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PSK modem system with improved demodulation reliability

  • US 4,807,251 A
  • Filed: 07/21/1987
  • Issued: 02/21/1989
  • Est. Priority Date: 07/21/1986
  • Status: Expired due to Fees
First Claim
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1. A modem system for digital data, comprising:

  • means for producing a transmission signal which is phase modulated in accordance with "mark" and "space" states of an applied digital signal in repetitive signal time slots, each of a predetermined duration, said transmission signal having a phase reference period of predetermined time duration in total provided at at least one of the front and rear portions of each of said time slots during which said transmission signal assumes a reference phase value, and in the first half of the remaining portion of each said time slot the phase of said transmission signal changes stepwise in a predetermined direction in correspondence to the "mark" state of said digital signal while, in the second half, the phase of said trasmission signal changes stepwise in a direction opposite to said predetermined direction to said reference phase value, and in correspondence to the "space" state of said digital signal the phase of said transmission signal is changed in a direction opposite to that in the case of the "mark" state of said digital signal, means for applying said digital signal to said producing means; and

    ,means for demodulating said transmission signal to reproduce said digital signal and comprising;

    means for dividing said transmission signal into two signals,means for delaying one of said two signals relative to the other to produce a pair of relatively delayed signals, andmeans for comparing said pair of relatively delayed signals to produce a signal representative of said digital signal.

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