Improved group-of-block synchronization for robust transmission of H.263 video over slow-fading channels

Among the techniques to limit the effect of error propagation in low bitrat e video coding, the best performance is achieved through the joint use of f orward error correction (FEC) and automatic repeat request strategies. Howe ver retransmission of corrupted data introduces additional delay which may be critical in some practical applications. In such cases, only a FEC strat egy is feasible at the expense of a significant increase of the overall tra nsmission bit rate. In this paper, a strategy is proposed which instead of protecting the whole H.263 video stream, uses all the redundancy to protect the most important parts of the bit stream, i.e., group-of-block (GOB) sta rt codes. More specifically, the 22-bit long start code used in the H.263 s tandard is replaced with longer Gold sequences which ensure a higher protec tion against noise. A different sequence is used for each GOB so that addit ional information can be obtained which can be used to improve the quality of the decoded sequence. The new technique is derived by assuming a slow-fa ding channel such as those encountered in pedestrian applications. Simulati on results prove the effectiveness of the proposed technique with respect t o classical FEC schemes in terms of PSNR and overall bit rate. (C) 2001 SPI E and IS&T.