Patent GB-1186385-A (GB)
Title: Improvements in or relating to Transmission Systems and Methods
IPC: H04J3/16
Filed: 1967-08-15
Abstract: 1,186,385. Multiplex pulse signalling. HASLER A.G. 15 Aug., 1967 [15 Aug., 1966], No. 37450/67. Heading H4L. In a time division multiplex pulse coded system wherein the frames are of equal duration and particular channel periods are permanently assigned to particular communication channels, a plurality of signals are transmitted as code words with a number of digits equal to the digits in one channel period, and other signals are transmitted as short code words with a lesser number of digits than in one channel period, the parts of the channel periods remaining after the transmission of short code words being used to transmit the code words of subsidiary channels to which no specific channel periods have been assigned. The system is described in relation to the transmission of teleprinter signals but is applicable to P.C.M. As described each channel period consists of 6 bits which is considered as two groups of 3 bits each. The signals to be transmitted are the normal intelligence or traffic signals consisting of 6 bits each, supervisory or control signals consisting of 3 bits (1 group) each, and synchronizing signals consisting of 9 bits (3 groups), i.e. 000000001. If control signals or sync. signals are transmitted, the resulting spare pulse groups are used to transmit subsidiary signals which are not allocated to any specific channel period. In the traffic signals the first bit is always " 1 " and the control and the sync. signals always start with " 0 ". Transmitter, Fig. 1.-A clock pulse generator 1 controls a distributer 2 having 6 outputs a to f the output f advancing a main channel counter 3 by one step. Counter 3 determines a frame period. Incoming traffic signals are supplied via lines 6(1) to 6(n-3) to a corresponding number of stores 11(1) to 11(n-3). A store 11(n-2) holds the combination 000000 (the first part of the sync. signal) and a store n-1 holds the combination 001 (the second part of the sync. signal). A store 11(n) is used in the synchronizing of the subsidiary channels. The signals stored at 11 are transmitted in sequence at pulse time d to a coder 12. During pulse period the output of the coder is supplied to a six digit main store 13 and during period f the first group of three bits of this signal are transferred to the output unit 14 and transmitted during pulses a to c to the receiver. The first bit of this word has also been transferred to a control circuit 5 and if it is a " 1 ", during pulse c the second group of bits is transferred to unit 14 and transmitted to the receiver during pulses d to f. If the first bit is a " 0 " this transfer is suspended. The subsidiary channels are supplied via lines 7(1) to 7(n) to input stores 21. At each pulse period a a signal from store 21 is transferred sequentially to the coder 12 whose output is transferred during pulse b to a subsidiary store 23. During pulse c one half of the subsidiary code word is transferred to the output unit 14 but only if there is no traffic signal held in store 13 as indicated by the first bit being a " 0 " and during pulses d to f it is transferred to conductor 15. A subsidiary channel counter 4 is advanced one half-step each time a control signal appears in the coder and controls the transfer at times a, b and c of the subsidiary signals. The subsidiary channels use a six digit code for traffic signals which begins with " 1 " and when the counter 4 is stopped on a whole number it indicates the first of a code word and when it has stopped on a " half-step " it indicates the second part of a code word. Supervisory signals as with the main supervisory signals, always begin with " 0 " and consist of three bits. In order to synchronize the subsidiary channels the position of counter 4 is transferred in each frame to the store 11(n) and transmitted via coder 12 and store 13 to the output stage. Alternatively a predetermined subsidary channel may carry a sync. signal. Receiver, Fig. 2 (not shown).-This comprises similar stores and counters and operates in an inverse manner to the transmitter.