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

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

Quality of Experience and Adaptation Techniques for Multimedia Communications

The widespread use of multimedia services on the World Wide Web and the advances in end-user portable devices have recently increased the user demands for better quality. Moreover, providing these services seamlessly and ubiquitously on wireless networks and with user mobility poses hard challenges. To meet these challenges and fulfill the end-user requirements, suitable strategies need to be adopted at both application level and network level. At the application level rate and quality have to be adapted to time-varying bandwidth limitations, whereas on the network side a mechanism for efficient use of the network resources has to be implemented, to provide a better end-user Quality of Experience (QoE) through better Quality of Service (QoS). The work in this thesis addresses these issues by first investigating multi-stream rate adaptation techniques for Scalable Video Coding (SVC) applications aimed at a fair provision of QoE to end-users. Rate Distortion (R-D) models for real-time and non real-time video streaming have been proposed and a rate adaptation technique is also developed to minimize with fairness the distortion of multiple videos with difference complexities. To provide resiliency against errors, the effect of Unequal Error protection (UXP) based on Reed Solomon (RS) encoding with erasure correction has been also included in the proposed R-D modelling. Moreover, to improve the support of QoE at the network level for multimedia applications sensitive to delays, jitters and packet drops, a technique to prioritise different traffic flows using specific QoS classes within an intermediate DiffServ network integrated with a WiMAX access system is investigated. Simulations were performed to test the network under different congestion scenarios

Multimedia

The nowadays ubiquitous and effortless digital data capture and processing capabilities offered by the majority of devices, lead to an unprecedented penetration of multimedia content in our everyday life. To make the most of this phenomenon, the rapidly increasing volume and usage of digitised content requires constant re-evaluation and adaptation of multimedia methodologies, in order to meet the relentless change of requirements from both the user and system perspectives. Advances in Multimedia provides readers with an overview of the ever-growing field of multimedia by bringing together various research studies and surveys from different subfields that point out such important aspects. Some of the main topics that this book deals with include: multimedia management in peer-to-peer structures & wireless networks, security characteristics in multimedia, semantic gap bridging for multimedia content and novel multimedia applications

Control-theoretic adaptive mechanisms for performance optimization of IEEE 802.11 WLANs: design, implementation and experimental evaluation

The media access control (MAC) layer of the IEEE 802.11 standard specifies a set of parameters that regulate the behavior of the wireless stations when accessing the channel. Although the standard defines a set of recommended values for these parameters, they are statically set and do not take into account the current conditions in the wireless local area network (WLAN) in terms of, e.g., number of contending stations and the traffic they generate, which results in suboptimal performance. In this thesis we propose two novel control theoretic approaches to optimally configure the WLAN parameters based on the dynamically observed network conditions: a Centralized Adaptive Control (CAC) algorithm, whereby the access point (AP) computes the con guration that maximizes performance and signals it to the active stations, and a Distributed Adaptive Control (DAC) algorithm, which is independently employed by each station with the same goal. In contrast to previous proposals, which are mostly based on heuristics, our approaches build upon (i) analytical models of the WLAN performance, used to derive the optimal point of operation of the IEEE 802.11 protocol, and (ii) mathematical foundations from single- and multi-variable control theory, used to design the mechanisms that drive the WLAN to this point of operation. Another key advantage of the proposed algorithms over existing approaches is that they are compliant with the IEEE 802.11 standard and can be implemented with current wireless cards without introducing any modifications into their hardware and/or firmware. We show by means of an exhaustive performance evaluation study that our algorithms maximize the WLAN performance in terms of throughput and delay under a wide set of network conditions, substantially outperforming the standard recommended configuration as well as previous adaptive proposals. Finally, we present our experiences with implementing the proposed adaptive algorithms in a real IEEE 802.11 testbed and discuss the implementation details of the building blocks that comprise these mechanisms. We evaluate their performance by conducting extensive measurements, considering different network conditions in terms of number of nodes, transmission power employed and tra c generated. Based on the obtained results, we provide valuable insights on the performance of the distributed and centralized algorithms and discuss the suitability of these schemes for real deployments. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------El nivel MAC (Media Access Control) del estándar IEEE 802.11 especifica una serie de parámetros que definen el comportamiento de las estaciones inalámbricas cuando acceden al canal. En dicho estándar se define un conjunto de valores recomendados para estos parámetros, si bien estos valores, constantes, no tienen en cuenta las condiciones de la red inalámbrica -en términos de, por ejemplo, número de estaciones o tráfico cursado- por lo que resultan en un rendimiento subóptimo. En esta tesis se proponen dos nuevos algoritmos para configurar de forma óptima estos parámetros partiendo de las condiciones observadas de la red. Dichos algoritmos, construidos sobre la base de la teoría de control, son los siguientes: CAC (Centralized Adaptive Control), que se ejecuta en el punto de acceso, el cual distribuye la configuración a usar al resto de estaciones; y DAC (Distributed Adaptive Control), ejecutado por cada estación de la red inalámbrica de forma independiente. A diferencia de las propuestas anteriores, casi todas ellas basada en heurísticos, los algoritmos se basan en (i) un modelo analítico del rendimiento de la red inalámbrica, necesario para obtener el punto de operación óptimo de la red; y (ii) fundamentos matemáticos de la teoría de control mono y multivariable, aplicados para diseñar el mecanismo que lleva la red a dicho punto de operación. Otra ventaja de los esquemas propuestos frente al trabajo previo es que son compatibles con el estándar IEEE 802.11, y pueden ser implementados sobre las tarjetas existentes sin necesidad de cambiar el hardware o el firmware. Mediante una extensa evaluación de rendimiento bajo diversas condiciones, se comprueba que los algoritmos maximizan las prestaciones de la red tanto en ancho de banda como en retardo, mejorando notablemente los resultados proporcionados por la configuración recomendada en el estándar así como por propuestas dinámicas anteriores. Por último, se presentan las experiencias del prototipado de dichos algoritmos sobre dispositivos IEEE 802.11, discutiendo los detalles de implementación de sus diferentes bloques. Se evalúan las prestaciones de los mismos mediante una extensa serie de experimentos, incluyendo diferentes escenarios en términos del número de nodos, potencia de transmisión usada y tráfico generado. Los resultados obtenidos permiten extraer valiosas conclusiones sobre el rendimiento de los esquemas adaptativos centralizados y distribuidos, así como la viabilidad de su despliegue en escenarios reales