Patent ID: 8331891

Claim:
An apparatus comprising: an input point receiving an RF signal; a frequency converter including a mixer and a local oscillator coupled to said input point operative to convert a gain-controlled version of said RF signal to an IF signal; a first gain-controlled amplifier coupled between said input point and said frequency converter operative to provide said gain-controlled version of said RF signal for said frequency converter; an analog-to-digital converter coupled to said frequency converter operative to digitize a gain-controlled version of said IF signal to a digitized IF signal; a second gain-controlled amplifier coupled between said frequency converter and said analog-to-digital converter operative to provide said gain-controlled version of said IF signal; an AGC generator coupled to said first and second gain-controlled amplifiers operative to adjust a gain of at least one of said first and second gain-controlled amplifiers in response to a degree of non-linear distortion; a demodulator coupled to said analog-to-digital converter demodulating said digitized IF signal, said demodulator being operative to estimate first and second signal-to-noise ratios independently, said first signal-to-noise ratio being estimated by direct noise power estimation based on averaging error signal power, said second signal-to-noise ratio being estimated based on the number of constellation points that fall within a radius of the center of a constellation cluster, and said demodulator being operative to compare said first and second signal-to-noise ratios for determining said degree of non-linear distortion.