Demodulator for demodulating a pi/4-shift DQPSK signal

• Main Author: SATO, TERUO
• Format: Patent
• Language: English; French; German
• Published: 23.09.1992
• Subjects: BASIC ELECTRONIC CIRCUITRY; DEMODULATION OR TRANSFERENCE OF MODULATION FROM ONE CARRIER TOANOTHER; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHICCOMMUNICATION

The present invention is directed to a differential phaseshift keying (PSK) signal demodulator in which an error rate provided when a signal modulated according to a pi /4-shift DQPSK modulation system is demodulated can be improved. The differential PSK signal demodulator of the present invention includes means for phase-shifting (13,15) a phase of a detection reference axis by a predetermined angle each in the counterclockwise direction in synchronism with a timing at which a symbol to be detected is supplied, wherein the modulated signal is synchronizing-detected (1,2) such that a rotation angle of the symbol and an angle of a detection reference axis are inhibited from becoming equal to each other, thereby a zero level being prevented from being output as a demodulated output. According to another aspect of the present invention, the differential PSK signal demodulator includes means (24 to 34) for judging changing traces of signal points from outputs of an I-axis level discriminating device (1) and a Q-axis level discriminating device (12) to select an optimum path, thus making it possible to reduce a bit error rate (BER).