Dual-Stage MIMO Equalizer for Rapid SOP Compensation
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Solution Overview
Problem
Current digital signal processing systems struggle to effectively track and compensate for rapid State of Polarization (SOP) changes induced by lightning strikes in Optical Ground Wire (OPGW) cables, particularly in coherent optical polarization multiplexed transmission schemes, as they exceed the capabilities of commercial digital signal processors designed for mechanical vibrations.
Innovation Solution
A dual-stage 2x2 MIMO equalization approach is implemented, comprising a first equalizer for chromatic dispersion and slower SOP changes, and a second equalizer for faster SOP changes, using separate channel and SOP estimation based on distinct training sequences, allowing for efficient compensation of SOP rotations up to several megaradians per second without feedback loops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If commercial digital signal processors are used for SOP tracking, then device complexity is kept low, but the SOP tracking speed is limited to hundreds of krad/s which is insufficient for lightning-induced changes
Solution Approach 1:
The equalizer is divided into two independent stages: a first 2x2 MIMO equalizer for chromatic dispersion and slow SOP changes, and a second 2x2 MIMO equalizer for fast SOP changes. This segmentation allows each stage to be optimized for its specific function, enabling high tracking speed while maintaining manageable complexity through modular design.
2Measurement precision
If training overhead is increased to improve SOP estimation accuracy, then measurement precision improves, but loss of time increases due to reduced data transmission efficiency
Solution Approach 1:
The system uses partial training sequences rather than complete training overhead. The first equalizer uses training sequences for channel estimation, while the second equalizer uses the same training sequences plus data symbols for SOP estimation. This partial action approach achieves sufficient estimation accuracy without requiring excessive training time that would reduce transmission efficiency.
3Reliability
If 2x2 MIMO equalization is applied to compensate fast SOP changes, then reliability improves, but device complexity increases due to additional processing requirements
Solution Approach 1:
The equalization process is segmented into two independent 2x2 MIMO equalizers operating in sequence. The first equalizer handles chromatic dispersion and slow SOP variations, while the second equalizer specifically addresses fast SOP changes. This segmentation improves reliability by comprehensively compensating different types of impairments while keeping each processing stage relatively simple and manageable.
Solution Approach 2:
The same training sequences serve multiple functions: they are used for channel estimation by the first equalizer and for SOP estimation by the second equalizer. This multi-functionality reduces the overall complexity by reusing existing signal components rather than requiring separate dedicated training sequences for each equalization stage.
Data Source
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AI summary
The present invention relates to the technical field of processing, particularly equalizing a digital signal, wherein the equalizing is supported by 2x2 MIMO channel estimation and State of Polarization (SOP) estimation. The invention presents an equalizing device, and optical receiver including said equalizing device, a corresponding method and an optical signal with a frame structure for enabling the method. The equalizing device includes a first 2x2 MIMO equalizer configured to perform a first equalization on the digital signal, supported by a 2x2 MIMO channel estimation of the channel based on the digital signal. Further, the device includes a second 2x2 MIMO equalizer, arranged after the first equalizer and configured to perform a second equalization on the digital signal, supported by a SOP estimation of the optical signal based on the digital signal.