Block DCT Based Optimization for Wireless SoftCast of Depth Map

With the recent emergence of naked-eye 3D mobile devices, the 3D video-based applications on the mobile terminal are showing great potential. However, the conventional transmission scheme based on separate source coding and channel coding may fail in the broadcast and mobile scenarios due to the drastic changes in wireless channel condition. Recently, an uncoded transmission scheme called SoftCast was introduced, which shows efficient performance for wireless 2D video transmission. However, it may not work well for 3D video wireless transmission, especially for the depth maps. Based on the piecewise smoothness of depth maps, we propose an uncoded wireless depth map transmission scheme, which incorporates three customized components of optimization into the SoftCast framework. First, compared with the frame-level discrete cosine transform (DCT) used in 2D video SoftCast, the mean removed block-based DCT is preferred as the decorrelation transform for depth maps to accommodate its piecewise smooth property, which also facilitates the following subsequent optimization. Second, view synthesis distortion-based chunk dropping is utilized for more efficient power allocation in the case of limited bandwidth, where the block DCT provides a better estimation for synthesis distortion. Third, inter-block DCT coefficients are rearranged to form chunks in terms of minimizing the intra-chunk variance, further enhancing the chunk-level power allocation efficiency. The experimental results demonstrate that the proposed scheme can provide superior performance than the state-of-the-art SoftCast methods while achieving graceful synthesis quality transition within a wide channel signal-to-noise ratio range.