Pulse or digital communications – Spread spectrum – Direct sequence
Patent
1990-08-07
1992-08-18
Safourek, Benedict V.
Pulse or digital communications
Spread spectrum
Direct sequence
370 47, 3701054, 370108, H04L 710
Patent
active
051406195
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a synchronization device for a sequence of variable length rasters. These rasters comprise variable length data preceded by a binary word having a fixed length and generally fulfilling two functions: to enable the synchronization of a device receiving the data in relation to a device transmitting the data, by separating the data belonging to distinct rasters; and to transmit parameters which are unique to the raster under consideration and which will enable use to be made of the data transmitted in this raster.
In order to protect the synchronization against transmission errors this binary word may be constituted from N identical words, referred to as prefixes, each comprising a word referred to as raster separator, constituted from a fixed pattern, and a word referred to as parameter word having a fixed length but a content unique to the raster which follows.
The aim of the invention is to propose a synchronization device enabling detection of the raster separators and extraction of the parameter words even in the presence of transmission errors. The subject of the invention is a synchronization device comprising correlation calculating means for detecting the separators even if they are all to some extent corrupted by transmission errors, and in order to deduce therefrom intervals of time during which the parameter words may be extracted from the sequence of rasters.
SUMMARY OF THE INVENTION
According to the invention, a synchronization device for a sequence of variable length rasters, each raster commencing by N separator words which are identical and separated by a constant interval, comprises:
means for calculating N correlation values, reflecting respectively the correlation between a sequence of bits which are identical to those of each separator and N sequences of binary data, constituted respectively by delaying the rasters for i times the interval of the separators, for i=0 to N-1;
means for supplying a recognition signal when these N correlation values are all greater than a threshold value, this signal indicating that N separators are recognized.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood and other details will emerge with the aid of the following description and the accompanying figures, in which:
FIG. 1 shows the chronogram of an example of a variable length raster;
FIG. 2 shows the synoptic diagram of an example embodiment of a synchronization device according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The variable length raster shown in FIG. 1 comprises a three times identically repeated prefix, each prefix having a duration Tpr and comprises variable length data 7. The first prefix is constituted by a separator 1 and by a parameter word 2. The second prefix is constituted from a separator 3 and from a parameter word 4. The third prefix is constituted from a separator 5 and from a parameter word 6. Each separator 1, 3 and 5 comprises the same binary pattern and has an identical duration Ts. It enables recognition of the boundary between two successive rasters. Each parameter word 2, 4 and 6 comprises the same number of bits and has an identical duration Tpa but has a content which is unique to the raster under consideration. The three prefixes of a given raster comprise three parameter words which are identical.
The synchronization of a decoding device requires recognition of the separators 1, 3 and 5 in spite of transmission errors and determination of their position so as to know when the data 7 commence. On the other hand, the decoding of the data 7 requires perfectly exact knowledge of the parameters obtained by the three parameter words 2, 4 and 6.
FIG. 2 shows the synoptic diagram of an example embodiment of the synchronization device according to the invention, for the synchronization of a decoder receiving variable length rasters such as those shown in FIG. 1. This example comprises: an input terminal 13 receiving the sequence of variable length rasters; a calculating device
REFERENCES:
patent: 3823266 (1974-07-01), Van Elk et al.
patent: 4277843 (1981-07-01), Duquenne et al.
patent: 4344180 (1982-08-01), Cummiskey
patent: 4773065 (1988-09-01), Kobayashi et al.
patent: 4811367 (1989-03-01), Tajika
Aubie Jean-Yves
Perron Claude
Safourek Benedict V.
Thomson - CSF
Tse Young
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