16-Symbol Constellation Mapping for 4/15-Rate LDPC Codewords
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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 conjugate complex number relationships among the constellation symbols, enhancing 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 and easy to implement, but the transmission capacity falls significantly short of the Shannon limit
Solution Approach 1:
The patent applies asymmetry by designing a non-uniform 16-symbol signal constellation where symbol distances are intentionally made unequal. The constellation includes four groups of symbols with different amplitude levels, creating asymmetric spacing that optimizes error correction performance and brings transmission capacity closer to the Shannon limit while maintaining manageable system complexity
Solution Approach 2:
The patent implements local quality by assigning different amplitude characteristics to different regions of the signal constellation. Specifically, symbols are organized into groups with varying amplitude levels (e.g., inner symbols with smaller amplitudes, outer symbols with larger amplitudes), allowing each region to be optimized for its specific function in error protection and data transmission
2Reliability
If traditional uniform 16-QAM modulation is used, then implementation is straightforward, but bit error rates and frame error rates remain high in noisy broadcast channels
Solution Approach 1:
The patent reduces error rates by creating asymmetric symbol spacing in the 16-symbol constellation. Symbols are arranged with non-uniform distances where inner symbols have smaller separation and outer symbols have larger separation, providing better error protection for more critical data bits while maintaining overall system efficiency
Solution Approach 2:
The patent changes the amplitude parameters of the signal constellation from uniform to non-uniform values. Specific amplitude relationships are defined (e.g., |real(w0)|=|imaginary(w1)|, |real(w1)|=|imaginary(w0)|) to optimize the constellation for LDPC-coded transmission, thereby improving error rate performance without excessive complexity
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.