Frequency-Domain GVD Compensation Using Segmented DFT Filters
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Solution Overview
Problem
The complexity of compensating group velocity dispersion (GVD) in optical transmission systems increases rapidly with transmission distance and symbol rate, making it challenging for long-haul, high-rate applications.
Innovation Solution
A digital filter arrangement (DFA) that transforms input signals from the time domain to the frequency domain using multiple discrete Fourier transform (DFT) filters, each of a smaller size, and applies a compensation filter to reduce complexity by employing a delay network and linear combination algorithm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital linear filters are used to compensate GVD, then signal quality is maintained, but implementation complexity grows rapidly with transmission distance and symbol rate
Solution Approach 1:
The patent divides the large filter into multiple smaller sub-filters arranged in a cascade structure. Instead of implementing one large filter with N taps, the system uses multiple smaller filters each with fewer taps, connected in series. This segmentation reduces the complexity of each individual filter while maintaining the overall compensation performance through the cascade arrangement.
Solution Approach 2:
The patent transforms the filter implementation from a single-dimensional large filter to a multi-dimensional cascade structure. By arranging filters in series across multiple stages, the system changes the dimensional approach from one large processing block to multiple smaller processing blocks, reducing the computational burden on any single filter while achieving the same overall effect.
2Measurement precision
If very long FIR filters are used to compensate GVD, then compensation accuracy is improved, but filter size and implementation complexity increase
Solution Approach 1:
The patent segments the long filter into multiple shorter sub-filters. Each sub-filter has a reduced number of taps compared to the original long filter, making them easier to implement with lower computational complexity. The cascade connection of these segmented filters maintains the overall frequency response characteristics needed for accurate GVD compensation.
Solution Approach 2:
The patent combines multiple smaller filters in a cascade configuration to achieve the equivalent performance of a single large filter. By merging the effects of several smaller filters working in series, the system achieves the same compensation accuracy as a long filter would provide, but with reduced individual filter sizes and lower implementation complexity.
Data Source
AI summary
The present disclosure relates to a digital filter arrangement (DFA) for compensating group velocity dispersion (GVD) in an optical transmission system (OTS) wherein the DFA is configured to receive a sequence of samples of a digital input signal in the time domain in the form of consecutive blocks of size L. The DFA is configured to generate M discrete Fourier transforms of a current overlap block of a size N greater than the size L and of M−1 delayed versions of the current overlap block. The DFA is configured to filter the entries of the generated M discrete Fourier transforms to generate an output discrete Fourier transform with N entries, wherein the compensation filter is implemented by a delay network and a linear combination algorithm.