Adaptive Equalization Filter With Dual-Rate Segmentation
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Solution Overview
Problem
The challenge is to maintain high polarization fluctuation resistance and distortion compensation while reducing the modulation symbol rate in optical transmission systems, as lower symbol rates decrease the polarization fluctuation resistance and follow-up speed of adaptive equalization filters.
Innovation Solution
The proposed solution involves an adaptive equalization filter configuration with a main signal filter and a coefficient computation unit. This unit includes pre-stage and post-stage filters connected in cascade, with the pre-stage filter coefficients updated using feedback control via the gradient method and the post-stage filter coefficients updated using feedforward control. The main signal filter coefficients are computed through convolution of the pre-stage and post-stage filter coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the modulation symbol rate is lowered to minimize non-linear degradation in optical fiber transmission, then distortion compensation resistance is improved, but polarization fluctuation resistance and following speed of adaptive equalization filter decrease
Solution Approach 1:
The patent divides the adaptive equalization filter into two separate filters: a first adaptive equalization filter that operates at a high symbol rate to track polarization fluctuations quickly, and a second adaptive equalization filter that operates at a low symbol rate to provide distortion compensation resistance. This segmentation allows each filter to be optimized for its specific function, resolving the contradiction between following speed and distortion compensation resistance
Solution Approach 2:
The patent introduces a temporal dimension by processing signals at different symbol rates through separate filter paths. The high-symbol-rate path handles rapid polarization changes while the low-symbol-rate path handles distortion compensation, effectively adding a time-scale dimension to the equalization process that allows simultaneous achievement of both fast tracking and robust compensation
2Reliability
If the symbol rate is decreased to reduce non-linear degradation, then distortion compensation performance is improved, but the symbol arrival time interval increases causing slower filter coefficient updates
Solution Approach 1:
The patent segments the equalization function into two parallel paths with different symbol rates. The first path processes symbols at high rate for rapid coefficient updates, while the second path processes at low rate for accurate distortion compensation. This segmentation decouples the update speed from the compensation accuracy, allowing both to be optimized independently
Solution Approach 2:
The patent uses an intermediary mechanism where the high-symbol-rate adaptive equalization filter acts as a mediator that provides rapid polarization tracking information to complement the low-symbol-rate filter. This intermediary high-rate path ensures continuous coefficient updates even when the main low-rate path would otherwise update too slowly
Data Source
AI summary
An aspect of the present invention is an adaptive equalization filter for an optical transmission system, including: a main signal filter; and a coefficient computation unit that updates the filter coefficient of the main signal filter. The pre-stage filter and the post-stage filter receive a sample of the main signal as an input. The pre-stage coefficient computation unit obtains the filter coefficient of the pre-stage filter by feedback control using the gradient method. The post-stage coefficient computation unit obtains the filter coefficient of the post-stage filter by feedforward control. The convolution computation unit obtains the filter coefficient of the main signal filter by convolution computation of the filter coefficient of the pre-stage filter obtained by the pre-stage coefficient computation unit and the filter coefficient of the post-stage filter obtained by the post-stage coefficient computation unit.