Cumulant based automatic modulation classification of QPSK, OQPSK, 8-PSK and 16-PSK

An automatic modulation classification (AMC) method based on the fourth-order cumulants is proposed to classify QPSK, OQPSK, 8-PSK and 16-PSK. The method consists of two steps: (1) classification of QPSK and OQPSK using the fourth order zero-conjugate cumulant of backward differences of the samples of the received nosiy signal and (2) classification of QPSK, 8-PSK and 16-PSK using the fourth order zero-conjugate cumulant of the received noisy signal and their squares. Step 1 is guided by the observation that the fourth order zero-conjugate cumulants of backward differences are distinct for those two modulation formats. Step 2 is based on the fact that the squaring of an MPSK signal results in another MPSK signal with M/2 phase states. The Monte Carlo simulation results show that the proposed method is able to classify the afore-mentioned modulation schemes at moderately low signal to noise ratios with a small sample size. The proposed method is robust to the presence of carrier phase and frequency estimation errors.