Improving Video Quality in 802.11 Networks

Many new emerging applications involving real-time multimedia communications require sufficient bandwidth, as well as limited delay and minimized packet loss. In special, video streaming, that accounts for a large portion of the traffic in future networks, poses a difficult challenge to wireless networks, due to their strong requirements as well as to the great variability of channel conditions and contention based access commonly present in the wireless transmission medium. When considering an infrastructured WLAN, a performance anomaly is inherent to the use of the different versions of the IEEE 802.11 standard: when stations operate at different rates, the lowest rate station penalizes the higher rate stations, producing a degradation of the performance of the network. Moreover, the instability in the transmission rates and a low tolerance to noises and interferences lead to a difficulty of these nets to support delay sensitive traffics. These aspects make clear the strong need of development of QoS techniques to provide an effective resources management. In this paper we propose a new mechanism, to be implemented at Access Points, that involves a classification of stations based on the control of CTS and a limitation on the time the stations can use the media to accomplish their transmissions. Then, considering specific network requirements of video transmission as well as objective and subjective metrics of video quality, we conduct several discrete event based simulations with the use of NS-2 [3] and the Evalvid toolset [4][20], which prove the efficiency of the solution.