IEEE 802.11e無線網路上針對H.264多媒體串流之動態封包選擇性傳輸機制
摘要
Abstract With the increasing usage of wireless networks and the demand for multimedia applications, such as video streaming, videophone, high definition television (HDTV) etc., it is very important to provide quality of service (QoS) for real-time applications over Wireless Local Network (WLANs). To support QoS in WLAN, the 802.11 Working Group has developed a new protocol, IEEE 802.11e, to provide service differentiation at the medium access control (MAC) layer. Because of wireless channel characteristics, such as shadowing, multi-path, fading, and interferences, the allocated bandwidth is usually not fixed. It results in ineluctable degradation in QoS. Solutions to deal with wireless bandwidth fluctuations consist of link adaptation (LA) and rate adaptation (RA). However, these approaches rely on the slow feedback of physical layer to adapt transmission rate and do not consider characteristics of traffic and codec. Thus, they may not satisfy requirements of strict bandwidth guarantee and latency limitation for video streaming. In this thesis, we propose a cross layer mechanism to improve H.264 video streaming transmission over IEEE 802.11e wireless networks, when encountering short-term bandwidth fluctuations. The proposed cross layer mechanism consists of slice classification in the application layer, a dynamic packet selective transmission (DPST) scheme in the MAC layer, and channel condition prediction using two-state Markov chain. Performance of the proposed mechanism is evaluated through extensive simulations. Results show that the proposed cross layer mechanism provides better video quality and lower packet delay.