Resolving the phase ambiguities for coherent demodulation of pi /4-DEQPSK

In recovering the carrier signal for coherent demodulation of pi /4-differentially encoded quaternary-phase-shift keying ( pi /4-DEQPSK), there is an inherent phase ambiguity which may significantly degrade the system performance. The authors propose a simple and novel technique to resolve this problem, i.e. to rotate the received signal vectors alternately by - pi /4 before phase-error estimation in the carrier-recovery loop. The proposed technique incorporated with carrier-recovery loops is studied by computer simulation. A good performance is achieved.<
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