A Cross-Layer Approach for Prioritized Frame Transmissions of MPEG-4 Over the IEEE 802.11 and IEEE 802.11e Wireless Local Area Networks

摘要

In this paper, we study MPEG-4 transmissions over the IEEE 802.11 wireless local area networks (WLANs). First, we provide a simulation of MPEG-4 using OPNET over the WLANs in terms of throughput, impacts of multiple MPEG-4 streams, and compression rate on throughput. Our simulation results show that a higher throughput does not always yield a better quality MPEG-4 video. We further observe that if an I frame of MPEG-4 video is lost, the next $N-1$ frames (all P and B frames) are useless [where $N$ is the total number of frames contained within one group of picture (GoP)]. Furthermore, we observe that the I, P, and B frames are in decreasing order of importance. Therefore, we propose a cross-layer approach to improve MPEG-4 transmissions over WLANs. In the proposed approach: 1) P and B frames will be discarded by the MPEG-4 decoder at the receiver's medium access control (MAC) layer if the corresponding I fame is lost; 2) the individual MPEG-4 frames are prioritized at the MAC layer so that I frames have a higher priority than P frames, which have a higher priority than the B frames; 3) each frame (I, B, P) has a time deadline field so that if the deadline cannot be reached, the frame and other related P and B frames in the same GoP are deleted without further transmissions/re-transmissions; and 4) if the delay between an I frame and the next P frame is too long, then it may be better to drop the least important B frames in an attempt to allow the video to catch up. Finally, we study MPEG-4 transmissions over the IEEE 802.11 e WLANs, and we adopt a measurement admission control scheme for IEEE 802.11e. Our results show the advantages of the proposed scheme.