad de los nodos de la red, especialmente en este tipo de redes, donde la alta velocidad de los vehículos limita drásticamente el tiempo de comunicación entre ellos o con la infraestructura fija. Mediante el uso de técnicas de codificación o compresión de vídeo, como el estándar High Efficiency Video Coding (HEVC), se reduce la cantidad de datos necesaria para su almacenamiento, así como el ancho de banda requerido para su transmisión. Sin embargo, la calidad de vídeo percibida por el receptor puede verse muy afectada por los problemas ocurridos durante la transmisión, por lo que se requieren otros mecanismos que aumenten la robustez de las secuencias de vídeo transmitidas. Esta Tesis Doctoral está enmarcada en la investigación de técnicas que permitan mejorar significativamente la calidad con la que un usuario percibe la recepción de un flujo de vídeo HEVC en entornos de redes vehiculares. Para la consecución de este objetivo, se comenzó con el desarrollo de ciertas herramientas software que permitieran la realización de los diversos experimentos necesarios. Como primer resultado se obtuvo la aplicación GatcomSUMO, que permite la generación de escenarios y movilidad de los vehículos para el simulador OMNeT++, el framework Veins y el simulador de tráfico SUMO. Posteriormente se desarrolló el entorno denominado Video Delivery Simulation Framework over Vehicular Networks (VDSF-VN), con objeto de realizar la codificación de secuencias de vídeo mediante el codificador HEVC, la ejecución de simulaciones con los simuladores mencionados, la decodificación de las secuencias de vídeo recibidas, y la generación de gráficos con las estadísticas recogidas de forma automatizada, entre otras utilidades. Con todo lo anterior se llevaron a cabo diversos experimentos mediante simulación para evaluar la calidad de secuencias de vídeo transmitidas bajo diferentes condiciones de tráfico en la red. En primer lugar, se actuó sobre los parámetros del codificador de vídeo HEVC, utilizando modos de codificación con distintos patrones de refresco Intra y variando el número de fragmentos (tiles) de cada imagen de vídeo (frame). Los modos de codificación con mayor refresco Intra (p. ej., All Intra) requieren un mayor bitrate para su transmisión, sufren una mayor pérdida de paquetes, un mayor retardo (delay) y una alta variación de retardo (jitter). Sin embargo, en presencia de otro tipo de tráfico en la red (tráfico de fondo), se evidenció que son más robustos que otros modos con menor refresco Intra, en los que la pérdida de un cuadro (frame) puede tener un mayor efecto negativo en la calidad final del vídeo recibido debido a las interdependencias existentes entre frames. En cuanto al uso de tiles, se utilizaron distintos patrones uniformes junto con varios modos de codificación. Cuando se incrementa el número de tiles por frame, aunque se pierde algo de eficiencia de codificación, se consigue mayor robustez en presencia de tráfico de fondo, es decir, una mejor calidad del vídeo reconstruido. Sin embargo, el uso de tiles introduce una sobrecarga en el bitstream resultante y, puesto que a partir de un determinado valor el incremento de calidad no es significativo, con objeto de no saturar la red se determinó que lo óptimo es el uso de valores intermedios (entre 4 y 8 tiles por frame). En segundo lugar, y en combinación con los mecanismos anteriores, se utilizó la calidad de servicio (QoS) definida en el IEEE Std. 802.11p-2010, mediante la asignación de una mayor prioridad a los paquetes correspondientes a los frames de tipo I, y a los de todos los frames de vídeo. Los mejores resultados se obtuvieron en este último caso. En comparación a cuando no se utiliza QoS, las pérdidas correspondientes a los frames prioritarios se reducen considerablemente, sin perjudicar demasiado al resto de tráfico de menor prioridad existente en la red (tráfico de fondo), obteniéndose un mejor aprovechamiento del canal inalámbrico.The transmission of multimedia content in vehicular network environments, or Vehicular Ad-hoc NETworks (VANETs), is gaining high relevance in the automotive industry due to the attractive applications and services that may be developed. However, the use of a wireless channel shared by all the vehicles in a particular area, joined with the constrained requirements in terms of bandwidth and delay of video delivery applications, can make the quality of the received video not acceptable, especially in real time applications (e.g., video streaming), where low delay and bounded jitter are required. Furthermore, the topology of the network suffers frequent changes due to the mobility of the network nodes, and the high speed of the vehicles drastically limits the communication time between them or with the fixed infrastructure. By using video coding or compression techniques such as the High Efficiency Video Coding (HEVC) standard, the amount of data required for storage and transmission bandwidth are significantly reduced. However, the video quality perceived by the receiver can still be greatly affected due to transmission impairments, so other mechanisms are required to increase the robustness of the transmitted video sequences. This Doctoral Thesis is focused in the research of techniques that allow to significantly improve the video quality perceived by a user receiving an HEVC video stream in a vehicular network environment. In order to achieve this objective, we began with the development of some software tools to properly carry out the required experiments. As a first result, the GatcomSUMO application was developed. This application allows the generation of network scenarios and vehicles mobility for the OMNeT++ simulator, the Veins framework and the SUMO traffic simulator. Subsequently, the environment called Video Delivery Simulation Framework over Vehicular Networks (VDSF-VN) was also developed with the aim of creating a high detailed simulation environment including all the steps of a video delivery service: encoding of source video using the HEVC encoder, packetization of the encoded bitstream, simulation of network packets delivery, reassembling of the received packets, and finally, decoding of the reconstructed bitstream to play the video by the user. Also, several auxiliar utilities were developed like the ones focused in the automatization and statistics graphs generation, among others. With all of the above mentioned tools, various experiments were carried out by simulation to evaluate the quality of video sequences transmitted under different traffic conditions on the network. First, the parameters of the HEVC video encoder were tunned, in particular, using encoding modes with different Intra refresh patterns and varying the number of fragments (tiles) of each video image (frame). Encoding modes with higher Intra refresh rates (e.g., All Intra) require a higher bitrate for transmission, suffer a greater number of lost packets, a greater delay and delay variation (jitter) than other modes with less Intra refresh rates. However, in the presence of other traffic on the network (background traffic), it was evidenced that they are more robust than the other modes, as the loss of a frame can have a greater negative effect on the final quality of the received video due to the interdependencies between frames. Regarding the use of tiles, different uniform patterns were used together with various coding modes. As the number of tiles per frame increases, even though some encoding efficiency is lost, greater robustness is achieved in the presence of background traffic, that is, a better quality of the reconstructed video is achieved. However, the use of tiles introduces an overload in the resulting bitstream, and as from a certain value upwards the quality increase is not significant, in order to not saturate the network it was determined that the optimum is the use of intermediate values (between 4 and 8 tiles per frame). Secondly, and combined with the previous mechanisms, the Quality of Service (QoS) defined in IEEE Std. 802.11p-2010 was used, by assigning a higher priority to the packages corresponding to I frames only, and all the video frames. The best results were obtained in the latter case. In comparison to an scenario where QoS is not used, the losses corresponding to the priority frames are considerably reduced, without harming the rest of the lower priority traffic existing in the network (background traffic), obtaining a better use of the wireless channel.Programa de doctorado en Tecnologías Industriales y de Telecomunicació

