Digital data transmission system for increasing information rate without increase of bandwidth

摘要

1,113,143. Data transmission systems. BENDIX CORPORATION. 2 Sept., 1966 [14 Sept., 1965], No. 39359/66. Heading H4P. Binary data is converted to a multi-level signal for transmission, each 1 bit causing a change in level, and the receiver includes means for recovering the binary data. At the transmitter the binary data feeds a counter which counts each one bit and has a capacity equal to the number of levels in the transmitted signal. The counter reverses when it is full. Its parallel output passes to summing resistors which give the multi-level signal. This signal feeds a ring modulator, so that the transmitted wave is amplitude modulated to represent the absolute signal level and phase modulated to represent the signal polarity. At the receiver the multilevel signal is recovered by synchronous demodulation. The multi-level signal triggers the appropriate ones of a number of threshold units, each level change causing a change in the number of units triggered. Each change sets a bi-stable circuit to its 1 state, the circuit being reset half a bit period later and read out to the receiver output. The resetting pulses are derived from a retroactively controlled oscillator whose phase is compared with the level transition instants found at the threshold units.