Modulation classification of QAM schemes using the DFT of phase histogram combined with modulus information

We present a method to classify various QAM signal constellations by separately analysing the DFT of the phase histogram and applying knowledge about the distribution of the magnitude. The analysis is carried out using the maximum likelihood approach in both cases. In the paper the likelihood functions are derived and a rule to combine these for classification is given. Furthermore the classification performance for BPSK, QPSK, 8-PSK, V.29Fallback (V.29F,8QAM), V.29 (16QAM) and V.32Fallback-signals (V.32F,16QAM) is shown by numerical simulations.