COHERENT DEMODULATOR FOR ˜/4 SHIFTED QPSK SIGNAL

摘要

A demodulator for coherent demodulation of a .pi./4 shifted QPSK signal includes -.pi./4 phase-shift circuit in a conventional QPSK signal decision/feedback type Costas loop to alternately rotate the phase of an inputted .pi./4 shifted QPSk signal by 0 and -.pi./4 for each symbol period interval from a timing controller, thus eliminating the .pi./4 shift component of the .pi./4 shifted QPSK signal. Thus, coherent detection demodulation for the .pi./4 shifted QPSK signal having stable points at intervals of .pi./2 phase angles is enabled.