Patent GB-1199789-A (GB)
Title: Improvements in or Relating to Time Division Multiplex Information Transmission Systems
IPC: H04L25/22
Filed: 1967-12-07
Abstract: 1,199,789. Multiplex pulse code signalling. SIEMENS A.G. 7 Dec., 1967 [8 Dec., 1966], No. 55641/67. Heading H4L. A time division multiplex binary coded transmission system wherein incoming binary coded signals on a plurality of channels are scanned cyclically, the scanning rate being such that each channel is scanned a plurality of times and thereby allotted a plurality of time slots in each time interval corresponding to the duration of a normal signal element in the binary coded signal in that channel, comprises means to measure the time between a time slot allotted to one of the channels and a subsequent change in the binary coded signal occuring on said channel before the next time slot allotted to that channel, and wherein a binary coded pulse group indicating said time is transmitted in the plurality of time slots allotted to said channel starting with the next time slot. The system is said to be " transparent," i.e. it can transmit binary coded information at any bit speed below a predetermined speed. General description.-As shown in Fig. 1, a binary signal N1 on one channel of an eightchannel system is sampled by pulses S the remaining pulses T between the pulses S indicating time slots for the other seven channels. At the transmitter a counter counts to its maximum between each pair of pulses S and if between two pulses S a change in the binary coded signal occurs then the counter is stopped and the count reached is converted into a binary coded pulse group G. Thus a count Z1 is transmitted as pulse group G1 and so on. In the pulse groups the first bit is always " 1 " to indcate to the receiver that the succeeding bits represent time information, the second, third and fourth bits represent the count and the fifth bit indicates whether a binary 1 or binary 0 is being transmitted. Additional bits " 0 " are added to make up the required duration equal to that of the signal N1. If there has been no change in N1 a binary 0 is transmitted in each time slot until there is a change in N1. Fig. 2 shows the arrangement when the incoming signal N1 is distorted, the second signal change of N1 being shown as delayed with respect to Fig. 1 but the third change appearing at the correct time. The time of the first change is indicated by pulse group G1 as before, and the time of the second change by pulse group G2. However, the third change occurs before the complete pulse group G2 is transmitted and it is arranged that the pulse group G3 is started at the pulse S which follows the last bit of group G2. If the signal N1 does not change for a long time a confirmation of this state (0 or 1) is sent by means of an appropriate one of two pulse groups which are as mutually different as possible. Transmitter, Fig. 3.-Four incoming channels K1 to K4 having different transmission speeds are connected to coding devices C1 to C4 respectively, which each contain a counter operating in the manner described. The coders are scanned at a rate T (or a multiple of T) in dependence upon the transmission speed, the higher speed channels being subdivided into channels operating at the basic speed. The outputs of the coders are supplied via a distributer Z and the resulting time division multiplexed output is supplied via a modulator M to the output L. Alternatively, a common coder may be used which is connected to the output of the distributer Z. A separate channel may be used for synchronzing purposes. The arrangement may be incorporated in an existing teleprinter or speech transmission system. Further embodiments are described in which transmission is effected over a P.C.M. time division multiplex system.