Cross-layer optimization of OFDM transmission systems for MPEG-4 video streaming

In this paper, we study the performance of a combined link- and physical-layer approach for the downlink of a dynamic OFDM-FDMA transmission system delivering MPEG-4 video streams. The approach consists of three different mechanisms — queue management, resource allocation, and subcarrier assignment — which can be used separately as well as in combination. This cross-layer approach allows to utilize channel-related knowledge and semantic information of the streams ’ packets. Consecutively adding these mechanisms to the studied system, we judge their respective impact on system performance. To do so, we present a new metric for quality assessment of long video transmissions (considerably longer than 10 s) and apply it to the simulation results. In particular, we introduce a local distortion threshold–based metric instead of an overall average judgment. We find that our combined system approach increases the number of supportable terminals per cell by up to 300 %. 1