Bit-Level Distribution Matcher for Optical Constellation Shaping
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Solution Overview
Problem
Optical communication networks face limitations in transmission reach due to high signal-to-noise ratio (OSNR) levels, especially when using advanced modulation formats like 16-QAM or 64-QAM, which result in reduced signal reach despite increased capacity.
Innovation Solution
The implementation of probabilistic constellation shaping using low rate loss bit-level distribution matchers, which assign codewords to input blocks based on a target probability distribution, effectively shaping the bit sequence to enhance noise tolerance and OSNR, thereby extending the transmission reach.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If advanced modulation formats (16-QAM, 64-QAM) are used to increase data capacity, then spectral efficiency is improved, but transmission reach deteriorates due to high OSNR requirements
Solution Approach 1:
The patent applies probabilistic constellation shaping by changing the probability distribution parameters of constellation points. Instead of uniform distribution, different probabilities are assigned to different constellation points based on their energy levels, creating a non-uniform distribution that optimizes the trade-off between data capacity and transmission reach. This parameter change allows the system to achieve higher spectral efficiency while maintaining better noise tolerance for extended reach.
2Device complexity
If constant modulus constraints are applied to distribution matching, then device complexity is reduced, but rate loss increases
Solution Approach 1:
The patent extracts and removes the constant modulus constraint from the distribution matching process. By taking out this restrictive constraint, the system can achieve more flexible probability distribution matching that better approximates the target distribution, thereby reducing rate loss while maintaining manageable complexity through the simplified bit-level matching approach.
Data Source
AI summary
Systems and methods for constellation shaping using low rate loss bit-level distribution matchers include receiving blocks of input bits and, for each input block of a predetermined size, assigning a respective codeword of a predetermined output block size. The number of bits of a given bit value in the codeword is dependent on a predetermined target probability distribution. A one-to-one mapping exists between each possible combination of input bits and a codeword for input blocks containing the combination. Some codewords include a number of bits having the given bit value that is different than the predetermined target probability distribution, but an average number of bits having the given bit value in the available codewords meets the predetermined target probability distribution. The disclosed methods result in more available codewords and a lower rate loss than in bit-level distribution matchers with a constant modulus, while achieving similar shaping.