Patent ID: 7315587

Claim:
A demodulator of a differential detection system for a π/4 shifted Quadrature Phase Shift Keying (QPSK) or Differential Quadrature Phase Shift Keying (DQPSK) modulation wave in digital communication, comprising: a plurality of differential detectors each connected to receive an orthogonal component of said modulation wave; a corrector connected to receive outputs of said differential detectors for correcting a deviated distribution of signal points on a constellation; and a slicer/decoder connected to receive outputs of said corrector, wherein said slicer/decoder decodes a received bit from the signal points after the deviated distribution thereof is corrected, and wherein said corrector has a plurality of average calculators each connected to receive an output of a respective one of the differential detectors and a plurality of subtractors each connected to receive an output of a respective one of the differential detectors and also receive an associated one of outputs of the average calculators for subtracting an average value of the output of the differential detector from the output of the differential detector.