A simple method for distinguishing modulation types

For distinguishing between two modulation types, A and B, one can simply correlate the output of two orthogonal filters. The optimum filters´ impulse responses can be expressed as the sum and difference of certain eigenfunctions of the difference of the autocorrelation functions of the two processes. A comparison of the simple method with a maximum likelihood system shows a measurable degradation in performance for a sample calculation; however, the simple method requires knowledge only of the autocorrelation function of the processes.