QAM Constellation Mapping for Lower BER and Reduced Bandwidth
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Solution Overview
Problem
Existing 2m QAM modulation schemes face challenges in achieving optimal error rate characteristics and suppressing bandwidth increase, especially for signal constellations with cross-shaped or circular arrangements where the average Hamming distance between adjacent signal points is small and Euclidean distance is large, particularly when applying error correction codes.
Innovation Solution
A data transmission method that rearranges 2n QAM signal points from a rectangular to a circular or cross shape, using area mapping tables to assign bits such that the average Hamming distance between adjacent signal points is minimized and the Euclidean distance between signal points with coinciding lower-bit portions is maximized, allowing for effective error correction and reduced bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error correction code is applied to all bits in conventional 2m QAM schemes, then error rate performance is improved, but bandwidth expansion increases
Solution Approach 1:
The patent applies error correction coding selectively to specific bit positions rather than uniformly to all bits. By identifying and encoding only the more significant bits that contribute most to error rate performance, the system achieves improved reliability while minimizing the amount of redundant data added, thus suppressing bandwidth expansion.
Solution Approach 2:
The patent changes the parameter of error correction application from a uniform approach (all bits) to a differentiated approach (selective bit positions). This parameter change optimizes the trade-off between error rate performance and bandwidth efficiency by adjusting which bits receive error correction protection based on their individual error susceptibility.
2Ease of operation
If signal points are arranged in rectangular shape, then mapping simplicity is maintained, but bit error rate characteristics deteriorate due to small Euclidean distance between adjacent points
Solution Approach 1:
The patent transforms the traditional rectangular signal point arrangement into a circular arrangement. This curvature-based reconfiguration increases the Euclidean distance between adjacent signal points, thereby improving bit error rate characteristics while maintaining systematic mapping procedures through the use of area mapping tables.
Solution Approach 2:
The patent introduces a new dimensional organization of signal points by arranging them in concentric circular areas rather than rectangular grids. This dimensional change allows for optimized bit assignment strategies that exploit the radial symmetry of the circular arrangement, achieving better error performance through a fundamentally different spatial organization.
3Reliability
If signal points are rearranged to circular shape to improve Euclidean distance, then bit error rate characteristics are improved, but average Hamming distance between adjacent points becomes small
Solution Approach 1:
The patent addresses the small average Hamming distance issue by applying differentiated error correction strategies to different bit positions within the circular arrangement. By identifying which bit positions are more susceptible to errors due to the circular geometry and applying error correction selectively to those positions, the system compensates for the reduced Hamming distance while maintaining the benefits of the circular arrangement's larger Euclidean distance.
4Reliability
If redundant bits are added for error correction, then error resistance is improved, but bandwidth expansion occurs
Solution Approach 1:
The patent minimizes bandwidth expansion by applying error correction redundancy only to specific bit positions that most benefit from protection. Rather than adding redundant bits uniformly across all data bits, the system identifies the most vulnerable bit positions in the circular QAM arrangement and applies error correction selectively, thereby optimizing the ratio of error resistance improvement to bandwidth consumption.
Data Source
AI summary
By using circularly-arranged signal points obtained by rearranging a part of signal points arranged in a rectangular shape or a cross shape, average signal power and peak signal energy are reduced to improve nonlinear distortion characteristics. Provided is a bit mapping method in which an average value of a Hamming distance in terms of a specified lower bit portion between adjacent signal points is small, and a Euclidean distance between signal points at which the lower bit portions assigned thereto coincide with each other becomes maximum. By applying error correction code only to the lower bit portion, a data transmission method excellent in bit error rate characteristics is provided while suppressing a band expansion rate.