Broadcast Signal Mapping Using Non-Uniform QAM Constellations
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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 ease of mapping and demapping is improved, but gap from Shannon limit increases
Solution Approach 1:
The patent applies local quality by creating different constellation point distributions in different regions of the complex plane. The non-uniform constellation assigns different probabilities and spacing to constellation points based on their local position, with inner points having higher probability and closer spacing than outer points. This local optimization improves overall reliability while maintaining reasonable mapping complexity.
Solution Approach 2:
The patent changes the fundamental parameter of constellation uniformity from uniform to non-uniform distribution. By modifying the distance parameters between constellation points and adjusting their probability distribution, the system achieves better Shannon limit performance. The mapping process adapts parameters like bit-to-point assignment based on the non-uniform structure.
2Reliability
If non-uniform constellation is used, then gap from Shannon limit is reduced, but mapping and demapping complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the non-uniform constellation map and its inverse demap relationships. The transmitter pre-generates the optimal non-uniform constellation configuration, and the receiver pre-stores the corresponding demapping tables. This preliminary preparation reduces real-time computational complexity during actual transmission and reception operations.
Solution Approach 2:
The patent uses copying by creating lookup tables that store the non-uniform constellation mappings. Instead of performing complex real-time calculations, the system copies pre-computed mapping relationships into tables that can be quickly referenced during transmission and reception, significantly reducing operational complexity while maintaining the benefits of non-uniform constellations.
3Ease of manufacture
If uniform distance between constellation points is maintained, then ease of manufacture is improved, but BER and FER performance deteriorates
Solution Approach 1:
The patent applies asymmetry by deliberately creating non-uniform distances between constellation points. The constellation design uses asymmetric spacing where inner points are closer together and outer points are farther apart, reflecting the different probabilities of symbol occurrence. This asymmetric structure optimizes BER and FER performance by matching the constellation geometry to the statistical properties of the communication channel.
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.