Method and apparatus for optical signal and noise analysis using pulse amplitude histogram
First Claim
1. A method of analyzing signal and noise characteristics of an optical communications signal, comprising:
- establishing a threshold;
comparing the optical communications signal to the threshold to generate a comparison result signal, the comparison result signal having a predetermined binary value when the respective amplitudes of the optical communications signal and the threshold satisfy a predetermined comparison relationship;
counting, over a count interval substantially longer than the signaling period of the optical communications signal, the number of sampling instants at which the comparison result signal has the predetermined binary value, the count being stored in association with the threshold;
repeating the threshold establishing, comparing, and counting for each of a range of thresholds corresponding to an expected range of amplitudes of the optical communications signal, the count and threshold from each repetition being stored in mutual assocation, the stored counts and thresholds from all repetitions collectively representing a function N(VT) relating a count variable N to a threshold variable VT over the range of thresholds;
calculating, from the stored counts and thresholds, a derivative function dN/dVT of the function N(VT); and
utilizing predetermined parameters of the derivative function dN/dVT to calculate corresponding signal and noise parameters of the optical communications signal.
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Accused Products
Abstract
In a method of analyzing an optical communications signal, a threshold is established under control of a processor, and a decision circuit compares the amplitude of the signal to the threshold. A counter samples the output of the decision circuit and counts, over many periods of the signal, those samples indicating that the amplitude of the signal is above the threshold. The threshold generating, comparing, and counting are repeated for several thresholds within a range corresponding to an expected amplitude range of the signal. The stored counts and thresholds represent an amplitude histogram N(VT) for the signal. The derivative dN/dVT of the function N(VT) represents the probability density function (PDF) for the signal amplitude and can be used to derive performance information such as bit error rate and optical signal-to-noise ratio (OSNR).
15 Citations
23 Claims
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1. A method of analyzing signal and noise characteristics of an optical communications signal, comprising:
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establishing a threshold;
comparing the optical communications signal to the threshold to generate a comparison result signal, the comparison result signal having a predetermined binary value when the respective amplitudes of the optical communications signal and the threshold satisfy a predetermined comparison relationship;
counting, over a count interval substantially longer than the signaling period of the optical communications signal, the number of sampling instants at which the comparison result signal has the predetermined binary value, the count being stored in association with the threshold;
repeating the threshold establishing, comparing, and counting for each of a range of thresholds corresponding to an expected range of amplitudes of the optical communications signal, the count and threshold from each repetition being stored in mutual assocation, the stored counts and thresholds from all repetitions collectively representing a function N(VT) relating a count variable N to a threshold variable VT over the range of thresholds;
calculating, from the stored counts and thresholds, a derivative function dN/dVT of the function N(VT); and
utilizing predetermined parameters of the derivative function dN/dVT to calculate corresponding signal and noise parameters of the optical communications signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. Apparatus for analyzing signal and noise characteristics of an optical communications signal, comprising:
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a processor;
a threshold establishing circuit operative to establish a value of a threshold signal under control of the processor;
a decision circuit operative to compare the threshold signal to the optical communications signal to generate a comparison result signal, the comparison result signal having a predetermined binary value when the respective amplitudes of the optical communications signal and the threshold satisfy a predetermined comparison relationship; and
a counter operative, over a count interval substantially longer than the signaling period of the optical communications signal, to count the number N of sampling instants at which the comparison result signal has the predetermined binary value, the count for each count interval being provided to the processor;
wherein the processor is operative (i) to store the count N in association with the threshold, (ii) to cause the repetition of the respective operations of the threshold establishing circuit, the decision circuit, and the counter for each of a range of thresholds corresponding to an expected range of amplitudes of the optical communications signal, the count and threshold from each repetition being stored by the processor, the stored counts and thresholds collectively representing a function N(VT) relating a count variable N to a threshold variable VT over the range of thresholds, (iii) to calculate, from the stored counts and thresholds, a derivative function dN/dVT of the function N(VT), and (iv) to utilize predetermined parameters of the derivative function dN/dVT to calculate corresponding signal and noise parameters of the optical communications signal. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 23)
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Specification