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 bitrate video coding, the best performance is achieved through the joint use of forward error correction (FEC) and automatic repeat request strategies. However retransmission of corrupted data introduces additional delay which may be critical in some practical applications. In such cases, only a FEC strategy is feasible at the expense of a significant increase of the overall transmission 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) start codes. More specifically, the 22-bit long start code used in the H.263 standard is replaced with longer Gold sequences which ensure a higher protection against noise. A different sequence is used for each GOB so that additional 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-fading channel such as those encountered in pedestrian applications. Simulation results prove the effectiveness of the proposed technique with respect to classical FEC schemes in terms of PSNR and overall bit rate.