Non-linear signal distortion detection using multiple signal to noise ratio measurement sources
View Patent ↗A television signal processing apparatus comprising a receiver comprises a distortion estimator and an automatic gain control signal generator. The automatic gain control signal generator generates a plurality of automatic gain control and filter response control signals in response to the magnitude or signal to noise ratio of an RF signal and a non-linear distortion figure generated from the information carried by said RF signal. The distortion estimator uses a plurality of statistical methods to generate a non-linear distortion figure from the signal constellation of the information carried by said RF signal.
1. 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.
2. The apparatus of claim 1 , wherein
said number of constellation points over a period of time is determined as a percentage of a total number of constellation points received over said period of time; and
said degree of non-linear distortion is determined by comparing a degree of said first signal-to-noise ratio and a degree of said second signal-to-noise ratio represented as said percentage.
3. The apparatus of claim 1 , wherein
an absence of said non-linear distortion is detected when said estimation of said first signal-to-noise ratio and said estimation of said second signal-to-noise ratio yield on average substantially comparable results.
4. The apparatus of claim 1 wherein
said demodulator estimates said first and second signal-to-noise rations simultaneously.
5. The apparatus of claim 1 wherein
said demodulator estimates said first and second signal-to-noise rations sequentially.
6. A method comprising the steps of:
receiving an RF signal;
amplifying said RF signal for providing a gain-controlled version of said RF signal;
converting said gain-controlled version of said RF signal to an IF signal;
amplifying said IF signal for providing a gain-controlled version of said IF signal;
digitizing said gain-controlled version of said IF signal to a digitized IF signal;
demodulating said digitized IF signal;
adjusting a level of at least one of said gain-controlled versions of said RF and IF signals in response to a degree of non-linear distortion,
determining 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
comparing said first and second signal-to-noise ratios for determining said degree of non-linear distortion.
7. The method of claim 6 , wherein
said number of constellation points over a period of time is determined as a percentage of a total number of constellation points received over said period of time; and
said degree of non-linear distortion is determined by comparing a degree of said first signal-to-noise ratio and a degree of said second signal-to-noise ratio represented as said percentage.
8. The apparatus of claim 6 , wherein
an absence of said non-linear distortion is detected when said estimation of said first signal-to-noise ratio and said estimation of said second signal-to-noise ratio yield on average substantially comparable results.
9. The apparatus of claim 6 wherein
said demodulator estimates said first and second signal-to-noise rations simultaneously.
10. The apparatus of claim 6 wherein
said demodulator estimates said first and second signal-to-noise rations sequentially.