GB1300927A - Digital data transmission systems - Google Patents

Abstract

1300927 Telegraphy POST OFFICE 1 May 1970 [1 April 1969] 16954/69 Heading H4P Each element of a binary data signal is encoded to increase the number of transitions in the signal to match the transmission speed of the channel over which the signal is to be transmitted and to ensure synchronisation between the transmitter and receiver. Several signals are encoded using different codes and multiplexed together. In Fig. 3 binary signals A1-4 having a low number of transitions each have their elements uniquely encoded by signals E1-4 applied to gates EG1-4 and then multiplexed into a single signal Q5 by gates GM1-4. Trigger stages TGA, TGB convert the presence or absence of a signal Q5 into a binary 1 or 0 signal H for transmission. At the receiver (Fig. 4, not shown) the reverse conversion takes place then the signals are separated and decoded by flow gates receiving signals identical to E1-4, after which the individual signals are demultiplexed to produce replicas of signals A1-4. One of the output signals is examined by logic circuits (Fig. 10, not shown) for lack of synchronisation of the receiver. A continual lack of synchronization over several multiplex-frames causes the counter supplying multiplex timing pulses to repeatedly skip pulses until synchronization is re-established.