2x2 MIMO Equalizer for Rapid SOP Compensation in Optical Networks
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Solution Overview
Problem
Current digital signal processing systems struggle to track and compensate for rapid State of Polarization (SOP) changes caused by lightning strikes in Optical Ground Wire (OPGW) cables, leading to traffic interruptions in metro and long-haul networks, as existing equalizers are not designed to handle SOP speeds exceeding a few hundred Krad/s.
Innovation Solution
A 2×2 MIMO equalizing device and method that combines blind gradient and data-aided adaptation schemes to generate a new instance of the equalization filter, allowing for continuous adaptation without signaling overhead and enabling symbol-by-symbol tap updates, thereby tracking and compensating fast SOP changes up to Mrad/s.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of information
If blind adaptation scheme is used for continuous equalization, then signaling overhead is reduced, but update speed is limited by feedback loop and parallelization factor
Solution Approach 1:
The patent segments the equalization process into two distinct stages: a fast feed-forward data-aided stage for initial rapid adaptation using training sequences, and a slower feedback blind stage for continuous refinement. This segmentation allows each stage to operate at its optimal speed without being constrained by the other, resolving the contradiction between fast update capability and low overhead operation.
Solution Approach 2:
The patent employs preliminary action by inserting training sequences at the transmitter before the actual data transmission. These training sequences enable the equalizer to perform rapid feed-forward adaptation in advance, establishing initial equalization coefficients before the main payload data is processed, thereby achieving fast update speed without requiring continuous feedback during data transmission.
2Speed
If data-aided adaptation with training sequences is used, then adaptation speed increases, but signaling overhead increases
Solution Approach 1:
The patent segments the transmission into training sequence portions and payload data portions, applying different adaptation strategies to each segment. The training sequences enable fast adaptation during their transmission, while the payload data benefits from the pre-computed equalization coefficients, thereby achieving high adaptation speed with minimal ongoing overhead.
Solution Approach 2:
The training sequences are transmitted in advance before the payload data, allowing the equalizer to compute and store optimal equalization coefficients beforehand. This preliminary action eliminates the need for continuous training sequences during payload transmission, achieving fast adaptation speed while minimizing signaling overhead during the critical data transmission phase.
3Adaptability or versatility
If feedback loop is used in blind adaptation, then continuous adaptation is enabled, but update speed is limited by parallelization factor p
Solution Approach 1:
The patent segments the adaptation process into a fast feed-forward phase using training sequences and a slower feedback phase using blind adaptation. During the feed-forward phase, the equalizer can update taps at the symbol rate without being constrained by the parallelization factor, achieving high update speed. The feedback phase provides continuous adaptation with lower speed requirements, resolving the contradiction between continuous adaptation and fast update capability.
Solution Approach 2:
The training sequences perform preliminary equalization computation before the feedback loop becomes active. This preliminary action establishes initial equalization coefficients that enable fast tap updates during payload transmission, while the feedback loop continues to refine the coefficients without limiting the update speed achieved during the feed-forward phase.
4Productivity
If high-order QAM modulation is used, then data rate increases, but SOP tracking capability is drastically reduced
Solution Approach 1:
The patent segments the equalization into two stages that work together to handle SOP changes in high-order QAM systems. The feed-forward data-aided stage provides fast initial tracking, while the feedback blind stage provides continuous refinement, collectively enabling SOP tracking capability sufficient for high-order QAM modulation at high data rates.
Solution Approach 2:
The training sequences perform preliminary channel estimation and equalization coefficient computation before high-order QAM data transmission. This preliminary action establishes accurate equalization coefficients that enable the system to track SOP changes rapidly enough to support high-order QAM modulation, resolving the contradiction between high data rate and SOP tracking capability.
Data Source
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AI summary
The present invention relates to the technical field of processing, particularly equalizing a digital signal representing samples of an optical signal, wherein the equalizing is supported by 2x2 MIMO channel estimation and State of Polarization (SOP) estimation. The digital signal comprises a training sequence followed by a payload. The invention presents an equalizing device, optical receiver including said equalizing device, and a corresponding method. The equalizing device is configured to generate a new instance of a 2x2 MIMO equalization filter based on one or more preceding instances of the equalization filter and on one or more samples of the payload. Further, the equalizing device is configured to equalize a sample of the payload by applying the new instance of the equalization filter to the sample.