Multimedia communication over wireless networks

Multimedia communications poses a number of challenges to the wireless networks. Traditional multiple access mechanisms in wireless local area networks (WLANs) are not suitable for conveying voice and video traffic. Various interferences, like intra-flow and inter-flow interference, detrimentally affects video streaming quality. Recently standardized multiple-input multiple-output (MIMO) technology in WLAN, IEEE 802.11n, although increases the data rate, its rate adaptation schemes cannot effectively support video streaming rates. On the other hand, the lossy nature of wireless networks results in inaccuracies in quality evaluation of video streaming. Such inaccuracies create hurdles for future development of multimedia communications in wireless networks. We propose to consider the characteristics of the multimedia application and that of wireless communications together, and take the advantages of these properties to develop communication protocols which can support multimedia delivery effectively. We propose a new multiple access protocol, Time Division Carrier-Sensing Multiple Access (TD-CSMA). Using the predictability of real-time traffic, TD-CSMA doubles the capacity of co-located multiple WLANs compared with the legacy CSMA. We also propose a new rate adaptation scheme, Video-aware Rate Adaptation (VARA). Based on the streaming rate variation of videos, VARA achieves the perfect quality for the high-definition (HD) video streaming in MIMO WLANs. Finally, by taking the impact of packet loss in wireless networks on video quality into account, we propose new video quality metrics. The new metrics can accurately evaluate the spatial and temporal quality of video streaming in wireless networks. From extensive experiments and subjective tests, our metrics show an correlation greater than 0.9 with the Mean Opinion Score (MOS) of human subjects. With the proposals in this thesis, we can greatly improve the performance of multimedia communications over wireless networks.