Method for detecting nonlinear distortion using moment invariants

In a communications system having a channel and a receiver coupled to said channel, said receiver comprising a plurality of processing stages including a slicer, a method of detecting the presence of nonlinear distortion, said method comprising the steps of:

• generating an error signal from the difference between the slicer input and the slicer output;
• calculating a moment invariant utilizing said error signal;
• and
• declaring the existence of nonlinear distortion when said moment invariant exceeds a predetermined threshold.

A communications receiver for detecting the presence of nonlinear distortion in a received signal, said receiver coupled to a communications channel, comprising:

• first filter means for filtering said signal received from said channel;
• conversion means for converting the analog signal output of said first filter means to a plurality of digital samples;
• echo canceler means for reducing the level of echo noise in said signal;
• a demodulator for demodulating voice band frequencies to baseband frequencies;
• second filter means for filtering the output of said demodulator;
• an equalizer operative to decrease the linear amplitude envelope and phase distortion of said signal;
• a slicer operative to generate data output in response to the output of said equalizer;
• a summer for generating an error signal from the difference between the slicer input and the slicer output;
• and
• nonlinearity detection means operative to detect the existence of nonlinear distortion in response to said error signal.