Pulse or digital communications – Spread spectrum – Direct sequence
Patent
1990-06-18
1991-12-31
Chin, Stephen
Pulse or digital communications
Spread spectrum
Direct sequence
358319, 358409, H04L 700
Patent
active
050777602
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for recognition of synchronization words in sequences of variable length encoded words. The invention is applied, in particular, in the construction of flow-rate compression systems.
In order to flow-rate limit information transmitted between transmitter and digital television receiver, appeal is often made to the statistical encoding method of Huffman. However, this method involves the construction of variable length code words whose maximum length, which is not controllable, leads to complicated constructions of encoding devices. On the other hand, as the codes have non-uniform lengths, the binary words which they form may be distorted; which thus provokes transmission errors.
In order to limit the propagation and the effect of these errors it is necessary, in general, to partition the information into blocks by inserting synchronization words between the blocks in order to safeguard the synchronization of the receivers in the case of an error. This protection can be obtained by three different methods. A first method consists in ignoring the type of information which is transmitted and in placing a synchronization word after a specific number N of bits used in the transmission. The interesting point in this method is that it fixes the lengths of the blocks and precisely determines the location of the synchronization words. Under these conditions, it is possible to use auto-corrector error codes to protect preferentially the synchronization words. A second method consists in placing a synchronization word after N encoded events. Under these conditions, the location of the synchronization words is not known. However, there exists a possibility of detecting errors since there must always exist a block separation word after N events. Finally, the third method consists in carrying out an encoding in which the number of encoded events and the number of bits per block are not necessarily known. In these last two cases, it is paramount to protect, or at least to recognize, the synchronization words in order to locate effectively the disturbances caused by the errors. However, the existing code correctors do not enable the favouring of the protection of the synchronization words when the locations of the latter are not known.
Hence, the aim of the invention is to palliate this disadvantage.
To this end, the subject of the invention is an encoding method adapted to the recognition of synchronization words in sequences of variable length encoded words, each word code corresponding to a specific message or event from a sequence of messages each assigned with a probability of occurrence, of the type consisting in the construction of a dichotomizing encoding tree comprising a specific number of leaves distributed over priority levels classifed in a decreasing order on proceeding from the root of the tree towards the leaves, the number of leaves being equal to the number of events to be encoded, characterized in that it consists in placing the leaves adjacent to one another on each level, the leaves corresponding to the most probable events being placed at a single right or left end on each level, and in prohibiting, in the encoded words, the sequences of Smax bits of equal value, zero or one.
The invention will be better understood and other characteristics will emerge with the aid of the description which follows with reference to the attached figures which show:
FIGS. 1A, 1B and 1C, synchronization words interposed in bit sequences;
FIG. 2, an illustration of a generation of a left complete encoding tree in the encoding algorithm according to the invention;
FIG. 3, an example to illustrate a left incomplete tree structure;
FIG. 4, an example of the obtainment of a left complete encoding tree comprising a maximum number of zeros equal to 2;
FIG. 5, an illustration of the conventional encoding method of Huffman;
FIG. 6, an illustration of the encoding method implemented by the invention;
FIG. 7, an illustration of the encoding method implemented by the invention obtained by l
REFERENCES:
patent: 4475174 (1984-10-01), Kanayama
patent: 4539684 (1985-09-01), Kloker
patent: 4853696 (1989-08-01), Mukherjee
patent: 4870695 (1989-09-01), Gonzales et al.
patent: 4899149 (1990-02-01), Kahan
IEE Proceedings, Part E, vol. 133, No. 1, Jan. 1986, Stevenage GB pp. 54-63; M. R. Titchener et al.: "Synchronisation Process for the Variable-Length T-Codes".
IEEE Transactions on Information Theory, vol. IT-17, No. 4, Jul. 1971, N.Y., U.S., pp. 478-487; Beulah Rudner: "Constructions of Minimum-Redundancy Codes with an Optimum Synchronizing Property".
Patent Abstracts of Japan, vol. 9, No. 332 (E-370)(2055) Dec, 26, 1985, & JP-A-60 163548, Aug. 26, 1985.
Chin Stephen
Thomson Consumer Electronics
LandOfFree
Encoding method adapted to the recognition of synchronization wo does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Encoding method adapted to the recognition of synchronization wo, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Encoding method adapted to the recognition of synchronization wo will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1515433