Error - Resilient Coding for H . 263

In this contribution we address the problem of robust video transmission in error prone environments. The approach is compatible with the ITU-T video coding standard H.263 and has been adopted in the ITU-T standard H.324 (\Terminal for Low Bitrate Multimedia Communication"). Fading situations in mobile networks are tolerated and the image quality degradation due to spatio-temporal error propagation is minimized utilizing a feedback channel between transmitter and receiver carrying acknowledgment information. In a rst step, corrupted Group of Blocks (GOBs) are concealed to avoid annoying artifacts caused by decoding of an erroneous bit stream. The GOB and the corresponding frame number are reported to the transmitter via the back channel. The encoder evaluates the negative acknowledgments and reconstructs the spatial and temporal error propagation. A low complexity algorithm for real-time reconstruction of spatio-temporal error propagation is described in detail. Rapid error recovery is achieved by INTRA refreshing image regions (Macroblocks) bearing visible distortion. The feedback channel method does not introduce additional delay and is particularly relevant for real-time conversational services in mobile networks. Experimental results with bursty bit error sequences simulating a DECT channel are presented with di erent combinations of Forward Error Correction (FEC), Automatic Repeat on Request (ARQ), and the proposed error compensation technique. Compared to the case where FEC and ARQ are used for error correction, a gain of up to 3 dB Peak Signal to Noise Ratio (PSNR) is observed if error compensation is employed additionally. 2