Non-Uniform 16-Symbol Modulation for LDPC 4/15 BICM
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Solution Overview
Problem
Bit-Interleaved Coded Modulation (BICM) systems, used in digital broadcast channels, exhibit a significant difference from the Shannon limit in terms of capacity, necessitating the use of a more efficient signal constellation for effective error correction coded data transmission.
Innovation Solution
A modulator utilizing a non-uniform 16-symbol signal constellation, optimized for an LDPC coder with a code rate of 4/15, is employed for error correction coded data transmission, which includes specific symmetry and amplitude relationships between the constellation symbols to enhance transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniform signal constellation is used in BICM systems, then the system structure remains simple, but the capacity approaches the Shannon limit poorly
Solution Approach 1:
The patent applies asymmetry by transitioning from a uniform signal constellation to a non-uniform 16-symbol constellation. The non-uniform constellation features variable symbol distances and asymmetric amplitude distributions, which better match the statistical properties of LDPC-coded signals. This asymmetric design improves capacity efficiency by reducing the gap to the Shannon limit while maintaining manageable system complexity through structured constellation design.
Solution Approach 2:
The patent implements parameter changes by modifying the signal constellation parameters from uniform to non-uniform distribution. Specifically, the 16-symbol constellation uses varied amplitudes and phases optimized for LDPC code rate 4/15, changing the fundamental parameters of the modulation scheme to achieve better performance without requiring complete system redesign.
2Reliability
If a non-uniform signal constellation is used to improve capacity efficiency, then the performance approaches the Shannon limit, but the implementation complexity increases
Solution Approach 1:
The patent applies local quality by designing the non-uniform 16-symbol constellation with specific local characteristics optimized for different parts of the signal space. The constellation points have locally optimized amplitudes and phases that account for the specific error patterns of LDPC decoding, providing enhanced protection where needed while maintaining overall system performance.
Solution Approach 2:
The patent implements preliminary action by pre-optimizing the non-uniform constellation parameters specifically for LDPC code rate 4/15 before transmission. The constellation design anticipates the decoding requirements and error patterns, pre-configuring the signal distribution to minimize bit error rates from the outset rather than adapting during transmission.
3Reliability
If traditional uniform constellations are used, then the modulation scheme is simple to implement, but the frame error rate performance is poor
Solution Approach 1:
The patent applies universality by designing a non-uniform 16-symbol constellation that serves multiple functions: it provides improved frame error rate performance, maintains compatibility with standard LDPC decoding processes, and can be implemented with moderate complexity using existing modulation hardware with adjusted lookup tables or parameter sets.
Data Source
AI summary
A modulator and a modulation method using a non-uniform 16-symbol signal constellation are disclosed. The modulator includes a memory and a processor. The memory receives a codeword corresponding to a low-density parity check (LDPC) code having a code rate of 4/15. The processor maps the codeword to 16 symbols of the non-uniform 16-symbol signal constellation on a 4-bit basis.