Patent GB-1462197-A (GB)
Title: Time division multiplexing transmission system
IPC: H04N21/434
Filed: 1973-12-27
Abstract: 1462197 Television NIPPON HOSO KYOKAI and HITACHI ELECTRONICS Ltd 27 Dec 1973 [29 Dec 1972] 59816/73 Headings H4F and H4M A plurality of channels of pulse-code-modulated, time-division multiplied audio signals divided at an audio frame period, and video signals divided at a line synchronizing period are to be transmitted alternately; the audio signals are modified so that they are divided at the video line synchronizing period and respective synchronizing signals, Fig. 7, at the video line synchronizing period, are added to the video signals and the modified audio signals, the synchronizing signals having a common pattern PFP and a respective mode control code MCC, the pattern PFP being used at a receiver to generate clock pulses to decode the codes MCC. The audio signals may be a plurality of pulse-code modulated audio signals accompanying respective video signals, each video signal representing a still picture, and the desired still picture and related sound being selected at a receiver. In the system described output signals occupying 5 sec. are repeatedly transmitted, each period of 5 sec. including 50 video frames VF, Fig. 1e, and 100 audio frames A 1 ,F,A 2 F, one video frame VF and two audio frames, A 1 F, A 2 F being transmitted in sequence. Every tenth video frame may be replaced by a code frame (CF, Fig. 1d, not shown). The audio signals are split into two groups PCMI, PCMII. The portion of PCMI from to to t 2  is delayed by two frame periods to form audio channel A and the portion of PCMII from t 1  to t 3  is delayed by one frame period to form audio channel C; the portion of PCMI from t 2  to t 3  is directly inserted into audio channel B as is the portion of PCMII from t 3  to t 4 . The gaps thus caused in the audio signals from t 4  to t 5  are used for the video frames VF. The signals in audio channel B are delayed at the receiver and inserted in the appropriate positions in the signals derived directly from channels A and C. These audio signals are transmitted in the prior art as shown in Fig. 10(a) which shows a period of two audio sampling periods which, in the embodiment described, is equal to three video line periods; R denotes signals in audio channels A and C, and M denotes signals in channel B which are temporarily memorized at the receiver, PWD indicates the respective time slots (channels), R 0  denotes the signal of the "0" frame sampled in the first of the pair of sampling periods and R 0 <SP>1</SP> denotes this signal in the second of the pair of sampling periods. In the present invention the audio signals are rearranged as shown in Fig. 10(b) or Fig. 10(c), divided at the video line synchronizing period. A synchronizing pilot signal having a frequency equal to that of the clock pulses may be added to the blanking portion BL preceding each synchronizing signal of Fig. 7; an NTSC subcarrier reference burst may follow the synchronizing signal in the video frames VF. In the synchronizing signal of Fig. 7 code bit H indicates coincidences of the clock pulses and the video horizontal synchronizing pulses, code bit A indicates coincidences of the clock pulses and the audio sampling signal, code bit F indicates the video frame synchronizing signal, and code bits M 0 , M 1 , M 2  and M 3  identify the frames VF, A, F, A 2 F.