Study On Effcient Wireless Multicast Strategies For Multimedia Based On Network Coding

With the rapid development of wireless broadband technology, the vol-ume of wireless network has been greatly improved. Meanwhile, the error control meth-ods provide good support for robust wireless communications. The combining of large capacity and efficient error control methods enhances the wireless network’s ability to provide appealing applications, for example, the wireless streaming services. Moreover, the scalable video codec has been proposed and standardized to meet the requirements of heterogeneous wireless users. The scalable video coding standard enables the source to satisfy all users through one multicast and thus makes the best use of wireless multicast. However, the exploiting and spread of wireless broadband applications still face many challenges:On one hand, although the network capacity is growing, it is not fast enough to meet the expanding need of market. The bandwidth limit still hold the whole market back. On the other hand, owing to the physic nature of wireless channels, the packets erasure is inevitable no matter what error control method we adopt. The retransmission delay can be a great factor for the quality of experience (QoE). Differ from the design of wireless transmission strategies for common applications, the old metrics of Quality of Service (QoS), such as packet delay, jitter and packet loss ratio, are no longer accurate to evaluate the transmission of multimedia data, and the QoE becomes a much powerful tool to score the multimedia transmission. However, QoE is a result of multiple factors that is difficult to map to specific parameters. When designing the wireless transmission strategy for multimedia applications, the transmission requirements posed by particular application as well as clients should be considered at the same time. A good strategy shall is able to provide transmission service with high QoE with limited resources. Net-work coding has been proved to be an efficient way to improve the capacity of wireless multicast and to reduce the retransmission delay. Thus, it is beneficial to apply network coding appropriately in the transmission process for multimedia applications. This thesis considers the problems that applying network coding to transmit multimedia data effi-ciently and to provide good QoE for end users in wireless network. First, we studied the optimization of access time in on-demand data dissemination system based on network coding, and proposed a heuristic algorithm to minimize the total access time. Second, we studied the optimization of scalable video transmission. The problem is a combinatorial optimization problem and we designed a heuristic algorithm to resolve it. Last but not least, inspired by the second optimization problem, we studied the optimization problem of progressive transmission for in-order data.The main research innovations are as follows:1) Studied the problem of minimizing the total access time in on-demand data dis-semination system. Analyzed the relevance between multiple users’ requested data items and proposed a heuristic algorithm. The proposed algorithm searches the best data items set that can meet the most users’ requirements, and conducts linear com-bination on the found data items before multicast. Comparing to the random linear network coding method, our algorithm considers the users’ instant reception status when searching the coding set, and thus achieves better delay performance in most cases, only when the reception status of all users are the same and they request the same data items that the random linear network coding method works better.2) Studied the minimization of video reconstruction time for scalable video in wireless network. Based on the structure characteristics of scalable video, proposed a two-stage transmission scheme.(a) The first stage is the multicast stage. All the enhancement layers of scalable video cannot be decoded until the base layer is decoded successfully, hence, the original video packets are encoded by hierarchical network coding method in order to provide some protection for the base layer, and to guarantee the base layer decodable probability.(b) The second stage is the retransmission stage, the sender retransmit packets based on receivers’ requirements for video reconstructed quality and the pack-ets reception status in the first stage. Proposed a maximizing decoding users algorithm to optimize the waiting time receivers experience to get enough packets to reconstruct the video. The proposed algorithm provides receivers a "soft" video recover process that the quality of reconstructed video improves with the receiving of video packets. Further, the proposed algorithm exhibits a "fairness" among receivers that low-demanding receivers wait shorter than high-demanding receivers.3) Studied the progressive retransmission of in-order data. The in-order data represent that data with priority that the decoding of low priority data depends on the decod-ing of high priority data. Thus, it is important to consider the practical decoding delay on the receiver side for the transmission of in-order data.(a) Studied the progressive retransmission of in-order data under assumption of perfect feedback. The packet’s priority and the decoding dependency of in-order data are addressed via weighting in the coded packets in the construction process to maximize a utility function. Proposed algorithms enable receivers to decode the retransmission packets instantly and progressively recover the original data, such that receivers can terminate the retransmission process at any point. Compared with the algorithm proposed in reference, our algorithms have shorter completion time and total access time.(b) Studied the progressive retransmission of in-order data under assumption of imperfect feedback. Based on the accomplished work, designed appropri-ate packets updating schemes and proposed corresponding coding algorithm-s. Extensive simulation results justify that the proposed algorithms achieve shorter completion time and total access time and thus fit for the imperfect feedback scenarios.The multimedia communications over wireless networks is rising, and the quality of experience of users is the key to its success. This thesis aims at optimizing delay and providing good QoE in multiple practical scenarios. The proposed algorithms not only serve users with better data transmission characteristics, but also provide an option that users can "customize" the service and cut off the transmission as long as the received data are enough for supporting their expecting QoE. These properties of proposed algorithms fit in with the heterogeneous property of wireless networks, and network resources can be saved when bandwidth is competed.