Polar Code Check Bit Placement for SCL Decoding Reliability
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Solution Overview
Problem
Conventional SCL decoders may eliminate the correct decoding path if it does not have a good path metric value, leading to decoding errors, and the placement of CRC or PC bits affects the error correcting performance of polar codes.
Innovation Solution
Selecting check bit indices from the frozen set in descending order of row weights and index reliabilities, and computing check bits from non-frozen bit indices to aid in decoding path identification and error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SCL decoder uses path pruning to restrict the number of decoding paths, then device complexity is reduced, but the correct decoding path may be eliminated leading to decoding errors
Solution Approach 1:
CRC check bits are introduced as an intermediary mechanism to verify decoding paths. The CRC check function acts as a mediator that identifies whether a pruned path is correct without requiring the decoder to maintain all possible paths, thus resolving the contradiction between path pruning complexity and decoding accuracy.
Solution Approach 2:
The CRC check provides feedback to the SCL decoder about the validity of decoded paths. This feedback mechanism allows the decoder to adjust its path selection and pruning strategy based on CRC verification results, improving reliability while maintaining controlled complexity.
2Device complexity
If check bit indices are placed at the end of codeword or scattered uniformly, then device complexity is reduced, but error correcting performance deteriorates
Solution Approach 1:
The patent changes the parameter of check bit placement from uniform or end-position placement to specific positions determined by row weights of the generator matrix. This parameter change optimizes error correcting performance by placing check bits at positions that provide better error detection capability, while the selection criterion based on row weights keeps the implementation complexity manageable.
Data Source
AI summary
A communication device includes: an encoder that encodes an input vector to output a codeword using a generator matrix of polar code; a memory that stores a frozen set including frozen bit indices and a non-frozen set including non-frozen bit indices; and a controller that is configured to: a) select at least one check bit index from the frozen set in descending order of row weights of the generator matrix and in descending order of index reliabilities of the input vector; b) select at least one non-frozen bit index from the non-frozen set to compute at least one check bit from at least one bit of information bits at the at least one non-frozen bit index; and c) put the at least one check bit at the at least one check bit index.