Ring Constellation Shaping for Lower-SNR Data Transmission
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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, particularly at high signal-to-noise ratios.
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 to maximize minimum distance between symbols, then reliability is improved, but capacity approaches the Shannon limit poorly resulting in bandwidth and power inefficiency
Solution Approach 1:
The patent applies asymmetry by transitioning from uniform constellation spacing to non-uniform spacing where symbols are positioned at different radial distances from the origin. This asymmetric arrangement allows inner symbols to be more densely packed while outer symbols maintain sufficient separation, thereby increasing overall capacity without sacrificing reliability.
Solution Approach 2:
The patent implements local quality by assigning different properties to different regions of the constellation diagram. Inner symbols have smaller minimum distances and are transmitted more frequently, while outer symbols have larger minimum distances and are transmitted less frequently. This localized optimization allows the system to achieve high capacity where needed while maintaining reliability where critical.
2Device complexity
If uniform constellations are used with equal likelihood symbol transmission, then device complexity is reduced, but capacity is limited compared to Gaussian distribution
Solution Approach 1:
The patent applies parameter changes by modifying the radial distance parameter of constellation symbols from uniform to non-uniform distribution. Symbols are positioned at different radii based on their probability of transmission, with more probable symbols placed closer to the origin. This parameter transformation enables the system to approach Gaussian capacity while maintaining practical implementation feasibility.
3Productivity
If non-uniform constellations with unequal symbol likelihoods are used to approach Gaussian capacity, then capacity is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the constellation into multiple rings or shells at different radial distances from the origin. Each ring contains symbols with similar transmission probabilities and can be independently designed and optimized. This segmentation reduces the overall design complexity by breaking down the complex non-uniform constellation into manageable modular components.
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.