Cooperative layered wireless video multicast

Wireless video multicast enables delivery of popular events to many mobile users in a bandwidth efficient manner. However, providing good and stable video quality to a large number of users with varying channel conditions remains elusive. In this work, we propose the use of cooperative communications for video multicast in infrastructure-based wireless networks. We first consider user cooperation at MAC layer (two-hop relaying) and integrate two hop relaying with packet level Forward Error Correction (FEC) and layered coding to enable efficient and robust video multicast. We study two different antenna transmissions at relays: omni-directional and directional. For transmission with conventional omni-directional antennas, the relays have to transmit in non-overlapping time slots in order to avoid collision. To improve the system efficiency, we investigate directional relay transmission where relays transmit simultaneously by scheduling their beams. In both systems, we consider a non-layered configuration, where the relays forward all received video packets and all users receive the same video quality, as well as a layered set-up, where the relays forward only the base-layer video. Our analysis shows that the non-layered system can provide better video quality to all users than the conventional direct transmission system, and the layered system enables some users to enjoy significantly better quality, while guaranteeing other users the same or better quality than direct transmission. The directional relay system can provide substantial improvements over the omni-directional relay system. To support our results, a prototype is implemented using open source drivers and socket programming, and the system performance is validated with real-world experiments.;Next, we consider a system that utilizes cooperation at physical and MAC layer, where multiple relays forward the video packets simultaneously using Randomized Distributed Space Time Codes (R-DSTC). This randomized cooperative transmission is further integrated with layered video coding and packet level FEC. We first consider a simple system where the parity packets are generated at the sender and transmitted in the same way as for video packets. Three different schemes are proposed to optimize the system parameters based on the availability of the channel information at the source station: R-DSTC with full channel information, R-DSTC with limited channel information and R-DSTC with node count. The performance of these three schemes are compared with rate adaptive direct transmission and conventional multicast that does not use rate adaptation. The results show that while rate-adaptive direct transmission provides better video quality than conventional multicast, all three proposed randomized cooperative schemes outperform both strategies significantly. Furthermore, the performance gap between R-DSTC with full channel information and R-DSTC with limited channel information or node count is relatively small, indicating the robustness of the proposed cooperative multicast scheme. We also propose an enhanced multicast system using R-DSTC where the sender only transmits video packets, and parity packets are generated by the nodes that receive all the source packets correctly. For this case, we consider two different schemes based on the available channel information (enhanced R-DSTC with full channel information and enhanced R-DSTC with node count). The performance of these enhanced schemes are evaluated and compared with the previous schemes. The results show that the enhanced multicast R-DSTC schemes substantially outperform the multicast R-DSTC schemes.;Finally, we study the randomized cooperation from information theoretical perspective where we consider the propagation of lossy source signal. Using end-to-end distortion as a performance metric and assuming a delay constraint, we investigate the relation among the decoding SNR threshold, number of hops, diversity level of underlying Space Time Code (STC), coverage range and the distribution of end-to-end quality over users in the coverage range. In order to provide differentiated quality to users with different channel strengths, we further employ layered cooperation. We study two different layering approaches: sequential layered transmission and super-imposed layered transmission. For the sequential layered transmission, we investigate the effect of the time division among different layers. For the superimposed layered transmission we investigate the effect of power allocation of different layers on the distribution of end-to-end quality of users under a real-time delivery requirement. We then compare these two schemes and show the benefits of superimposed layered transmission over sequential layered transmission.