VisualJVM: a visual tool for teaching Java technology

This paper presents a laboratory session of an advanced programming course to introduce students to the technology involved with the Java programming language. In this special lab session the educational software tool VisualJVM is used, providing a graphical front-end to a Java virtual machine (JVM). This tool helps students learn about JVM architecture, learn how JVM works, and consequently, to understand why a Java program is platform independent. The student reaction to this experience was very positive and the authors are planning to use the tool in other contexts

Source Coding Options to Improve HEVC Video Streaming in Vehicular Networks

Video delivery in Vehicular Ad-hoc NETworks has a great number of applications. However, multimedia streaming over this kind of networks is a very challenging issue because (a) it is one of the most resource-demanding applications; (b) it requires high bandwidth communication channels; (c) it shows moderate to high node mobility patterns and (d) it is common to find high communication interference levels that derive in moderate to high loss rates. In this work, we present a simulation framework based on OMNeT++ network simulator, Veins framework, and the SUMO mobility traffic simulator that aims to study, evaluate, and also design new techniques to improve video delivery over Vehicular Ad-hoc NETworks. Using the proposed simulation framework we will study different coding options, available at the HEVC video encoder, that will help to improve the perceived video quality in this kind of networks. The experimental results show that packet losses significantly reduce video quality when low interference levels are found in an urban scenario. By using different INTRA refresh options combined with appropriate tile coding, we will improve the resilience of HEVC video delivery services in VANET urban scenarios