Multi-Dimensional Symbol Shaping for Nonlinear-Tolerant Optical Links
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Solution Overview
Problem
Existing modulation formats with constant symbol energy, such as BPSK and QPSK, offer improved nonlinear performance but are limited to a single data rate, whereas high-cardinality QAM formats like 64 QAM or 256 QAM suffer from increased nonlinear interference in low-dispersion metro or submarine applications.
Innovation Solution
The development of novel constellations that utilize shaped and unshaped bits for bit-to-symbol mapping and symbol-to-bit demapping, allowing for adaptive spectral efficiency while maintaining power-balancing and polarization-balancing properties, which are beneficial for nonlinear tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-cardinality QAM formats (64 QAM or 256 QAM) are used to increase spectral efficiency, then the number of bits per symbol increases, but nonlinear interference increases significantly in low-dispersion metro or submarine applications
Solution Approach 1:
The patent changes the probability distribution parameter of constellation symbol selection from uniform to non-uniform (Gaussian-like distribution), where symbols with lower energy are selected more frequently. This parameter change in the selection probability allows achieving spectral efficiency between 2-6 bits per symbol while reducing the average symbol energy and minimizing nonlinear interference effects in the optical channel.
2Object-affected harmful factors
If constant symbol energy modulation formats (BPSK, QPSK) are used to minimize amplitude variations and improve nonlinear performance, then nonlinear tolerance improves, but spectral efficiency is limited to a single data rate
Solution Approach 1:
The patent introduces dynamic adaptability by allowing the spectral efficiency to vary continuously between 2 and 6 bits per symbol through adjustment of the probability distribution parameter μ. The system dynamically selects constellation symbols based on their energy levels according to a Gaussian-like distribution, enabling flexible spectral efficiency adaptation while maintaining power-balancing properties that improve nonlinear tolerance.
Solution Approach 2:
The patent changes the probability distribution parameter of constellation symbol selection from uniform to non-uniform (Gaussian-like distribution), where symbols with lower energy are selected more frequently. This parameter change in the selection probability allows achieving spectral efficiency between 2-6 bits per symbol while reducing the average symbol energy and minimizing nonlinear interference effects in the optical channel.
3Productivity
If probabilistic constellation shaping with varying symbol energies is used to achieve flexible spectral efficiency, then spectral efficiency can be varied continuously, but constellation symbols with different energies increase nonlinear interference
Solution Approach 1:
The patent changes the probability distribution parameter of constellation symbol selection from uniform to non-uniform (Gaussian-like distribution), where symbols with lower energy are selected more frequently. This parameter change in the selection probability allows achieving spectral efficiency between 2-6 bits per symbol while reducing the average symbol energy and minimizing nonlinear interference effects in the optical channel.
Data Source
AI summary
An optical transmitter device includes a digital signal processor (DSP) having digital hardware. The DSP is operative to generate shaped bits from a first set of information bits, and to apply a systematic forward error correction (FEC) scheme to encode the shaped bits and a second set of information bits, where the first set of information bits and the second set of information bits are disjoint sets. Unshaped bits and the shaped bits are mapped to selected symbols or are used to select symbols from one or more constellations. The selected symbols are mapped to physical dimensions. Each unshaped bit is either one of the second set of information bits or one of multiple parity bits resulting from the FEC encoding. In this manner, a target spectral efficiency is achieved.