Service-Aware Performance Optimization of Wireless Access Networks

Internet was originally designed to offer best-effort data transport over a wired network with end machines using a layered network protocol stack to provide mainly reliability and quality of service for end user applications. However, the excess of wireless end devices and the demand for sophisticated mobile multimedia applications forces the networking research community to think about new design methodologies. In fact, this kind of applications is characterized not only by a large amount of required data-rate, but also by a significant variability of the data-rate over time due to the dynamics of scenes, when state of the art of video encoding techniques are considered and are especially challenging due to the time varying transmission characteristics of the wireless channel and the dynamic quality of service (QoS) requirements of the application (e.g., prioritized delivery of important units, variable bit rate and variable tolerance vs. bit or packet errors). One of the focused issues in the improvement of multimedia transmission quality is to combine the characteristics of the video applications and the wireless networks. Traditional approaches, in which the characteristics of the video application and wireless networks are isolated, would induce the resources not being optimized. Cross-layer design also known as Cross-layering is a new paradigm in network design that not only takes the dependencies and interactions among the layers of the Open System Interface (OSI) structure into account, but also attains a global optimization of the layer-specific parameters. However, most existing cross-layer designs for Quality of Service (QoS) provisioning in multimedia communications are mainly either aiming at improving throughput of the network or reducing power consumption, yet regardless of the end-toend qualities of multimedia transmission. Therefore, the application-driven cross-layer design over various multimedia communication systems is needed to be extensively investigated. Following the extensive study of performance bounds and limitations of the sate of the art in this research area, we argue that performance improvement of multimedia applications over wireless access networks can be achieved through considering the application-specific requirements also called service- or context-awareness. Indeed, we designed two cross-layer design schemes called CORREC and SARC for Wi-Fi and 3G networks respectively. We show that further performance improvement can be achieved by tuning ARQ and HARQ strength respectively based on the application requirements and protocol stack operation on the mobile terminal. In the other hand, the Transmission Control Protocol (TCP) which accounts for over 95% of Internet traffic shows poor performance in wireless domain. We propose a novel approach aiming at TCP performance improvement in WLAN networks. It consists in proposing a joint optimization of ARQ schemes operating at the transport and link layers using a cross-layer approach called ARQ proxy for Wi-Fi networks.