a method for determining the signal constellation of a received signal establishes a moment based on each waveform , squares the moment , fourth powers the moment , divides the fourth power by the square to obtain a ratio , and compares the ratio to a threshold . if the ratio is less than threshold , the signal constellation corresponds to a first type , and if greater than the threshold , the signal constellation corresponds to a second type . the method can be generalized to a magnitude mean in place of a second moment .