Optical Receiver LLR Feedback for Lower-Load 8D Symbol Decoding
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Solution Overview
Problem
The calculation of log likelihood ratios for multidimensional symbols in optical communication systems is computationally intensive due to the need to calculate Euclidean distances for all candidate symbols, which increases the amount of calculation required for soft-decision error correction.
Innovation Solution
An optical receiver is designed with a first calculation unit to obtain log likelihood ratios for each M-dimensional symbol and a second unit to calculate the log likelihood ratio for an N-dimensional symbol, using feedback from a soft determination error correction code decoding circuit to reduce the number of necessary calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multi-leveling modulation (DP-64QAM or higher) is used to increase transmission capacity, then frequency utilization efficiency is improved, but minimum Euclidean distance between symbols reduces and noise resistance decreases
Solution Approach 1:
The patent transitions from conventional 2D QAM modulation to 8D modulation by incorporating polarization, time, and wavelength dimensions. This dimensional expansion increases the minimum Euclidean distance between symbols while maintaining high frequency utilization efficiency, thereby improving noise resistance without sacrificing transmission capacity.
2Reliability
If LLR calculation for multidimensional symbols is performed using conventional methods, then soft-decision error correction is achieved, but computational burden increases due to Euclidean distance calculations for all candidate symbols
Solution Approach 1:
The patent segments the 8D symbol calculation into multiple 2D QAM symbol calculations. By dividing the multidimensional LLR computation into independent lower-dimensional components, the system avoids exhaustive Euclidean distance calculations for all candidate multidimensional symbols, significantly reducing computational burden while maintaining error correction capability.
Solution Approach 2:
Instead of calculating LLR for all possible 8D candidate symbols, the patent performs partial action by calculating LLR only for the constituent 2D QAM symbols. This selective approach reduces computational complexity while still providing sufficient information for soft-decision error correction.
Data Source
AI summary
An optical receiver includes: a first calculation unit that obtains a log likelihood ratio for each M-dimension (M is a natural number), based on a received signal; and a second calculation unit that obtains a log likelihood ratio of an N dimensional symbol (N is a natural number), based on the log likelihood ratio for each M-dimension.