PDM-QAM Signal Processing Convergence via Preliminary Action
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Solution Overview
Problem
Existing signal processing methods for optical signals with PDM-QAM modulation face challenges in converging filter coefficients, especially when started from arbitrary initial values, leading to inefficient polarization rotation tracking.
Innovation Solution
A signal processing apparatus and method that includes polarized wave separation, carrier compensation, determination, and coefficient updating mechanisms, using a 90° optical hybrid for interference and photoelectric conversion, along with error calculation and selection units to converge filter coefficients by switching between different modulation schemes for accurate demodulation and coefficient adjustment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the DD algorithm is used for polarized wave separation with feedback to filter coefficient, then tracking performance to polarization rotation is improved, but the filter coefficient hardly converges when started from any initial value
Solution Approach 1:
The patent applies preliminary action by using a constant modulus algorithm to preliminarily converge the filter coefficient before applying the DD algorithm. This preliminary convergence ensures that the filter coefficient starts from a valid initial value, enabling the DD algorithm to achieve reliable tracking performance without convergence issues.
Solution Approach 2:
The patent substitutes the purely mechanical feedback mechanism of the DD algorithm with a two-stage approach that incorporates the constant modulus algorithm. This substitution replaces the problematic direct feedback system with a more robust sequential process that guarantees convergence.
2Productivity
If multi-level modulation signal (PDM-QAM) is used to increase transmission capacity, then data communication volume is improved, but signal processing complexity increases
Solution Approach 1:
The patent segments the signal processing into distinct functional blocks: a 90° optical hybrid for interference, photoelectric conversion units, and separate processing paths for in-phase and quadrature components. This segmentation manages the complexity of PDM-QAM demodulation by dividing it into manageable stages.
Solution Approach 2:
The patent introduces intermediate processing stages including the 90° optical hybrid and photoelectric conversion as mediators between the optical signal and digital processing. These intermediaries transform the complex optical signal into electrical domains that can be processed more easily, reducing overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables easy convergence of filter coefficients even from arbitrary initial values, improving polarization rotation tracking performance and demodulation accuracy for optical signals with PDM-QAM modulation.
Implementation Method 1
making the signal light having undergone polarization division multiplexing and multi-level modulation and local light interfere with each other by using a 90° optical hybrid
Implementation Method 2
performing photoelectric conversion and analog-digital conversion on four output light beams
Data Source
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AI summary
Signal processing means includes carrier compensation means for compensating for a phase difference and a frequency difference between signal light and local light in relation to two polarization signals, so as to generate two carrier compensated signals, symbol determination means for demodulating the two carrier compensated signals on the basis of a signal arrangement of multi-value modulation, symbol rough-determination means for demodulating the two carrier compensated signals on the basis of a signal arrangement in which the number of multi-values of the multi-value modulation is reduced, selection means for selecting either of an output of the symbol determination means and an output of the symbol rough-determination means, and coefficient setting means for updating filter coefficients of polarized wave separation means by using an output selected by the selection means.