Adaptive Filter Frequency Domain Coefficient Adaptation
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Solution Overview
Problem
Existing digital filtering methods in optical communication systems, such as those employing Fast Fourier Transforms (FFTs) and inverse FFTs, face inefficiencies in updating filter coefficients to effectively compensate for chromatic dispersion and wavelength-specific attenuation, leading to residual distortion in optical signals.
Innovation Solution
An adaptive filter configuration that includes Fourier transforming, weighting, correlating, and adapting filter coefficients in the frequency domain, utilizing auto-correlation or cross-correlation techniques to iteratively refine filter coefficients for improved chromatic dispersion compensation and wavelength-specific attenuation reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional FFT-based filtering methods are used to compensate for chromatic dispersion, then signal quality improvement is achieved, but filter coefficient updating efficiency deteriorates
Solution Approach 1:
The patent inverts the conventional approach by performing correlation operations in the frequency domain rather than transforming error signals back to time domain for coefficient updates. This inversion allows direct frequency-domain adaptation without iterative time-domain processing, improving updating efficiency while maintaining signal quality compensation
Solution Approach 2:
The patent extracts the essential adaptation function from the time domain and implements it directly in the frequency domain. By separating the correlation and adaptation operations into the frequency domain, the system eliminates the need for repeated FFT-IFFT cycles, thereby improving coefficient updating efficiency without compromising chromatic dispersion compensation performance
2Manufacturing precision
If iterative filter adaptation is performed to reduce residual distortion, then manufacturing precision of signal reconstruction is improved, but processing time increases
Solution Approach 1:
The patent performs preliminary frequency domain transformation of the input signal and pre-calculates correlation values in the frequency domain before final signal reconstruction. This preliminary action in the frequency domain avoids repeated time-domain transformations during iterative adaptation, reducing processing time while maintaining reconstruction accuracy
Solution Approach 2:
The patent replaces the mechanical iterative time-domain processing system with a frequency-domain correlation system. By substituting time-domain convolution with frequency-domain multiplication and correlation, the system achieves faster coefficient adaptation with reduced processing time while maintaining or improving signal reconstruction accuracy
Data Source
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AI summary
An adaptive filter being configured to filter an input signal comprises Fourier transforming means (101) being configured to transform the input signal into a frequency domain signal upon the basis of the Fourier transform, weighting means (103) being configured to weight at least a portion of the frequency domain signal with a filter coefficient of the dispersion filter in frequency domain to obtain a filtered signal in frequency domain, correlating means (107) being configured to correlate the filtered signal in frequency domain to obtain a correlation value, and adaptation means (109, 111) being configured to adapt the filter coefficient upon the basis of the correlation value.