GB1272603A - Time division multiplex communication system - Google Patents

Abstract

1,272,603. Multiplex pulse signalling. INTERNATIONAL BUSINESS MACHINES CORP. 30 July, 1969 [15 Aug., 1968], No. 38212/69. Heading H4L. Voice signals on twenty-four input channels 10, Fig. 1, are sampled sequentially at 18 and converted into pulse position modulated signals at 20, Fig. 4. The output of the modulator 20 controls a bi-stable circuit 30 to produce a square wave output, Fig. 5, which has zero crossings corresponding to the leading edges of the position modulated pulses, this output being supplied via a filter 36, producing the sinusoidal waveform 34, Fig. 6, to the transmission channel 14. By this means the bandwidth requirements are reduced. In some applications the filter 36 may be omitted, the transmission line itself producing the waveform 34 at the receiver. At the receiver the incoming signal is amplified and squared at 50 to produce the waveform of Fig. 5, amplitude modulated signals are produced at 52 in response to the position-modulated zero crossings and the resulting signal samples are supplied to a distributor 54. In a modification, Fig. 8 (not shown), crosstalk is reduced by providing a sampling circuit (70) controlled by a signal generator (76) to operate in a pseudo-random manner which is followed by a sequential distributor (68) supplying the pulse position modulator (20) so that the channels are arranged in differing sequences in successive channels. The receiver includes a distributor (74) operating in an inverse manner to the distributor (70) under the control of a signal generator (78). This arrangement also provides an element of secrecy. In an alternative arrangement, Fig. 11, using time compression for reducing crosstalk, the incoming voice signals are sampled sequentially at 88, converted to digital form at 92 and stored at 94 under the control of timing circuits 96. After a desired number of samples from each channel have been stored all the signals of the first channel are read out in sequence to a digital-to-analogue converter followed after a blanking interval, by all the signals of the second channel and so on, the resulting analogue signals being converted to pulse position modulation at 20 and then converted to a square waveform and subsequently a sinusoidal waveform as previously described. At the receiver, the amplitude modulated signals produced at 52 are supplied to an analogue-todigital converter 102, stored at 104 and read out to a digital-to-analogue converter 106 under the control of timing circuits 108 the resulting signals being distributed sequentially to the appropriate channels at 110. The blanking intervals synchronize the timing circuits 108.