Cochannel FM Demodulation via the Multi Angle-Centered Discrete Fractional Fourier Transform

The problem of demodulating multiple frequency modulated signals that overlap spectrally is seen to pervade communication systems both military and civilian, where bandwidth is a precious resource. In this paper, we extend the use of the recently developed multiangle discrete fractional Fourier transform (MA-CDFRFT) for the purposes of cochannel FM demodulation and also investigate its use for the demodulation of cochannel continuous phase modulation (CPM) signals used frequently in wireless systems, using rectangular, triangular, or trapezoidal pulse shapes. Simulation results demonstrate that the approach is able to accomplish cochannel signal separation and demodulation, where existing multicomponent AM-FM demodulation algorithms fail. It is further demonstrated that for cochannel CPM demodulation, symbol error probabilities that are comparable to or smaller than that of coherent BPSK detection in additive white Gaussian noise.