Concatenated Polar Code Decoding with SCL Bit Flips for Short Blocks
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Solution Overview
Problem
Existing channel coding techniques, such as pure polar codes, struggle to achieve the finite-length theoretical bound in the short blocklength regime, leading to performance penalties due to insufficient polarization of subchannels.
Innovation Solution
The proposed solution involves a concatenated polar code construction using a CRC-PC-Polar code scheme, which includes evaluating channel reliabilities, selecting reliable channels, constructing polar codes, attaching CRC and PC bits, and using a bit-flip-based SCLF decoder to correct errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pure polar codes are used, then the encoding and decoding complexity is low, but the error correction performance is inferior to LDPC codes and Turbo codes
Solution Approach 1:
The patent segments the polar code structure by dividing the N channels into different reliability groups and applying different decoding strategies to different segments. Specifically, it identifies and separates the most unreliable bits (which require bit-flip operations) from the more reliable bits (which can be decoded using standard SCL operations), thereby improving overall error correction performance without uniformly increasing complexity across all code bits.
Solution Approach 2:
The patent creates a composite coding scheme by combining Successive Cancellation List (SCL) decoding with bit-flip operations. This hybrid approach integrates two different decoding mechanisms: the probabilistic SCL decoding for most bits and deterministic bit-flip operations for highly unreliable bits, forming a composite decoding strategy that achieves performance comparable to LDPC and Turbo codes while maintaining polar code structure.
2Reliability
If traditional SCL decoding is used, then the decoding complexity is manageable, but the bit error rate is higher in short blocklength regimes
Solution Approach 1:
The patent introduces dynamic adaptivity into the SCL decoding process by implementing bit-flip operations based on real-time reliability assessment. The decoder dynamically identifies bits with extremely low reliability metrics and applies bit-flip operations selectively, rather than using a static decoding threshold. This dynamic adjustment allows the system to adapt to varying channel conditions and achieve lower bit error rates in short blocklength regimes.
Solution Approach 2:
The patent changes the decoding parameter space by introducing bit-flip operations that modify the LLR (Log-Likelihood Ratio) values of highly unreliable bits. By adjusting these parameters (LLR values) for specific bits based on their reliability metrics, the system can correct errors that would otherwise propagate through the decoding process, thereby reducing the overall bit error rate without requiring a complete redesign of the SCL framework.
3Reliability
If more redundancy bits are added to improve error correction, then the bit error rate decreases, but the transmission rate and latency increase
Solution Approach 1:
The patent applies partial correction actions by implementing bit-flip operations only for the most unreliable bits rather than applying uniform error correction to all code bits. This selective approach corrects the critical errors that most impact performance while avoiding the overhead of comprehensive redundancy processing, thereby maintaining higher transmission rates and lower latency compared to full-strength error correction schemes.
Data Source
AI summary
A method of encoding a concatenated polar code is provided, including evaluating channel reliabilities; selecting channels based on each channel's relative reliability; constructing a polar code of information bits arranged with a front and a rear; attaching additional cyclic redundancy checking (CRC) bits to the rear of the information bits; inserting parity bits at proper locations to yield a bit string; feeding the bit string into a polar encoder; and obtaining a codeword. A successive cancellation list and bit flipping decoding method for concatenated polar code also is provided, including initializing a LLR of the codeword; screening paths; performing a CRC check on the screened paths and if the CRC check is not met; determining, in response to the CRC check not being met, at least one most unreliable bit based on a revised critical set (RCS); reversing a previous decision if the most unreliable bit was previously selected; and restarting the decoding method.