Soft-Decision LDPC Diversity Combining for Wireless Signal Decoding
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Solution Overview
Problem
There is a need for non-coherent diversity combining techniques for LDPC coded signals, particularly with soft decisions, to enhance decoding performance in communication systems with multiple signal copies, as existing methods are limited in achieving performance gains compared to hard-decision combining schemes.
Innovation Solution
A method for combining soft-decision outputs of non-coherently modulated signals using a diversity combiner that selects bits based on the highest likelihood ratio (SC) or adds likelihood ratios (LRC) before inputting them into a single LDPC decoder, improving signal-to-noise ratio (SNR) and reducing computational complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If hard-decision decoding is used for diversity combining, then device complexity is reduced, but decoding performance deteriorates
Solution Approach 1:
The patent introduces likelihood ratios as an intermediary between the received signals and the LDPC decoder. Instead of directly using hard decisions from multiple diversity branches, the system computes likelihood ratios that capture the reliability information from each branch, then combines these soft values before decoding. This intermediary representation enables soft-decision decoding to achieve better performance while maintaining manageable complexity through the structured likelihood ratio combination process.
2Reliability
If soft-decision decoding is used for diversity combining, then decoding performance is improved, but device complexity increases
Solution Approach 1:
The patent changes the parameter representation from hard decisions (binary values) to soft decisions (likelihood ratios). By transforming the input data format to include reliability information through likelihood ratios, and by establishing specific combination rules for these ratios across diversity branches, the system achieves improved decoding performance. The parameter change is implemented through systematic computation and combination of likelihood ratios before feeding them to the LDPC decoder.
3Reliability
If multiple diversity branches are combined, then signal-to-noise ratio is improved, but computational complexity increases
Solution Approach 1:
The patent segments the diversity combining process into distinct stages: (1) computing likelihood ratios from received signals in each diversity branch, (2) combining these likelihood ratios using specific rules, and (3) feeding the combined soft values to a single LDPC decoder. This segmentation allows the system to process multiple diversity branches efficiently by breaking down the complex operation into manageable steps, reducing overall computational complexity while maintaining SNR improvement benefits.
Data Source
AI summary
A method of decoding a plurality of diverse signals for low-density parity-check (LDPC) decoders that takes advantage of signal diversity. The method allows for the combining of soft-decision LDPC encoded non-coherently modulated signals, which is in contrast to existing approaches where hard decision combining is used for non-coherently modulated signals. The method includes the steps of inputting each diversity signal into a unique demodulator, and calculating the LLR of each demodulated signal. When the diverse demodulated signals are combined into a single combined signal, each bit of the combined signal is selected according to the value of either the highest LLR value of each bit across the demodulated signals or according to the sum of the LLR of each bit across the demodulated signals.