Hierarchical DCT coding of HDTV for ATM networks

A hierarchical discrete cosine transform (DCT) coding scheme is described for 135-Mb/s HDTV (high-definition television) transmission in ATM (asynchronous transfer mode) networks. Cell loss due to network congestion and cell misdelivery in the ATM may seriously degrade picture quality. To cope with cell loss, a hierarchical system employing an intrafield 8×4 DCT that segments the coefficients into a main signal and an enhancement signal is proposed. The two signals are separately assembled into cells for transmission over the ATM networks. The cells from the main signal are protected by labeling them with a high priority. The enhancement signal is labeled with a lower priority and is subject to higher cell-loss rates. Considerations for signal segmentation, packet assembling, and effect of cell loss on picture quality are addressed. Computer simulation of the hierarchical DCT system was performed on two HDTV sequences. For comparison, simulations were also applied to nonhierarchical DCT systems with and without cell concealment. The results indicate that the hierarchical system offers very effective protection against cell loss