Error protection for VLC coded data

Details Error protection for VLC coded data Error protection for VLC coded data

1993-01-07

1994-10-11

Beausoliel, Jr., Robert W.

Excavating

371 31, G06F 1100, H04L 100

Patent

active

053553799

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to the field of codes using variable length codewords and, in particular, to error protection for code streams comprising variable length codewords.
Bit rate reduction techniques are coming into wide use for the electronic transmission, distribution and storage of a wide range of media including audio, text, still and motion video.
Many of the coding algorithms used to achieve a bit rate reduction rely on the use of variable length codewords to achieve data compression. FIG. 1 shows a block diagram of a typical coder in which "block structured" digital data is coded into variable length codewords.
Digital errors (from the transmission or storage medium) give rise to difficulties in the decoding of these variable word length code words (VLC) due to the problem of synchronization loss at the decoder. The nature of many VLC streams, such as Huffman code streams, is such that a single error will commonly desynchronize the decoding process over a number of symbols before self-resynchronization occurs. This causes n encoded symbols to be incorrectly interpreted as m decoded symbols.
Early techniques for addressing this problem relied on the periodic insertion of multi-bit synchronizing patterns to allow re-alignment of the decoder (where m.noteq.n), perhaps also with optimization of the variable length code tables to reduce the number of symbols "n" over which synchronization loss occurs. The overhead of these techniques often impaired the efficiency of the compression processes. Further, because the synchronizing words were inserted at periodic intervals, resynchronization performance was limited by the spacing of these words; widely spaced words offered limited resynchronization capability whereas more closely spaced sync words degraded the compression gain achieved through the use of variable length codewords.
In European patent application, EP-A-0370291, in the name of Telettra, an alternative approach is suggested. The Telettra application suggests generating a repeating pseudo-random sequence and using successive bits of the sequence to modulate, or select between different possible, block end words (ie. words or bits used to mark the end of a block of variable length codewords). A system of this type is illustrated in block diagrammatic form in FIG. 2.
By regularly placing into the codestream information related to bits of a pseudo random sequence it becomes possible in the Telettra system to detect errors which carry across block boundaries. Such "inter-block" errors are detected because of the effect they have on the pseudo-random sequence information carried in the codestream and the extent of such an inter-block error is assessed by determining how far apart in the pseudo-random sequence are the two correctly recognized bits recovered from the codestream on either side of the error.
However, there are a number of advanced VLC schemes now in widespread use which have improved self-resynchronization properties. When schemes of this sort (such as the B2 code also developed by Telettra) are used then, typically, around 80-90% of single errors do not carry across block boundaries. Such "intra-block" errors will not be detected by the above-mentioned prior art schemes and, although confined to one block, will often have a disturbing effect in the fully encoded data.
For example, in a Hybrid-Discrete Cosine Transformation coding scheme used to compress video data, blocks of 8 by 8 or 16 by 16 pixels are commonly coded into blocks of VLC words, separated by End Of Block codewords. Intra-block errors within these VLC blocks can commonly lead to disturbing 8 by 8 pixel artefacts within the decoded image over a significant number of frames.
Embodiments of the present invention allow the detection of intra-block errors as well as interblock errors. The scheme allows many of the error events described above, affecting only information within the protected blocks, to be detected and processed at the decoder (eg. in the Hybrid DCT scheme by concealing erroneous blocks with data from the

REFERENCES:
patent: 3872430 (1975-03-01), Boudreau et al.
patent: 3873920 (1975-03-01), Apple, Jr. et al.
patent: 4723246 (1988-02-01), Weldon, Jr.
patent: 4837617 (1989-06-01), Brusewitz
patent: 5016010 (1991-05-01), Sugiyama
patent: 5148271 (1992-09-01), Kato et al.
patent: 5151784 (1992-09-01), Lavagetto et al.
Han et al "Feedback Codes with Uniformity Banded Codeword Lengths and Zero-Error Capacities" IEEE Trans. on Information Theory vol. 37 No. 3 May 1991.

Affiliated with

Also associated with

Rating

Error protection for VLC coded data does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Error protection for VLC coded data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Error protection for VLC coded data will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1664610