MIMO Equalizer Timing Misalignment Compensation in Coherent Optical Receivers
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Solution Overview
Problem
Conventional optical coherent receivers face challenges in compensating timing misalignments among electrical baseband tributaries due to imbalances in analog paths, which degrade performance, especially at high data rates and larger constellation sizes, and existing solutions are either impractical or inadequate for adaptive compensation.
Innovation Solution
A signal processing device comprising a multiple-input multiple-output (MIMO) equalizer configured to receive and equalize real value signals, providing equalized real and imaginary components, and chromatic dispersion equalizers, allowing independent correction of time misalignment and polarization-dependent effects, with adaptive filter coefficients for dynamic channel adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bulk CD equalizers process H and V polarizations separately, then chromatic dispersion compensation is achieved, but timing misalignment among electrical baseband tributaries cannot be corrected
Solution Approach 1:
The patent segments the equalization process into two distinct stages: first, bulk CD equalizers compensate chromatic dispersion for each polarization separately; second, a MIMO equalizer corrects timing misalignments by processing all four tributaries (HI, HQ, VI, VQ) jointly. This segmentation allows each equalizer to specialize in its respective function without interference.
Solution Approach 2:
The MIMO equalizer acts as an intermediary stage between the bulk CD equalizers and the detector. It receives the already dispersion-compensated signals and applies additional cross-polarization and timing equalization, serving as a bridge that resolves the remaining timing misalignment issue without affecting the previously achieved CD compensation.
2Adaptability or versatility
If MIMO equalizer continuously adapts to polarization effects, then dynamic channel conditions are compensated, but computational complexity increases
Solution Approach 1:
The patent divides the equalization tasks into two segments with different adaptation requirements. The bulk CD equalizers operate in a quasi-static mode with infrequent reconfiguration, while the MIMO equalizer handles dynamic polarization effects with continuous adaptation. This segmentation allows the system to maintain high adaptability where needed while reducing overall computational burden.
Solution Approach 2:
The patent applies dynamic adaptation only where necessary - the MIMO equalizer continuously adapts its coefficients to track fast-varying polarization effects, while the bulk CD equalizers remain relatively static since chromatic dispersion changes slowly. This selective dynamics approach optimizes the balance between adaptability and computational complexity.
3Manufacturing precision
If independent correction of time misalignment is performed before chromatic dispersion compensation, then timing alignment is improved, but signal processing order becomes more complex
Solution Approach 1:
The patent segments the processing order into two clear stages: first bulk CD equalization, then MIMO equalization for timing and polarization effects. This segmentation provides a systematic and reproducible processing order that, while multi-stage, is clearly defined and easier to implement than fully integrated approaches.
Data Source
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AI summary
The present invention relates to signal processing in an optical receiver, in particular to equalization performed in coherent optical receivers. A multiple-input multiple-output (MIMO) equalizer receives and equalizes a plurality of real value signals, for example four sampled electrical baseband tributaries (HI, HQ, VI, VQ). The outputs of the multiple-input multiple-output (MIMO) equalizer provide equalized real or imaginary components of complex signals. The complex signals including the real and imaginary components are then each and individually equalized to remove chromatic dispersion.