Adaptive Equalizer Step Size Control for Polarization Tracking
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Solution Overview
Problem
Existing adaptive filters in coherent optical data transmission suffer from deteriorated signal-to-noise ratio due to inappropriate step size settings, which either fail to track high-speed polarization state fluctuations effectively or consume excessive power for low-speed fluctuations.
Innovation Solution
An adaptive equalizer that updates the step size of tap coefficients based on time-series input and output of the adaptive filter, using a method that adjusts the step size according to the magnitude of update vectors to optimize tracking performance for both high-speed and low-speed polarization state fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a large step size is used in the adaptive filter to improve tracking performance of high-speed polarization fluctuations, then the tracking performance is improved, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The patent implements dynamic step size adjustment by introducing a forgetting factor that adapts the step size based on the correlation between current and past polarization states. When polarization fluctuations are rapid (low correlation), the step size increases to improve tracking. When fluctuations are slow (high correlation), the step size decreases to maintain signal-to-noise ratio. This resolves the contradiction by making the step size variable rather than fixed.
Solution Approach 2:
The patent changes the parameter of step size from a constant value to a dynamically adjusted value based on the forgetting factor. The forgetting factor is derived from the correlation of polarization states over time, allowing the system to automatically adjust the step size parameter to match the current fluctuation conditions, thereby resolving the trade-off between tracking speed and signal quality.
2Speed
If a large step size is used to track high-speed polarization fluctuations, then tracking performance is improved, but power consumption increases
Solution Approach 1:
The system dynamically adjusts the step size based on actual polarization fluctuation characteristics detected through the forgetting factor. During high-speed fluctuations, larger step sizes are used temporarily to maintain tracking performance. During low-speed periods, smaller step sizes reduce computational load and power consumption. This dynamic adaptation resolves the contradiction between maintaining tracking speed and reducing energy usage.
3Speed
If a large step size is used to ensure tracking performance during high-speed fluctuations, then high-speed tracking is improved, but margins for other deterioration factors are wasted
Solution Approach 1:
The patent changes the step size parameter from a fixed conservative value to a dynamically adjusted value based on the forgetting factor. This allows the system to use larger step sizes only when necessary (during high-speed fluctuations) and smaller step sizes during normal operation, thereby preserving system margins for other deterioration factors while maintaining tracking performance when needed.
Data Source
AI summary
An adaptive equalizer includes an updating unit that updates a step size of a vector of a tap coefficient used for controlling an adaptive filter based on a time-series update vector in accordance with a time-series input and output of the adaptive filter that tracks a polarization state of an optical signal received by a coherent optical receiver. The updating unit updates the step size based on a DC gain of the update vector. The updating unit may update the step size for each update vector component based on a DC gain for each update vector component.