Adaptive QAM Constellation Selection for AWGN Channel Coding Gains
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Solution Overview
Problem
Second-generation cable systems, such as DVB-C2, face challenges in achieving maximum coding and shaping gains due to the use of uniform symbol constellations for LDPC codes, which result in limited performance in AWGN channels and are not effective in fading environments.
Innovation Solution
Adapting the symbol constellation in cable transmission systems to switch between non-uniform and uniform constellations based on the selected coding rate, allowing for better coding gains and increased capacity by using a non-uniform constellation for lower coding rates and a uniform constellation for higher coding rates, specifically for LDPC coding rates and QAM schemes like 1024-QAM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If uniform symbol constellations are used for all LDPC coding rates, then device complexity is reduced and ease of operation is improved, but coding gains are limited and system capacity cannot be maximized
Solution Approach 1:
The patent applies dynamics by making the symbol constellation adaptable rather than fixed. The system dynamically switches between uniform and non-uniform constellations based on the LDPC coding rate being used. For coding rates of 8/9 and 9/10, uniform constellations are employed to simplify operations, while for lower coding rates (1/4 through 5/6), non-uniform constellations are used to maximize coding gains. This dynamic adaptation resolves the contradiction by allowing the system to optimize performance when needed while maintaining simplicity when possible.
Solution Approach 2:
The patent changes the parameter of symbol constellation uniformity based on the coding rate. By adjusting this parameter, the system achieves better coding gains for lower coding rates where non-uniform constellations are used, while maintaining operational simplicity for higher coding rates where uniform constellations suffice. This parameter change approach allows the system to navigate the trade-off between performance and complexity.
2Reliability
If non-uniform symbol constellations are used for lower coding rates, then coding gains are improved, but device complexity increases
Solution Approach 1:
The system dynamically selects the appropriate constellation type based on the coding rate. The adaptability mechanism automatically chooses non-uniform constellations for lower coding rates (1/4 through 5/6) to maximize coding gains, while switching to uniform constellations for higher coding rates (8/9 and 9/10) to maintain ease of operation. This dynamic selection resolves the contradiction by applying complexity only when it provides performance benefit.
3Productivity
If uniform symbol constellations are used for all coding rates, then ease of operation is improved, but system capacity is limited
Solution Approach 1:
The patent implements dynamic constellation adaptation to maximize system capacity. By switching to non-uniform constellations for lower coding rates, the system achieves better coding gains that directly increase overall capacity. The adaptability mechanism ensures this capacity enhancement is achieved without permanently increasing complexity, as the system reverts to simpler uniform constellations when appropriate.
Solution Approach 2:
The system changes the constellation uniformity parameter based on coding rate requirements. This parameter adjustment enables the system to achieve higher capacity through optimized coding gains at lower coding rates, while maintaining operational simplicity at higher coding rates where uniform constellations are sufficient.
Data Source
AI summary
A cable transmitter supports a number of low density parity check (LDPC) coding rates, e.g., ¼, ⅓, ⅖, ½, ⅗, ⅔, ¾, ⅘, ⅚, 8/9 and 9/10; and supports a number of quadrature amplitude modulation (QAM) schemes, e.g., 4-QAM, 16-QAM, 64-QAM, 256-QAM, 1024-QAM or higher. For a selected modulation scheme, the cable transmitter selects between using a non-uniform symbol constellation or a uniform symbol constellation as a function of a selected coding rate.