Non-Uniform QAM Mapping for Better BER in Transmitters
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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 based on signal-to-noise ratio (SNR) and coding rate, using algorithms to reduce the number of parameters and improve computational efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform QAM constellation is used, then the system is easy to map and demap, but the capacity leaves a big gap from the Shannon limit
Solution Approach 1:
The patent applies local quality by creating non-uniform spacing between constellation points. Specifically, the distance between adjacent constellation points varies depending on their position in the constellation diagram. This allows different regions of the constellation to have different properties: outer points have larger spacing for better error tolerance, while inner points can be closer together to increase capacity. This resolves the contradiction by maintaining ease of mapping through structured design while improving BER performance through optimized local spacing.
Solution Approach 2:
The patent changes the spacing parameter between constellation points from uniform to non-uniform. By adjusting the distance parameter dynamically based on position, the system achieves better capacity utilization. The invention modifies the fundamental parameter of constellation point spacing to close the gap with the Shannon limit while preserving the systematic structure needed for practical implementation.
2Reliability
If non-uniform constellation is used, then the capacity approaches the Shannon limit, but the mapping and demapping complexity increases
Solution Approach 1:
The patent manages complexity by applying local quality principles with a structured approach. Rather than completely arbitrary non-uniform spacing, the invention uses a systematic method where spacing variations follow specific patterns based on position. This structured non-uniformity maintains manageable complexity for mapping and demapping while still achieving the performance benefits of non-uniform constellations.
Solution Approach 2:
The patent employs dynamics by making the constellation structure adaptable to different transmission conditions. The non-uniform spacing can be configured based on channel conditions, allowing the system to optimize performance dynamically. This flexibility helps manage complexity by only applying complex non-uniform structures when necessary, while maintaining simpler structures under other conditions.
3Productivity
If higher QAM size is used, then the throughput increases, but the gap from Shannon limit remains significant
Solution Approach 1:
The patent applies parameter changes by optimizing the spacing parameters of high-order QAM constellations. For 1024-QAM and higher orders, the invention adjusts the distance parameters between constellation points to achieve better spectral efficiency. This allows the system to fully utilize the capacity available at high QAM orders, closing the performance gap with the Shannon limit while maintaining the high throughput benefits of elevated QAM sizes.
Solution Approach 2:
The patent uses local quality to optimize high-order QAM by creating position-dependent spacing variations. In high-order constellations like 1024-QAM, this approach ensures that points throughout the dense constellation are optimally spaced, preventing performance degradation that would otherwise occur at higher modulation orders. This enables throughput increases while achieving near-optimal performance.
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.