Demodulator for demodulating a .pi./4-shift DQPSK signal

Details Demodulator for demodulating a .pi./4-shift DQPSK signal Demodulator for demodulating a .pi./4-shift DQPSK signal

1992-03-19

1993-04-13

Mis, David

Demodulators

Phase shift keying or quadrature amplitude demodulator

Input signal combined with local oscillator or carrier...

329310, 375 82, 375 85, H03D 300, H03K 904

Patent

active

052026434

ABSTRACT:
The present invention is directed to a differential phase-shift 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 a phase of a detection reference axis by a predetermined angle each in the counter-clockwise direction in synchronism with a timing at which a symbol to be detected is supplied, wherein the modulated signal is synchronizing-detected 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 for judging changing traces of signal points from outputs of an I-axis level discriminating device and a Q-axis level discriminating device to select an optimum path, thus making it possible to reduce a bit error rate (BER).

REFERENCES:
patent: 5128967 (1992-07-01), Durkin et al.

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