Societe Anonyme Dite: Alcatel Cit

Jean-Luc Abaziou

Bernard Le Mouel

Jean-Claude Billy

The method enables transmission of a digital service channel by means of the parity channel of a digital bit stream transmitted in a parity checking code with parity words inserted at specific times by modifying certain parity words violating the parity checking code parity law. It consists in modifying spaced groups of even number of consecutive parity words so as not to disrupt analog detection of line errors. A digital service channel insertion circuit is included among the component parts of an MBIPIC type encoder whereby the data of a digital bit stream is transmitted by consecutive code words each formed of a block of data bits completed by a parity bit and an inversion bit. The digital service channel insertion circuit includes a modulator operative in a first computation logic circuit delivering the real value of the parity bit and a shaper circuit which strobes the digital service channel data at a timing rate that is low compared with that of the code words and selectively applies to the modulator according to the result of said strobing a pulse having the width of two code words.

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Pleumeur Bodou, France

Jean-Luc Abaziou