Soft Demapping Apparatus for Rotated QAM Signals
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Solution Overview
Problem
Current soft demapping algorithms for rotated quadrature amplitude modulation (QAM) signals require excessive calculations due to correlation between in-phase (I) and quadrature (Q) channels, leading to increased complexity and performance degradation, especially in high modulation scenarios.
Innovation Solution
A soft demapping apparatus and method that includes interference cancellation units to cancel interference in rotated QAM signals, allowing for one-dimensional (1D) soft demapping, which reduces computational complexity by calculating log likelihood ratios (LLR) based on interference-cancelled signals and signal-to-interference-plus-noise-ratios, and selects appropriate interference cancellation methods based on channel gains.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If maximum likelihood scheme with 2D Euclidian distance calculation is used for soft demapping of rotated QAM signals, then demapping accuracy is improved, but calculation complexity increases significantly
Solution Approach 1:
The patent segments the 2D rotated QAM signal space into two independent 1D PAM signal spaces by performing interference cancellation. This division allows the complex 2D demapping problem to be solved as two simpler 1D problems, reducing calculation complexity while maintaining demapping accuracy through sequential processing of I and Q channels
Solution Approach 2:
The patent extracts and removes the interference component from the received rotated QAM signal before demapping. By taking out the interference term caused by signal rotation and using it to cancel the corresponding channel, the patent eliminates the correlation between I and Q channels, enabling simplified 1D soft demapping without sacrificing accuracy
2Reliability
If full search rotated signals method is used for soft demapping, then demapping performance is optimized, but calculation amount increases with modulation order
Solution Approach 1:
The patent divides the full search 2D problem into two separate 1D problems that can be processed independently. Instead of searching through all rotated signal points in 2D space, the method performs interference cancellation and then conducts separate 1D searches in each PAM dimension, reducing the computational burden from O(M²) to O(M) where M is the modulation order
Solution Approach 2:
The patent changes the parameter space from 2D rotated QAM coordinates to 1D PAM coordinates through interference cancellation. This parameter transformation converts the complex 2D Euclidian distance calculations into simpler 1D distance calculations, maintaining accuracy while improving calculation efficiency
Data Source
AI summary
Provided are a soft demapping apparatus and method that may cancel interference included in a rotated quadrature amplitude modulation (QAM) signal, using at least one interference cancellation unit, and may perform one-dimensional (1D) soft demapping of the interference-cancelled rotated QAM signal.