In mobile communication systems, one of the most significant factors of the bit-error-rate (BER) performance degradation of M-ary phase-shift keying (MPSK) is random phase error caused by phase-locked loop (PLL) or imperfect channel estimation. For high-signal-to-noisepower- ratio (SNR) regions, the effect of random phase error on BER performance becomes dominant and results in an irreducible BER called the bit error floor.