Constellation Labeling for Probabilistic Amplitude Shaping and FEC
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Solution Overview
Problem
Current communication systems face inefficiencies in energy usage and error correction, particularly in high signal-to-noise ratio scenarios, due to uniform distribution of constellation points in conventional modulation schemes, leading to a performance gap of at least 1.53 dB compared to theoretical capacity.
Innovation Solution
The implementation of probabilistic amplitude shaping (PAS) in conjunction with low-density parity-check (LDPC) codes, where parity bits are placed in selected least significant bits (LSBs) and sign bits are generated using a logic function, such as XOR, to optimize constellation labeling and reduce error propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional modulation schemes with uniform distribution of constellation points are used, then the system is simple to implement, but the energy efficiency is poor and there is a performance gap of at least 1.53 dB compared to theoretical capacity
Solution Approach 1:
The patent applies parameter changes by transitioning from uniform distribution to non-uniform probabilistic amplitude shaping of constellation points. This changes the statistical parameters of the transmitted signal, concentrating energy on lower-amplitude points and reducing the probability of high-amplitude points, thereby improving energy efficiency and reducing the gap to theoretical capacity.
Solution Approach 2:
The patent introduces asymmetry in the constellation point distribution through probabilistic amplitude shaping, where different amplitude levels are assigned different probabilities of occurrence. This asymmetric distribution optimizes the trade-off between energy efficiency and error performance, achieving approximately 1.19 dB shaping gain.
2Reliability
If parity bits are placed in sign bits of transmitted constellation symbols, then error correction is simplified, but the most reliable bits are not protected and performance losses occur
Solution Approach 1:
The patent applies local quality by differentiating the treatment of different bit positions in the constellation labeling. Instead of uniformly placing parity bits, the system identifies specific least significant bits (LSBs) as optimal locations for parity placement based on their reliability characteristics. This localized approach ensures that parity bits are placed in positions that maximize error correction effectiveness.
Solution Approach 2:
The patent employs preliminary action by pre-determining the optimal placement of parity bits in specific LSB positions before transmission. The constellation labeling is designed in advance to reserve certain bit positions for parity information, allowing the receiver to efficiently extract and process error correction data without complex real-time analysis.
3Productivity
If probabilistic amplitude shaping is implemented without optimized constellation labeling, then shaping gain can be achieved, but performance losses occur due to improper placement of parity bits
Solution Approach 1:
The patent implements feedback mechanisms where the receiver detects errors in received constellation symbols and uses the predefined constellation labeling structure to identify and correct errors in parity bits. The systematic placement of parity bits in specific LSB positions enables efficient feedback-based error correction, maintaining both high throughput and reliability.
Solution Approach 2:
The patent introduces an intermediary structure through the optimized constellation labeling scheme that mediates between the probabilistically shaped amplitudes and the error correction process. This intermediary labeling structure systematically maps shaped amplitude levels to bit patterns with predetermined parity bit positions, enabling efficient error correction while preserving shaping gain.
Data Source
AI summary
A communication system in which a constellation employing partially anti-symmetric amplitude labels is used to transmit probabilistically shaped amplitudes such that said amplitudes are also used to determine the signs applied thereto for transmission. In an example embodiment, a data transmitter is configured to use a suitable logic function (e.g., an XOR function) to place the parity generated by an FEC code into a selected amplitude bit while using the partially anti-symmetric amplitude labels to avoid placing the parity into the sign bits of the transmitted constellation symbols. In some embodiments, the FEC code can be a low-density parity-check code. Some embodiments are compatible with layered FEC coding, e.g., employing an outer FEC code and an inner FEC code. In some embodiments, FEC coding may be optional. Some embodiments can advantageously be used in communication systems relying on DMT modulation, such as the systems providing DSL access over copper wiring.