Blind Equalization Algorithm for Polarization Mode Dispersion Compensation

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Solution Overview

Problem

Advanced modulation formats like PDM-8QAM and PDM-16QAM pose challenges for polarization de-multiplexing and PMD compensation due to non-constant symbol amplitudes, leading to ineffective error signals and noise introduction in traditional constant modulus algorithm (CMA) blind equalization.

Innovation Solution

A blind equalization algorithm utilizing multiple reference circles with different moduli to calculate error signals, allowing the error to approach zero for ideal M-ary QAM signals, as opposed to the conventional CMA which uses a single reference circle.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional constant modulus algorithm (CMA) blind equalization is used, then the system is simple to implement, but it introduces noise and fails to effectively compensate for polarization mode dispersion in advanced modulation formats with non-constant symbol amplitudes

Engineering Contradiction:

ImprovePMD compensation effectivenessVSAvoidNoise introduction

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the fundamental parameter of the reference model from a single constant modulus circle to multiple circles with different moduli. This parameter change allows the error signal to approach zero for ideal M-ary QAM signals, eliminating the noise introduction problem of CMA while effectively compensating for PMD in advanced modulation formats with non-constant symbol amplitudes

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If traditional CMA with a single reference circle is used, then the algorithm is computationally simple, but it cannot achieve zero error for ideal M-ary QAM signals with non-constant symbol amplitudes

Engineering Contradiction:

ImproveError signal accuracyVSAvoidAlgorithm complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the single reference circle into multiple reference circles with different moduli. This segmentation allows the error signal to be calculated more accurately by comparing against multiple reference levels, enabling zero error for ideal M-ary QAM signals while maintaining manageable computational complexity through systematic organization

Inventive Principle:

Principle #1Segmentation

3Reliability

If traditional CMA is applied to advanced modulation formats, then the implementation remains straightforward, but polarization de-multiplexing and PMD compensation become ineffective

Engineering Contradiction:

ImprovePolarization de-multiplexing effectivenessVSAvoidAlgorithm implementation simplicity

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent changes the reference model parameters from constant modulus to multiple moduli, which fundamentally improves polarization de-multiplexing and PMD compensation effectiveness for advanced modulation formats. The implementation remains relatively straightforward by extending the existing CMA framework with additional reference circles and modified error signal calculations

Inventive Principle:

Principle #35Parameter changes

Data Source

PatentUS8320778B2Blind equalization algorithms for adaptive polarization recovery and PMD compensation

Publication Date: 2012.11.27 AT&T INTELLECTUAL PROPERTY I L P

AI summary

A device and method are disclosed for blind equalization of an optical signal to implement adaptive polarization recovery, Polarization Mode Dispersion (PMD) compensation, and residual Chromatic Dispersion (CD) compensation in a digital coherent optical communication system.