在IEEE 802.11e下針對視訊串流之動態優先分配

Abstract

The wireless environment is built everywhere, especially IEEE 802.11 WLANs. More users use wireless network for searching information in Internets, TV program streaming, and video/voice conference. The packets include not only traditional data but also interactive multimedia data. There is an extension to IEEE 802.11 standards called IEEE 802.11e, improving the QoS capabilities on WLANs. This protocol enhances QoS data as above applications and features. The contribution, Cross-Layer Adaptive Video Prioritization (CAVP), in this thesis paper is divided into two parts. First, it provides MAC-Layer adaptive prioritization (MAP) to prioritize the packet which has the information of video frames at the Medium Access Control (MAC) Layer of IEEE 802.11e. In IEEE 802.11e, the priority of packets is very important, and it affects the order of received packets and the probability of successfully-received packet. The method to prioritize packets is estimating the access time of each access category (AC) for the arrived packet and putting the packet into the AC which has the minimal access time. Second, Video Frame Prioritization (VFP) prioritizes the video packet. Because the importance of video frames is different, we set the initial priority at Application Layer by choosing the maximal PSNR-difference frame as the highest priority frame. The maximal PSNR-difference frame critically influences the overall video sequences. These two parts of our contribution can greatly improve the quality of video streaming. The cross-layer design, CAVP, involves MAC Layer and Application Layer. The information of a packet arrived at MAC Layer is gotten from Application Layer. The benefit of cross-layer design is effectively using the information of different layers and combining their feature. In simulations, we use the popular simulator ns-2 as the experiment platform. We design several scenarios to show that our cross-layer design improves the quality of video streaming. The result shows that our cross-layer design proposal not only greatly increases PSNR of video but also improves the video in vision after the wireless transmission.