Transmission Optimization of Digital Compressed Video in Wireless Systems

Abstract

Studies illustrated in this chapter show that dynamic scheduling of VBR streams in wireless systems is very effective in reducing losses. Two different transmission scenarios have been analyzed where dynamic scheduling can be fruitfully applied: the DVB-H system, where a number of time multiplexed services share the same channel resources, and the UMTS network where schedule calculated by the streaming server is influenced by user actions reported back to server by RTCP packets. Regarding DVB-H, the simultaneous dynamic variation of all service burst durations is of great help in reducing losses when VBR videos are transmitted. It is performed by taking into account service data, receiving buffer size and available bandwidth. Further work in this direction can be done in the improvement of the optimization method that finds the minimum of a nonlinear function of several variables. The method implemented in the proposed study finds local minimum, that in any case provides very good results. Nevertheless the optimization method could be further refined by finding a global TLF minimum, possibly with a relatively lower computational cost. Regarding the UMTS network, the dynamic schedule derives from user actions that modify the client buffer status. Simulation have been performed over different types of video streams, TOW lengths and buffer sizes, testifying the effectiveness of the proposed method. Performance results are strongly influenced by the sequence of the user actions and especially by the slide length values calculated by the server. Further improvements in this direction can be done by testing other methods for dynamic calculation and adopting