US 4,835,790 A · Carrier-to-noise detector for digital transmission systems

Abstract

A carrier-to-noise detector comprises an A/D converter (1) which samples an output of the demodulator of a digital transmission system at a symbol clock rate and converting it to a digital signal having positive and negative values. An absolute value converting circuit (2) converts the output of A/D converter into an absolute value which is averaged by a first averaging circuit (3) over a period sufficient to suppress short term variations and then squared by a first squaring circuit (4) to give an output representing the carrier component. The output of A/D converter is, on the other hand, squared by a second squaring circuit (5) and averaged by a second averaging circuit (6) to suppress short term variations to give an output representing a total of the carrier and noise components. The carrier component in the output of the second averaging circuit 6 is subtracted by a subtractor (7). A ratio between the outputs of the first squaring circuit (4) and subtracting circuit (7) is derived by a divider (8) as a representation of a carrier-to-noise ratio.

Claims13

Dependent claims

A carrier-to-noise detector for a digital transmission system, comprising:

an analog-to-digital converter for being connected to a demodulator of said digital transmission system for sampling an output signal of said demodulator at a symbol clock rate of said demodulator and converting the sampled signal to a digital output signal having positive and negative values;
absolute value converting means for converting said digital output signal from said analog-to-digital converter into a digital signal of an absolute value;
first averaging means for averaging said absolute value digital signal over a period of a plurality of symbols sufficient to suppress short term variations;
first squaring means for squaring the value of said absolute value digital signal from said averaging means;
second squaring means for squaring the value of the digital signal from said analog-to-digital converter;
second averaging means for averaging said squared digital signal from said second squaring means over a period of a plurality of symbols sufficient to suppress short term variations;
means for subtracting the squared digital output signal of said first squaring means from the averaged digital output signal of said second averaging means;
and
means for deriving a ratio between an output of said first squaring means and an output of said subtracting means.

6 more elements

A phase controlled demodulation system for digital communication, comprising:

a quadrature detector for receiving a modulated digital signal for generating therefrom a pair of I and Q demodulated signals;
a phase difference detection and filter circuit for detecting a phase difference between said I and Q demodulated signals;
means for detecting a carrier-to-noise ratio of one of said I and Q demodulated signals;
means for detecting a ratio difference between the detected carrier-to-noise ratio and a predetermined value;
and
a voltage controlled oscillator responsive to the detected phase difference and the detected ratio difference for generating a carrier which replicates the carrier of said received digital signal and applying said carrier to said quadrature detector.

3 more elements

A carrier-to-noise detector for a digital transmission system, comprising:

first means, connected to an output signal of said transmission system which contains a signal component and a noise component, for converting the output signal to a digital output signal;
second means coupled to the first means and effective for generating a first signal which is proportional to said signal component contained in said output signal of said digital transmission system;
third means coupled to said first means and effective for generating a second signal which is proportional to the sum of said noise component and said signal component contained in said output signal;
fourth means coupled to said second and third means and effective for generating a third signal which is proportional to a difference of said first and second signals;
and
fifth means coupled to said second and fourth means and effective for generating a fourth signal which is proportional to the ratio of said first and third signals and is indicative of the carrier-to-noise ratio of the signal component to the noise component in said transmission system.

3 more elements

Dependencies are inferred from the claim text.

Carrier-to-noise detector for digital transmission systems

Life of this patent

Carrier-to-noise detector for digital transmission systems

Life of this patent

Abstract

Claims13