Mobile service clouds: a self-managing infrastructure for autonomic mobile computing services
SelfMan'06 Proceedings of the Second IEEE international conference on Self-Managed Networks, Systems, and Services
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A wireless local area network (WLAN) is a flexible data communication system implemented as an extension to, or as an alternative for, a wired LAN within a building or campus. By using electromagnetic waves, WLANs transmit and receive data over the air, minimizing the need for wired connections. Thus, WLANs combine data connectivity with user mobility in a convenient and simple way. With rapid advances in wireless technology, mobile users can now be provided with not only voice and data connections, but also video communication services. Many emerging mobile applications involve the delivery of the video streams to mobile hosts (MHs). Some, such as video-on-demand and video-clip browsing, deliver recorded video to users. Others, such as video conferencing, require real-time delivery of live, interactive video streams. However, WLANs are less reliable than wired LANs due to the higher error rate in wireless channels. Many error control methods may be used to enhance the reliability of wireless communications, with the penalty of more bandwidth consumption and longer delay in delivery. A buffering mechanism is usually adopted if a large delay (e.g., in seconds) is acceptable. But for those applications that demand interactive video streaming over a WLAN, buffering cannot meet the real-time requirement. This research investigated how to deliver interactive video streams in 802.11 WLANs. Interactive in this study means that each video frame in the stream has a real-time deadline in which to be played back. The main focus of the research was on multicast video streaming, where multiple MHs receive the same video stream. Although unicast can be considered as a special case of multicast with only one receiver, wireless multicast is fundamentally different from unicast. In particular, error control for multicast is more difficult than for unicast in current WLANs, due to the minimal support of multicast in IEEE 802.11 MAC layer protocol. The contributions of this research can be summarized as follows: First, a packet corruption model was proposed to describe the error behavior in WLANs more accurately in simulations. Secondly, forward error correction (FEC) was studied and evaluated for its positive impact on the quality of the video streaming service in WLANs. Thirdly, to further improve the video quality, two new error control methods were proposed: extra packet request (EPR) in the application layer and leader-driven multicast (LDM) in the MAC layer. Finally, the combinations of multiple error control methods were investigated, each combination's performance was evaluated, and the run-time adaptation of error control strategies was studied in order to match the changing conditions. Both experiments and simulations were conducted. The results indicated the best ways to stream video in WLANs under different situations.