Non-Uniform Constellation Mapping for Lower BER in QAM Transmission
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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 (NUC) that relax the square shape and uniform distance properties of traditional uniform QAM, optimizing constellation design for specific signal-to-noise ratios (SNR) and fading channels to enhance BER and FER performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If uniform QAM constellation is used, then mapping and demapping is easy, but the capacity leaves a big gap from the Shannon limit resulting in suboptimal BER/FER performance
Solution Approach 1:
The patent changes the parameters of the QAM constellation from uniform spacing and square shape to non-uniform spacing and non-square shape. Specifically, the constellation points are redistributed with varying distances between adjacent points, and the overall shape is transformed from a square grid to an optimized geometric pattern. This parameter transformation allows the system to achieve better BER/FER performance by reducing the gap from the Shannon limit while maintaining reasonable mapping complexity through pre-computed lookup tables.
2Reliability
If non-uniform constellation is used, then the gap from Shannon limit is reduced improving BER/FER performance, but the constellation design becomes more complex
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing the optimal non-uniform constellation point mappings in lookup tables before actual transmission. The complex optimization process of determining the non-uniform constellation geometry, spacing, and point positions is performed in advance based on channel characteristics and performance requirements. During real-time operation, the system simply retrieves the pre-optimized mapping from the lookup table, thereby achieving excellent BER/FER performance without the computational burden of real-time optimization.
3Productivity
If QAM size is increased to increase throughput, then more bits per cell are mapped, but the gap from Shannon limit increases worsening BER performance
Solution Approach 1:
The patent applies local quality by optimizing the spacing and positioning of constellation points locally within the QAM grid rather than using uniform spacing throughout. In regions where higher reliability is needed, the constellation points are spaced farther apart to reduce error probability. In regions where higher throughput is acceptable, points are packed more densely. This local optimization allows different parts of the constellation to serve different functional requirements, enabling the system to achieve better overall BER performance at higher QAM sizes by adapting the local point distribution to the specific throughput and reliability requirements.
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.