Telegraphy – Systems – Line-clearing and circuit maintenance
Patent
1975-04-02
1976-07-27
Martin, John C.
Telegraphy
Systems
Line-clearing and circuit maintenance
178 695R, 178DIG3, H04N 504
Patent
active
039718883
ABSTRACT:
In a digital transmission system that encodes each sample of a video signal into a variable bit length data word to form a consecutive stream of variable bit length data words, synchronization between the received data words and their properly associated spatial addresses is maintained by periodically interposing synchronization words into the transmitted data stream. After initialization at the beginning of a video field, each picture element along each active scan line is consecutively sampled and encoded into a variable bit length data word. Each scan line is divided into segments having a predetermined number of sample positions included therein. A word counter cyclically counts each sample as it is encoded to provide a representation of the horizontal position of each code word within a segment along a scan line. The relative horizontal position of each code word is thus represented by the count of the word counter. The cumulative number of bits in the data stream is simultaneously cyclically counted as each sample is encoded. At each instant at which the bit counter reaches a predetermined count, an error correction encoded representation of the present count of the word counter (i.e., a synchronization word) is inserted into the data stream. At the receiver, after initialization, each successive variable bit length code word is decoded and directed to the next consecutive picture element. A word counter counts each word as it is decoded while a bit counter cyclically counts each received data bit. At each instant at which the bit counter reaches the predetermined count, the synchronization word in the data stream is decoded and the relative horizontal position indicated by the synchronization word is compared with the spatial position indicated by the word decoder. If a deviation exists between the two spatial positions, indicative of a transmission error in the data stream, the word counter is updated and the next successively decoded variable length data words are addressed to their proper spatial positions.
REFERENCES:
patent: 3597539 (1971-08-01), Clark
patent: 3772475 (1973-11-01), Loffreda
patent: 3795763 (1974-03-01), Golding et al.
patent: 3798378 (1974-03-01), Epstein
patent: 3830965 (1974-08-01), Beaudette
patent: 3867579 (1975-02-01), Colton et al.
Ching Yau Chau
Chow Ming-Chwan
Bell Telephone Laboratories Incorporated
Gurey Stephen M.
Martin John C.
Mullarney John K.
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