Non-Uniform QAM Constellation Mapping Near the Shannon Limit
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Solution Overview
Problem
Current broadcasting systems, such as DVB-T2, utilize uniform QAM constellations that leave a significant gap from the theoretical Shannon limit, resulting in suboptimal bit error rate (BER) and frame error rate (FER) performance.
Innovation Solution
The implementation of non-uniform constellations (NUCs) that relax the geometric constraints of uniform QAM, allowing for optimized constellation design using algorithms that reduce the number of parameters and improve computational efficiency, thereby enhancing BER and FER performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If uniform QAM constellation is used, then ease of mapping and demapping is improved, but capacity and BER/FER performance deteriorate due to significant gap from Shannon limit
Solution Approach 1:
The patent applies local quality by transitioning from uniform spacing to non-uniform spacing of constellation points. Different regions of the constellation diagram have different point densities and spacing, optimizing performance for specific SNR ranges while maintaining manageable complexity through structured design
Solution Approach 2:
The patent changes the spacing parameter of the constellation points from uniform to non-uniform. This parameter change allows the system to achieve better capacity and error performance by optimizing the distribution of constellation points according to the probability density function of the channel, while still maintaining practical implementability
2Reliability
If non-uniform constellation is used, then capacity and BER/FER performance are improved, but complexity of constellation design and optimization increases
Solution Approach 1:
The patent segments the constellation design into structured components with specific geometric relationships. By dividing the constellation into organized patterns with defined spacing relationships, the design complexity is reduced while still achieving non-uniform optimization benefits
Solution Approach 2:
The patent creates a universal non-uniform constellation design that can be applied across different modulation orders (16-QAM, 64-QAM, 256-QAM, etc.). The structured approach with configurable parameters allows the same design methodology to serve multiple modulation schemes, reducing overall system complexity
3Productivity
If higher QAM size is used, then throughput is increased, but gap from Shannon limit and BER performance worsen with uniform QAM
Solution Approach 1:
The patent applies parameter changes by optimizing the spacing distribution of constellation points for higher-order QAM schemes. The non-uniform spacing is specifically tailored to match the probability density of the channel, allowing higher throughput while reducing the gap to Shannon limit even in challenging channel conditions
Data Source
AI summary
A transmitting apparatus is disclosed. The transmitting apparatus includes an encoder to perform channel encoding with respect to bits and generate a codeword, an interleaver to interleave the codeword, and a modulator to map the interleaved codeword onto a non-uniform constellation according to a modulation scheme, and the constellation may include constellation points defined based on various tables according to the modulation scheme.