Non-Uniform Constellation Mapping for Broadcast Transmitters
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Solution Overview
Problem
Current broadcasting systems, such as DVB-T2, utilize uniform QAM constellations which 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 development of non-uniform constellations (NUCs) that relax the rectangular shape and uniform spacing constraints of traditional QAM constellations, using algorithms to optimize constellation design for improved capacity and performance based on signal-to-noise ratio (SNR) and coding rate, specifically for Bit Interleaved Coded Modulation (BICM) systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If uniform QAM constellation is used, then mapping and demapping is simple and easy to implement, but capacity is far from Shannon limit and BER/FER performance is suboptimal
Solution Approach 1:
The patent changes the geometric parameters of the constellation from uniform spacing and rectangular shape to non-uniform spacing and optimized shapes. This allows the constellation to be tailored for specific SNR conditions and coding rates, improving capacity and error performance while maintaining practical implementability through algorithmic generation.
Solution Approach 2:
The patent applies local optimization by designing constellation points with different spacing and distribution characteristics in different regions of the complex plane. This local differentiation allows better adaptation to the probability density function of the channel and improves overall system performance for specific operating conditions.
2Reliability
If non-uniform constellation is used, then capacity approaches Shannon limit and BER/FER performance improves, but constellation design becomes complex and requires optimization algorithms
Solution Approach 1:
The patent performs preliminary optimization by pre-calculating and storing optimal constellation parameters for different SNR values and coding rates. This allows the system to achieve near-Shannon-limit performance without real-time optimization complexity, as the optimal constellation is selected from pre-computed tables based on current operating conditions.
Solution Approach 2:
The patent introduces dynamic adaptation by making the constellation parameters variable according to SNR conditions and coding rates. This dynamic approach allows the system to optimize performance for each specific operating point while using efficient algorithms to determine the appropriate constellation configuration.
3Productivity
If higher QAM size is used, then throughput increases, but gap from Shannon limit remains and performance is not optimal
Solution Approach 1:
The patent optimizes the constellation parameters specifically for higher-order QAM (64-QAM, 256-QAM, 1024-QAM) by adjusting point spacing and distribution to match the probability density function at higher signal-to-noise ratios. This optimization closes the gap to the Shannon limit while maintaining the high throughput benefits of higher-order modulation.
Data Source
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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.