Detection of amplitude modulation using bispectra

The two sidebands generated around the carrier frequency by amplitude modulation (AM) can be treated as the result of quadratic phase coupling (QPC) between the frequency of the information bearing signal and the frequency of the carrier. Although the bispectrum is useful for detecting QPC, it will generate ambiguity. To avoid the ambiguity observed in the bispectrum, a simple fix of the existing bispectrum estimator, which allows the detection of amplitude modulation and distinguishes spontaneous frequencies from those due to nonlinear coupling, is proposed. A simulation example is provided to illustrate the effectiveness of the approach, followed by discussion of its possible use