Non-Uniform 16-Symbol Constellation for 3/15-Rate LDPC Modulation
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Solution Overview
Problem
Bit-Interleaved Coded Modulation (BICM) systems, used in digital broadcast channels, face a significant gap in performance compared to the Shannon limit due to the use of uniform signal constellations, which can be improved by employing non-uniform signal constellations optimized for specific code rates.
Innovation Solution
A modulator and modulation method utilizing a non-uniform 16-symbol signal constellation, specifically designed for an LDPC coder with a code rate of 3/15, which maps codewords to 16 symbols with non-uniform distances and symmetric amplitudes, optimizing performance for next-generation broadcast systems like ATSC 3.0.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform signal constellation is used in BICM systems, then the system structure remains simple and implementation is straightforward, but the performance gap compared to the Shannon limit increases significantly
Solution Approach 1:
The patent applies local quality by transitioning from a uniform signal constellation to a non-uniform 16-symbol constellation specifically optimized for LDPC code rate 3/15. The non-uniform constellation assigns different amplitude and phase characteristics to different symbols based on their position in the constellation diagram, creating locally optimized signal properties that match the statistical characteristics of the LDPC code output. This local optimization reduces the performance gap to the Shannon limit while maintaining systematic implementation.
Solution Approach 2:
The patent implements parameter changes by modifying the signal constellation parameters (amplitude and phase) from uniform to non-uniform distribution. Specifically, the 16-symbol constellation uses varied amplitude levels and phase angles that are optimized for the LDPC code rate 3/15, rather than using equal spacing and amplitude as in traditional QAM. This parameter transformation improves reliability by better matching the code characteristics.
2Reliability
If a non-uniform signal constellation optimized for specific code rates is employed, then error correction performance improves significantly, but the system loses flexibility in adapting to different code rates and modulation orders
Solution Approach 1:
The patent applies segmentation by designing separate optimized non-uniform constellations for different code rates (e.g., 3/15, 5/15, 7/15) and modulation orders. Each constellation is specifically tailored to its target code rate, allowing the system to achieve optimal performance for each specific configuration. The receiver can select the appropriate constellation based on the detected code rate, maintaining adaptability while benefiting from specialized optimization.
Solution Approach 2:
The patent implements dynamics by making the signal constellation adaptable and configurable rather than fixed. The system can dynamically switch between different non-uniform constellations based on the selected code rate and modulation order. This dynamic capability allows the system to maintain optimal performance across multiple operating conditions, resolving the contradiction between specialization and versatility.
Data Source
AI summary
A modulator and a modulation method using a non-uniform 16-symbol signal constellation are disclosed. The modulator includes a memory and a processor. The memory receives a codeword corresponding to a low-density parity check (LDPC) code having a code rate of 3/15. The processor maps the codeword to 16 symbols of the non-uniform 16-symbol signal constellation on a 4-bit basis.