Patent GB-1057024-A (GB)
Title: Improvements relating to multiplex transmission systems
Inventor: URQUHART-PULLEN DAVID IAN
IPC: H04J3/17
Filed: 1962-06-27
Abstract: 1,057,024. Multiplex pulse signalling. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Aug. 20, 1963 [June 27, 1962], No. 24722/62. Heading H4L. A multiplex signal transmission system having a smaller number of transmission channels than information channels comprises means at the transmitter whereby signals from existing busy channels have priority. The system is generally similar to that described in Specification 873,934 wherein T.D.M. pulses are stored by writing them vertically in a storage matrix and then read horizontally to provide groups of pulses relating to each channel in turn. In Fig. 7 (16, not shown), information channels shown as SENDERS provide pulses which are fed alternately to two stores A and B via gate circuits, store A covering channels 1-8 and store B channels 9-16. During the first writing column a pulse X opens gate GA to allow a speech detector to indicate to a queue control circuit which information channels are busy and which are idle. During a reading cycle the Y deflection of the relevant store is governed according to which channels are busy so that, for example, four busy channels are read from store A and pass to the output, the channels being separated by two channel information pulses which are inserted to indicate to the receiver which channels are busy. Gates A and B are opened alternately so that information is read from store A whilst information is being recorded in store B and vice-versa. Queue control circuit.-The units CQ, GA and GX in Fig. 10 are common whilst all the other units are repeated for each information channel. During a first line scan of a frame period pulse x is present and opens gate GA to allow respective pulses P1 &c. to pass through gates G1 &c. and set stores BMA1 &c. if the corresponding channel is busy. Store BMB1 was set via gate GA1 during the previous frame if the channel was busy then. The busy pulse passes through GM1, if BMB1 is set, to counter CQ which counts up to the number m of available transmission channels, e.g. eight. The first pulse P1 of the next line sets BMB1 to zero if BMA1 is at zero. If there has been a change of channel state since the last frame CQ will not have counted up to m and input multiplex pluses will step on the counter and produce output pulses through GX. If BMA1 and BMB1 are both set the pulse from CQ will pass through GD1 to the second stage. If BMA2 and BMB2 are both off, gates GA2 and GC2 are open and gate GD2 shut, so the pulse passes through GC2. If BMA3 is on and BMB3 off, indicating that the channel has changed from vacant to busy, gate GA3 is open and gates GC3 and GD3 are shut. The CQ pulse is diverted by GA3 and triggers BMB3 to its on state, so opening GD3 and allowing a succeeding CQ pulse to pass on to the next stage. The pulses from those BMB stores which are set control the Y deflection of the reading scans (Fig. 11, not shown) and insert the channel information pulses between sets of signal pulses (Fig. 12, not shown). Thus the queue controller discriminates for one frame in favour of existing busy channels; discrimination could be extended by the incorporation of an additional memory chain for each additional frame desired to be remembered. Receivers.-At the receivers the signals are written vertically into a store similar to that at the transmitter except that the number of columns is equal to the number of transmission channels, whilst at the transmitter the number of rows is equal to the number of information channels. The channel information pulses are used to control the Y deflection of the store during reading. Thus if channels 1 and 3 are busy and channel 2 idle the scan dwells for two periods on column 1, the second pulse being blanked off by a gate circuit, and then passes to column 2 so that a blank time slot is inserted corresponding to the idle channel. Thus the " comb " transmission is altered back to " slot " transmission before the signals are passed on to the receivers proper. The channel information pulses are modified at the transmitter to act also as line and frame synchronizing pulses for the receiver stores.