DIGITAL MODULATION/DEMODULATION SYSTEM

PURPOSE:To obtain the digital modulation demodulation system with a small bit error rate with respect to the digital modulation/demodulation system implementing the pi/4 shift QPSK modulation and demodulation. CONSTITUTION:The digital modulation/demodulation system modulating a differential code having a delay time by a prescribed symbol at a sender side while shifting the code by pi/4 each and demodulating the code at a receiver side through delay detection based on the delay time is provided with a delay means delaying two symbols and a differential coding means implementing differential coding by a delay time by two symbols to generate a pi/4 shift QPSK modulation wave subjected to differential coding having a 2-symbol delay time, and with a delay detection circuit 11 using the delay means for 2-symbol delay to implement delay detection of 2-symbol delay, a phase shift means 12 rotating an output of the delay detection circuit by pi/4 and a data discrimination means 13 discriminating the data based on an output of the phase shift means at the receiver side to implement pi/4 shift QPSK demodulation.