US 5,317,599 A · Method and circuit for detecting CN ratio of QPSK signal

Abstract

The invention is a method and a circuit for detecting the carrier-to-noise ("CN") ratio of a quaterary phase-shift keying ("QPSK") signal. A binary signal including in the QPSK signal is reproduced by a converting circuit including a QPSK demodulator and a difference converter. The binary signal is then error-controlled by an error detecting circuit and the detection of a double-error. The occurrence number of the double-error is counted during a predetermined time period which is long enough to compare with the occurrence time when two successive double-errors occur. A microcomputer stores a conversion table corresponding to the theoretical relation between the CN ratio and the occurrence number. The microcomputer computes the CN ratio from the detected occurrence number. The theoretical relation is formulated based on the assumption that noise distributes isotopically around the QPSK signal in the signal space in accordance with the nomal distribution.

Claims8

Dependent claims

A method of determining the carrier-to-noise ratio of a quaternary phase-shift keying ("QPSK") signal which includes a binary signal representing at least a message and an information for error-control in order to detect a double-error, said method comprising the steps of:

receiving said QPSK signal and reproducing said binary signal from said QPSK signal,
detecting said double-error included in said binary signal and generating an occurrence pulse in response to a detection of said double-error,
counting said occurrence pulses and providing an occurrence number of said double-errors over a predetermined time period which is long enough to compare said occurrence number with an average occurrence time to indicate that successive double-errors have occurred, and
computing said carrier-to-noise ratio from said occurrence number in accordance with a theoretical relation between carrier-to-noise ratios and occurrence numbers of said double-errors.

1 more element

A circuit for detecting the carrier-to-noise ratio of a quaternary phase shift keying ("QPSK") signal which includes a binary signal representing at least a message and an information for error-control in order to detect a double-error, said circuit comprising

converter means which receives said QPSK signal and reproduces said binary signal from said QPSK signal,
error-control means which at least detects said double-error included in said binary signal, and which delivers an occurrence pulse in response to a detection of said double-error,
counter means which counts said occurrence pulses and provides an occurrence number of said double-errors during a predetermined time period which is long enough to compare said occurrence number with an average occurrence time to indicate that successive double-errors have occurred, and
computer means which computes said carrier-to-noise ration from said occurrence number in accordance with a theoretical relation between carrier-to-noise ratios and occurrence numbers of said double-errors.

1 more element

Dependencies are inferred from the claim text.

Method and circuit for detecting CN ratio of QPSK signal

Life of this patent

Method and circuit for detecting CN ratio of QPSK signal

Life of this patent

Abstract

Claims8