A NOISE RESISTANT SYNCHRONIZATION SCHEME FOR HDTV IMAGES

A method that increases the error resistance of the HDTV system and of fers graceful picture degradation in the presence of bit errors, is pr esented. Due to the nature of the presently proposed compression schem es for HDTV systems, an error in a data bit does not only affect the b lock the bit belongs to, but unfortunately the effects of this error m ay perpetuate to the following blocks. This is because a bit error may cause loss of synchronization between the data bits and the picture b locks they represent. Our method restricts the effects of a bit error to a picture block whose size is significantly smaller than those used by the HDTV systems. We achieve synchronization by transmitting a hea der-word for each such synchronization block. Each header-word contain s the number of data bits representing the compressed block. This head er-word is protected by two levels of FEC code. To decrease the number of extra bits needed by the header-words, two different synchronizati on block sizes are used, a relatively small block size for the referen ce frames and a larger size for the inter-frames. The resulting method improves the quality of the picture in the presence of errors and def ers the SNR at which the HDTV picture suddenly deteriorates by 2.5 to 3 dB. It also allows operation at higher order modulation transmission schemes, e.g., 32-QAM instead of 16-QAM, without the requirement of i ncreased signal power.