QoS of Video Delivered over 802.11e WLANs

Many home networks now use 802.11 wireless local area networks (WLAN)s. The 802.11e amendment has been designed to improve quality of service (QoS) over these networks allowing for multimedia applications such as IPTV to be better supported. The H.264 video compression standard is suitable for IPTV due to its high compression and error resilience. Video packets of different slice types are of varying importance to the decoded video quality so can be mapped into different priority queues using 802.11e enhanced distributed channel access (EDCA). We investigate several mapping schemes for a variety of video content to see how the quality of the decoded video is affected as the number of concurrent video connections is increased. The different mapping schemes exhibit different loss patterns in the video sequences and their impact on the video quality is content dependent. Subjective tests were therefore carried out which allow us to perform an accurate and valid assessment of the video quality. Packet loss rate is also reported. Our results show that as the number of concurrent videos approaches the network capacity some mapping schemes show a cliff-edge drop in quality while others offer a more acceptable gradual quality degradation. These schemes cause B-frames to be dropped and in effect reduce the video frame rate. These schemes are more successful for videos that have low or medium temporal activity.