LDPC-Coded SCMA Decoding With Lower Storage and Complexity
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Solution Overview
Problem
Current multiple access schemes, particularly LDPC codes, face challenges such as high complexity, large storage requirements, and increased complexity in decoding processes, which hinder their widespread adoption in communication systems, especially in satellite transmissions where low code rates and high data rates are needed without compromising system performance.
Innovation Solution
The implementation of a scrambled division multiple access (SDMA) and spread scrambled division multiple access (SSDMA) scheme using low density parity check (LDPC) encoding, which involves scrambling bit streams with unique scrambling signatures, joint detection, and interference cancellation to efficiently decode and transmit data, reducing complexity and storage needs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LDPC encoding is implemented using its generator matrix, then error control performance is improved, but storage requirements increase due to the large non-sparse matrix
Solution Approach 1:
The patent segments the LDPC encoding process by using a sparse parity check matrix H instead of the full generator matrix G. The sparse matrix H is divided into sub-matrices that can be processed independently, reducing storage requirements while maintaining error control performance through iterative decoding algorithms.
Solution Approach 2:
The patent employs a sparse parity check matrix with many zero elements (analogous to porous materials) to reduce storage requirements. The sparsity pattern allows for efficient iterative decoding algorithms that only process non-zero elements, achieving both reduced storage and maintained reliability.
2Reliability
If LDPC codes are used to achieve low error rates, then system reliability is improved, but decoder design complexity increases
Solution Approach 1:
The decoder is segmented into multiple processing engines or nodes that work in parallel. Each node handles a portion of the decoding task based on the sparse parity check matrix structure, distributing the computational complexity across multiple simpler units rather than requiring a single complex decoder.
Solution Approach 2:
The patent employs dynamic iterative decoding algorithms that adapt the decoding process based on the received signal quality and convergence criteria. The decoding complexity dynamically adjusts rather than being fixed, allowing the system to achieve low error rates without always requiring maximum decoder complexity.
3Adaptability or versatility
If conventional CDMA techniques are used for satellite transmission, then multiple users can share bandwidth, but bandwidth expansion factor increases and power control complexity increases
Solution Approach 1:
The patent segments the multiple access scheme by combining CDMA with LDPC coding, where different users are assigned different sparse parity check matrices or sub-matrices. This segmentation allows multiple users to share the bandwidth without requiring tight power control, as the sparse structure provides inherent interference rejection capabilities.
4Productivity
If high data rates are transmitted via satellite, then productivity is improved, but radiated power density limits are exceeded
Solution Approach 1:
The patent changes the coding parameters by using low code rate LDPC codes that provide higher coding gain. This allows the system to achieve high effective data rates after error correction while transmitting at lower power densities that comply with regulatory limits. The sparse matrix structure enables efficient use of the available power.
Data Source
AI summary
A multiple access scheme is described. One or more encoders are configured to encode a plurality of bit streams using Low Density Parity Check (LDPC) coding. The bit streams correspond to a respective plurality of terminals. The plurality of bit streams are converted to provide a multiple access scheme for the terminals.