University of Konstanz
Graduiertenkolleg / PhD Program
Computer and Information Science

Guest Talks

title

The virtue of patience in low complexity scheduling of packetized media with feedback

speaker

Prof. Dr. Pascal Frossard, Swiss Federal Institute of Technology (EPFL)
Lausanne, Switzerland

date & place

Monday, 14.08.2006, 14:00 h
Room Z714

abstract

In this work, we consider streaming pre-encoded and packetized media over best-effort networks in the presence of acknowledgment feedbacks. We first review a rate-distortion optimization framework that can be employed in such scenarios. As part of the framework, a scheduling algorithm selects the data to send over the network at any given time, so as to minimize the end-to-end distortion, given an estimate of channel resources and a history of previous transmissions and received acknowledgements. Due to the high computational complexity of full search solutions, we propose to limit the solution search space by implementing a greedy scheduling strategy. However, our work highlights the rate-distortion sub-optimality of popular greedy schedulers, which are strongly penalized by early retransmissions. Therefore, we propose a scheduling algorithm that avoids premature retransmissions, while preserving the low computational complexity aspect of the greedy paradigm. Such a scheduling strategy maintains close to optimal rate-distortion performance when adapting to network bandwidth fluctuations. Our experimental results demonstrate that the proposed patient greedy (PG) scheduler provides a reduction of up to 50% in transmission rate relative to conventional greedy approaches, and that it brings up to 2dB of quality improvement in scheduling classical MPEG-based packet video streams.