Unequal error protection of the reference grid for robust transmission of MESHGRID-represented objects over error-prone channels

The heterogeneous nature of modern communications stems from the need of transmitting digital information through various types of mediums to a large variety of end-user terminals. In this context, simultaneously providing a scalable source representation and resilience against transmission errors is of primary importance. MESHGRID, which is part of the MPEG-4 AFX standard, is a scalable 3D object representation method especially designed to address the heterogeneous nature of networks and clients in modern communication systems. A MESHGRID object comprises one or several surface layers attached to and located within a volumetric reference-grid. In this paper we focus on the error-resilience aspects of MESHGRID and propose a novel approach for scalable error-resilient coding of MESHGRIDs reference-grid. An unequal error protection approach is followed, to acquaint for the different error-sensitivity levels characterizing the various resolution and quality layers produced by the reference-grid coder. The code rates to be employed for each layer are determined by solving a joint source and channel coding problem. The L-infinite distortion metric is employed instead of the classical L-2 norm, typically used in case of images and video. In this context, a novel fast algorithm for solving the optimization problem is proposed. The proposed approach allows for real-time implementations. The experimental results demonstrate the benefits brought by error resilient coding of the reference grid. We conclude that the proposed approach offers resilience against transmission errors while preserving all the scalability features and animation capabilities that characterize MESHGRID.