Nonbinary LDPC Coding for Low-PAPR Underwater OFDM Links
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Solution Overview
Problem
Current underwater acoustic (UWA) communication systems face challenges with plain OFDM's poor performance in channel fading and high peak-to-average-power ratio (PAPR), limiting their effectiveness due to factors like multi-path propagation, time variability, and signal attenuation.
Innovation Solution
The implementation of nonbinary low density parity check (LDPC) codes, specifically irregular and regular LDPC codes, to enhance UWA communications by reducing PAPR and improving performance in fading channels, utilizing generator matrices with high density and parallel processing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If plain OFDM is used for underwater acoustic communication, then the system can handle high-rate transmissions over long dispersive channels, but the performance deteriorates in the presence of channel fading and the peak-to-average-power ratio becomes excessively high
Solution Approach 1:
The patent transforms binary LDPC codes into nonbinary LDPC codes by changing the algebraic structure from GF(2) to GF(q), where q matches the modulation order. This parameter change enables the code to directly operate on modulation symbols, simultaneously improving fading resistance through better error correction and reducing PAPR through optimized code structure and selected mapping techniques
Solution Approach 2:
The patent creates a composite coding scheme by combining nonbinary LDPC codes with OFDM modulation and selected mapping. This composite approach integrates the error correction capability of LDPC codes with the spectral efficiency of OFDM and the PAPR reduction of selected mapping, achieving superior overall performance
2Reliability
If binary LDPC codes are used with high order modulation, then coding gain can be achieved, but the system complexity increases due to iterative processing requirements
Solution Approach 1:
The patent extracts the iterative processing requirement from the coding scheme by designing nonbinary LDPC codes that can be decoded using simplified algorithms. By taking out the complex iterative demapping and decoding process and replacing it with direct nonbinary decoding, the system maintains high error correction performance while significantly reducing computational complexity
Solution Approach 2:
The patent employs simpler decoding algorithms that require less computational resources and can be implemented with lower complexity hardware or software, making the system more practical for real-time underwater acoustic communication applications
Data Source
AI summary
Advantageous underwater acoustic (UWA) apparatus, systems and methods are provided according to the present disclosure. The apparatus, systems and methods employ nonbinary low density parity check (LDPC) codes that achieve excellent performance and match well with the underlying modulation. The nonbinary LDPC codes of the proposed apparatus, systems and methods are formed, at least in part, from a generator matrix that has a high density to reduce the peak-to-average-power ratio (PAPR) with minimal overhead. The disclosed apparatus, systems and methods employ nonbinary regular LDPC cycle codes if the constellation is large and nonbinary irregular LDPC codes if the constellation is small or moderate. The nonbinary irregular and regular LDPC codes enable: i) parallel processing in linear-time encoding; ii) parallel processing in sequential belief propagation decoding; and iii) considerable resource reduction on the code storage for encoding and decoding.