Guenther Liebl

H.264/AVC video transmission over MBMS in GERAN

In this work, we investigate the integration of H.264/AVC based video into the multimedia broadcast/multicast service (MBMS). MBMS allows simultaneous distribution of live video with reasonable quality to several or even a large number of users within a serving area. We discuss several system design options and propose a simple, but nevertheless efficient cross-layer design concept, which helps to determine an optimal set of both application and transmission parameters for maximizing the quality at the user terminals for different link conditions. In order to validate our concept, we present detailed performance results using realistic test conditions provided by 3GPP.

Interactive Error Control for Mobile Video Telephony

Error robust video communication for hand-held devices is a delicate task because of limited computational resources and hostile channel conditions in mobile environments. The loss of coded video data on the channel can result in spatio-temporal error propagation in the video. In addition, stringent end-to-end delays for conversational applications make this challenge even more difficult. In this work, we investigate several techniques which exploit feedback from the receiver to enhance the performance of conversational video in realistic mobile communication environments. Specifically, we show how a low-complexity interactive error tracking technique can be combined with multiple reference picture selection (RPS) based on the existing syntax of H.264/AVC. This technique outperforms other interactive error protection strategies by a margin of more than 2 dB for moderate channel loss rates, with minimal impact on end-to-end delays.

Proxy-based transmission strategies for wireless video streaming

We present proxy-based transmission strategies for improving the quality of delay-critical video streams which are transmitted in parallel on the downlink of a cellular system. Compared to state-of-the-art radio link buffer management, our solution allows to shape the rate of the incoming video streams in a rate-distortion optimized way before congestion may occur. Furthermore, joint optimization across multiple parallel streams is possible to avoid blocking of certain users by less important data units of others. The proposed solution only requires periodic reporting of abstract side information from the radio link layer in terms of the current buffer status and the average throughput. We demonstrate the improved perceptual quality and fairness that can be achieved with our solution for a simple downlink scenario.