GB1030194A - Improvements in or relating to binary information transmission systems - Google Patents

Abstract

1,030,194. Data transmission. SIEMENS & HALSKE A.G. June 27, 1963 [June 28, 1962], No. 25549/63. Heading H4P. The invention provides a binary data transmission system in which, from a series of data bits, are selected groups of n bits, each group commencing with the first mark bit to occur after the end of the preceding group. Each group is characterized in transmission by one of 2<SP>(n-1)</SP> " characterizing signals." Any space bit which is not included in one of the selected groups, e.g. the final S in a series MSS when n = 2, is represented by no change of characterizing signal from that previously transmitted. The arrangement permits increased input and output data bit rates without increasing the transmission rate. Phase-shift transmission is employed. In one arrangement of the transmitter in which n = 2, Fig. 1 (not shown), binary data feeds a logic circuit which provides a pulse whenever there occurs a 2-bit group starting with a mark bit. These pulses, together with the input data, are fed to a 3-stage reversible counter. The group MS causes stepping of the counter in one direction, and the group MM stepping in the other. The counter output controls the phase of a carrier, which is thus shifted to one of three phases, the direction of the shift relative to the previously received phase indicating the group being transmitted. No change in phase indicates the presence of an ungrouped space pulse. At the receiver, Fig. 3 (not shown), the phaseshifted signals are limited and passed to modulators both direct and via a delay and phase shifters. The modulator outputs, after processing to reduce the effect of parasitic pulses, are respectively stretched to 1 and 2-bit lengths. By summing these stretched signals the original data is reproduced. Because the rate of change of phase corresponds to the frequency change relative to a constant carrier frequency, a receiver as in Fig. 7 (not shown), may be employed. Here the received signals, after limiting, pass to a frequency discriminator which provides a pulse of polarity dependent on the direction of change of frequency (and hence of phase). These pulses are separated to positive and negative channels and act on a pulse-stretching arrangement similar to that described for Fig. 2 to reproduce the original data.