Method and apparatus for SNR measurement
AssigneeNortel Networks Limited
InventorMatthew Brown
Life of this patent
Estimating the term…
Abstract
A method and apparatus for monitoring the signal to noise ratio (SNR) of a noisy data signal in an optical communication system. In a receiver, input of a noisy data signal to a limiting amplifier results in a regenerated data signal. The regenerated data signal is compared to the noisy data signal and the difference signal is assumed to be, for the most part, noise. A measure of the amplitude of the regenerated data signal is divided by a measure of the energy of the difference signal to result in an indication of the SNR of the noisy data signal.
Claims43
A method of determining an indicator of signal to noise ratio in a noisy data signal comprising:
- receiving said noisy data signal;
- limiting said noisy data signal to obtain a regenerated data signal;
- generating a noise signal by subtracting said regenerated data signal from said noisy data signal;
- determining a magnitude of energy of said noise signal;
- determining an amplitude of said regenerated data signal;
- and
- determining said indicator from said amplitude of said regenerated data signal and said magnitude of energy of said noise signal.
A monitor for determining an indicator of a signal to noise ratio of a noisy data signal, based on input comprising said noisy data signal and a regenerated data signal, said monitor comprising:
- a difference circuit for determining a noise signal comprising a difference between said noisy data signal and said regenerated data signal;
- an energy detector for determining a magnitude of energy of a signal output from said difference circuit;
- an amplitude detector for determining an amplitude of said regenerated data signal;
- and
- a ratio circuit for determining an indicator from output of said energy detector and output of said amplitude detector.
A monitor for determining an indicator of a signal to noise ratio of a noisy data signal, based on input comprising said noisy data signal and a regenerated data signal, said monitor comprising:
- means for determining a noise signal comprising a difference between said noisy data signal and said regenerated data signal;
- means for determining a magnitude of energy of a signal output from said difference circuit;
- means for determining an amplitude of said regenerated data signal;
- and
- means for determining an indicator from output of said difference signal energy determining means and said regenerated signal amplitude determining means.
A monitor for determining an indicator of a signal to noise ratio of a noisy data signal, based on input comprising said noisy data signal and a regenerated data signal, said monitor comprising:
- a first conversion means for converting said noisy data signal from analog to digital;
- a second conversion means for converting said regenerated data signal from analog to digital;
- a processor operable to:
- receive a digital representation of said noisy data signal from said first conversion means;
- receive a digital representation of said regenerated data signal from said second conversion means;
- generate a noise signal by subtracting said digital representation of said regenerated data signal from said digital representation of said noisy data signal;
- determine a magnitude of energy of said noise signal;
- determine an amplitude of said regenerated data signal;
- and
- determine said indicator from said amplitude of said regenerated data signal and said magnitude of energy of said noise signal.
A receiver in an optical transmission system comprising:
- a photodetector and preamplifier for converting a received optical signal to a noisy data signal;
- a limiting amplifier for limiting said noisy data signal to obtain a regenerated data signal;
- a clock and data recovery circuit for obtaining a retimed data signal and a recovered clock signal from said regenerated data signal;
- a signal to noise ratio monitoring circuit operable to:
- receive said noisy data signal;
- receive said regenerated data signal;
- generate a noise signal by subtracting said regenerated data signal from said noisy data signal;
- determine a magnitude of energy of said noise signal;
- determine an amplitude of said regenerated data signal;
- and
- determine an indicator of a signal to noise ratio of said noisy data signal from said amplitude of said regenerated data signal and said magnitude of energy of said noise signal.
Dependencies are inferred from the claim text.