| To transmit video through erasure networks effectively, it is essential to reduce the impact of packet loss on transmitted video quality. The problem of robust video transmission in erasure networks using network coding (NC) is investigated in this research. NC theory, which has been developed recently, offers an alternative to encode video packets at intermediate nodes to improve the throughput. We consider an NC-based video delivery system that performs random linear network coding (RLNC) at intermediate nodes in erasure networks. RLNC linearly combines a group of packets by randomly selecting weighting coefficients on a finite field in a distributed way. The loss of an RLNC-coded packet is equivalent to the lost of one dimension in a constrained system of equations required for the RLNC decoding. Unless the global network coding coefficient matrix (or simply the global coding matrix) is of full rank, we are not able to recover all source packets by network decoding. Three innovative schemes are proposed and analyzed to address the problem of robust video transmission in erasure networks.First, we propose a way to construct a sparse global coding matrix (GCM), called the ladder GCM, for layered H.264/SVC (scalable video coding) video transmission. The ladder shape of the sparse matrix is maintained through the RLNC process. The sparse GCM is designed to exploit scalable layers of H.264/SVC with two objectives: (1) to enable partial decoding of a block and (2) to provide unequal erasure protection for H.264/SVC priority layers. Quality degradation is minimized by optimizing the amount of redundancy assigned to each layer. Graceful quality degradation is achieved by error concealment (EC).Next, we present an interleaving scheme that facilitates an integrated NC/EC method. This scheme distributes the impact of one long burst erasure into many short ones which are distributed in adjacent GOPs so that lost packets can be recovered more easily by NC and spatial/temporal EC. Moreover, we partition one GOP into priority levels. Packets from the same priority level of several GOPs form one RLNC generation. Then, unequal erasure protection can be applied to different generations. The optimal interleaving length and the redundancy assignment are determined to achieve graceful video quality degradation.Finally, we study the problem of applying NC to multi-party wireless video conferencing. The network coding scheme can be used to enhance the robustness of video transmission in wireless channels. The erasure protection procedure can be simplified and the downlink bandwidth can be reduced by leveraging opportunistic NC and wire-less broadcasting. Specifically, we propose a pipelining schedule that can meet the delay requirement for real-time video conferencing. The proposed NC method outperforms the opportunistic NC method by a significant margin in terms of video quality and downlink bandwidth. |
