Ring Constellation Mapping for Lower-SNR Data Reception
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Solution Overview
Problem
Existing digital communication systems face limitations in achieving maximum capacity due to the use of constellations that do not approach the Gaussian channel capacity, resulting in inefficiencies in bandwidth and power usage, despite attempts to optimize constellations for minimum distance and coding gains.
Innovation Solution
The development of geometrically shaped symbol constellations that optimize capacity by iteratively optimizing the location of constellation points to maximize capacity measures such as parallel decode and joint capacity, allowing for reduced signal-to-noise ratios and increased data transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional constellations are used that maximize minimum distance between points, then reliability is improved, but capacity approaches the Gaussian limit poorly resulting in bandwidth and power inefficiency
Solution Approach 1:
The patent applies local quality by creating non-uniform constellation distributions where different regions of the signal space have different point densities. Specifically, the constellation uses higher point density in certain angular sectors and lower density in others, allowing the system to achieve both good minimum distance properties for reliability and optimized capacity for bandwidth efficiency. This is accomplished through selective mapping of coded bits to constellation points based on their local density characteristics.
Solution Approach 2:
The patent employs asymmetry by designing constellations that are not uniformly distributed in the complex plane. The constellation points are arranged with asymmetric angular spacing and radial distances from the origin, creating an irregular pattern that better matches the optimal Gaussian distribution. This asymmetric arrangement allows the system to approach the Shannon capacity limit while maintaining robust error performance.
2Ease of manufacture
If constellation points are uniformly spaced to simplify implementation, then ease of manufacture is improved, but capacity is reduced compared to optimized non-uniform constellations
Solution Approach 1:
The patent applies segmentation by dividing the constellation design into multiple independent components: radial distance selection, angular position selection, and bit-to-point mapping. Each component can be optimized and implemented separately, allowing the complex non-uniform constellation to be constructed from simpler modular elements. This segmented approach maintains implementation feasibility while achieving superior capacity compared to uniform constellations.
Solution Approach 2:
The patent utilizes parameter changes by varying the radial distances and angular positions of constellation points according to optimized values that approach the Gaussian distribution. Instead of fixed uniform spacing, the system employs continuously optimized parameters for point locations, which can be pre-calculated and stored. This allows the system to achieve high capacity while maintaining practical implementability through lookup tables or simplified generation algorithms.
3Productivity
If coded modulation is used to increase capacity, then productivity is improved, but the constellation still limits the achievable coding gains
Solution Approach 1:
The patent merges the constellation design and coding scheme into a unified coded modulation framework. Rather than treating constellation points and coded bits as separate entities, the system jointly optimizes the mapping between coded bit sequences and constellation point selections. This merging allows the constellation structure itself to contribute to coding gains, pushing the system closer to the Shannon limit by eliminating the separation between modulation and coding optimization.
Data Source
AI summary
Communication systems are described that use unequally spaced constellations that have increased capacity compared to conventional constellations operating within a similar SNR band. One embodiment is a digital communications system including a transmitter transmitting signals via a communication channel, the transmitter including a coder capable of receiving user bits and outputting encoded bits at a rate, a mapper capable of mapping encoded bits to symbols in a constellation, and a modulator capable of generating a modulated signal for transmission via the communication channel using symbols generated by the mapper, wherein the constellation is unequally spaced and characterizable by assignment of locations and labels of constellation points to maximize parallel decode capacity of the constellation at a given signal-to-noise ratio so that the constellation provides a given capacity at a reduced signal-to-noise ratio compared to a uniform constellation that maximizes the minimum distance between constellation points of the uniform constellation.