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

In recovering the carrier signal for coherent demodulation of π/4-differentially encoded quaternary-phase-shift keying (π/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 -π/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