Ákos Kovács

Cross-layer optimized wireless multicast for layered media

This paper discusses the maximization of user-perceived quality of layered media in wireless networks. We present a system model and an optimization framework for such networks assuming: (i) the data rates are nested, (ii) the media is multicast, (iii) layered and (iv) the media layer information is available in lower network layers based on cross-layer information. In order to show the general applicability of the proposal, different maximization targets and algorithmic solutions are presented.

Cross-layer quality-based resource reservation for scalable multimedia

Resource reservation for Variable Bit Rate (VBR) multimedia streams is a complex task if both the requirements of service providers and of end-users need to be considered. In this paper we present a novel static reservation scheme for VBR multimedia traffic that takes into account the end-user Quality of Experience (QoE). We apply a two-step process for the reservation. In the first step, we map the target user-perceived quality to an upper limit on packet loss. The second step applies a numerical method, that uses a simple video model and a Markov queue model to determine the required bandwidth for the given level of packet loss. For the validation of the video and the system model we use simulation studies. Although our method is static, it is still able to capture the characteristics of a VBR multimedia, which is the main benefit.

The Layer-Independent Descriptor Concept

With the fast improvements of broadband technologies, more and more demanding services can be accessed. Broadband access is supported by a range of wireless and wireline technologies. Well known representatives are WLAN and UMTS for wireless and xDSL for wireline access. However, the highly varying nature of wireless channels and the crosstalk behavior of the DSL channel are typical traits, and most challenging to combat. Moreover, the stringent requirements of real-time applications require enhancements in service delivery. The tremendous interest in communication has driven the deployment of new access systems. Hence, for the End-to-End point of view, the service delivery multifarious due to the heterogeneity of the underlying transport network. Therefore, to enable a transport independent path set-up, application and network properties that may influence the user-perceived quality need to be unified. Thereby, media scalability plays a key role. Recently, cross-layer communication is getting acceptance as a method that efficiently increases the system performance. Unlike previous works that mainly addressed the issue of application based feedback, we focus on the information that the application can provide to guide the network for local stream management. We present the necessary set of Application Layer information for scalable audiovisual streams to offer individual QoS, at lowermost packet overhead. Finally, we show the sustainable gain in system performance based on a DSL use-case.

A general signalling approach for local adaptation

With the fast improvements of broadband wireless technologies more and more demanding services can be provided over wireless access networks. However, the highly varying nature of wireless channels and the stringent requirements of real-time applications require enhancements of service delivery. To achieve high user-perceived quality adaptive applications and adaptation-supportive network entities play a key role. Recently, cross-layer adaptation is getting acceptance as a method that efficiently increases the performance of wireless communications. Although several cross-layer optimisation methods have been proposed over the past years, the research for end-to-end concepts was rather short-handed. The multimedia pipe (M-Pipe) project was started, among others, to research existing approaches and propose a conceptual solution for cross-layer optimisation of multimedia delivery. In this paper, we overview some of the concepts under investigation in the project

Forward information - a general approach for scalable audiovisual service delivery

Over wireless networks, real-time service delivery is a highly non-trivial task as the varying channel condition makes difficult to meet the strict delay constraints. To achieve high user-perceived quality adaptive applications and adaptation-supportive network entities play a key role. Recently, cross-layer adaptation is getting acceptance as a method that efficiently increases the performance of wireless communications. Unlike previous works, which mainly addressed the issue of adaptation-feedback to the application, we focus on the information that the application can provide to the network to guide local adaptation. We collect a set of relevant application layer information for rate adaptation and error protection of audiovisual services. As a key enabler of cross-layer adaptation, we present a general, codec independent, framework for the distribution of these parameters in the network.