Log-likelihood Ratio Calculation for High-order QAM Decoding
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Solution Overview
Problem
High-order QAM modulation in mobile communication systems incurs increased calculation loads for log-likelihood ratio (LLR) calculations, leading to higher reception error rates due to the complexity of decoding processes.
Innovation Solution
The method involves determining selection bits to distinguish quadrants and domain bits in the constellation, allowing the received signal to be divided into real and imaginary components, calculating absolute values, and origin-shifting to reduce the complexity of LLR calculations, effectively applying the same LLR calculation form as QPSK to high-order QAM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high-order QAM modulation is used to increase data transmission rate, then the amount of data transmitted per symbol increases, but the calculation load for LLR increases causing higher reception error rates
Solution Approach 1:
The patent segments the constellation diagram into multiple domains (e.g., 4 domains for 16QAM, 16 domains for 64QAM) using selection bits and domain bits. This segmentation allows the receiver to process each domain separately with simplified calculations, reducing the overall computational complexity of LLR calculation while maintaining high-order QAM modulation capabilities.
Solution Approach 2:
The patent applies different calculation approaches to different parts of the constellation diagram. By identifying which domain a received signal falls into using selection bits and domain bits, the receiver can apply localized simplifications to the LLR calculation formula specific to each domain, rather than using a complex universal calculation for the entire constellation.
2Reliability
If conventional LLR calculation method is used for high-order QAM, then decoding accuracy is maintained, but the complexity of the decoding process increases
Solution Approach 1:
The patent changes the parameters used in LLR calculation by introducing selection bits and domain bits that divide the constellation into multiple domains. This parameter transformation allows the use of simplified LLR calculation formulas for each domain while maintaining overall decoding accuracy, as the division into domains preserves the essential signal characteristics needed for accurate decoding.
Data Source
AI summary
A method and apparatus are provided for calculating a log-likelihood ratio (LLR) for decoding in a receiver for a mobile communication system, wherein the method and apparatus determine selection bits for distinguishing four quadrants in a constellation representing signal points of transmission symbols, determine domain bits for distinguishing the signal points in each domain of the four quadrants according to a modulation order of the transmission symbols, repeat an operation of dividing a received signal into a real component and an imaginary component according to the number of determined domain bits, calculate and origin-shift absolute values of the real component and the imaginary component, and calculate LLRs for the selection bits. Further, the method and apparatus can subsequently calculate LLRs for corresponding domain bits each time the origin-shifted received signal is received.