| IEEE 802.11-based wireless LAN,commonly referred to as Wi-Fi,has become a universal solution for the last-hop network access.With the rapid growth of smart mobile terminals,in large and public assembly places,people may use their mobile devices to view the video of the same popular events via the same wireless access points(APs).Accordingly,video multicast service is facing a real demand on the deployed public Wi-Fi hotspots.For video multicast over WLAN,the problems of low reliability and low transmission rate for the legacy 802.11 multicast should be solved first,and the sensitivity of information loss for the video transmission should also be considered.The existing solutions for video multicast over WLAN mainly adopt the idea of cross-layer optimization.According to the different types of video coding carrier(frames or bits),the proposed cross-layer optimization solutions for Wi-Fi video multicast can be divided into two categories: linklayer-based cross-layer optimization and physical-layer-based cross-layer optimization.Both of them have a common problem,that is the need to modify 802.11 protocol.Therefore,they are difficult to be implemented on the deployed public Wi-Fi hotspots.As the last hop of internet video multicast service,Wi-Fi video multicast solutions can be impacted by the network layer protocols.Named data networking(NDN)is a new kind of content-centric network architecture proposed in recent years.Due to the native support of multicast,compared with IP network,NDN has a huge advantage in achieving large-scale internet video multicast services.However,NDN's receiver-driven data transmission mode introduces duplicate data request overheads,which limits the scalability of NDNbased Wi-Fi multicast.In this dissertation,we focus on the video multicast optimization over WLAN.For the deployed 802.11 APs,the performance optimization problems of video multicast over WLAN are discussed and studied.The main contributions are:1.Pseudo-broadcast is a recent proposed multicast technology based on 802.11 unicast,in which the sender explicitly chooses a unicast receiver,and other clients listen for the packets in the promiscuous mode.Since pseudo-broadcast cannot completely guarantee the reliability for the listeners,for the reliable multicast mechanism combining pseudo-broadcast with forward error correction(FEC),we propose to use clients' received signal strength indicator(RSSI)as the main dimension to measure the goodput of pseudobroadcast.The results show that the receiver's RSSI and the listeners' RSSI have a combined effect on the goodput of pseudo-broadcast.We also give some reference RSSI intervals in which the listeners can receive the packets with a high probability.These RSSI intervals can be important reference values to select the unicast receiver in practical utilizing pseudo-broadcast.2.Combining multi-receiver pseudo-broadcast with Scalable Video Coding(SVC),a network-layer-based cross-layer optimization scheme for Wi-Fi video multicast(M~3)is proposed.By forwarding different video coding layers to different unicast receivers,M~3 achieves differentiated reliable multicast transmission for SVC video stream.In order to maximize the total video quality received by all clients,M~3 utilizes binary integer linear programming to optimize the SVC-layer allocation.M~3 prototype system is implemented in a real network testbed and a comprehensive verification test is conducted.Compared with conventional single-layer video multicast,M~3 can greatly improve the total effective video rate over 200%.3.Combining the Interest forwarding suppression in the network layer with the Interest transmission control in the application layer,an optimization scheme for NDNbased Wi-Fi video multicast(ISM)is proposed.A leader-based Interest suppression mechanism is designed to effectively avoid Interest conflicts over WLAN.To guarantee the reliability and the real-time requirements of NDN-based Wi-Fi video multicast,a pipeline-based Interest transmission control mechanism is designed.ISM prototype system is implemented in a real network testbed and a comprehensive verification test is conducted.Under the limitation of 6Mbps multicast bandwidth,ISM can support 20 concurrent viewers of a 1Mbps streaming video.Compared with ordinary NDN multicast scheme,the number of clients supported by ISM increases by 300%. |
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